Can a non-IFR rated pilot accept an IFR clearance, provided the operation occurs in VMC only? According to this FAA ruling a pilot can operate an aircraft under an IFR flight plan even if the aircraft is not IFR certified, provided the operation occurs in VMC.

What the ruling doesn't differentiate is whether the pilot doing that operation must be an IFR rated pilot (the ruling is with respect to instrument training, which implies there will be a properly rated CFII onboard).
I can't find the regulation that states that you must have an IFR rating to accept an IFR clearance/operate on an IFR flight plan. So, my questions are:

What regulation (if there is one) requires a pilot to have an IFR rating in order to operate an aircraft on an IFR flight plan?
Would a "VMC only" modifier change this requirement?

Operating as PIC under IFR always requires an instrument rating and currency, regardless of flight conditions.
14 CFR 61.3(e) requires the rating, and there's no exception for VFR conditions:

(e) Instrument rating. No person may act as pilot in command of a
civil aircraft under IFR or in weather conditions less than the
minimums prescribed for VFR flight unless that person holds:
(1) The appropriate aircraft category, class, type (if required), and
instrument rating on that person's pilot certificate for any airplane,
helicopter, or powered-lift being flown;

61.57(c) requires instrument currency, again regardless of flight conditions:

(c) Instrument experience. Except as provided in paragraph (e) of this
section, a person may act as pilot in command under IFR or weather
conditions less than the minimums prescribed for VFR only if:

See this question for more details on filing IFR flight plans without being instrument rated (not a good idea).
Michael Hall suggested in a comment that some pilots might think that to operate under IFR they only need to file a flight plan and get a clearance, because of the wording in 91.173:

No person may operate an aircraft in controlled airspace under IFR
unless that person has—
(a) Filed an IFR flight plan; and
(b) Received an appropriate ATC clearance.

However, 91.173 doesn't override or invalidate any other regulation. The general rule is that regulations add up and you have to follow all of them unless the wording makes it clear that something doesn't apply (e.g. 91.1(e) says that part 91 regulations don't apply to part 103 ultralights).


Is co-flow jet wing technology workable? Coflow Jet claims that their idea of sucking air from the trailing edge and blowing it out the leading edge improves efficiency.
But this looks like nothing but flow control done wrong to me. And by blowing at the leading edge, they give up on achieving laminar flow(!).
They also claim that it increases transonic efficiency.
Does this work?

Amazing! British pioneer JW Dunne proposed this as a propulsion system around 1901 but Sir Hiram Maxim told him it would not work. (ref. unpublished documents in the Science Museum Archive's Dunne collection). Nine years later Henri Coanda built a ducted "jet" plane on broadly similar principles, which failed miserably (The Wikipedia article is not very good, but I know of none better online). But they all failed to understand the opportunities for suction lift, instead trying to exploit it to entrain a greater volume of air and create thrust.
More modern blown-wing systems have tried to improve on suction lift using similar methods, but have always foundered on the power requirements for the blower and structural weight penalties of all that wing ducting.
Here is a PDF from their web site. It appears to achieve high lift/STOL performance through high AoA and the Coanda effect, basically turning itself into a giant blown flap. Alternatively it provides modest forward thrust by stimulating circulation and thus maintaining lift at a slight negative AoA.
Well, it probably does work - see wind tunnel images - but I would also want to see those wing weights, blower power figures and cost-benefit analyses before believing it is any more practicable than yesterday's approach.


What happend to the airframe of the Aloha Airlines Flight 243? What happened to the airframe of Aloha Airlines Flight 243, after the explosive decompression?
I know that the structures were studied for a while after the aircraft safely landed in  Kahului Airport, but what happened after that?

According to Planespotters, it appears that the airframe in question was destroyed in August 1988.


Why are some A350s missing SSA probes on their nose? I recently just noticed that some A350s are missing their iconic set of 3 main SSAs (Side Slip Angle Probes) on their nose. I'm not sure if its an issue of newer variants or varied airline options, but I'm sure it has something to do with a less needed sense of redundancy. Any exact answers behind this?

Thanks!

Picture sources:
Top:https://www.traveller.com.au/the-inside-story-of-the-a350-airbus-rival-to-the-boeing-787-dreamliner-12c17x
Bottom: https://airwaysmag.com/airlines/british-airways-takes-off-a350-1000/

You are right: the three side slip angle probes are redundant because side slip can be calculated by the ADIRS without these probes. Airbus included them in earlier A350 models to crosscheck this calculation, but they are removed now:

Spot the difference 2: SSA (Side Slip Angle) Probes.

This one’s a bit more technical. If you look closely around the nose of the aircraft, you can see an array of sensors. These form part of the Air Data and Inertial Reference System – in other words, they feed flight parameters to the pilots, such as the angle the aircraft is flying, the outside temperature, and the barometric and static pressure.
As the A350 entered service, Airbus still wanted to gather more information to compare the data between different systems that help pilots fly on approach in crosswinds. To do that, a few early models had extra probes added to cross check the data from the other instruments. You can see these three extra vanes on the front of the aircraft just below the ‘Zorro’s Mask’ windscreens. Having now gathered enough side slip information to establish that they’re not required, they’re being removed on all new A350s. They’ll also be taken off our first two aircraft in the coming months, which will save weight and maintenance costs.

(Virgin Atlantic Blog: Airbus evolution: Can you spot the difference?, emphasis mine)


What is the red barb for in the NOAA weather briefing? Wind barbs are well-defined symbols, but I noticed in my WX briefing that there are now occasional red barbs in the chart.
The red appears on both the 5kt and 10kt barbs, and sometimes for largest 10kt barb or the smallest 5kt barb.

They do represent gusts:
From AviationWeather.gov:

Figure 1: Station Model Plot
In many cases, the data are plotted using standard symbols and
plotting models. Fig. 1 shows the station model used in the METAR and
TAF plots.

Ceil - Ceiling height in hundreds of feet. This represents the height of the lowest broken or overcast cloud layer.
Id - The 4 letter ICAO identifier for the site. KRFD is Rockford IL.
Windbarb - The wind barb. The stick points in the direction the winds are coming from. Each full barb represents 10 knots of wind.
Each half barb represents 5 knots. Red represents wind gusts. In this
case, you have winds from the SSW at 25 knots with gusts to 30 knots.

So for example, these:

The one on the left represents wind of 15 knots gusting 20, and the one on the right is 15 knots gusting 25.
Odd ones like this:

Mean 5 knots gusting 10. Why they don't overlay I'm not sure.


Becoming a CFI in the USA as a non-US citizen This question is not about aviation itself, but rather about job opportunities in aviation.

It kind of goes into law a little, maybe somebody has some experience with this issue though:

Being from Germany, I'd like to become a FAA CFI. This itself is not a huge problem, but working as a CFI in the US is one, as I would need a citizenship or a green card to work there... or would I not?

Does anybody know anyone who is a CFI or works as a pilot in the US and is not a US-citizen?
Or does anybody have an idea of how to work as a CFI without a green card or citizenship?

Knowing this isn't pure aviation, this still appears to me as one of the best places to ask, you all know that experience can not be out ruled!

You do not need to be a citizen to be a U.S. CFI.

You need to have US ratings, so you would have to have all your German licenses/ratings converted, which takes some time.

You have to be absolutely FLUENT in both spoken and written English.

If you want to charge students money for your services, you have to have US residency or other work visa authorization. You do not need a work visa if you train students for free.


Can control surfaces for slow aircraft be 3D printed? Can control surfaces for slow aircraft be 3D printed or even just printed as a core and then wrapped in fibreglass or carbon fibre?
I understand that 3D printing of wings, etc. is pretty common in the RC Aircraft world.
What about for slow flying aircraft such as Ultralights, etc.
In Rutan's book, "Moldless Composite Sandwich Aircraft Construction", Rutan strictly notes that only certain foams can be used as a core for structural components. Other foams are just for shaping of non-structural components such as interior panels, etc.
I assume there are certain engineering/material properties of the structural components that need to be met such as flexibility, no delamination, no structural degradation, high number of loading cycles, etc.
The question is, do any 3D printed materials meet these engineering/material properties.
Any help would be appreciated.

There are plenty of 3D printing methods available now with FDM being the most common. In my experience as small fixed wing UAV designer, all the 3D printing processes that are financially viable always under perform in comparison to alternatives. I can tell you the main issues I have encountered leaving the printing defects out:

additive manufacturing doesn't lend itself well to mass production.
It is too heavy for a core material.
melts under heat, Fire hazard and safety issues.
FDM prints are susceptible to fatigue especially when stress is transverse to the layers
for commercial use , the end customer doesn't like 3d printed parts on his aircraft. simple as that
machined metal parts are always stronger and cheaper than metal 3D printed parts.

However, it has some major benefits but mostly as a prototyping method. You can test the fits and physical size rather cheaply. I use it sometimes as a mold pattern for small parts. Also, 3D printing wings is not as common as you would think in RC world.
TLDR; with current technology, 3D printing is not suitable for stress critical components.


What is the German / European equivalent of FAA Order 7110.65? FAA Order 7110.65 prescribes air traffic control procedures and phraseology for use by personnel providing ATC services in the USA.

Which documents regulate these aspects in Germany, or, more generally, in Europe?

Please provide also the valid versions of these documents as of the 1st of April 2020.

The „handbook“ for ATCOs in Germany (!) is the MO-ATS (Manual of Operations for Air Traffic Services) which is an internal DFS (Deutsche Flugsicherung - the German ANSP) document and therefore not available to public.

However it is based on the German AIP and ICAO DOC 4444 which are both available to public. For the international legislation check Milo Morkus’ answer.

In the German AIP phraseology examples are found in AIP ED GEN 3.4 Communication Services


What kind of work you can get with a private pilot licence? I´m planning to be a pilot, i just want to know if you can work only with the private licence and where.

You cannot do so.  A private pilot’s license - at least in the US - prohibits you from offering airman services for compensation or hire.

If you intend to fly professionally, you will need at least a commercial pilot’s certificate.  An instrument rating is also highly recommended as is multi engine class ratings for the greatest chances of employment.  Air carrier operation will require you to hold an airline transport pilot’s license for part 121 operations.


What effect does driving convictions have on a PPL? Recently, I was driving some friends around when they started complaining that I was driving "too slow" (basically not over the speed limit). I stated that my reason for being cautious was I did not want to jeopardise my PPL / NPPL (in progress).

I would like to know however, what driving convictions actually do affect pilot licenses or get them revoked?

In the US, driving while under the effects of alcohol and drugs may have a adverse effect on your medical certificate.  Additionally, I have heard (from an FAA inspector) second hand that in one instance, someone who had a driver's license revoked for a large number of speeding and reckless driving circumstances, eventually had a medical certificate revoked.

Arrests, and administrative actions require reporting to the FAA Aeromedical branch within 60 days and failure to do so can not only affect a medical certificate, but also pilot certificates, instructor certificates, A&P certificates, controller certificates, etc.  The penalties for non-reporting are significant.

Addendum:  US pilots are required to make TWO reports relative to substance and alcohol issues.  Part 67 requires reporting notifications, arrest, etc. to the Aeromedical Branch. Part 61 requires a notifying Security at FAA upon conviction  or disposition.

Reference item 8 in the below FAQ which is provided for AME guidance:

  https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/media/SubstancesAbuseDependenceFAQ.pdf

Also, according to FAA documentation, the normal look back on substance abuse is 2 years.


What is the correct ATC phraseology in the US for an immediate - no delay takeoff? Just wondering - what's the correct ATC phraseology for a takeoff where a plane does not stop first after lining up with the runway centerline before starting their takeoff roll?

Redwood five-two-six-three, runway three-zero cleared for takeoff, no delay.
Redwood five-two-six-three, runway three-zero cleared for immediate takeoff.

The FAA AIM and ATC (7110.65) documents don't mention the ICAO equivalent. But I found it in the US AIP:

  34.1 (...) At times a clearance may include
  the word “IMMEDIATE.” For example:
  “CLEARED FOR IMMEDIATE TAKEOFF.” In
  such cases “IMMEDIATE” is used for purposes of air
  traffic separation. It is up to the pilot to refuse the
  clearance if, in the pilot’s opinion, compliance would
  adversely affect the operation.


Why would an aircraft drastically reduce in speed and then accelerate during landing? I was on a flight today and I noticed that as we were approaching to land, the plane drastically reduced its speed for few seconds and then regained its speed.

Can somebody tell me why?

Your question uses the adverb "drastically". It's very unlikely that whatever happened was drastic. When an airliner does something drastic, it's a pretty memorable experience. In the absence of visual cues, some other sensations can be magnified in our experience, so it's quite possible that any change was less extreme than it seemed to be.

Sometimes, the plane is actually slowing down and speeding up. This could be in response to an air traffic control instruction, a not-quite-right adjustment that needs to be corrected, changes in local wind condition and so on.

It could also be that the plane needed a little adjustment after intercepting the glide-slope.

At this stage of its flight, the crew many need to respond to many different kinds of factors in its environment.

However, just because you had sensations of speeding up or slowing down doesn't mean that that is actually what happened. Changes in pitch can also produce these sensations, especially when combined with changes in engine sound.

In short, if that did actually happen, it could be for all kinds of reasons, but just as likely, it was an illusion.


Why would a flight from North America to Asia sometimes fly over the Atlantic? I am going to take AC031 from Toronto to Beijing in a couple of weeks, I searched its flight path, most of the time it will fly westbound after taking off from Toronto and continue west across the north pole area and land in Beijing, but yesterday it flew eastbound, across the Atlantic, this is very strange since the distance is a little bit more than flying westbound.

Why?

Those routes are extremely similar.

They're basically two almost-a-straight-line routes over the arctic ocean, except that the second one has deviated a bit to the right, so that it's gone just on the right of the North Pole instead of passing by the left. At the pole itself, there's no such thing as "East" or "West", and if you pass very close to it, there is a discontinuous jump between passing it "going East" and "going West".

You can see this explicitly by going to FlightAware, asking to View track log, and downloading the flight tracking data to be viewed on Google Earth:

 Actual tracking data in white. Interpolations for the missing-data parts in green.

As you can see, there is indeed a nontrivial deviation of what's probably several hundred kilometers in clipping Nunavut vs the northeast corner of Greenland, but that deviation is within the normal ranges of what you'd get in your standard transatlantic flight, say. The only change here is that the variation now includes the North Pole itself.


When flying a circling approach, is it permitted to begin the visual circling segment prior to the final approach fix? If it were a beautiful sunny VFR day and you were cleared for a circling approach, can you begin the circle prior to the final approach fix/circling DH in order to maneuver visually to land?
Here are two examples of situations where it would be very useful, and both are real life clearances that I have gotten multiple times:

Example 1 - KASE
Clearance:

N1234, Cleared for the VOR/DME-C approach, cleared to land runway 15

If you follow the step downs until the final approach fix (ZIGBU) you will be at 2,983 ft. above the runway (10,820 ft. MSL) with 2.9 miles to go (9.61 degree descent angle).  To put this in perspective, on a normal 3 degree descent, you should be at 870 ft. above the runway so are over 2,000 ft. high on less than a 3 mile final.
Could you begin the circle early and descend while visually avoiding any obstacles prior to the step-down fixes?  Say cross ALLIX at 11,000 ft. and ZIGBU at 9,000 ft. (assuming that this cleared all obstacles)? Keep in mind that this is a circling approach so we will be operating below the MDA visually at some point on final anyway.
If not, then it would be nearly impossible to land straight-in while flying most jets, and yet I have never seen anyone do a 360 or a similar maneuver while on final here (and who would want to do that in the valley anyway??).

Example 2 - KTEB
Clearance:

N1234, Cleared for the ILS Runway 6 Circle Runway 1 Approach, cleared to land runway 1

If I fly the ILS (localizer and glideslope) until reaching circling minimums, especially in a category C or D airplane and with this runway layout, it will take a lot of room to turn right for a base leg to runway 1 and then turn back left to intercept final and lose the required altitude.
Could you start the circle a little sooner by making the right turn early (prior to DH, but still within the protected circling area) in order to intercept the extended final for runway 1?

While researching this subject, I found a few things that shed light on the subject:

Procedures

FAA ATC Order 4-8-1 Note 1 says:

  1. Clearances authorizing instrument approaches are issued on the basis that, if visual contact with the ground is made before the
  approach is completed, the entire approach procedure will be followed
  unless the pilot receives approval for a contact approach, is cleared
  for a visual approach, or cancels their IFR flight plan.

So we have to follow the entire approach, which includes all mandatory altitudes.

Aspen Approach

AIM 5-4-20. Approach and Landing Minimums says:

  c. Straight-in Minimums are shown on the IAP when the final approach
  course is within 30 degrees of the runway alignment (15 degrees for
  GPS IAPs) and a normal descent can be made from the IFR altitude shown
  on the IAP to the runway surface. When either the normal rate of
  descent or the runway alignment factor of 30 degrees (15 degrees for
  GPS IAPs) is exceeded, a straight-in minimum is not published and a
  circling minimum applies. The fact that a straight-in minimum is not
  published does not preclude pilots from landing straight-in if they
  have the active runway in sight and have sufficient time to make a
  normal approach for landing. Under such conditions and when ATC has
  cleared them for landing on that runway, pilots are not expected to
  circle even though only circling minimums are published. If they
  desire to circle, they should advise ATC.

The key part for this discussion is that, for approaches that would be straight-in if it weren't for the high descent rate on final (like the KASE approach), pilots are not expected to circle even though only circling minimums are published. If they desire to circle, they should advise ATC.

Well, in this case we can't land straight-in after making the last crossing restriction, so what can we do?

Combining the two quoted passages, our options are:

Get approval for a contact approach
Get approval for a visual approach
Cancel our IFR flight plan
Get approval to circle since we can't land straight-in.

The first three are pretty straight-forward and can be used if you pick up the airport visually in time.

If you need to circle, I found a great article called Circle-To-Land Tactics which was written by a former chairman of the ALPA TERPs committee.  He suggests overflying the runway and then flying a modified pattern:

Teterboro Approach

We can't start our circle until we are within the protected circling area.  This means that for my category C airplane, I have to wait until 1.7 NM from the runway threshold before I can begin my turn.

We could make a right 90 degree turn followed by a left 90 degree turn to line up on final, but that would eat up about one mile just by turning.  Since runway 1 is actually closer to us than 6 at this point, I have even less distance to work with and can't even see the runway during the first turn because we are banking the wrong direction.  This would be pretty tight.

In this case, the previous article recommends a circle like this (which would be modified for our actual runway layout):

In good visual conditions, I would just ask for a visual approach so that we can start the turn a little sooner and land "more" straight-in without flying all over the airport.

One last point:  Since there is a control tower at both of these airport, make sure that they know what we are going to do!


Is trigonometry used by commercial pilots? Do pilots (for example commercial pilots) need to use trigonometry (directly, with trigonometry knowledge) as part of their routine job?

If so, when is it most used and for what?

Note that this answer was given to the original question, Do pilots need to use trigonometry as part of their routine job? If so, when is it most used and for what? The question was subsequently edited, after this answer was accepted. Much of the information provided in this answer does not now apply directly to the current question, but it does serve to provide context and for this reason it has been retained.

Pilots use trigonometry primarily for calculations involving wind angles, either for navigation or for cross-wind components for takeoff or landing. Note that pilots often accomplish these calculations with a flight computer such as the E6B, a circular slide rule:

Image by Dave Faige — Source — used under CC BY-SA 3.0

Many such flight computers are available, including electronic versions, such as the Sporty's electronic E6B. Personally, I now prefer to use web-based software, but in flight school my preferred calculation method was a TI-83 programmed to do vector addition and other pre-flight calculations. In the cockpit, the CR-3—a pocket version of the larger E6B mechanical flight computer and which can be operated with one hand—is usually the most functional method.

Regardless of how they are performed, such calculations are typically for the purpose of either:

Calculating wind correction angles for cross-country navigation based on forecast wind conditions, or
Calculating crosswind component for takeoff or landing based on reported wind conditions.

The later are fairly straight-forward; the former are more complex. Crosswind component is a simple tangent calculation. Wind correction angles are more complex involving vector addition taking into account magnetic course, true airspeed, forecast wind angle, and forecast wind speed.

Now, the original question was merely, do pilots need to use trigonometry. The answer to that question is, "Yes". The question has since been edited to specify the use of trigonometry "directly, with trigonometry knowledge". The answer to that question is, "No", pilots do not need to have a working understanding of trigonometry, though they do need to be capable of computing the above described wind problems. A pilot need not understand the trigonometry used by the calculator, slide rule, or FMS that he or she uses to perform these calculations. I know good pilots who have no real working knowledge of trigonometry and do quite well without it.

For a pilot flying in the IFR environment, wind correction calculation is less frequently a needed calculation since most navigational means provide for wind correction in some way. This is especially true of GPS or RNAV navigation, because the ground track can be compared to the aircraft's heading to show wind correction angle.


What avionics systems are interfaced with ACARS? I am a librarian looking for sources of information to help answer the following questions for one of our researchers: 1. what avionics systems are interfaced with ACARS and 2. how is the interaction between ACARS and these systems designed to occur in practice? As I am not very familiar with this subject, any information or pointers to information would be appreciated.

ACARS, otherwise known as Aircraft Communications and Addressing Reporting System, is almost always interfaced with the #3 VHF Communication System. Ordinarily, that #3 VHF system is set for "Data Mode." Some aircraft have the ability to use the #3 VHF as an auxiliary communications system by putting it in voice mode, and other aircraft dedicate it to strictly data mode.

However, I have seen operators tie the ACARS system to the #2 VHF system when there is no #3 VHF system installed. In this case, it's ordinarily up to the pilots to switch between voice and data mode on the #2 VHF system. I can only imagine how annoying that must be!

While VHF is most frequently used on domestic flights, its relatively short range does little good on international flights over water. On aircraft meant for such long hauls, the ACARS system is usually tied to the HF radios and the SATCOM system. If I recall correctly, the ACARS system opts for VHF communications as the primary method. If there is no VHF available, or its rendered inoperative, the secondary method is often SATCOM; failing that, the HF systems.

In order for the aircrew to interface with the ACARS system, there is some sort of display with a keypad they interface with. On the vast majority of aircraft I've worked on, that display is often referred to as either the MCDU or CDU. On aircraft with MCDU's (Multifunction Control Display Unit), the pilot can select the mode they prefer to be in (ACARS, FMS, etc...), and can interface with the appropriate system through that singular central display - kind of like selecting what program you'd like to run on your computer. If the pilot selects ACARS, they can interface with all the relevant data pertinent to the ACARS system. If they select FMS, they can interface with the FMS (Flight Management System); and so on and so forth.

On aircraft equipped with CDU's (Control Display Units), usually there are completely separate displays/interfaces for the FMS and ACARS. In that case, there are a plethora of options from a number of different manufacturers. I've seen touch screens, a secondary but different style CDU dedicated to ACARS communications, and so on and so forth. It's wide and varied.

The MCDU and/or CDU usually interfaces with an ACARS Management Unit. That management unit is ordinarily the "brain" of the ACARS system. All pilot interactions with the MCDU/CDU are sent to the ACARS system, usually via a 429 Databus. The best way to think of this is that the MCDU/CDU setup is like your computer monitor and keyboard. You input data and see those inputs with keyboard and monitor, but the real "action" is taking place with the memory and processor "behind the scenes." That behind the scenes action is the ACARS Management Unit.

The ACARS Management Unit (MU) can then interface with a variety of other systems and subsystems largely based on operator configuration. Some operators choose to log crew hours with the use of OOOI (Out, Off, On, In) times based on subsystem inputs to the ACARS MU. For example, when the beacon turns on, an input to the ACARS MU generates the "Out" time. When the aircraft takes off, the ground sensing mechanism of the aircraft sends a separate signal to the MU letting it know that the aircraft has left the ground. When that ground sensing mechanism changes state again (aircraft lands), it sends another signal to the MU letting it know that the aircraft has landed. Finally, when one of the doors (usually the L1 door) is opened after flight, the ACARS receives a signal from the door switch, and the "In" time is generated.

Sometimes the MU is tied to an ACARS Aircraft Personality Module (APM). This is usually just a separate unit with DIP switches set to a certain configuration so no matter what MU is installed on a particular aircraft, it can pick up the "correct identity" and act accordingly. Other times, there is no APM and the configuration control is handled exclusively by the software load often verified by the mechanic after installation.

Also, with the advent and implementation of ADS-B aircraft, GPS position data has begun to tie in to the ACARS system. If you want to see a mechanic roll his eyes, ask him to do a full functional check of the ADS-B system in the rain or cold. It's hours long, it never fails, and the consequences of what happens if it is failed are negligible. Most of us see it as a giant waste of time... But I digress.

Finally, I'd like to note that all of this information is with the caveat that every operator is different, and so is every aircraft. There are endless combinations of systems that could or could not be tied into the ACARS system. Generally speaking, though, what I've mentioned above is a fairly standard installation.


CO-meter indicates 10ppm of Carbon Monoxide when I turn on Cabin heat - should I be concerned? Our Cessna 172P is equipped with a digital CO-meter rather than the traditional Quantum eye carbon monoxide detector.
Today I was flying along in winter conditions, and naturally used cabin heat. During the flight, I heard some occasional short beeps, and couldn't figure out what it was. I looked at the CO-meter which has a red alarm light, but that light was definitely off.
On the ground, after shutting down the engine, I heard another short beep, and it definitely came from the CO-meter! The digital readout was showing 10ppm.
During post-flight, with the door open, the readout dropped to 0 ppm.
I routinely check the CO-meter battery during preflight, so I'm pretty sure the beep is not a reminder for a dead battery.

According to these sources: http://www.coheadquarters.com/ZerotoMillion1.htm , http://library.thinkquest.org/10121/textonly/exposure.htm and wikipedia 10ppm is nothing to be concerned about with exposure over a two-hour flight.

Does anyone else have a digital CO-meter and can tell if a reading of 10ppm is normal with cabin heat?
Or should I be concerned our exhaust or heat exchanger is faulty?

The short answer is you should be concerned.

Although 10PPM of carbon monoxide doesn't pose an immediate health risk for short term exposure the fact that the level is rising when you turn on the cabin heat & falling when you ventilate the cabin (by opening the door) indicates you may have an exhaust leak, and those tend to get worse over time.
You should have your shop open the heat muff & inspect the exhaust system for cracks/leaks before your next flight (or if that isn't possible avoid (or limit) use of cabin heat & defrost & monitor the CO meter as part of your scan until the exhaust system can be checked).

You should also check your CO meter: electronic CO meters have a finite life, just like chemical spot detectors (though they generally last several years) - your detector's manual will specify a replacement interval. As the sensors age they may give inaccurate readings.

A note about ground operations - Electronic CO detectors are sensitive enough to occasionally generate transient alarms during ground operations due to exhaust gasses entering the cabin. This can happen during summer or winter.
As long as the levels are low and the alarm clears when you're moving (taxi or during climb-out) this is probably not a problem, but you should know what is "normal" for your aircraft.


Is it more efficient to have many or a few rotors? Wouldn't it be smarter to design VTOL rotorcraft with many smaller rotors than one big rotor? With more rotors you have more redundancy and smaller blade velocity (and perhaps better stabilisation) thus leading to a safer more reliable system. It seems like the problem with lots of rotors is that you lose all efficiency. I don't get this though. If a rotor prop produces x thrust at y efficiency, couldn't this be simply scaled up to produce the same thrust and efficiency ratio?

Rotors need something to power them and the current generation of aircraft (once you get bigger than model size) burn hydrocarbons to get that power. If you want twelve rotors, then you either need twelve engines or you need a smaller number of engines plus a bunch of heavy driveshafts and gearboxes.

I assume from the fact that most contemporary aircraft designs use a small number of engines (usually one or two; sometimes three or four) that having a few larger engines is generally more efficient than having more smaller engines. This seems to apply equally to jet engines, turboprops and piston engines.

It's possible that the tradeoffs will change if you move to electric motors. However, at the moment, batteries are so heavy that electric motors don't seem to be a practical option.


Why are several of the Tu-104’s cabin windows oddly positioned? The Tu-104 (the fourth jetliner to fly1 and the second to enter revenue service2) has a cabin-window layout that is... somewhat odd, to say the least.

From front to back:

What appears to be the second cabin window from the front (although, given how far forward it, and the window in front of it, are, I’m not sure that they are actually cabin windows; I’m not familiar with the location of the Tu-104’s cockpit bulkhead) is mounted so high on the side of the fuselage (the whole window is in the white region above the blue livery striping on the sides; in contrast, most of the Tu-104’s cabin windows are mounted near the middle of this blue band) that one would only ever be able to see the sky through it, unless something was going really wrong.  It and the one in front of it also appear to be slightly smaller than the windows further back, but this could just be perspective or a trick of the eye.
The two consecutive windows over the front middle section of the wing are mounted higher than the windows in front of and behind them, although not as high as the window discussed in point #1 (most of the area of these windows still falls within the blue area, with only the tops of the windows breaching the white).  The more forward of these two windows appears to form part of the second overwing escape hatch - but the window in front of it looks to be part of the forwardmost overwing exit, and, yet, is mounted at the normal height - and these two windows have Aeroflot’s winged hammer and sickle painted in the space underneath them - but I’m having a hard time believing that a simple livery detail would have any significant influence on the design of the aircraft itself (it’s usually the other way around!).
The fourth window from the rear is mounted about as high as the windows discussed in point #2.  It lies above the numeric portion of the aircraft’s tail number, but - again like with point #2 - I’m having great difficulty believing that the window placement was simpler to alter than the paint job.
Finally, the three rearmost cabin (I think?) windows are mounted very high on the fuselage - about as high as the window in point #1.  These three windows overlie the “CCCP” portion of the aircraft’s tail number (but, again, see points #2 and #3!).

Why the wonky window work?

1: ...preceded by the Comet, Jetliner, and Caravelle.

2: ...preceded only by the Comet.

I found a cutaway diagram of the Tu-104B. It appears that, at least on this model, some of the seats in the middle were raised a bit to perhaps accommodate some engine parts (there appears to be a label on the diagram which I can't quite read). The windows were raised correspondingly to match the seats. The mid-positioned one at the aft may have been placed there to match one in a door on the port side of the aircraft. The three high-positioned ones appear to be windows in the toilets (туале́ты).


Can a lightning strike lead to structural damages of the fuselage and eventually cause decompression? I know that modern aircraft are designed to withstand lightning strikes. Still is there a possibility for aircraft to sustain significant damages of the fuselage due to lightning strikes and subsequently face decompression?

Decompression is a tricky thing.  The aircraft is already quite "leaky" and without a steady flow of pressurized air from the engine bleed air (or compressors, in the case of the 787) the altitude in the cabin will rise slowly. There is a pressure controlled outflow valve in the back of the aircraft that is usually about 10-20cm square. The pressurization system stuffs air in constantly, and the outflow valve opens and closes to keep the interior pressure at the correct altitude.  Any hole smaller than the amount of air the pressurization system can pump in will just be handled by the outflow valve closing somewhat.  Depressurization due to structural failure is fairly rare.  Most recent would be Southwest 1380, where an uncontained engine failure broke a window.

I have not heard of a lightning strike even piercing the aircraft fuselage in modern civilian aircraft, much less in the cabin area.  There are a few cases I have heard of it happening to military aircraft, and in those the hole was fairly small (about 2-5cm in diameter).  Aircraft are regularly hit by lightning, and extensive testing is done to simulate lightning strikes before an aircraft can be certified.


Is recurrent simulator training required every 12 months whilst acting as SIC under Part 91? What are the regulations on recurrent training for a crew member who is type rated as PIC but is acting as SIC, flying internationally on a Bombardier Global Express Part 91 operation (not subpart K)? The last recurrent training for the crew member was 18 months ago.

Part 61.55 stipulates SIC qualifications but i would like to know if recurrent simulator training is required every 12 months whilst acting as SIC? If not, then what 'currency' values are required to maintain your privileges as SIC?

The only Part 91 recurrent training and testing requirements are in subpart K, so if they don't apply to you then only the general currency requirements in Part 61 would apply.

The SIC currency requirements in 61.55 are (every 12 months):

  (1) Become familiar with the following information for the specific
  type aircraft for which second-in-command privileges are requested—

  (i) Operational procedures applicable to the powerplant, equipment,
  and systems.

  (ii) Performance specifications and limitations.

  (iii) Normal, abnormal, and emergency operating procedures.

  (iv) Flight manual.

  (v) Placards and markings.

  (2) Except as provided in paragraph (g) of this section, performed and
  logged pilot time in the type of aircraft or in a flight simulator
  that represents the type of aircraft for which second-in-command
  privileges are requested, which includes—

  (i) Three takeoffs and three landings to a full stop as the sole
  manipulator of the flight controls;

  (ii) Engine-out procedures and maneuvering with an engine out while
  executing the duties of pilot in command; and

  (iii) Crew resource management training.

Practically speaking, what the FAA requires is only part of the picture because your insurance company will probably mandate certain training and currency requirements that may go well beyond the regulations.


Can one become a scheduled airline pilot with just one functional eye? I was reading about TACA Flight 110 that amde a successful emergency landing on a New Orleans levee and I found out that the Pilot in Command was blind in one eye.

Just curious, under current FAA rules would such a pilot be able to get the Airman's Medical Certificate needed?

There's a related question, but that only discusses getting a PPL and even there the responses are quite skeptical. And here we're talking about a CPL, or more accurately a type-certified ATPL.

Have regulatory regimes become stricter? Even if the rules allowed it, would risk-averse/litigation-averse airline companies allow it? Are there other cases known?

Under current FAA medical regulations a pilot with one functional eye (called monocular vision) can get any class of medical, including the class 1 required for airline pilots:

  An individual with one eye, or effective visual acuity equivalent to
  monocular, may be considered for medical certification, any class,
  through the special issuance section of part 67 (14 CFR 67.401)

As the same page says:

  it has been repeatedly demonstrated that binocular vision is not a
  prerequisite for flying

Incidentally, one of aviation's most famous pioneers, Wiley Post, had only one eye. As for today, it's legal and possible to get any class of FAA medical with only one eye and therefore in principle you could fly for any US airline. Whether or not an airline would hire you is a different question, but if you're legal and qualified then why not? Blindness in one eye isn't even considered a disability by the US government if the other eye is fine.

It's also possible that if an airline declined to hire you because of your monocular vision even if you hold an ATP and class 1 medical, you might have a case for suing them for discrimination. But that's speculation, and you would need to ask another site about that. In any case, there may be more pilots out there than you think with physical limitations (for want of a better word), including ones with prosthetic limbs.


Does it matter in which country I obtain my EASA Part 66 AME licence? I have completed EASA Part 66 B1.1 exam modules (some from the UK CAA and some from the German 147 organisation).
My queries are:

Can I apply to any member state (e.g., Belgium, The Netherlands, Germany, Ireland, UK, etc.) to get my initial Part 66 licence?
I have already emailed few country’s licensing departments; they declined and advised me to apply only to the UK CAA.

If I can apply to any member state, why did I get these replies? If I can’t, why not?

Does it affect job prospects in the UK if someone has a Part 66 license issued by another European country? (And vice versa?)

To which authority (country) can I apply to get my Part 66 licence as soon as possible if I am eligible to do so.

Does it affect aircraft type rating endorsement in future on a Part 66 licence? For example, if my license is issued from Belgium but I’m working in the UK.

When you have to deal with the authority, the theory and the practice varies a lot. So, there are things that theoretically you should be easily able to do, but that the authority won't accept, for no real reason. Sometimes it's just how the guy at the desk woke up in the morning.

Anyway:

1) Yes, you can apply in any country of the EU28. I know Switzerland won't accept your appliances unless you work in Switzerland, don't know about Norway and Iceland. Have no idea regarding the new situation in UK after the Brexit.

2) Because Europe is not a federation of States like in USA, and each authority want to impose own power and rules and protect our market. Ask them why.

3) Theoretically no. Pratically, maybe.

4) All EASA countries. Where do you work? Where did you get your theoretical modules and practical experience? Try starting from there.

5) Repeat the question again, it's not very clear to me.

To apply you need to compile and send the EASA Form 19 (You can find it here) to any European competent authority.

You can also find the Annex III, the Part 66 of the Easa Regulation 2042/2003 here, with all the pertinent information. (In particular check the 66.A.10 Application)


Are the communications between captain and flight attendants standardized? Premises

For usual communications between pilots and ATC, a specific phraseology is followed.
In case of an an unexpected event (e.g. a sick passenger), flight attendants and pilots can communicate through intercom.
Pilots (particularly the captain) can speak to all people in the cabin (including flight attendants) through the public address system.

Questions

Do the communications made between the cockpit and the cabin (thanks to the public address system) follow a specific phraseology to deliver information to flight attendants?
Are there some messages following a specific phraseology that trigger a reaction among the flight attendants (e.g. preparation for flying across turbulence), but passenger may think the message is address to them?

I think of the coordination of the preparation of the cabin for the different flight phases (taxiing, taking off,...) or indication of the strength of turbulence (implicating the flight attendant may not begin to move carts along the cabin).

Again, since there has been a sparsity of answers, I'll try to add to Simon's excellent answer and give a bit of a different perspective. My answer is dated in that it comes from flying 747-100 and -200 aircraft in the 1990s at the last airline I worked for. Given what I am sure is a wide variability of cockpit crew & cabin crew communication practices around the world, it may still be relevant. Remember, though, this is pre 9/11.

The cabin crew typically would arrive at the airplane before the cockpit crew. The first interaction other than a quick hello as we came onto the airplane was usually the upper deck flight attendant coming into the cockpit within a few minutes of the cockpit crew (captain, first officer, flight engineer) getting settled. Company policy was that the upper deck flight attendant was to check with the cockpit at least every 20 minutes to see if they wanted anything. It's the captain's airplane, though, and she/he could set the tone. I always declined anything until we had reached cruise. Additionally, I would tell the flight attendant that checking every 45 minutes to an hour would be sufficient but that if they just wanted to come up to chat at any time that would be fine. We were usually flying 8 to 12 hour legs. I would also tell them that I preferred to be called Terry rather than Captain, though more often than not they still called me captain.

Company policy was that the purser (chief flight attendant if you like) was to personally come to the cockpit to inform the captain that "all doors are closed, all passengers seated." That was my cue to call for the before-start checklist. Likely the purser had already been to the cockpit earlier to let me know how the loading was going, who was in back, and any problems. I in turn would give the purser the expected flight conditions, estimated time en route and such. I wasn't big on the captain making announcements to the cabin. My policy was to give the info to the purser and let them handle cabin announcements as much as possible.

The next company-required communication was hitting the button that sounds the beep throughout the cabin when we climbed through 10,000 feet, and I'd turn off the seat belt sign then as well. If there were no weather/turbulence problems en route, the next usual communication was a call to the purser shortly before the start of descent. However, typically the purser would have come to the cockpit every couple of hours during the flight to chat.

Descending through 10,000 feet I'd hit the cabin tone button twice and turn the seat belt sign on.

Last cabin communication was hitting the cabin tone button and turning off the seat belt sign after the parking brake was set.

Hajj flights were a special case. The purser was always one of our people, but the flight attendants were supplied by the national airline we were doing the flights for under contract. The requirements included that the captain be notified if anyone became seriously ill. All Hajj flights were required to have at least one doctor onboard, who would be a Hajji as well. The purser would come into the cockpit to tell the captain, and the captain would ask if the doctor wanted to land for a medical emergency (they never did). The captain was also to be notified if someone died. This was not unusual on Hajj flights, and we carried body bags for that contingency. A death was not a cause for landing short of the destination.

There is an area that starts before descent that has religious significance to Muslims because of the proximity to Mecca. It was marked on the IFR en route maps. We were supposed to announce entering that area. I always did that personally because I had learned how to properly pronounce it's name (well, as close as I could). The irony of the situation was that here was a 747 from a Jewish-owned airline, captained by an atheist, telling a plane load of Muslims they were approaching Mecca, Islam's holiest city.


Where can I find United 757 Checklists? (CRM, Pre Start, Pre Takeoff) Where can I find United 757 Checklists (CRM, Pre-Start, Pre-Takeoff)? I need these for a writing project that I am doing. Any help is greatly appreciated. Thanks in advance!

Thanks, Charlie :)

I doubt that you can get an airline specific checklist for an airplane, but for Boeing 757-200, a generic one is available. Please note that they might be for simulators (as Ben mentioned) but are close enough.

PDF
Trello
X-Plane (screenshot below)


How dangerous was the turbulence on this commercial flight? EDIT: Having read these great answers I feel a little ashamed for the fear I felt on this recent flight. However, judging by my reaction to the experience and the reaction of those around me on the flight I imagine I am not the only one who felt this way. As others have mentioned here I will agree that passengers are pretty bad at judging turbulence. For those who come to this Stack Exchange site with similar concerns, I hope that you read these answers from those knowledgeable in the field to assuage your concerns.

I was recently on a flight that flew in to central Texas coming from Denver. There was bad turbulence on the flight in the last 45 minutes -- the worst I have ever experienced -- and I was curious about what else was going on behind the scenes from the perspective of the pilot and crew.

I do not know the airplane model. It has ~38 rows and 3 seats on each side of the aisle. I was in row 35. It was a standard commercial airplane that would fly across the United States.

We were first told that we were about to enter a turbulent area based on reports of other airliners in the region. We soon entered an area of lightning and dense clouds so thick that there was no visibility outside the windows.

The first drop came unexpectedly in what I can only describe as similar to a bad, bumpy landing on the freeway. The bags rattled pretty hard and loudly and I felt myself leave the seat. It was loud and jarring enough for most of the people in my area to scream out loud. Over the next 45 minutes, these drops happened continuously and randomly, up to 15 times.

Between these big drops the plane felt like it was swaying from the left and right. There were also many tiny dips between the bigger dips. It was extremely tense for everyone on the plane and generally it felt very uneven below us so there was a constant anticipation of another drop.

After the landing gear went down, it was clear that we were ascending again. The pilot explained that there was a "spacing" issue on the ground so he was going to fly around and try to land again. The guy next to me said (jokingly?) that this meant the pilot was too scared to land.

The cabin crew looked pretty terrified, and they were chatting to each other throughout the whole ordeal. People were sobbing and weeping all around me and they would yell every time a drop happened.

Obviously, you have little information to go off of but I was curious, from what I have provided, about the following questions:

Many people on board were fairly traumatized by the experience. Was there any real danger from turbulence this bad? Is this something a pilot might encounter routinely that they would be equipped to handle or does this seem unusually bad?
What was happening behind the scenes? How does a pilot handle a situation like this? Was there other information about the turbulence that we were not being told?

Any other interesting, related information to give me insight into this experience would be appreciated.

Very little to go on (non-pilots are lousy at classifying turbulence) but my best guess is that you experienced moderate turbulence.

If it was severe, your description would have been something more like this:

  I couldn't focus my eyes to see. Someone who wasn't belted down was
  flung violently against the ceiling, then slammed to the floor. The
  captain was very assertive, telling the FAs to be seated immediately and
  that all passengers must strap in. The flight attendants wedged the
  service carts into the gaps between the seats and asked some
  passengers to hold them down, before sitting down and securing
  themselves in with their full 4 point harness. During the worst of it, there was no way anyone would have been able to stand, even if you were holding onto the seats or walls. Some overhead bins
  popped open strewing their
  contents about the cabin. There was coffee, cups, plastic glasses,
  books, etc. flying around EVERYWHERE. Several
  people had to be taken off the plane by stretcher.

Pilots are not "scared to land". If it's not safe, they will divert. If the approach is wrong, they will "go around" (both perfectly normal) and spacing issues are the most likely reason. Why would the captain lie?

Ask a pilot.

The reaction of passengers is not a good indicator of the level of turbulence but the bottom line is, aircraft are designed to cope with the worst turbulence, and then some. You were perfectly safe.

I have to take issue with your use of "air hostesses", I believe you mean "cabin crew" or "flight attendants".  We stopped calling them that when we realised that they are actually professionals with a vital safety role as their primary function and are of both genders.


Why do we refer to "power" for turboprop engines and "thrust" for turbojet/fan engines? In jet engines, I read that thrust is related to the fuel flow rate, whereas in turboprop engines power produced is related to the fuel flow rate. What is the reason and brief math behind this?

Ultimately what you want from all three types of engines is quantification of thrust available to push an airplane through the sky. The turbofan/jet engines are self contained and produce thrust directly but a turboprop engine requires the addition of a propeller, which may have differing characteristics based on the installation.

Since thrust is not known for a turboprop until its installation has been determined, manufacturers instead quantify the power available to drive a prop. This allows engines to be compared so that an airframe manufacturer can make the proper selection.

Fuel flow is then related to either thrust or power as a measure of efficiency, depending on type of engine. There is generally no published mathematical relationship between power and thrust for a given engine. It is not needed for turbofans/jets and not possible to determine at time of manufacture for turboprops.


How can I customize my training to become a flight instructor? I plan on starting my flight training soon at the age of 41, but I don't want to stop at PPL and simply fly for fun: I want to ultimately be a CFI.

With this goal in mind, my question is what recommendations can my fellow aviation enthusiasts and experts give me in the planning I should do for my aviation education? Is there a specific type of facility to select for training, a progression of obtaining certificates and ratings I should follow, etc.?

First, if you haven't already go check out AOPA's Let's Go Flying site - specifically their page on how to pick a flight school/instructor. Some of the advice I'm going to give you is pretty much ripped right from them.

For my two cents, if you're going for a career move (even a part-time side job type career), you want to optimize your training path - you do not want to be like me where you're doing this whole aviation thing "just for kicks" and can be be a perpetual student pilot taking as long as you want to get each rating!

Generally speaking this means you want to follow the "traditional" path of certificates and ratings in your chosen aircraft category and class. For Airplanes that would be Private Pilot, Instrument Rating, Commercial Pilot, and CFI.
You probably don't want to "detour" to ratings like Sport Pilot (unless you want to become a sport pilot instructor and don't intend to ever become a "regular" CFI, in which case this path lets you skip the instrument and commercial ratings).

The private->Instrument->Commercial->CFI path is "typical" in my experience, and it generally seems to make sense because the skills you use in each phase naturally build on each other and will help you with the more difficult tasks the next rating will demand.

It's probably also worth spending a little time with the Part 61 requirements for each certificate and rating you intend to pick up and planning ahead -- for example, if you can economize by making sure your instrument rating cross-country flight time requirements also satisfy some or all of the requirements for the Commercial rating you can avoid having to do basically the same flying twice.

As far as where you do your training, a lot of that depends on your personal situation (funding, schedule and personality).  The general rule here is "the more you fly the faster the training goes".  I was a weekend warrior for most of my private training, and between weather delays and extended gaps between lessons it took me a LONG time to get that first ticket - the instrument rating may end up taking just as long!

If you're a good student, can take a substantial block of vacation, and have the money to throw at your training an accelerated/immersive program is often the most cost-effective and shortest route to a given certificate or rating: You are effectively becoming a full-time flight student, flying and studying every day, and when you eat, breathe, and sleep aviation you generally pick things up a lot quicker.
As an added advantage these are often Part 141 programs, which reduces the hour requirements for the certificates and ratings (but even if the training is conducted under Part 61 you're still at an advantage because of the immersive nature of the program).

If becoming a full-time student is not an option for you a structured Part 141 program may still be: Some Part 141 schools have "weekend warrior" programs that follow the same syllabus, and have the same benefit of reducing the hour requirements. The drawback is they're not as "immersive", so information may not sink in as quickly and skills will probably take longer to develop - you'll take longer (and probably spend more money) as a weekend student than you would as a full-time student.

The last option is "regular" Part 61 training, which is what most of the folks I know with day jobs they can't escape from do. This is certainly the most flexible option as you're basically training on your own schedule and program. Good instructors will almost universally still be working from some kind of syllabus to keep your training on-track and moving forward, but there's more freedom to jump around and change up the order of lessons, which is nice if you're getting stuck, or bored, or need to really work on a specific maneuver/concept for a while.
The downside is the same as I already mentioned for "weekend warrior" 141 training: the time between lessons really puts a hurting on your mechanical skill development and knowledge retention, and you'll probably wind up taking longer to finish your training.
There is however no reason you couldn't finish up a Part 61 training program right around the bare minimums for each certificate/rating, assuming you fly frequently and don't hit too many personal stumbling blocks along the way.


What is meant by a “cold soak" of an APU? What is the exact meaning of "cold soak" of an Auxiliary Power Unit (APU)? Is it to do with long flights at high altitude and the fuel getting cold? Will it affect the ignition of the APU? Can anyone tell how this affects the function of APU?

It means the APU has been in active or not operating in a cold environment for an extended period of time. Here, like any other piece of machinery and operating fluids are “cold soaked“, that is, has reached the ambient temperature of the environment.   During extended flight at high-altitude, and APU would encounter this as it is not normally used during cruise flight.   This does affect the ability of the unit to power up in the event of an emergency, as most machines don’t like being operated in extremely cold weather, and usually require a period of time in order to warm up.


What is the proper technique for using rudder pedals with toe brakes? I just had my first flight lesson the other day and I had some issues with using the rudder pedals and toe brakes for taxiing.  For example, how do you steer and brake at the same time when making turns?  I also sometimes inadvertently press the toes brakes when trying to steer the plane. Is there any advice that you can give me to help me coordinate steering with toe brakes? I find that steering the plane on the ground with the rudder pedals is quite foreign to me, I have never had to use this level of foot coordination before.

I am flying a Piper Cherokee with steerable nose wheel and toe brakes.  Also does anyone else have this problem or is it just me?

Unless you have extra long feet, keeping your heels on the floor of the plane is usually sufficient to keep them off the toe brakes.  Or pull your legs back a little and press with the balls of your feet near the middle of the pedal and not the top.  You'll get the hang of it pretty quick.

Learning to relax helps also, otherwise you'll fly with your legs all tensed up and just have the rudder pedals all mashed down all the time.  Very tiring.


Can any aircraft have ETOPS? I am wondering if any plane can become ETOPS certified? And, is ETOPS the right acronym?

Theoretically anything can be certified if resources are allocated to meet certification requirements. It may not be practical though:

The plane must have at least two engines (obviously)
It must have the range to fly to an alternate on one engine only
Engine failure should not increase cockpit workload too much. Mostly this means some automation system that can operate with asymmetrical thrust.

(2) rules out small twin-engine planes that only have a few hours of endurance on a full tank, and (3) rules out anything without a glass cockpit and avionics suite.

Also, ETOPS is not just about aircraft design; it deals with aircraft maintenance as well. The manufacturer and operator need to come up with a maintenance program that reduces in-flight failures by monitoring various metrics and taking preventive actions before a component fault happens.

Therefore, on some aircrafts, it may not be worth the effort to obtain ETOPS.


Why does the diffuser section generate thrust in a jet engine? I am studying the thrust distribution of jet engines.
But I'm now a bit confused.

In Rolls-Royce's "The Jet Engine" book,

http://aeromodelbasic.blogspot.com/2012/05/thrust-distribution-distribution-of.html

  At the start of the cycle, air is induced into the engine and is compressed. The rearward accelera- tions through the compressor stages and the resultant pressure rise produces a large reactive force in a forward direction. On the next stage of its journey the air passes through the diffuser where it  exerts a small reactive force, also in a forward direction

I understand the first part of the paragraph that the compressor is providing forward thrust, as it is pushing (so compressing) air rearward. But why is the diffuser also providing forward thrust?
And also why the nozzle is providing rearward thrust?

The similar conculsion is also shown here:
http://www.pulse-jets.com/phpbb3/viewtopic.php?t=2183, that the diffuser is providing positive thrust by calculating the pressure force.

From my understanding of basic fluid mechanics,
shouldn't a nozzle be providing forward thrust, like the sprinkler in the garden or a fire hose?
And shouldn't a diffuser be providing rearward thrust, as the outlet speed is slower than the inlet speed, and so m dot X (v - u) is negative?

What's wrong with my understanding?

But why is the diffuser also providing forward thrust?

The diffuser slows down the flow to ease fuel-air mixing and combustion a bit later. If you only focus on entry and exit speeds, there would be no thrust.

However, if you look at the pressures on the diffuser walls, a different result emerges. Slower flow means higher static pressure, and the total pressure right at the compressor exit is already the highest within the whole engine. The pressure on those widening diffusor walls does indeed push the engine forward because of the forward slant of the pressure vector (which acts perpendicularly to the diffusor walls). Your linked pulse jet page explains this quite well.

Of course, no thrust would result if the flow were not heated and thus accelerated further downstream. So the diffuser all by itself will not create thrust; this happens only when it is placed inside a working jet engine.

  And also why the nozzle is providing rearward thrust?

This is not always the case, but here the nozzle has a converging shape which helps to accelerate the subsonic flow and converts the remaining pressure to speed. The walls now have a backward-facing slant, so the pressure vector on them will contribute a backward-facing component. In addition, the high flow speed along the large nozzle walls causes some friction, which needs to be considered, too.

For a comparison, look at the cone behind the turbine wheels. Its thrust contribution only stems from the forward-facing pressure acting on it.


Why we don't see the "SkyRider" seats in action? In 2010 nearly all newspaper reported on the new invention of the company Aviointeriors.
They created new airplane seats called "SkyRider" which you can "stand" in. This should increase Airlines profitability.
I'm not a big fan of the SkyRider seats but who can I thank, or why don't we see them in Action?

There are a lot of disadvantages, even if the possibility of lowering costs and increasing profits is a huge advantage for the airlines. This article discussed several issues from a passenger perspective:

Limited space in general (e.g. to use a laptop)
Face too close to the video screen in front of you (if there is one)
Doesn't fit tall, large, short or young people well (and I guess that older people might not be strong enough to use it)
Very limited space for carry-on luggage (because you lose space both under the seats and in the overhead bins)
Passenger resistance to the basic idea

The author's conclusion was that the seat isn't actually uncomfortable, just cramped, but he was very sceptical that passengers would be willing to use it.

Another article added some concerns from the airlines' point of view:

Could make cabin evacuations more difficult (and certification costs in general would be high for a completely new seating concept)
Difficult to market successfully
The manufacturer intended the seats to be used in a new budget fare class, not to replace current economy class seats (this adds more complexity to everything: aircraft layout and maintenance, marketing, booking systems etc.)

Both articles (and others) concluded that there's no fundamental technical or regulatory barrier to introducing them, the main problem would be convincing passengers to accept them. Even Ryanair - which is notorious for cutting costs wherever possible - rejected them although Wikipedia says that both Ryanair and Airbus have proposed an alternative but very similar concept in the past.

If the airlines really wanted to introduce this seating arrangement, I would expect them to keep the idea in the news as much as possible and generally work on convincing people that the seats are comfortable and it's a great way for them to get even cheaper tickets. Since they haven't done that (if they have, I haven't noticed) it seems unlikely that the airlines are actively working on them.


Why don't airships / blimps use frontal stabilizers or thrusters? Is there any reason why frontal stabilizers aren't used on blimps or airships to ease maneuverability in, e.g., gusty winds? Even the indoor blimps have a tail rotor, not the nose rotor for rapid yaw movements.
Also, is there any reason why the "pusher" motors are used instead of puller-ones in the front (with an exception for the Lockheed Martin P-791)?

It depends if you want stability or manuverability. see this video.

It also has to do with if you want to attempt to keep laminar flow over the nose of the airship...


How can you stop your missile locking onto a friendly target? In the modern day we have advanced planes, and advanced missile systems, however, how can you stop your missile firing at a friendly aircraft?

In planes like the F22 Raptor you can turn on sight lock, which is when you look at a plane through your helmet, the computer registers that there is a plane there, and it locks onto the plane with a missile.

However, let's say a friendly aircraft were to fly in front of you when you had sight lock turned on; would the missile fire at the friendly aircraft, or is there a piece of technology in the friendly aircraft which registers that it's with you? If so, could that potentially be used against you in modern day aerial warfare?

First off, very rarely will you shoot at an unidentified aircraft.  Most engagements require a visual ID, or a hostile action, prior to engagement. However, you will also program your aircraft with specific ROE logic that will indicate that certain aircraft are friendly, as identified by IFF transponders, Link 16, etc.

You can still lock up friendly aircraft, and we frequently do to facilitate rendezvous with friendly aircraft and to clear ourselves from traffic, but if your master switch goes to ARM and you have a friendly locked up, there's a good chance you won't be flying again for awhile, if ever.

When we lock up an aircraft, 99% of the time, it does not indicate an intention to shoot.  By using our radar and "locking up" a target we get target aircraft altitude, speed, range, target aspect, heading, $Vc$, etc, all useful things that come in handy for routine events.


What is the difference between a fix, a waypoint and an intersection? It seems these terms are used interchangeably. Are they the same thing? Do they all refer to the points in space that are given 5-letter names?

No, they are not interchangeable and indeed, have well defined meanings.

A fix is an arbitrary point in space used to establish current position calculated by referring to external references.  You take a fix to determine where you are now.  A fix might be permanent, for example a compulsory reporting point, or it might be determined by the pilot in advance in order to fly a non-airways route (e.g. when flying VFR) and then checked along the way using dead reckoning and reference to external systems or features to check that the plan is being flown accurately.  It might also be requested by ATC, e.g. "report when overhead the railroad yard" or calculated to establish where you are, e.g. taking a fix from an astrolabe on a night oceanic crossing.

From FlightGear.

A waypoint is fixed point in 2D space (latitude and longitude) used to define points along a route.  They are named, and are referenced in a plan.  You fly from one waypoint to the next, along a route.  A waypoint is where you are flying to.  It is normally positioned where there is a change of course or altitude.

These are the navigation positions given the 5 letter names you ask about.

From SailTrain.

An intersection is where two airways cross. Here, the Victor airways 15 and 76 cross at the intersection.  In this particular case, the chart symbol further shows that the V76 airway does not use the intersection, in which case the chart will include a note of the intersection usage.

From Jepptech.

Now sorry about this, but having said they are not interchangeable, it's not that simple.  A waypoint is also a fix (a fix is any 2D point).  But you do not call a waypoint a fix.  A fix is a 2D point which is not a waypoint, but is used for navigation.  A fix might be also be a lat and long defining the beginning of an arrival or departure procedure where you leave or enter an airway.

An intersection is also a fix, but it only exists to define where two airways cross (or where any other 2 lines cross, e.g. the 170 degree and 046 degree radial from two NDB beacons) so is called an intersection, not a fix.

In that sense, they are all fixes but the name has meaning.


What sources of weather are approved by the U.S. National Weather Service? Part 135 and (I believe) Part 121 operations all have a requirement to use a source of weather that has been approved by the U.S. National Weather Service:

  §135.213   Weather reports and forecasts.

  (a) Whenever a person operating an aircraft under this part is
  required to use a weather report or forecast, that person shall use
  that of the U.S. National Weather Service, a source approved by the
  U.S. National Weather Service, or a source approved by the
  Administrator. However, for operations under VFR, the pilot in command
  may, if such a report is not available, use weather information based
  on that pilot's own observations or on those of other persons
  competent to supply appropriate observations.

  ...

Does the FAA or the U.S. National Weather Service maintain a list of weather providers that have been approved and are legal for us to use?

If not, then how do we know whether a particular source has been approved?

There is an ongoing issue with this, as far as I am aware. First off, this does not apply to part 91, and nothing does as far as I am aware: you can get your weather from anywhere, but having it on record with FSS or DUATs gives you a little more padding if something goes wrong.

If you're going to get weather online, which most large operations do, the FAA requires air carriers to get weather information only from Qualified Internet Communications Providers (QICP). This is outlined under AC 00-62. Or rather, it was outlined there. 00-62 was quietly cancelled in mid 2013. In addition, the only list of QICPs (which would have answered your question) I know/knew about was removed from the FAA website.

A few weeks after it was cancelled I found out about it and called the FSDO to ask (Memphis or Louisville, I don't remember which). The man who should know told me that I knew about as much as he did. Their regional offices hadn't told them anything, and he was telling everyone to continue using the qualified service they were previously using until they learned more.

I have not called them back since, but after a quick search, I only found this OpSpec document and one that it supersedes from a few months before (8900.199). There is also a newer one in the series (8900.242) but it seems to have no information relevant to the question. I must adimit that this document is a bit over my head, but it seems that they did an overhaul of the weather regulations regarding 135 and 121, and that use of a QICP is no longer required. So I take it that unless your carrier is only certified to use a certain system, you're now allowed to use whatever you want to get the weather.

You can read those documents here, the three I mention were published under AFS-200. Search for that and you'll find them and more.

So I did some more research:

Check out 8900.1 Ch 26 Section 2. Regulatory Sources of Aviation Weather Information and Aviation Weather Information Systems – Parts 91K, 121, and 135. The first bit has a good overview of all the weather products and their intended purposes. Relevance to the question starts at 3-2073(A) Weather Reports Prepared by the NWS or a Source Approved by the NWS. (page 6 in the PDF version).

Much further down it says (in reference to part 135, 121, 125, etc certificate holders only):

  B. Accessing Weather Information via the Public Internet. Certificate holders and
  program managers often access weather information via the public Internet. When accessing
  weather information this way, certificate holders and program managers are required to use
  weather information that is provided by a weather source authorized by regulation, or approved
  by the Administrator, and is listed in the certificate holders’/program managers’
  OpSpecs/MSpecs. In the past, the FAA maintained a list of approved QICP. However, the FAA
  no longer approves QICPs. The FAA has canceled AC 00-62, Internet Communications of
  Aviation Weather and NOTAMS, and no longer maintains a list of approved QICPs. Certificate
  holders and program managers using the public Internet to access weather information are
  responsible for ensuring accurate and timely delivery of information without data corruption
  during the transmission.

That's all pretty cut and dry, I think, but keep in mind that those OpSpec papers mention that everything in 8900.1 Ch. 26 is under review and has been edited recently and will be further edited in the near future.


How to compute quaternions from raw IMU and magnetometer data? I have raw accelerometer data (w_ib^b) and magnetometer data from a UAV test flight. I would like to reconstruct the quaternion dynamics of the UAV without accumulating error from integration.

The method I was using involves solving the following integration: d(q_b^w)/dt = 0.5*Omega(w_ib^b)*q, where Omega(w_ib^b) is of the form: [-skew(w_ib^b) w_ib^b; -w_ib^b' 0].

I was wondering whether there was an alternative method of computing the aircraft attitude given raw angular velocity and magnetometer information from a UAV?

If all equations are digitally computed multiple times per second, all variables are updated at every frame and the integration error is only one time-step old. Full Flight Simulators use four sets of quaternions to compute the state of the aircraft in earth reference frame. To illustrate how it is done in FFS flight dynamics, here is a partial set of the steps that take place:

$$ \dot{E_1} = 0.5 \cdot (-E_4 \cdot p - E_3 \cdot q - E_2 \cdot r) + E_1 \cdot C_Q * C_{Q\Delta t}\tag{1}$$
$$ E_1 = \dot{E_1} * \Delta t \tag{2}$$
$$ \Sigma E^2 = {E_1}^2 + {E_2}^2 + {E_3}^2 + {E_4}^2 \tag{3}$$
$$ C_Q = 1 - \Sigma E^2 \tag{4}$$
$$ E_{1P} = E_1 * \frac {1}{\sqrt{\Sigma E^2} } \tag{5}$$

Equation (1) is one of four equations for $\dot{E_1}, \dot{E_2}, \dot{E_3}, \dot{E_4}$, while $p,q,r$ are aircraft roll, pitch, yaw rates.
$C_Q$ is a quaternion correction factor which uses the sum of all quaternions squared.
$C_{Q\Delta t}$ is a timing correction factor and should be less than the iteration rate in Hz. A constant value is empirically chosen that gives good stability.
Equation (2) is a simple Euler integrator using the actual time step of the computation frame. So if we're computing at 1000 Hz, $\Delta t$ = 0.001.
$ E_{1P}$ is the prime quaternion substituted in the transformation matrix from body to earth axes.


who owns the abbreviated name of an airport is the name of an airport such as LAX the act of the FAA or the ICAO?  from reading, it looks as though the process starts at the ICAO as a recommendation, then is adopted by the FAA?

4-letter names are too trivial to be protected by copyright. Trademark protections require 1) specific applications, 2) commercial usage, 3) that the offending use is relatable enough to the original business to dilute the trademark or harm the business.

(Thus, for instance, an "Airbus" car would be a clear a trademark violation, for a model plane called "Airbus A320" some agreement is preferred just to be safe, and for a book titled "Airbus A320" no communication with Airbus is needed, as it does not compete with any Airbus product, nor does such a title on a book imply being one.)

IATA and ICAO codes amount to nothing more than telephone numbers. They cannot be copyrighted, since they represent abstract concepts rather than a creative expression of one, and they aren't trademarked.

More than that is a question for Law.SE.


Why is it not allowed to dispatch an Airbus A320 with an inoperative ELAC 2? In the case of ELAC 2 failure, ELAC 1 will take over. However, it is not allowed to dispatch an Airbus A320 with an inoperative ELAC 2. Why is that?

As pointed out by this discussion on PPRune, ELAC 1 only controls elevator actuators hooked in to the Blue hydraulic system. ELAC 2 is split across Green and Yellow.

If ELAC 1 is the only operational computer and the aircraft enters emergency electrical configuration, blue hydraulics will be lost until the RAT deploys. Further, the fallback for ELAC 2 (G/Y hyd) is SEC 2, which is not powered in EEC. Thus, the aircraft will have no primary pitch control.

The solution is that if the fault is in the ELAC computers themselves, to swap the units before dispatch.

In general, if there's something weirdly asymmetric about the A320, the first guess should be something to do with EEC. This is because EEC, by design, tries to only power one unit, typically number 1, of each system.


In an engine failure, should I expect less range than with the engine in idle? I fly a C172 (fix pitch propeller) and when my instructor and I practice a simulated engine failure, we do not turn off the engine, instead we set the engine to idle.

In an actual engine failure, should I expect less range than with the engine in idle?

Yes to some degree.  It depends on the idle rpm, prop pitch, engine compression and your gliding speed, but if the engine is off but windmilling, there is substantial drag from the energy needed to windmill the prop without any help from the engine and it will knock some measurable amount off the glide ratio.

When it's idling, it might still be windmilling a bit if there is still a negative angle of attack on the blades.  At some rpm just above idle, the prop's rotation speed will be at the zero thrust point (blade AOA at zero) and the glide will be like there is no prop there at all. To know where that is, you'd have to be able to measure the thrust load directly somehow.  So it's quite a moving target, trying to come up with a gliding value with different conditions with a running engine.

With the engine off completely, the windmilling drag drag case is at its worst, and the best glide is achieved if the propeller can be stopped completely so that the blade is fully stalled with a near 90 deg AOA, but this is not something advocated in training.

A stationary fixed pitch propeller makes way less drag that one being driven around by airflow, which is effectively in an "autorotation" making substantial lift aft. You an visualize this by imagining an autogyro, which can descend vertically with the airflow going straight up through its rotor to drive it - it's windmilling - and the rotor creates enough lift to limit the gyro's descent rate to about 500 fpm. Make the rotor stop completely and the autogyro becomes a falling anvil.   Turn the gyro 90 degrees, make the rotor really small, like propeller size, and there's your gliding 172.

Problem is, while it's theoretically beneficial to get the prop to stop, you usually have to slow down quite a lot, maybe close to stall speed, not a good idea at low altitude. And a tired engine with low compression might keep windmilling right down to the stall speed (and an engine with tight cylinders may stop windmilling right at glide speed - a nice bonus).  Under a few thousand feet, there are too many risks and other priorities to bother with this just for the L/D improvement.

If the engine quit at a substantial altitude and glide distance was absolutely critical (like over the water and trying to make it back to shore), I might try slowing it down to get the prop to stop windmilling. How slow I have to go to get it to stop, and how fast I can go before it starts windmilling again depends on the cylinder compression in the engine, so it may work well or it may not, and I may have used up most of the benefit trying to get the thing to stop.

As a student pilot, don't go there on your own (thinking about slowing down to stop the prop) but it wouldn't hurt at all to ask for a demonstration at altitude to observe the glide performance with the prop windmilling vs stopped vs idling.  You'd get some sense of the drag differences by noting the descent rate at the same airspeed for each case.

The above applies to fixed pitch propellers.  If you have a constant speed prop (variable pitch, non feathering, and if it's feathering, like on a turboprop, well it's not an issue at all), it gets more nuanced.  Normally if the engine quits the prop goes to full fine pitch with the blades nearly flat and it likely will stop windmilling at gliding speed.  Some people argue that moving the prop control to full coarse (low RPM) before the oil pressure decays can get the blades to kind of "part way to feather" and this will reduce the drag of the prop to less than a stationary prop at full fine with the blades nearly flat.  On the other hand, the coarse pitch might just get it windmilling... Hard to say without some testing.


What are fuel biases? Does anyone have an idea of what is it? From what I gathered from the web, it seems that this is the margin of error between the actual, real fuel consumption of the aircraft and the fuel consumption recorded in the aircraft systems (FMC?). I read that the system only estimates the fuel consumption via the fuel flow, which has some degree of inaccuracy.

Airbus and Boeing seemed to have different terms for this, PERF Factor, Fuel factor. The seem to be close in definition but I'm not really sure.

Fuel bias is as you described it. As the engine ages, it burns more fuel than a brand new one.
The fuel flow (and drag) corrections are entered into the FMS. This would allow the FMS calculated quantity not to disagree with the tanks totalizer. The figures are based off previous flights and engine tests.

Maintenance personnel can refine the database by entering correction factors for drag and fuel flow. (737 manual)

also

There are also "biases" to consider, depending on the make and model of aircraft. For example with Gulfstream aircraft, our flight planning experts typically add a 16% bias for flights of less than three hours. However, biases depend on the age of the aircraft, how the operator flies it, planned flight level, and speed.
So, it’s best practice for operators to compare actual fuel burns with flight plan burns to confirm accuracy. (Source)

Boeing does not call it bias when I checked the 787/737 manuals, but 'bias' is likely a flight planning software term.
(Source) From a flight planner for a flight sim.
(Source) Random real flight plan. Note: company software differs.
Boeing 787 FMS interface where the drag and fuel flow corrections are entered.


What exactly is VMO and how does it affect a plane when it is exceeded? I read an article that mentioned "VMO" speeds of a 747 and that the plane, when it exceeds its VMO, shakes uncontrollably and destroys itself.

I've never heard of planes doing this and the article explained VMO in a way that is beyond my understanding.

For someone that doesn't know much about aviation:

What does VMO stand for and how does it affect planes when exceeded? If it does cause the plane to shake to the point that it destroys itself, why is that?

$V_{MO}$ is a “maximum operating speed”. It is one of many “V-speeds” defined for an aircraft that limit operation at various flight phases. All V-speeds are indicated airspeeds¹.

The $V_{MO}$ is the maximum permitted speed for the aircraft. This includes a safety margin, so pilots can reasonably fly near that speed. Exceeding it is not immediately dangerous, but as it reduces safety margins, is an incident that should be investigated.

There is another speed, $V_{NE}$, the “never exceed speed”, which is somewhat higher and which marks the point where things start to get dangerous. When the aircraft exceeds $V_{NE}$, aeroelastic flutter may develop that will destroy the aircraft and/or important parts may break off as the dynamic pressure becomes higher than what they are designed for.

Also these speeds have their Mach number counterparts², $M_{MO}$ and $M_{NE}$. At high altitude, the same indicated airspeed (IAS) corresponds to much higher true air-speed, since indicated airspeed decreases with pressure, while the same Mach number corresponds to slightly lower true air-speed, since speed of sound only depends on temperature. So at high altitudes, the Mach limits are reached first while at low altitudes the IAS limits are.

Exceeding the $M_{NE}$ has different effect, though also dangerous. Above that speed flow separation occurs above the wing due to supersonic speed of the flow. This leads to loss of lift and significant down-pitching moment (a.k.a mach tuck), which aircraft not designed for supersonic flight may not have enough elevator authority to compensate.

¹ The airspeeds are given as IAS, the speed measured by pitot probes, so they can be directly compared to the indication in cockpit (aircraft with EFIS (“glass cockpit”) usually correct those measurement errors that can be estimated, showing so called calibrated airspeed (CAS)). However it may not be just a simple number but may be tabulated depending on other parameters.

In particular $V_{NE}$ and $V_{MO}$ may depend on altitude, because flutter depends on true airspeed (TAS) and at lower density (due to lower pressure at altitude) the same TAS corresponds to lower EAS/CAS/IAS.

² Mach number is true airspeed as fraction of speed of sound. In this case the limiting factor is formation of shockwaves due to the flow speed locally exceeding speed of sound around some parts of the aircraft.


Is it ever possible to auto-rotate with a missing rotor blade? A couple of years ago a UH-60 managed an auto-rotation landing with "badly damaged rotor blades."  (Couldn't find further details on that incident.)

Is it ever possible to auto-rotate in a helicopter that has lost a segment or entire blade of a main rotor?

My guess is that, in general, it would be impossible to control the lift asymmetries and such in-flight damage would always result in an uncontrollable crash.  If that's correct, then what about the special case of a helicopter with 4 or 6 main rotor blades, and if it were possible to jettison the blade opposing the one that was lost or damaged?  (Are any helicopters equipped with an emergency ability to jettison rotors in flight, other than the ones with vertical ejection seats?)  Is it known whether such a damaged rotorcraft can reliably auto-rotation in that scenario?

Highly improbable. If you've ever seen how much a washing machine can shake with a little imbalance in the laundry, at a relatively low energy spin, imagine the destructive forces that would be experienced by the imbalances in your theoretical rotors. Even if your missing blade manages to get away without causing impact damage to the other blades, there is going to be an immediate violent force translated through the aircraft. Your newly configured rotor formation is still going to try to spin around its center of mass, which is no longer concentric with the mast. The degree of imbalance will tell you how far off center the new center of rotation wants to be. The mast is still going to be trying to keep the rotor rotating on its own center, so now the rotor and mast are fighting to circle their common center, and basically this means the rotor, it it doesnt just go to pieces from all this force, will be yanking HARD and fast on the mast, which would probably rip it off the airframe.... but, if your magic rotor and mast stay intact, the violent motion would be translated to the airframe which will now be shaking super violently around you, which would likely cause it to rapidly disassemble. If it magically stayed together, the people inside (hello pilot) would be experiencing forces through the body like riding the paint shaker at the hardware store, but harder and farther, if not faster, on every shake. Watch that paint shaker and imagine your head being in that.

I do not believe your scenario would be survivable, even on the ground. It's odd to think, but a complete rotor disintegration is not the worst thing that could happen after blade loss.


Why does IAS decrease with lower air density if power is constant? TAS increases with less dense air, which is intuitive. What I don't understand is why IAS decreases.

This is assuming sub-transonic speeds where compressibility effects are negligible.

To phrase this in more practical terms, if you look at the climb table in a POH for a turbocharged airplane you will see full throttle climb rate drops with an increase in altitude/temp, even before the MP drops. EAS and propeller efficiency would not seem sufficient to explain the IAS drop seen.

I would think that given a TAS, pressure altitude, and temperature, one could derive the IAS but I have not seen any math to do this.

This is in reference to a turbocharged propeller driven airplane that is capable of maintaining power at higher altitudes.

Because even with constant power, thrust decreases with velocity, also known as TAS.

Drag depends mainly on the dynamic pressure, which is what IAS represents, so if you had the same thrust, you'd have the same IAS too.

However a piston engine produces approximately constant power (if your RPM is in the optimal range), and power is thrust times velocity. So the turbocharger lets you have the same power in the less dense air, but because your true airspeed is higher, the thrust is a bit lower and therefore your (maximum attainable) indicated airspeed is as well.

And then there is the effect of RPM. Engine power (of any engine) is limited by RPM, growing up to some optimal speed and then declining (and then you get to the red line). If you have a fixed propeller, your available power grows with speed first as the RPM increases with decreasing effective pitch, but then you cross the optimum and the power starts reducing and then you hit the red line and have to retard the throttle. And effective pitch again depends on TAS.


Why are critical flight computers redundant? At least in airliners, the truly critical computers are redundant. Typically three identical copies of the autopilot computers run in parallel and compare results; if one computer disagrees with the other two, its output is ignored. The system allows some processors to be faulty while maintaining the operation of the overall system.

But why? I've never heard of microprocessors suddenly failing. Sure, there could be manufacturing errors, but those would have been caught at the factory. Perhaps the program (and its proof) is wrong, but it would be wrong in the same way across the processors. Similarly, bad input would cause bad output across all three computers. What kind of errors does this redundancy protect against? Do microprocessors sometimes just do math wrong?

If a microprocessor is overheated or overloaded and spontaneously fails, I would expect it to stop doing anything and produce no output. To deal with this kind of failure, you'd want to have a backup processor, but you wouldn't need to compare the outputs of three computers—any output produced would be assumed correct, so you'd be happy to directly use the output of any processor that was producing output.

Related: The answer to What is the purpose of multiple autopilots? simply says "redundancy" before going into how this is achieved.

Failure modes to consider:

Overheating. This changes the chip's timing properties and eventually results in error. This can manifest as single-bit errors in the middle of seemingly normal operation; it will eventually crash, but may output bad data first.
Water damage. Manifests as a parasitic resistance on the board and may cause you to misinterpret bits as high or low. May be leaky housings, condensation, etc.
Electromagnetic interference. (The system is supposed to be resistant to this, but it's still worth thinking about).
Physical connection problems. Either during construction (soldering faults) or induced afterwards (heat, vibration). Microscopic cracks in boards or joints can pass QA but result in intermittent faults. Again this can lose you a single bit at a time. This is related to the Xbox "red ring of death" issue.
Failure of other components. Capacitors are the usual suspect; electrolytic, tantalum, ceramic all have different failure modes. Again this may result in a system that mostly works but is prone to misinterpreting marginal values or suffers from timing drift.
Weird materials science ("Purple plague", tin whiskers due to lead-free solder)
Part QA may not be up to the standards you expect (suppliers shipping inferior parts with a bogus "aerospace grade" label). Hard to detect even after it's happened.

It's important to recognize that in high-speed digital systems you don't get nice clean "one" and "zero", you get a series of rising and falling edges that are smeared out by the parasitic capacitance and inductance of the wiring. This is inherently vulnerable to being misinterpreted in marginal electrical conditions.