How much should it cost to get IFR-rated? What to look for? (Related to this question)

Many pilots have told me that an IFR rating is the most valuable thing i can do to improve my flying and margin of safety.

I know there are courses as quick as, "Get your IFR in 10 days!", but I'm unsure if that's  quality training that will stick with me.

How much should it cost for a robust, worthwhile IFR program for single engine land airplanes?
What would distinguish a worthy program from one that merely meets minimums?

The Part 141 flight school that I used to work at quoted around \$7,000 for their instrument package, which was 30 hours of dual flight, 20 hours of ground instruction, and 10 hours of PC-ATD simulator time. They were a Cessna Pilot Center using the old CPC King Schools course. It was a good course, and while numbers varied, I did have a couple of students who squeaked by right on the Part 141 course minimums. Other pilots added 5 to 10 hours more flight training into the mix.

In general, my gut says that it should cost an average pilot who has 100+ hours and flies semi-regularly between \$7,000 and \$9,000; probably closer to the low end than the high end, especially if the student does a bunch of self study at home on a flight simulator, possibly using VATSim as a simulated ATC.

As far as what to look for, I would recommend a Part 141 course just because the FAA is involved in the course standards, and instructor standardization is (supposed to be) part of the 141 criteria. It might be worth asking what their first-attempt pass rate is on checkrides, but that's not a meaningful long-term measure of the course's quality, just a short-term one.

You should find a course whose syllabus makes sense, includes simulator training and scenario-based flights, and make sure you work with an instructor you like. They can't be your best friend - they very well might need to give you some serious critique or cut a lesson short because things aren't going well - but you should be happy to spend a couple of hours a foot away from them in the cockpit.

I'm trying to track down the average hours to attain an instrument rating in the US; if I find it, I'll update my answer.


Navier-Stoke vs Prandtl lift calculation Why Prandtl had need to calculte lift with his lifting line theory (1933) if Navier-Stoke published equation long time ago 1822?
Also Navier-Stokes option is far more "accurate" then lifting line,N-S  are basics of CFD...

The Navier-Stokes equations represent a highly non-linear set of equations. Actually, although the have almost 2 centuries, they are one of the Millennium Prize Problems. Most of the interesting phenomenas represented by these equations include turbulence.
In specific conditions and hypothesis, analytical solutions have been demonstrated which is allowing us to understand the problem and physicis by reducing the complexity of the equations.
The law of Poiseuille appeared also after Navier-Stokes, and event the Darcy equation is empirical, not derived from Navier Stokes.
The interest of aerodynamics started to increase at the end of sXIX (first wind tunnel was constructed on 1871), so, in front of the complexity of this phenomena and the challenge the Navier-Stokes equations are some simplified equations appeared with some specific conditions. One of them was the the Prandtl lifting line theory.
One of the advantages of this theory is that relates the aerdoynamic properties of a wing to its geometry, without the need to calculate the complete flow field... think about that in CFD you have to calculate the complete flow field during hours (days?) in order to understand the properties and behaviour of a surface, this theory gives an analytical answer...
Still this theory is useful today, as helps to understand the behaviour of the wing.


Is interfering with the "go/no-go" decisionmaking of a flight crew a violation of 14 CFR 91.11? ASRS Callback #216 tells the sordid tale of a pilot who was inappropriately intimidated by an armed guard at a public-use airport into performing an unsafe and illegal flight after landing there for an unplanned overnight stay and fuel stop:

I estimated that we had just under one hour of fuel remaining, and as it was getting dark and I was completely unfamiliar with the mountainous terrain, I decided not to fly on. I landed at ABC, a public-use airport. The only telephone available connected us to the lodge, which also operated the FBO. We told the desk clerk that we could simply camp overnight and buy fuel in the morning. The desk clerk said OK. We parked on a corner of the ramp, pitched a tent under the wing, and went to sleep.
Around midnight, we were awakened by an armed man in a "Special Police" uniform, who declared, "Leave immediately or I will arrest you for trespassing and you will spend the night in jail." We told him everything noted above, but he was adamant: leave or spend the night in jail.
I estimated that I had enough fuel to make it, although certainly not enough for legal night VFR flight. Faced with the alternative of going to jail, I decided to depart. It was a pitch black, moonless night. Although clear and with about 10 miles visibility, there were no lights visible and there was no discernible horizon. I climbed above the MOCA, flew on instruments for about 20 miles to the nearest airport, and landed. The FBO there pumped 21.6 gallons of fuel into my tanks, which have 22.5 gallons usable.
My mistake was in allowing myself to be forced, even by an armed guard, into making a flight which was against my better judgement, probably beyond my capabilities, unsafe, and illegal. It was only luck that it turned out all right.
I was able to reach the manager of the FBO later. He said that the "special police" had no authority to order a pilot to take off from the airport and that he would make certain the police knew this in the future so they would never do this to another pilot.

While this behavior from any sort of airport security personnel is beyond the pale and the FBO manager's response to hearing about it is absolutely correct -- the incident raises a burning question in light of 14 CFR 91.11:

No person may assault, threaten, intimidate, or interfere with a crewmember in the performance of the crewmember's duties aboard an aircraft being operated.

Is intimidating or threatening a pilot into taking off (vs staying put) considered a 91.11 violation by the thug, considering that the "go/no-go" decision is one of the most safety-critical decisions a pilot makes when preparing for a flight?

If the airport received (US) federal funding, then it must be available for emergency or distress landings. The guard could require the people not camp, but forcing a flight to an aircraft without sufficient fuel, reserves, WX briefing, etc. is unprecedented.

As a matter of practice, disoriented pilots who land at private and uncharted corporate airports in northern Canada are normally given fuel, food, and calls to get WX and file flight plans.

Perhaps someone better versed in Admiralty Law might comment.


How can we avoid running out of airport abbreviations? As far as I know, airport name abbreviations are a 3 letter name. For example:

MEL for Melbourne/Australia airport
LAX for Los Angeles/USA airport
YYZ for Toronto/Canada airport

And that means all the options we have for naming are 26 * 26 * 26 = 17,576

Sometimes these match the IATA code, but not always. IATA codes are also 3-letter codes, but are not assigned to every airport as shown in this answer. But what about all of the other airports in the world? Will the world ever run out of "regular" airport codes?

A simple Google search about the number of the airports worldwide shows there are 17,678 airports. So are they going to extend airport codes to 4 letters or use numbers 0,1,2,...9?

Even by starting to use numbers they may reach a point where they run out of options. What is the approach to fix that ?

Only major airports get all Letters.   Many of the smaller airports also incorporate numbers.

Here are some examples:

Osage City: 53K
Cle Elum: S93
De Vere: 2W1

And many, many, many more...
Once you add in letters and numbers, you'll find plenty of combinations.


What does scheduled departure time exactly mean? I am trying to understand the (sometimes subtle) differences between various terminologies concerning flight schedules. What I find difficult to understand is how exactly the scheduled departure time is defined. My initial thought was that it refers to the time where the aircraft leaves the gate, after the boarding of passengers. However, I noticed that this definition is closer to the term "Target Off - Block Time".
ICAO ATFM TERMINOLOGY AND COMMUNICATIONS, page 7:

Target Off - Block Time:
The time that an aircraft Operator or Ground
handler estimates that an aircraft will be
ready to startup/pushback immediately upon
reception of clearance from the tower.

Could someone clarify this issue?

"Scheduled departure time" is not a term used in the operational environment. It is a term you will find on the passenger side of things, and means the time at which the aircraft is scheduled to leave the departure gate.
There are several different operational terms related to departure time:

ETD, Estimated time of departure. The estimated time at which an aircraft will become airborne.
SOBT, Scheduled off block time. The time that an aircraft is scheduled to depart from its parking position. More or less identical to "scheduled time of departure".
EOBT, Estimated off block time. The estimated time at which the aircraft will commence movement associated with departure.
TOBT, Target off block time. The time that an aircraft operator / handling agent estimates that an aircraft will be ready, all doors closed, boarding bridge removed, push back vehicle present, ready to start up / push back immediately upon reception of clearance from the TWR.
AOBT, Actual off block time. The time the aircraft pushes back / vacates the parking position.
TSAT, Target start up approval time. The time provided by ATC taking into account TOBT, CTOT and/or the traffic situation that an aircraft can expect to receive start up / push back approval.
ETOT, Estimated takeoff time. Forecast of time when aircraft will become airborne taking into account the EOBT plus EXOT.
EXOT, Estimated taxi-out time. The estimated time between off-block and take off. This estimate includes any delay buffer time at the holding point or remote de-icing prior to take off.
TTOT, Target takeoff time. The Target Take Off Time taking into account the TOBT/TSAT plus the EXOT. Each TTOT on one runway is separated from other TTOT or TLDT to represent vortex and / or SID separation between aircraft.
CTOT, Calculated takeoff time.A time calculated and issued by the Central Flow Management unit, as a result of tactical slot allocation, at which a flight is expected to become airborne.
ATOT, Actual takeoff time. The time that an aircraft takes off from the runway.
ATD, Actual time of departure. Used either to have a meaning identical to ATOT, or AOBT, depending on context.

I've probably missed some, too.


What is this string on the 737? The other day I was spotting at Miami International (MIA/KMIA) and noticed something hanging out of the fuselage.

A man with a green jacket is holding a device attached to a cable. Can somebody determine what that is?

The ground crew has connected a headset to the communication jack outsiede for flight pushback communication with the flight crew. from b737.org.uk:

The External Power Hatch is located beneath the F/O's DV window. It is used by groundcrew to connect the Ground Power Unit and headset for pushback communications with Flight Interphone.
The service interphone is used by engineers to communicate with the service interphone stations inside the aircraft.

Here is a closeup of the connection point

Image from b737.org.uk
About flight interphone System

The flight interphone system is an independent communication network. Its
primary purpose is to provide private communication between flight deck
crewmembers without intrusion from the service interphone system. The ground
crew may also use the flight interphone through a jack at the external power
receptacle.

And here is a nose section of 737-200, showing it from a not so close angle.

Image from rigger.smugmug.com


Can thrust be selected manually in a plane with autothrust? If yes, how? I'm getting into the autothrust world and I have the question of whether it would be possible to disengage it and select the thrust manually in a plane that already has autothrust. How could it be done? Maybe it differs from plane to plane.

You are correct that different planes operate slightly differently, but they are mostly pretty similar. Just as with the autopilot, the autothrust can be disconnected and the airplane can be controlled manually.

Below is an image of the Mode Control Panel on the 737 NG, which is located just below the windshield. The section that controls autothrust is located towards the left side. To disconnect the autothrust, you can just flip the "arm" switch to off.

Source

Below is an image of a 737 NG cockpit, with the thrust levers located in the middle. With autothrust on, the levers are moved by the autoflight system to correspond to the autothrust setting. The levers can be moved by the pilots but the system will try to drive them back to the commanded position. Once autothrust is turned off, the system no longer moves the levers and they can be controlled by the pilot manually.

Source

Airbus planes such as the A320 are a bit different. The levers do not move to match the autothrust setting, but autothrust can still be turned off to use the levers manually. The levers can also be pushed forward past the "climb" detent, which overrides autothrust to choose higher thrust settings.


Was this an unusual landing sequence for an airliner? About a month ago I encountered an unusual landing during a flight from Bangkok to Krabi airport. We were flying Boeing 737.

We took off 30 minutes late. Our flight should've taken 90 minutes but it actually took less than 70 minutes so we arrived almost on time.

The seatbelt sign turned on around the 60th minute while we were still probably in 10000 meters (I don't know the cruising altitude for sure). The whole landing took less than 10 minutes. I guess the landing gear was deployed at around 6000 meters which seemed unusually high to me. The pilot also performed several rather sharp roll maneuvers and at one point he broke his descend and even entered a rather sharp climb. All this with landing gear out. I have to say that many passengers were quite terrified at the moment. The landing itself was hard but not that much.

I have been  wondering if it was a common maneuver (to decrease speed perhaps?) and would be interested to learn more about it. Does it have something to do with the flight speedup? How is it even possible to be so much faster on such a short flight?

Why do you think the flight "should" take 90 minutes?
You really mean it was listed for 90 minutes on the schedule.
Airlines almost always pad their scheduled times so that their on-time arrivals stats are favorable, and to account for normally expected delays.

Scheduled time is also typically measured "gate-to-gate", while most passengers only observe the flight-time (takeoff-to-landing)

I see the distance is 350 miles, and would probably take a 737 about 60 minutes of actual flight time.  So I don't think your flight was speeding or otherwise behaving abnormally.


What does the preliminary report on the Ethiopian B737 MAX accident show? In early April the Aircraft Accident Investigation Bureau of Ethiopia released a preliminary report on the crash of Ethiopian Airlines flight 302 that happened on March 10, 2019.  There apparently is some technical detail in it from the "black boxes".  What are some of the main technical things the report shows about the flight?

In the short summary, the preliminary report (33-page PDF available here) gives these details:

  Shortly after takeoff, the Angle of Attack sensor recorded value became erroneous and the left stick shaker activated and remained active until near the end of the flight. In addition, the airspeed and altitude values from the left air data system began deviating from the corresponding right side values.

Among the few initial findings, the preliminary report has these:

  Shortly after liftoff, the value of the left angle of attack sensor deviated from the right one and reached 74.5 degrees while the right angle of attack sensor value was 15.3 degrees; then after, the [left] stick shaker activated and remained active until near the end of the flight.
  After the autopilot disengaged, the [Flight Data Recorder] recorded an automatic aircraft nose down (AND) trim command four times without pilot’s input. As a result, three motions of the stabilizer trim were recorded. The FDR data also indicated that the crew utilized the electric manual trim to counter the automatic AND input.

In the section giving details derived from the Flight Data Recorder and Cockpit Voice Recorder, the following items are included:

  At 05:40:00 shortly after the autopilot disengaged, the FDR recorded an automatic aircraft nose
  down (AND) activated for 9.0 seconds and pitch trim moved from 4.60 to 2.1 units. The climb was
  arrested and the aircraft descended slightly.
  At 05:40:03 Ground Proximity Warning System (GPWS) “DON’T SINK” alerts occurred.
  The column moved aft and a positive climb was re-established during the automatic AND motion.
  At 05:40:12, approximately three seconds after AND stabilizer motion ends, electric trim (from
  pilot activated switches on the yoke) in the Aircraft nose up (ANU) direction is recorded on the
  DFDR and the stabilizer moved in the ANU direction to 2.4 units.

A second similar sequence (automatic nose down trim, “DON’T SINK” from GPWS, and pilot-commanded electric nose up trim) then occurred from 05:40:20, to 05:40:28.

The diagram below, from a report appendix, shows aircraft pitch related data from the FDR from the first automatic nose-down to the end of the recording.  (Time advances from left to right.)

  At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and FirstOfficer confirmed stab trim cut-out.
  At 05:40:41, approximately five seconds after the end of the ANU stabilizer motion, a third instance
  of AND automatic trim command occurred without any corresponding motion of the stabilizer,
  which is consistent with the stabilizer trim cutout switches were in the "cutout" position.
  From 05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved
  in the AND direction from 2.3 units to 2.1 units. During this time, aft force was applied to the
  control columns which remained aft of neutral position. The left indicated airspeed increased from
  approximately 305 kt to approximately 340 kt (VMO). The right indicated airspeed was
  approximately 20-25 kt higher than the left.
  At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied
  that the trim was not working and asked if he could try it manually. The Captain told him to try.
  At 05:41:54, the First-Officer replied that it is not working.
  At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,400 ft, two
  momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in
  the ANU direction from 2.1 units to 2.3 units.
  At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic
  trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in
  approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft
  column force was applied, but the nose down pitch continues, eventually reaching 40° nose down.
  The stabilizer position varied between 1.1 and 0.8 units for the remainder of the recording.
  The left Indicated Airspeed increased, eventually reaching approximately 458 kts and the right
  Indicated Airspeed reached 500 kts at the end of the recording.

The "automatic aircraft nose down" events mentioned in the above can be ascribed to the MCAS (Maneuvering Characteristics Augmentation System), which Boeing only started informing pilots about in late November, 2018.


What's the difference between racetrack and holding pattern? Is there any difference between them or they are only synonymous?

What's the difference between racetrack and holding pattern?
  Are they only synonymous?

When used in the context of holding, racetrack pattern and holding pattern refer most of the time to the same pattern, because a holding pattern is a usually designed as a racetrack. Holding terminology:

Holding (or flying a hold) is a maneuver designed to delay an aircraft already in flight.
A holding pattern is the pattern used to hold, regardless of the design of the pattern.
A racetrack holding pattern is a specific design of holding pattern. From Wikipedia:

  A holding pattern for instrument flight rules (IFR) aircraft is
  usually a racetrack pattern based on a holding fix.

Holding patterns are defined relative to a holding fix and are usually timed because aircraft have to remain within a given protected space around the fix.

However a holding procedure which uses a racetrack pattern and a racetrack procedure which uses a racetrack pattern are two different things aimed at two different purposes.

Racetrack procedure

ICAO makes a specific use of the phrase "racetrack procedure" in Doc 8168 (PANS-OPS):

  Racetrack procedure: A procedure designed to enable the aircraft to
  reduce altitude during the initial approach segment and/or establish
  the aircraft inbound when the entry into a reversal procedure is not
  practical.

and

  A racetrack procedure consists of: a) a turn from the inbound track
  through 180° from overhead the facility or fix on to the outbound
  track, for 1, 2 or 3 minutes; followed by b) a 180° turn in the same
  direction to return to the inbound track.

For ICAO, a racetrack procedure is a turn procedure, or course reversal procedure, in the instrument approach procedure, comparable to other procedural turns, and has nothing to do with delaying the aircraft. The procedure turns come in different flavors:

Source.

Holding procedure

Holding procedure definition from ICAO Doc 8168 (PANS-OPS):

  A predetermined maneuver which keeps an aircraft within a specified
  airspace while awaiting further clearance.

It can be used to delay the aircraft, but also to change its altitude using a holding pattern and stack. Note there is no reference to a specific pattern.

Source.

However, when holding, the pattern followed is often a racetrack pattern (more details about this in: How is a standard holding pattern flown?)

Depiction on instrument plates

Holding patterns are depicted using regular lines, they are optional
Procedure turns patterns are depicted using bold lines, meaning they are mandatory. Exceptions are noted "NoPT" with indication of the arriving course.

Adapted from AirNav.com.


Where do I land if I fly from KLAX with a constant east heading, crossing the US and the Atlantic ocean? Los Angeles KLAX and Casablanca GMMN (Morocco) are at the same latitude.
If the aircraft follows a magnetic 090° heading, the initial true heading will be 102° due to the declination.

(source University of Alabama.)

That means the path will start slightly southerly.
What will be the path followed until reaching a continent on the other side of the Atlantic?

If an aircraft is following a magnetic course changes in magnetic declination as the aircraft moves along its route of flight will affect the true course, and on a long flight such as the hypothetical trip posed here we need to take that into account.

Magnetic declination is empirical data, i.e. there are tables of it, and while formulas exist to approximate it you would normally use the reference tables. There are several sources of data for the worldwide declination of the magnetic field, for example here.
  Following the link "Magnetic Model maps and grids" I took D_map_mf_2010.zip which contains a simple lat/lon/declination table (0.5° steps) and wrote a small simulation which moves the aircraft 10 km along the heading, calculates & records the new angular coordinates, moves again and so on. The result is this figure:

The green arrows show the direction of north as displayed by a compass, the blue shows the direction of east.
The black line was generated by the simulation shows the true course of an aircraft with a constant magnetic heading of 90°. While it will fly over north Florida, it deviates markedly to the north over the ocean and just touches the north coast of Spain.

Note that this only accounts for the magnetic declination, since your question assumed no wind.
During a real flight the aircraft may experience unknown crosswinds, so the actual position has to be determined from time to time, and a look into the table / map shows the correct heading at the current position leading to your destination. (If the aircraft only has this map, a compass and a sextant aboard.)

So, if you have this data, you can correct the compass headings such that you fly the true course you want. However, I don't know how it's actually done in aviation.

EDIT:

Here is the code. It is written in python and gnuplot, and you will not need any programming skills to use it.

Have fun!

To answer one question from the comments:

  If you carried on around the world, would you return to your starting point? I'm guessing yes as we would be following a contour of equal magnetic potential?

From the physics side, magnetic fields are not conservative and so do not have a potential. However, I think it's clear what you mean.

As long as the heading is +90° or -90°, you will end up where you started. The following figure again shows a travel from KLAX heading 90°, but with a total lengh of 40mio km (i.e. 1000 times the circumfence of the earth and a little more turns for the track as it's not at the equator)
As you can see, there is just a single black track, no deviation.

And if you want to fly to Casablanca, you will need a constant heading of 93,6°. And if you don't land there and have enough fuel, strange things happen:

I would also like to emphasize Bob Jarvis' comment, about how it's done in the real world:

  Long distance journeys, whether by air or sea, will generally use a "great circle" where the heading steered is not constant. In practice the continuously changing great circle course is broken up in to a series of segments of constant heading. Reference here.


How much fuel does an airliner consume during passenger boarding? As I understand, sometimes APU is running during the passenger boarding. How much fuel do the APU consume during this process?
Of course, it must depend on the total boarding time, so I think it should be estimated in amount of fuel consumed per minute.

Is there an approximation for different aircraft sizes? How does it change if the aircraft is connected to GPU or PCA?

This depends on the aircraft and airport and how they are equipped. The time varies as it takes between 30 and 120 minutes to turn around an aircraft. So ill provide GPH numbers that can be used as desired.

Some airports have umbilicals that can provide ground power. This is often fed via a cable that feeds out of the terminal. This is usually fed from what ever power supply is feeding the airport.

Some airplanes (many these days) have an APU (auxiliary power unit). These are capable of feeding the power demands during a turn around. The also make it far safer for the ground crew by not having the engines running when there is crew on the ground working around them. The fuel burn of an APU can be found in the answer to this question.

Some airports supply power through the use of a ground power unit. These can be diesel powered or run on Jet-A and their output varies. They even have them for the small GA aircraft I fly to charge the battery if it dies on the ramp. This article lists a burn of 5 gallons an hour for a GPU although sizes vary. This maker lists their GPU's by Gallon per kilowatt hour which may be more appropriate for matching load demands.


PT-6 Starting problems - PT6A - 67B, installed on a PC12 we are having trouble starting our PC12. After introducing fuel at stabilized 13% ng, the engine spools up very slowly - it takes forever to get through 20, 30, 40%ng. We've had several hung starts, and aborted starts.
Battery discharge test is fine - 106% on the first test, and it is a new battery.
Any suggestions for next step trouble shooting? Our mechanic doesn't seem to have a clue.

Either the starter generator isn't making the torque it should be making, or there is a fuel flow issue.  If I was betting 10 bucks on the result, I'd go with weak starter/generator and swap it out if another was available, or do diagnostic testing on the unit like insulation resistance checks and other electrical tests on the motor.

Regardless, if your mechanic is not sure how to proceed he/she should be on the phone to Pratt & Whitney Canada tech support or going through the PWC online portal to access the Fault Isolation Manual for that engine and just follow the steps.

If you're a pilot standing by watching the action, you'll really piss off the mechanic by relaying him troubleshooting instructions from some anonymous nobody from ASE, so I would only intervene if the mech was hiding in the bathroom and refusing to come out.


How does the RQ4-Global Hawk improve stability? I have seen several videos recorded from an UAV in which the stabilization of the camera is almost perfect. Cameras are installed in a gimbal, of course, but do new drones introduce some new technology in order to improve the stability?

We can take, for example, the RQ-4 Global Hawk (first flight in 1998) and the Chendgu HQ (First flight in 2012). Note that the HQ-4 Xianglong's airframe topology its quite similar to the RQ-Global Haw, however it has a special wing configuration.

What you are looking for is "gyroscopic-stabilization".

As you can see in this video, the camera is mounted on gimbals that can rotate over all axis. Movements are controlled thanks to gyroscopes. For sensors mounted on larger aircraft, optronics systems are ball-shapes. That way they can rotate without modifying aerodynamics. There is no need to compensate for translation as targets are far away.

I didn't find any sources for shake reduction thus I can only assume techniques are the one that Wikipedia name "vibration reduction" and "anti-shake".


Pilot announcement PA quality On a recent passenger flight my son asked me, "How come we're able to build a 737 for \$50M - \$80M with fantastic reliability and technology but can't design a PA system so that we can understand the pilot's announcements?" Many are quite un-intelligible but the cabin crew announcements generally are intelligible. I didn't have a good answer. Does anyone know?

As a follow on and of more concern, if pilots' microphone technique / equipment is so poor then how does air-traffic control understand them? I know there is a limited vocabulary set and that standard phrases are used to avoid mis-hearing but there must be some problems.

Many pilots prefer to use their headset boom mic or hand mic instead of the dedicated interphone handset for PA announcements.

I don't know why, but I know from personal experience that the dedicated interphone handset has much better PA readability.


Why is there no alarm when the transponder is turned off? When the transponder on Malaysia Airlines Flight 370 went off, there was no ALARM. The satellite kept getting pings, and apparently "knew" that the transponder was off. Would it not be a great idea if the Malaysia Airlines got an alarm indication that the transponder was off on one of their planes? The airline could have radioed the pilot and asked what the trouble was. If the pilots did not respond, some jets could have been scrambled to checkout what is going on. The scrambled jets could have followed the airliner for hours and watched them crash in the ocean, when they ran out of fuel. We would know EXACTLY where the airline crashed!

Because it's not worth it.
Quick, name me another accident where a transponder-off alarm would have been exactly what was necessary to save the crew, the passengers, or the airframe?
Hint: there aren't many.
The number of false positives would drastically outweigh the number of actual events where a transponder alarm would have been able to do some good.  For example, air traffic control might ask an aircraft to turn off their transponder.  Nothing dangerous there, but alarms would be going off back at dispatch.  Good idea on paper, but not practical enough to make it worthwhile in the real world.


Why do double-ended ILS runway share the same frequency from both sides? Let's find a runway where there are localizer-related procedures at both ends, e.g.

KMRY: 110.7 for both ILS RWY 10R and LOC/DME RWY 28L
KLAX: 108.5 for both ILS OR LOC RWY 06L and ILS OR LOC RWY 24R

However, this doesn't align with the ILS back course concept. When I fly one procedure, how can I can tell that I am not on the back course of the other? Getting down to instrument interpretation, for an HSI, how to set the front course? In a traditional VOR, is it positive or negative sensing?

POST EDIT:
Tried in a SIM, it seems that when well above the slope, it shows back course. When I get lower, it shows front course.

Listen to the identifier... That will tell you if you have the 10R I-MRY or the 28L I-MTB ils.  Some runways use the same frequency like this, while others use different frequencies for opposite direction ILS's.  The identifier will always be unique, though.

The 10R transmitter doesn't operate at the same time as the 28L transmitter. One transmits "this" ils beam in "this" direction using "this" ident on whatever frequency; the other transmits a different ils beam in a different direction using a different ident; the fact that it is or is not the same frequency is incidental.

Usually, the two reciprocal ILS's to the same length of pavement use the same frequency, with one switched off when the other is switched on.  MRY in the OP is a good example of this, and most other airports I looked at have the same behavior, but this is not universal.  Reno, NV -- KRNO -- is an example where the opposite ILS's are not on the same frequency: 16R ils is 110.9, but 34L ils is 109.9. Same pavement, different frequencies.  Also, Detroit, MI -- KDTW -- appears to have two full ILS's set up for runway 4R/22L, with one pair on 111.75, and the other on 111.95.

One other note: the various flight simulator programs may or may not accurately model this behavior.  Some may simply have every ILS "on" at the same time, so if you're west of "this" airport, you'll receive the ILS for landing east, and vice versa.  Works well for a flight simulator program, but that's not how the real world works.  It takes a call to tower to have the one ILS turned off and the other turned on, and it isn't something they prefer to do repeatedly or on short notice.  In the sim, it's convenient to fly approaches back & forth to 16C then 34C then 16C and so on, but even if traffic permitted, in the real world they'd probably prefer you flew your ILS's to one runway, and use something that doesn't need the ILS or the LOC when landing in the opposite direction.


Application of Bernoulli Energy Conservation In what cases does the static pressure decrease when the velocity increases in a flow.

And in what cases does the static pressure remain constant whilst the velocity and stagnation pressure increases?

Please answer with respect to Bernoulli's equation: Po1 = Ps1 + 0.5*rho*v1^2

For example in a closed circuit wind tunnel to what extent does the fan convert static pressure to dynamic pressure and to what extent does it just add energy by increasing the dynamic pressure.

Bernoulli's equation holds only if there is no energy source in the system. Since the fan adds energy, Bernoulli's does not apply across the fan; in the context of 1-D flow, pressure changes discontinuously across the fan.

Due to conservation of mass (no mass source for a simple fan), airspeed cannot change discontinuously across the fan interface. Therefore, right after the fan interface, both the static pressure and the total pressure have increased.

For more information, refer to this tutorial.


What is the relationship between speed, torque and pitch in a helicopter? Can someone clarify the relationship between aircraft speed, torque, prop length and pitch and how this applies to a helicopter.

In addition I want to know if the amount of lift a helicopter generates changes dependant on pitch, how much does the pitch change?

I'm afraid that a thorough answer requires the contents of chapters 2 and 3 of Leishman, but here is an outline. The relationship between power and true airspeed from this answer:

Power equals torque times angular velocity of the rotor: $ P = Q * \Omega$. Most helicopters have constant speed rotors, so the relationship between torque and speed would be similar to the power curves.

Rotor blade length and pitch appear as follows. Power P and torque Q equations for momentum theory in the hover:

$$P = C_P \cdot ½ \rho A (\Omega R)^3$$

$$Q = C_Q \cdot ½ \rho A (\Omega R)^2  R$$

At forward speed the momentum based power becomes less due to lower induced power requirements. An inflow equation relates forward velocity of the helicopter with blade tip speed - too much scope for an answer here.

Blade length appears in the rotor disk area A. Torque and power are functions of the rotor solidity $\sigma$, defined as (total blade area)/(disk area). Note that $C_P$ is always the same value as $C_Q$

From Leishman:

..if the amount of lift a helicopter generates changes dependant on pitch, how much does the pitch change..

Thrust T of the rotor Again from Leishman:


What modifications are required for automotive fuel STC? What actual engine modifications are required to allow certificated piston engined general aviation aircraft to run automotive fuel under an FAA Supplemental Type Certificate (STC)?

For most engines it would require a hardened valve seat.

The reason why lead is required for aviation engines is that the value seats are not hardened and the lead in the gas helps prevent "micro-welding" that can occur on a valve seat.  Micro-welding happens when the valves are hot and the the valve is pressed against the valve seat; the valve will start to weld to the seat before it is torn away when the valve opens.  This causes a jagged edge at the valve seat which causes a bad valve seal.  Old engines relied on the lead in the gas to prevent this. When the automotive industry switched to unleaded gas, the engine makers had to use valve seats out of hardened materials that were more resistant against heat.

The lead is also a great octane booster although many airplane engines can use octanes lower than 100.  In automotive fuels today ethanol is used to boost octane and that has its own host of problems since ethanol is very corrosive.  So before you switch to automotive fuels you need to make sure you engine and fuel system can handle the ethanol.

For a discussion of micro welding among mechanics check this link out.

EDIT:  After doing more research I discovered that Lycoming has always used hardened valve seats so the modifications on a Lycoming engine would be very minimal.  However, most Continental engines do not have hardened seats and major modifications would be required.

Lycoming has a good article on the use of unleaded fuel in the their engines here.  Notice however that Lycoming states that ethanol CANNOT be used in their engines.  In the US at least it is getting very hard to find fuel that does not contain ethanol.


What are these large yellow circles painted across the runway? There are not many yellow markings on a runway. This row of six is painted about 400m from the threshold at both ends:

Montgomery Airport (Alabama) - Source: Google Maps

What does it mean for a pilot? Why yellow?

That would be the "line" telling military pilots where the arresting cables are. If you look to the side of those circles, you can see the arresting mechanism these. It would be yellow so that it would still stand out to the pilot and not be confused with the white runway markings.

You can find more about them here.


Is it harder to get a first pilot certificate in a motorglider compared to a normal powered aircraft (near St. Paul, MN.)? Is it harder to get a first pilot certificate in a motorglider (glider - self launch) vs. normal powered aircraft near St. Paul, MN.

It seems like a self launch glider certificate would be a great way to start because of better stick and rudder skills, lower age requirements (for my son), cheaper operating costs, glider hours apply toward power aircraft requirements, etc but I'm concerned that it might be a bad path because it appears to be rare and hard to find instruction near St. Paul, MN.

It will be harder to get initial training in a motor glider near St. Paul, because motor gliders are kind of rare around here.

However, consider this:

Instruction in a un-powered glider is mind-bogglingly cheap compared to power instruction. And it has the other mentioned benefits - stick and rudder skills, low age limits, etc.

After getting a first pilot certificate in a non-motor glider (and after suitable further training), one may add Motor Glider ("self-launch") privileges with only an instructor endorsement - no Designated Pilot Examiner needed!

One may also add Light Sport - Airplane privileges with a two-instructor endorsement process - also no Designated Pilot Examiner needed! If you or your son want to fly LSAs, starting with a glider rating can be a great bargain.

And you have options! Some clubs: Minnesota Soaring Club in Stanton, Red Wing Soaring Association in Osceola (* note NOT in Red Wing, despite the name); and a commercial operation: Cross Country Soaring in Faribault. Not to mention any private instructors you may ferret out in the community.

I personally am a member of RWSA and hope to get my self-launch and LSA endorsements one of these days, but I'm having plenty of fun soaring in towed gliders in the meantime.


How are skis stowed on retractable gear aircraft? This image of a LC-130 taking off from a snow runway shows that in addition to wheels on the landing gear, it's also been equipped with skis.

Source: Wikimedia Commons.We're getting a lot of use out of this image lately!

How do these skis get stowed when the gear retract?

Do the skis become part of the gear door?
Is there enough room in the gear bay for the skis?
Are modifications to the gear bays necessary to accommodate the skis?
Is there any modification necessary to the movement of the gear to accommodate the skis? (i.e. some gear rotate as they stow. I'm not sure if the C-130s do or not.)

The skis partially retract.

Here is an image of one with the gear retracted:

Source: UW Oshkosh

  Do the skis become part of the gear door?

From looking at the images with the gear deployed and then the ones with the gear stowed, it appears that the skis do form the gear doors.

  Is there enough room in the gear bay for the skis?

No, the skis are not retracted into the aircraft.

  Are modifications to the gear bays necessary to accommodate the skis?

It doesn't appear to be, but there may be modifications to the retraction mechanism to allow the wheels to be stowed while the ski is still outside of the aircraft.

  Is there any modification necessary to the movement of the gear to accommodate the skis? (i.e. some gear rotate as they stow. I'm not sure if the C-130s do or not.)

It does appear that there is, yes. The ski's can be deployed without the wheels touching the ground, or the skis can remain retracted and the wheels extended for paved runway operations. Take a look at these two photos:

Source: PIntrest

Notice how the wheels are on top of the skis? Now take a look at this one:

Source: FlyIan.net

You notice that the skis are still retracted and the wheels are extended through the skis.

If you want to know what was modified for the gear doors, take a look at this image of a "normal" C-130:

Source: YouTube

Notice how the rear gear door goes a quarter way up the "pontoon"? The version with skis has a fixed panel that replaces the gear door and matches up with the profile of the skis to reduce drag.


Why does the aerodynamic center exist? I am a glider pilot and instructor with a master’s degree in actuarial mathematics. I teach aerodynamics every winter for upcoming glider pilots.

As you surely know, the aerodynamic center is the location where the aerodynamic moment remains constant regardless of the angle of attack – the leverage of the lifting force acting through the center of pressure gets larger for decreasing angles of attack while the force acting through this location gets smaller.

Although I find it easy to understand the mechanisms behind the aerodynamic center, I struggle with understanding how it can exist? How can we be sure that there is such a point in the wing? I know that by definition it is a fixed point, but will it be exactly fixed in practice or just approximately fixed?

Is it not possible to construct an airfoil which will somehow have a discontinuity in center of pressure leverage but delivering the same lifting force in the two situations, yielding non-constant moment around the aerodynamic center?

It exists as a mathematical abstraction for conventionally shaped aerofoils at moderate speeds. In the end it is derived from the centre of pressure. The centre of pressure is the point where the moments of the individual aerodynamic forces over the aerofoil give 0 momentum. This always exist on any aerofoil. Now, the centre of pressure is not at a constant location, it is continually shifting as a function of angle of attack, and it moves quite a lot. However the rate of movement and change in lift force is in proportion to each other, and based on that, the stable point can be found, which for conventional aerofoils at normal speeds is about 25% chord.

Note, that to get this, the proportionality between lift and CP location is a must. You can create any shaped wing cross sections (might not want to call it an aerofoil) which will not have this property and won't necessarily have an aerodynamic centre. Whether it is fit to fly is questionable though. However, they will always have a CP, as it is a simple mathematical property, and it will very likely move with angle of attack. Also note, that the AC does change location with increasing speed, for supersonic speeds it moves significantly backwards.


How the pitch of a blade must change along the length so that the blade does not stall? I have to finish an assignment in the next couple of days. One of the questions asks to show how the pitch of the blade must change along the length so that the blade does not stall. I have no idea what I have to do or how, can someone help me please?

The question should really read, "how the pitch must change along the length to keep lift distribution reasonably constant while respecting stall considerations" or something like that.  Rotor blades twist nose down going outboard, like propellers but with less twist, to account for the higher velocity toward the tip, so that the slower moving root end is doing a decent amount of work making lift.
This tends to make the root end operate closer to stall AOA than the tips.  Whether it actually stalls or not is a more complex function of blade forward velocity (rpm) and vertical circulation velocity down through the rotor disc, whether forward airspeed is involved, whether you want to optimize for hovering or forward flight, and so on.
You're going to have to do some reading.  I found an ASE post from a couple of years ago by @Koyovis, relating to a question about blade twist, that links to a great information source, a book at Google Books that you can read online, called  Helicopter Aerodynamics Vol. 1 by Ray Prouty, who wrote a column for Rotor & Wing for many years.  You should be able to assemble the information you need from that.


How are rotary engines controlled? Listen closely to the engine sound here.

It seems to me all rotaries continuously sound on/off. Is that a pilot application to manage the engine's torque (with the whole block rotating), or as mentioned when I brought it up in chat, due to the throttle control choosing which cylinders to fire?

  (...) the Camel gives you throttle control by simply not firing some cylinders.

This question pertains to both the control (mechanism) and application (in-flight) of rotary engines. Prior to the comment I received, I always thought it was the pilot walking the lever up/down. Perhaps due to too much power and not enough fine control.

Some of the early radial engines that operated by rotating the entire engine along with the prop, specifically, the very popular Le Rhone didn't have proper throttles. The pilot controlled engine speed by switching the ignition on and off.

This wasn't so much a limitation of that particular design, as a limitation of engine tech in general at that time. Wilhelm Maybach first devised the jet spray carburetor (patterned after a scent spray) in 1893, but the throttle body didn't appear for another ten years. Those early engines had only two speeds: wide open, or off.

Thus, the reason that many of the early WW1 fighters are constantly revving their engines on the ground... the pilot was switching the ignition on and off. Must have made for interesting ground handling.


What modifications would be required to use a DHC-6-400 for Carrier Onboard Delivery work? In the spirit of our small airplane landing on a carrier question, I decided to up the ante slightly in a couple of ways.

Let us say some enterprising foreign navy has found a small flattop under their Christmas tree this year, and is in need of some aircraft to fly off it.  Of course, tactical aircraft are a necessity, and to that end, they could obtain some used A-4s as a starting point for their fledgling naval aviation branch.  However, there are other important aircraft on a carrier deck, one of them being the Carrier Onboard Delivery plane.  A bright young naval officer there decides "Hey, we should see if some small civil planes might work for what we need", and does a bit of research, stumbling upon the DHC-6-400 with its widespread support base, ease of maintenance, good STOL performance, and current production availability.

How much modification would our enterprising foreign navy need to ask Viking Air to do to their order of DHC-6-400s to be fully usable from a carrier deck?

DHC-6 has a reported takeoff roll of 210m and landing distance of 155m and as such can be operated from most of the aircraft carriers in service, albeit with limited capability. If required, the aircraft can takeoff into the wind and for arrested recovery rear fuselage can be strengthened, though this looks unnecessary.

It may need some changes for operating in marine environment like,

better corrosion protection
strengthened landing gear
Required naval equipment (for TO/landing).

Of course, all these modifications will eat into the payload. DHC-6 would be a rather small COD aircraft. The C-2 Greyhound used in USN has a payload greater than the MTOW of the twin otter.


Does TCAS II equipment satisfy the required ADS-B installation? The title says it all.

If TCAS II is installed and functioning, does it satisfy the ADS-B OUT mandates?

TCAS II and ADS-B are two entirely different systems, with entirely different functions, and they have different regulations. Having TCAS II installed & functioning does not satisfy any of the ADS-B OUT mandates.

ADS-B regulations European Union

For Europe, the regulations for ADS-B are published in the surveillance performance and interoperability requirements Implementing Rule (SPI-IR), Commission Implementing Regulation (EU) No 1207/2011, amended by Commission Implementing Regulation (EU)  No 1028/2014 and Commission Implementing Regulation (EU) 2017/386.

TCAS regulations European Union

TCAS II, version 7.1 is regulated by Commission Regulation (EU) No 1332/2011 amended  Commission Regulation (EU) 2016/918.


Can a MEI CFI give a valid flight review in a plane for which he is not endorsed? A friend of mine is working towards his initial CFI.  I'm helping him work through regulatory, weather, and other knowledge stuff when time permits.  During our most recent ground session he asked me a question that I had never been asked.  Here's the setup...

A CFI with a freshly minted MEI (airplane, land) is asked to conduct a flight review for a customer in the customer's own Cessna 421C, a pressurized piston twin certified to >30,000'.  This CFI has only flown one type of twin (pick a common training twin, doesn't really matter).  He has no time at all in a 421 of any sort or any other twin aside from the trainer in which he trained for his commercial-multi and MEI.  Our MEI is otherwise current in all categories and classes for which he is certified, holds a complex endorsement gained during his commercial training, and holds a First Class with no limitations.

The customer is current in all categories and classes for which he is certified, is within the 24mo flight review window, and has a First Class.  In short, the customer is fully qualified to be PIC for the flight portion of the flight review.

What's obvious:

The five hour rule does not apply since a flight review is not
instruction given for a certificate or rating.
Our MEI cannot act as PIC of the customer's 421C because the MEI is missing a high altitude endorsement and a high performance endorsement even though he is category and class certified for airplane multi land.
A CFI does not need to be PIC, or even hold a medical, in cases where the student/customer is able to act as PIC.
Edit: it's a really bad idea to do fly an aircraft type with which you are not familiar.

The question is this:
Can our fresh MEI give the customer a valid flight review in the customer's 421C?

The flight instructor is limited to give training in the category and class ratings of their pilot and instructor certificates, not by make and model.

Per §61.193 and §61.195 the flight instructor is authorized to train and issue endorsements for a flight review so long she or he holds a pilot certificate and flight instructor certificate with the applicable category and class rating.

Furthermore, per §61.51(e)(3), the flight instructor may log pilot in command flight time for all flight time while serving as the authorized instructor in an operation if the instructor is rated to act as pilot in command of that aircraft.

The instructor is advised according to Advisory Circular: AC 61-98C,  Section 4-2 Paragraph e. Instructor Qualifications:

  Instructors should also consider their own experience and
  qualifications in a given make and model aircraft prior to giving a review in that model... ...To conduct a flight review in a multiengine
  airplane, the instructor must hold an airplane multiengine rating on their pilot and flight
  instructor certificates. For aircraft in which the CFI is not current or with which he or she is not
  familiar, he or she must obtain recent flight experience or sufficient knowledge of aircraft
  limitations, characteristics, and performance before conducting the review. In any case, the CFI
  must observe the rating limitations of § 61.195.

So, yes.  An appropriately rated flight instructor (whether or not they should) is authorized to conduct the flight review.

What's more, even if the instructor is not qualified to act as PIC (e.g. does not have a high-performance training endorsement), that instructor will still log pilot-in-command time as instructor because he or she is appropriately rated to do so.


What do you call the portion of a tail-dragger takeoff when the tail is in the air? During a take-off roll out down the runway, in a tail-dragger airplane, what is the period of time called where the plane is level, with the main gear still on the runway, but the tail has come up off the ground and before you pull back on the stick to begin climb-out?

There is no term (that I am aware of) referring to only the portion of the takeoff while the tail is off the ground.

In general, the attitude where just the two main wheels are touching the ground is called "two-point." Likewise, with the tail wheel also on the ground, it is called "three-point."

Specifically, a two-point landing is sometimes called a "wheel landing".

Source


Do airliners have any cockpit indication of open doors? A recent report into an "unnecessary" plane evacuation reports that, following an aborted takeoff

[The senior flight attendant] then ordered an evacuation of the 169
passengers onboard, but the pilot and co-pilot were not informed nor
aware until they noticed the evacuation slide had been deployed and
passengers were moving across the front of the aircraft. [my emphasis]

This led to dangerous situation because the pilots, unaware of the evacuation, kept the engines running while the passengers were trying to get out.
It raises questions about crew and cabin crew communication, but what I found most surprising is that apparently there is nothing in the cockpit to alert the pilots that the doors had been opened.
Even my car does that!
Is this something specific to the A320 or is it generally true that the cockpit doesn't 'know' what's happening with the doors?
 Laudamotion Airbus A320-214 which had emergency evacuation (source)

The Airbus A320 has an ECAM (Electronic Centralized Aircraft Monitor) Door Page:

(A320 FCOM - Doors - Controls and Indicators)
When a door is opened, this will also trigger a caution. According to the FCOM, a MASTER CAUT is triggered together with a SINGLE CHIME. The lower ECAM page will also automatically switch to the Door page.
Other aircraft may have similar pages or individual warning lights, like e.g. the Boeing 737 on the overhead panel:

(Boeing 737 NG FCOMv2 - 1.30.15 - Airplane General, Doors - Controls and Indicators)

I can only speculate why the pilots did not recognize the open door earlier in the incident you linked. My best guess would be that they were preoccupied with the engine failure that had just occurred, which will obviously create a lot of other warnings. It is easy to miss the door warning in all of those.


What happened with the balloons of project Excelsior? After the flight to the ISS yesterday I am reading more stuff about mankind in the universe.

Reading about the Excelsior project makes me wonder what happened with the helium balloon after Joseph Kittinger jumped. I haven't found an answer to that, does anyone now?

In general, those kinds of balloons cannot be reused. There was a concern, I don't know if it was a Manhigh flight, where one balloon had burst when strong winds bounced it on the ground, and the spare was used on another day. But the weather was iffy, and if that flight had to be scrubbed they couldn't reuse it once they had started inflating it, and they didn't have another on hand, so that could have delayed the entire project. Used balloons were sometimes given to farmers, who used them to cover hay. I don't know specifically what happened to the Excelsior balloons, but I presume they made it to the ground since the gondola was recovered and reused. Ground control could operate the valves in addition to receiving data, and they had a man on the team who could predict the landing site. But there is no reason they would have kept them.

If you want to read about that in more detail, you might look for the book The Pre-Astronauts: Manned Ballooning on the Threshold of Space, by Craig Ryan.


Why was the VC10 unusually prone to reverser-induced buffeting? According to Wikipedia, the original (“Standard”) version of the Vickers VC10 had thrust reversers only on the outboard engines, as putting reversers on the inboard engines produced severe tailplane buffeting and attendant fatigue problems.  The larger, heavier Super VC10 had modified and repositioned engine pods in order to resolve this issue, allowing the Super to have reversers on all four engines; despite these changes, the buffeting from the inboard reversers proved to still be severe enough to necessitate their near-immediate removal.

In contrast, the vast majority of jetliners with tail-mounted engines (leaving aside oddities like the F28, which has no thrust reversers at all, and the Il-62, which has four engines, with reversers only on the outboard pair, like the VC10) experience(d) little or no trouble with reverser-induced buffet, even though their engines - like the VC10’s inboard pair - are (or were) located immediately adjacent to the empennage, and, thus, should be just as prone to inducing buffet as the inboards on the VC10.  1-11, DC-9, 727, Tu-154, F100, CRJ900 - all have (or had) tail-mounted engines with thrust reversers, but none experienced the buffeting problems seen with the VC10’s inboard engines.  Why is this?

It may just be that other airframes mount their engines with sufficient clearance to avoid the buffeting issues that were seen on the early VC-10's. Ultimately it only took of a move of 11 inches to solve the issue

  ...testing was prolonged by the need to move each engine pair 11 in (27
  cm) outboard. This major redesign was needed to resolve tail-plane
  buffeting and fatigue issues due to thrust reverser operation. The two
  inboard engines could have thrust reversers installed at last,
  matching the 707.

So while it may appear in photos that other aircraft have similarly mounted engines you would need to look at actual technical drawings to truly compare mounting distances.

Its also worth noting that there is nothing saying other aircraft do not also see buffeting from their aft mounted thrust reversers, however they may not see enough to cause structural issues as was the case with the VC-10.


Can someone identify this warplane silhouette? I saw this picture today in a news article about the current conflict in Iraq/Syria.

The caption claims it is a US warplane, but I don't recognise the silhouette. Can someone identify this plane?

This is a B-1B Lancer.

It is a 4 engine (afterburning engines mind you, very rare for a bomber) variable sweep wing bomber, designed during the Cold War to use its terrain-following radar to stay low and fast, weaving between the mountains of Russia to stay below radar to deliver nuclear warheads.

It carries more bombs than the B-52 as well.

Essentially, it is a bomber built like a fighter. It is actually the only swing-wing aircraft in the entire US military right now.

Fun fact: The canards near the nose aren't for control. Because the aircraft is flown by autopilot using terrain-following radar (TFR), weaving into and out of mountains, autopilot makes many quick pitch adjustments. The canards are to cancel out sine waves in the structure of the fuselage.

It can carry a whole lotta' bombs:

24 nuclear bombs, 48 JDAMs, 84 Mk82 bombs, or 48 AGM missiles.

100 were built, 66 remain.

I leave with my current desktop background:


How do airline pilots contact their company while in the air? Sometimes airline pilots need to get in touch with their company while in the air, for example diagnosing cautionary messages or reporting a diversion. By what means is the communication channel established?

VHF / HF radio? If that's the case, who allocates the frequencies to each airline?
Satellite phone? (Are all aircrafts equipped with one in the cockpit?)
Something else?

While enroute the primary communication with company is via ACARS. (Aircraft Communications Addressing and Reporting System)

This is a digital datalink system and is kind of like sending text messages. On modern aircraft like a B777 it operates on HF, VHF, or SATCOM so there is coverage almost anywhere in the world.

If the aircraft is close to an airport with a company frequency, regular VHF radio communication can also be used.  Some airlines may even have company Peripheral stations (PAL) at certain locations so they can use a VHF radio to talk directly to Dispatch from hundreds of miles away.

In the USA, VHF company frequencies are allocated by Aviation Spectrum Resources, Inc. (ASRI) ASRI Ground Station Administration Service (AGSA)

SATCOM is also be used to make Satellite phone calls so we can talk directly to Dispatch or Maintenance from thousands of miles away. You can use pre-selected company numbers or manually enter any phone number.

Aircraft without SATCOM can use VHF or HF radios to contact ARINC (Aeronautical Radio, Incorporated) who can create a phone patch to any phone number.  Aeronautical Radio, Incorporated (ARINC)

Source: B777 Aircraft Operating Manual Volume 2 (2.23 Communications)


How did they solve the compressor stall issue of the F-14A in the B? I know that the F-14A was notorious for having compressor stalls during high AOA or with quick thrust changes, and most of the issues were solved in the B. Externally there doesn't seem to be much difference in the intake, so how did they solve it?

Grumman changed the F-14 powerplant from the Pratt and Whitney TF-30 engine to the General Electric F-110 engine when the F-14B was developed.  This not only provided the airframe with an extra 16,000 lbs of thrust compared with the old TF-30 engines but also a much more stable, reliable gas core as compared with the P&W design.  I don’t know if they have managed to wring out the issues in the F119 and F135 engines, but Pratt and Whitney engines have been notoriously finicky and prone to compressor stalls if not petted nicely.  GE engines, particularly military aircraft engines, are some of the most robust and reliable jet engines out there.


Is there an equation which allow us to perfectly match a helix propeller and an engine? Is there an equation which allow us to perfectly match a helix propeller and an engine? I'm looking for an equation that allow me to correctly dimension an helix propeller for my engine. I mean that allow me to maximize efficiency and thrust, calculate the optimal number of blades, the optimal number of rpm, and the maximum rpm of my helix propeller given a certain engine power, etc.

Should I ask this question on the physics division of this website?

Did you try Mark Drela's XROTOR? I have difficulty with your term "helix", but that software should do what you ask if your blade loading is not too high.

From the linked page:
XROTOR is an interactive program for the design and analysis of ducted and free-tip propellers and windmills.
It consists of a collection of menu-driven routines which perform various useful functions such as:

Design of minimum induced loss rotor (propeller or windmill)
Prompted input of an arbitrary rotor geometry
Interactive modification of a rotor geometry
Twist optimization of an arbitrary rotor for minimum induced loss
Analysis of a rotor with a wealth of choices of operating parameters
Incoming slipstream effects (from an upstream propeller, viscous wake...)
Multi-point parameter display
Structural analysis and corrections for twist under load
Acoustic analysis with dB noise footprint predictions
Interpolation of geometry to radii of interest
Plotting of geometry, aerodynamic parameters, and performance maps
...


Do small business jets have HEPA filters? Do small business jets (Phenom 300 for example) have HEPA filters for recirculated air? Or don't they recirculate air at all?

Embraer's own website confirms that their business jets can recirculate or draw fresh air, but HEPA filters don't seem to be an option until you get into the Praetor size and above -

In addition, the now standard HEPA filter for the Praetor jets can
capture 99.97% of bacteria, viruses, and fungi — further providing
fresher, cleaner air inside the cabin. So when you fly on an Embraer
business jet, you can breathe easy.


Why are KACV and KTLV depicted differently on sectional charts than KSGU, KBIH, and KTPL, even though each is E2 w/ E4 extensions? This question specifically is about non-towered airports surrounded by round circles of E2 airspace, with one or more "extensions" of E4 airspace that abut the E2 airspace.  Therefore it is not the same as the related question that may be noted above.  Also the question noted above is about how certain airspace functions when the tower is open versus closed, not about why it is drawn a certain way on the sectional chart.

Note that this configuration-- a non-towered airport surrounded by a round circle of E2 airspace, with one or more "extensions" of E4 airspace that abut the E2 airspace -- is a somewhat unusual airspace configuration. In the vast majority of cases where a non-towered airport is surrounded by Class-E-to-surface airspace that has one or more rectangular projections, the entire Class-E-to-surface airspace is designated as E2 airspace.  No E4 "extensions" are designated.  Examples: KONP, KSHR.  This question is not about that airspace configuration.

The question:

According to the FAA's "Airspace Designations and Reporting Points" document Order 7400.11C ( https://www.faa.gov/documentLibrary/media/Order/JO_7400.11C.pdf ) , KACV, KTLV, KSGU, KBIH, and KTPL all share the same airspace configuration: a round E2 circle around the airport, with one or more E4 "extensions".

Why then on the aeronautical sectional charts is the Class-E-to-surface airspace near KACV and KTLV depicted differently than the Class-E-to-surface airspace near KSGU, KBIH, and KTPL?

The first two are depicted with a dashed magenta circle going all the way around the airport, while the last three are not.  In the case of the last three the charts give the impression that all the Class-E-to-surface near the airport may be E2, with no E4 "extensions".

KACV: California Redwood Coast Humboldt County near Arcata -- http://vfrmap.com/?type=vfrc&lat=40.978&lon=-124.108&zoom=10

E2 described on page E-127 of the "Airspace Designations and Reporting Points" document, E4 described on page E-211

KTLV South Lake Tahoe --
http://vfrmap.com/?type=vfrc&lat=38.894&lon=-119.995&zoom=10

E2 described on page E-135, E4 described on page E-220

KSGU -- St. George Regional Airport, UT --
http://vfrmap.com/?type=vfrc&lat=37.036&lon=-113.510&zoom=10

E2 described on p. E-84, E4 described on p. E-190

KBIH -- Bishop Airport, Bishop CA --
http://vfrmap.com/?type=vfrc&lat=37.373&lon=-118.364&zoom=10

E2 described on p. E-130, E4 described on p. E-211-212

KTPL -- Temple, Draughon-Miller Central Texas Regional Airport, TX --
http://vfrmap.com/?type=vfrc&lat=31.152&lon=-97.408&zoom=10

E2 described on on p. E-127, E4 described on p. E-209

It seems that it would be good for the chartmakers to standardize on the notation used at KACV and KTLV rather than the notation used at KSGU, KTPL, and KBIH, since there appear to be some functional differences between the E2 and E4 airspaces, as explored in the related question linked below.

Related question with links to additional related content --
What is the primary reason that the non-towered airports KACV and KTLV have E4 extensions to E2 airspace?

It looks like the answer is "it's a mistake or inconsistency in the sectional charts".  Whether or not it's an outright mistake is debatable, but it certainly appears to be an inconsistency, and one can argue that the depiction used for KACV and KTLV provides some useful information that the depiction used for KSGU, KBIH, and KTPL does not.

It is the case that at KTLV-- but not at KACV or the other 3 airports mentioned here-- the description of the E4 airspace in the "Airspace Designations and Reporting Points" document has a note to see the A/FD for effective hours, while the E2 airspace has no such note.  The sectional chart has a similar notation, with an arrow pointing specifically to the E4 airspace.  (It also is the case that the current A/FD entry for KTLV simply reads "Airspace: Class E".)  It seems possible that the policy of the charting agency is to depict the adjoined E2 and E4 Class-E-to-surface areas as two distinct areas in any case where there is a possibility why their effective hours may be different.  If this is true, it doesn't explain why that style of depiction was also used for KACV.


Engine out over a mountain road. Do you land upwind or up hill? You're flying solo in a late-model, fixed-gear Cessna 172 with half-full fuel tanks.  You are at 1000 feet AGL, 100 knots indicated, directly above the middle of a 2000 foot long straight section of paved road.  There is a steady 15 knot wind blowing up the 10 degree, wide, flat and clear slope that the road runs straight up.  Your engine suddenly seizes, prop horizontal, with no possibility of restarting it.  Everything else about the aircraft is perfectly functional and the height of the terrain is not significantly above sea level for performance purposes.  The road section heading is 360 degrees, due north up the hill.  Choose any initial heading for the engine failure and remember it occurs directly over the mid-point of the road section (runway).  Please provide information on the specific flight segments in terms of speed, turn rate, descent rate, etc. and consider the effects of the wind blowing directly upslope (without any crosswind component with respect to the roadway).  Explain why your answer is (nearly) optimal.  How do you make the safe landing?

Admittedly, the 10 degree sloped roadway is an anomaly, and you would never see an actual runway built on this grade.  Don’t try to apply any of this logic to a shallower runway without some careful analysis.
Here's my take on the possible landing approaches.  I think my performance estimates are generally conservative.  I think the flight maneuvers are fairly pedestrian until landing and roll-out.  Your mileage may vary.  These are not optimal, but I think it is possible to land either uphill or downhill with varying degrees of risk and maneuver aggressiveness from nearly any initial heading.  Obviously, some headings significantly reduce the risk of one direction over the other.  In half of all cases you may have to make right turns instead of left.
Here are my assumptions:
Altitudes are all referenced to the roadway midpoint elevation
Aircraft weight is 2000 lbs.
40 KIAS -- stall in landing configuration
45 KIAS -- 1320 ft/min descent - 30 degrees flaps
48 KIAS -- stall in clean configuration
50 KIAS  -- 780 ft/min descent - 10 to 20 degrees flaps
55 KIAS  -- 725 ft/min descent
60 KIAS  -- 800 ft/min descent
65 KIAS  -- 870 ft/min descent - best glide angle through the air  approx. 7.5 to 1 glideslope
70 KIAS  -- 970 ft/min descent
75 KIAS  - 1115 ft/min descent
80 KIAS - 1285 ft/min descent
The wind is blowing from the South at 15 knots
Horizontal wind component up the slope:  ~1500 ft/min
Vertical wind component (upward) up the slope:  ~264 ft/min
Uphill landing

Using your cat-like reflexes and finely-honed piloting skills, track outbound on a heading of 235 for 16 seconds while trading your 100kts of airspeed for a little more altitude.  I calculate you can pop up about another 80 feet from the mid-field starting altitude during that time.
Fly for an indicated airspeed of 70 kts because you must now turn (~1.1G load factor) at 6 degrees per second to a heading of 180.  This takes about 9 seconds; you are 1600 feet south, 2280 ft west, and about 950 ft above mid-field.  26 seconds have elapsed.
Fly on a heading of 180 for nearly 40 seconds.  Think about making a radio call stating position and situation.  Maintain 70 KIAS for better penetration into the wind.  You are in your downwind leg and it has been over 1 minute since your engine failed.  You are 5230 ft south, 2280 ft west, and 495 ft above mid-field.  About 65 seconds have elapsed.
Now turn, maintaining 70 KIAS, at 6 degrees per second to the "runway" heading of 360.  Take a few extra seconds to roll out and line up with the roadway.  You are about 3935 ft south (thanks to that upslope wind), aligned with the centerline of the road, and 108 ft above midfield (about 750 ft AGL because of the slope).  About 97 seconds have elapsed.
Slow to 65 KIAS and fly this heading for about 27 seconds.  Wait until the end to drop maybe 10 degrees flaps to preserve speed for the zoom-climb, flare landing.  Nose-high attitude will be your friend on the upslope landing so don't use too much flap deflection.  About 114 seconds have elapsed.
You cross over the landable portion of the road at 65 KIAS with over 100 ft AGL.  It has been about 118 seconds since your engine failed.  Fly the aircraft through an energy-preserving flare (actually climbing at the last) until a few feet above the rapidly rising road.  You will touch down just past the first third of the landable roadway a little over 2 minutes since your engine failed.  Your speed will bleed off, the airplane will stop flying, and because of the upslope, you will roll to a stop, with or without brakes in 10-20 seconds.  Apply brakes so you don't roll backward down the hill!
Downhill landing

Track outbound from the midfield point on a heading of 90 degrees for 7 seconds while trading airspeed for altitude.  The maneuver takes about 15 seconds to complete, but half-way through, begin a 6-degree-per-second turn, stabilizing at 70 KIAS and rolling out on a heading of 360.
Fly the 360 heading for about 4 seconds.  You are now about 2340 feet north, 2255 ft east, and about 925 ft above the midfield point.  26 seconds have elapsed.
Maintaining 70 KIAS, begin a 30-second, 6 degrees-per-second turn to heading 180.  You are now about 2940 ft north (upslope wind again), aligned with the roadway, and 550 ft above the middle of the roadway.  Your height AGL is only about 65 ft (!), but that’s okay.  You are on final approach and you can fly into and out of ground effect as you like to fly to the threshold of the landable portion of the roadway which is on the steeply descending slope.   It has been about 56 seconds since your engine failed.
Just under 60 seconds have elapsed.  At this point you need to increase your rate of descent to more than the 10 degrees (17% gradient) downslope of the hill and roadway.  You might choose to drop 30 degrees flaps and decrease airspeed to 45 KIAS and plunk down on the roadway at about 30 knots groundspeed, but you have to bleed off 35 knots of airspeed without ballooning too much and end up at only about 5 knots above stall.  Your angle of attack would be so high that you would not be able to see the roadway at all - not even the far end because of the down slope. And you would strike the tail on the ground before the main wheels touched.
Instead, you will need to increase your airspeed to about 80 KIAS and use about 30 degrees of flaps to keep from flying up and away from the ground.  This feels like a fairly steep approach but you are only descending at about 250 ft/min with respect to the ground which is falling away steeply.  You are about 2000 feet from the landable portion of the runway.
In about 20 seconds you are down and on the roadway about 100 yards down from the start of the landable portion.  About 1 minute and 17 seconds have elapsed since your engine failed.
Here's where things start to get a little sketchy.
You are rolling down the roadway with 80 knots indicated (65 kts ground speed) – give yourself 6-8 seconds to get the flaps fully retracted while you try to keep the aircraft “stuck” on the ground.  On a 10 degree downslope your brakes are (cosine 10 degrees) still about 98% as effective, if you weren’t still generating a lot of lift.  Conservatively, you might get 50% of your weight onto the wheels initially.  And don’t forget your mass is effectively pulling you down the slope (sine 10 degrees * 2000 lbs) with about 345 pounds of force.
For reference, this source: (https://aviation.stackexchange.com/questions/67979/is-there-an-actual-rated-thrust-for-a-cessna-172-engine-at-takeoff-power#:~:text=As%20John%20K%20said%2C%20it,be%20aware%20of%20before%20takeof) puts the thrust of the 160hp, fixed pitch 172N at between 500-600 lbs force when at takeoff power.
You will trade lift at higher speeds of the roll-out, which will make your brakes less effective, for the drag at the higher speeds which will counter-act the downhill force.
It’s probably a 30+ second, white-knuckle ride down the roadway managing your energy, trying to keep the plane “stuck” on the ground and to not lock up the lightly loaded mainwheel brakes until you get it stopped just before the end of the useable portion.
I conclude that the uphill/downwind landing is the better choice for the following reasons:

Time.  Compared to the downhill/upwind landing you have about 30 seconds more seconds to collect your thoughts, take calming breaths, and possibly make a radio call reporting your position and situation on one of the straight legs of your “pattern”.  You buy the extra time by landing on the end of the roadway that is almost 350 feet lower than the top end.
Distance.  Right up until touchdown, the proximity of the ground is not a factor at any part of the uphill/downwind approach.  Contrast this with virtually skimming the ground for 15 seconds at the last of the downhill final.
Energy.  Granted, change in energy on the uphill approach happens much more quickly at the landing, but because you are flying up the slope there is some leeway on the timing and aggressiveness of the landing flare.  And once you are down, you will roll to a stop even if you don’t use the brakes.  On the downhill landing both your kinetic energy and your potential energy are working against you getting your aircraft stopped.  The relatively feeble upslope wind does little to help you here, and in fact, hurts you once down by producing more lift and reducing the weight on wheels for braking.  There will likely be an excruciating 30 seconds of managing flaps, brakes, and elevator so you can brake to a stop before the end of the useable roadway.


What do these white on red words indicate on a London Heathrow taxiway chart? What do the words in white block capital letters over a red background denote on this aerodrome chart of LHR?

They are named holding points; this allows them to say things like "taxi to RABIT" rather than "taxiway Bravo, hold short of taxiway Charlie". This saves a lot of time for ground controllers at busy, complicated airports.


How heavy are the Boeing 747 landing gear? Does anyone know how heavy are the combined landing gear on a Boeing 747?

It would be interesting if someone has also weight statistics per gear (nose gear and the four other main gear).

It seems I misspoke in my comment in which I gave the moments for 747-400BCF gear retraction. I didn't realize the component weights were further on in the document I referenced. The weights for the BCF are:

body gear 6447 lbs (2924 kg) each

wing gear 6508 lbs (2952 kg) each

nose gear 3157 lbs (1432 kg)

However, @Gurkan's comment is relevant in that you have to decide what all should be considered as part of the gear. So, I put up a PDF of the WEIGHT AND BALANCE CONTROL AND LOADING MANUAL for each of two 747 freighter variants. You can access them at terryliittschwager.com/wbmanuals.php. The most relevant sections are 1-86-041 and 051.


Is ETOPS satisfied solely by range circles? Consider a scenario where an airplane is operated on an ETOPS 180 route where the ETOPS alternate is open, available and above minima, but there is terrain between the route and the airport which makes it absolutely unreachable. If, in that scenario, an engine failure or decompression alternate is available but more than 180 flying minutes away, and enough fuel is carried to reach it while satisfying the terrain clearance requirements, would that flight be legal (not: practical, safe, desirable - only legal!) according to EASA/FAA regs? In other words, is ETOPS satisfied solely by looking at range circles around available airfields, or are there additional considerations required (not: prudent, desirable - required!) by regulations?

No, ETOPS is not satisfied solely by range circles, but (among other things) by the "time needed to fly to that airport".

See the requirements of 14 CFR 121.633 (emphasis mine):

  (a) For ETOPS up to and including 180 minutes, no person may list an airport as an ETOPS Alternate Airport in a dispatch or flight release if the time needed to fly to that airport (at the approved one-engine inoperative cruise speed under standard conditions in still air) would exceed the approved time for the airplane's most limiting ETOPS Significant System (including the airplane's most limiting fire suppression system time for those cargo and baggage compartments required by regulation to have fire-suppression systems) minus 15 minutes.

Paragraph (b), for ETOPS beyond 180 minutes, gives the same "time needed" requirement.

So, if a scenario existed as the question describes where "there is terrain between the route and the airport which makes [the ETOPS alternate] absolutely unreachable", then that flight could not reach that alternate in the required time (since the alternate is not reachable), and the flight could not be dispatched listing that alternate.


Is the MTOW determined by the wheel maximum supported weight? I was on a LATAM flight a couple days ago, and decided to have a read through their VAMOS magazine. As a lot of airlines do, they had a couple of pages on their fleet, and also a double spread on one specific plane.

This plane was the 777, which was a little bit surprising as they are about to get rid of those I think. Anyway, it had all the usual facts and figures, and also a couple of highlights about the plane.

I managed to find a web copy of the magazine, and the picture is below:

https://issuu.com/spafax/docs/vamos_latam_junio_2017_web

One of these highlights is the wheels, and it says (roughly translated):

  Each of the wheels is capable of supporting a maximum of 29,294 kg.

My first reaction was "That's pretty impressive!", then "I wonder how much above the MTOW that is?" The MTOW is specified at the side there: 351,530 kg, which correspondes to the 777-300ER.

So 29,294 x 6 x 2 = 351,528

Oh. That's under the MTOW. I wonder if there's some rounding off here:

So 351,530 / 2 / 6 = 29,294.166 - yes there is.

I was surprised that the maximum each tyre/wheel could take summed up to the MTOW, as I thought that they would experience larger forces on landing. Also, what would happen if a tyre blew?

So, does the maximum load for a tyre/wheel have anything to do with the MTOW? Or is this just marketing guys jumping the gun?

I have seen this question How is Maximum Take Off Weight determined? and that says that the manufacturers determine it, and it is based on the required payload of the aircraft and the design configuration, which doesn't really answer this question.

Edit with extra info mentioned in comments:

When stationary, the wheels will have a total force on them of 351,530 kgs, which according to this magazine is their max. When landing, the wheel like have to bear a weight of 251,290 kgs, plus the force of the landing. In my mind, the extra force of the landing would push the total above the MTOW, but this is just in my mind so I'm probably wrong :P

Boeing1[pdf] specs for 777-300ER:

Max taxi weight: 777,000 lbs (352,442 kg)
Max take off weight: 775,000 lbs (351,535 kg)
Max landing weight: 554,000 lbs (251,290 kg)

Bridgestone2 specs for approved tires:

Main: 66,500 lbs (30,264 kg) x 12 = 798,000 lbs (361,967 kg)
Nose: 44,500 lbs (20,185 kg) x 2 = 89,000 lbs (40,370 kg)
Total tire rated load = 887,000 lbs (402,337 kg)

So at taxi weight on all 3 gear there's roughly a 110,000 lbs / 50,000 kg margin (about 14%).

At max landing weight, main gear only, there's a 244,000 lbs / 110,677 kg margin (44%).

At MTOW there's about a 112,000 lbs / 51,000 kg margin (14%) on all gear, but only a 23,000 lbs / 10,400 kg (3%) margin after nose gear lift off.

But, when the nose gear lifts off the ground the wings are supporting nearly all of the weight. Their numbers are pretty close to what the manufacturers list. I think you're just not accounting for the nose gear at takeoff and the weight difference at landing.

As far as Is the MTOW determined by the wheel maximum supported weight? It's the other way around. The MTOW determines how many tires of what weight rating are needed.

A more important tire consideration is speed. The tires are rated at 204 kt. This paper gives an example of a 747 at 825,000 lb there is a weight margin of 30,000 lb. But liftoff speed is 199 kt, so there's only a 5 kt speed margin.


How do you know if a VOR is High, Low, or Terminal? Is there any way of telling on both a VFR and IFR chart what type of VOR we are looking at?

The range of the VOR is included in the Airport/Facility Directory data under the name class
From A/FD legend:

Example:

Service volume for each class:


In an articulated hub rotor craft, what could cause the blade to flap negatively? For example in forward flight what could cause the blade to flap lower than parallel to the CF at the front of the aircraft ?

The first thing that comes to mind does not occur in forward flight. That would be a hard landing. Depending on the rotor design and the amount of articulation and the landing gear type, a hard landing can result in some serious problems, notably, Ground Resonance.

In-flight, it may be possible to achieve with a rapid unloading of the rotor (Zero - G) plus cyclic input. One adverse condition which causes negative flapping is Mast Bumping. Usually, if not always fatal. Mast bumping takes a specific set of conditions and control inputs, to take place. It is typically occurs with 2 bladed teetering rotor systems at zero G.


In WW2 aircraft, where were gun cameras mounted, and did they suffer performance penalties? During WW2, some aircraft had gun cameras that activated whenever the guns fired, so that people on the ground could evaluate performance and help with kill ratios and other statistics. These were actual video cameras, using film.

I want to know, where were the guns cameras mounted? And how much performance penalty did they incur, in terms of weight and drag added? I cannot imagine that they were actually inside the cockpit, because video cameras back then were big things.

It was a small 16mm film camera usually mounted, in single engine fighters, in the inboard area of the wing, within the leading edge behind a little window (the P-38's is also about the same location between the center pod and left engine) or in the nose in twins.

Look carefully at a lot of gun camera film on something like a P-51 when the sun is lighting up the prop from behind and you can see that the camera is viewing through the lower left quadrant of the propeller arc, being just a couple feet to the right of the left side wing guns.  Most fighters only had up to 30 seconds of continuous firing time in ammunition, so it didn't need to have a really large film supply.

On some systems the camera could be set to run only during firing or could be run independently and there was a little flag that appeared in the upper left corner of the film image and lifted out of the way when the guns were firing and dropped into view then they weren't.

A lot of pilots started to do away with tracer ammunition when lead computing gyro gunsights started to appear in 1944, so often the little flag is the only way you can tell the pilot is firing other than bullet strikes (and vibration from the guns sometimes) when you watch gun cam movies where no tracer is being used.

The weight penalty was negligible, only weighing a few pounds, and the drag penalty was also negligible, being buried in the leading edge behind a clear panel, like a small landing light.


Is a helicopter ride unsafe for young children? Recently we were in London and noticed how so many helicopter rides were there. While booking a ride I found out that they do not take a child under 4 years of age, none of the Heli ride companies I found in London allowed any child under 4 to take their rides.

So we were unable to take that ride since our child is  3 years old. I was wondering why is it unsafe for children to fly in a heli when the same or much younger children fly in a commercial airliner all over the world all the time?

Obviously I do not question their judgment and I do appreciate their concern for safety I just would like to know what makes it unsafe so we can prepare accordingly before taking that ride when he is 4.

I have been in helicopters I do not find them particularly challenging for a passenger. Could the primary reason be that these heli tours are not ordinary flight from A to B, they do quite some sprints and sharp turns up there to add to the fun.

Edit

Some references to support the question

  Must be 4 or over, under 16’s must be accompanied by an adult.

HeliAir

  No children under the age of 4 are permitted to fly with us.

RedHill Helicopters

  No children under the age of four are permitted to fly with us.

The London Helicopter

  Minimum age: 4 (under 16s must be accompanied by a paying adult)

Virgin Experience Days

A few notes of update.

Evidence from other operators that there is no hard age limit

  There is no upper or lower age limit for pleasure flight however we recommend that children under 12 are accompanied by an adult.
  Central Helicopters T&C

  Generally anyone can be a passenger on a pleasure flight. Young children should be accompanied by an adult.
  Hields Aviation FAQ

GUIDANCE FOR EVENT ORGANISERS
AND HELICOPTER OPERATORS AT SPECIAL EVENTS covers Local flights (They call it A to A) and makes no special mention of minimum or maximum age limits. You can be fairly sure this document would be where any such specification would be made. Along with CAP 789, which is linked below, which also has no special mention of age limits for flights on helicopters

It is very hard to prove a negative, but I hope this is enough to convince you. Operators are under no obligation to justify their rules.

Original answer follows:

There is nothing inherently stopping an infant taking a flight on board a helicopter.

I suspect this has everything to do with the operators of these flights do not have the equipment to properly ensure the security and safety of infants.

Airlines typically provide extender belts for infants on laps. They also have provision for dealing with emergency situations with infants on board. This is because it is what their customers require and makes commercial sense to provide those services.

CAP 789 (which is guidance for operators) has something to say about this (emphasis mine)

  EU-OPS, JAR-OPS 3 and the ANO require the aircraft commander to ensure that at
  certain times each passenger on board occupies a seat or berth with his safety belt
  (or harness where provided) properly secured. These regulations also require the
  aircraft commander to ensure that multiple occupancy of seats does not occur except
  by one adult and one infant who is properly secured by a supplementary loop belt or
  other restraint device.

The clientele of helicopter pleasure flights probably do not regularly require bringing infants aboard. So there is little requirement or commercial pressure for them to do so.

The "must be 4 years of age" is quite possibly entirely arbitrary - in that they are probably large enough to use the standard harnesses/belts/noise protection provided. Operators probably do not routinely carry things like infant noise protection, and helicopters are noisy environments.

Some child restraint systems used in cars are appropriate for use in aircraft, and some operators may have allowed you to bring your car child seat on board for use with your infant (More info is available here). You would need to call around a few operators to find out.


How are the NEO LEAP-1A engines attached on the A320? How many bolts hold the NEO LEAP-1A engine to the pylon at the forward mount and at the aft mount?

This page shows a schematic of the mounts for the original A320.  There are 4 bolts and 2 shear pins at the front mount, and another 4 bolts and 2 shear pins at the aft mount. In general terms, the A320neo pylon and mount system design was kept very similar to the original A320 design.  So it's a good guess that the number of bolts is the same, although I was not able to find any source to confirm that.


Why would smoke enter the cabin if the batteries are switched off before the APU flap closes? In the A320 FCOM SOPs securing if the APU flap doesn't fully close smoke may occur in the cabin in the next flight

In the NORMAL PROCEDURES SECURING THE AIRCRAFT. It states that before switching off the batteries we have to wait for the APU flap to fully close if we don't and we switch offf the batteries before the flap fully closes it states that smoke may occur in the cabin during the next flight. Could someone please explain as to how smoke will occur.?

Switching off the battery too soon interrupts the auto shutdown sequence.

In that sequence is an automatic de-oil procedure that is carried out. A de-oil valve introduces air into the oil pump to break the suction (reduce the drag) for the next start.

The air forces the oil back to the oil reservoir and out of the bearing chambers. If it doesn't the once warm oil will contract and add extra forces to overcome when it's cooled. The second benefit of the system is starting the APU in cold weather, with all the oil back in the reservoir, it can be uniformly heated before it is reintroduced into the lubrication system.

If that didn't happen, the next start will stress the oil system, a small leak may occur, which will burn and re-enter the cabin as burned oil (smoke).

If unsure about the last shutdown, the APU can be started and left running with no load whatsoever for 5 minutes to make sure it doesn't happen.

Also see this [somehow related] story on avherald.com. The mentioned Airbus publication link is broken, you can find it here.

Here's the APU shutdown sequence:

  At 95% speed, APU "AVAIL" lights go off.
  At 50% speed, the de-oil solenoid valve opens to decrease drag during the next start.
  At and below 7% speed:

  the de-oil solenoid closes,
  the APU fuel LP valve closes,
  the data memory module is updated,
  the air intake flap closes,
  the ECB de-energizes itself.

  (Airbus training manual.)

Do not use for flight.