Why is volcanic ash hazardous? What happens on the engine after ingesting volcanic ash? Is volcanic ash dangerous for the cockpit crew too? Despite the ground stations, is there any other way to identify volcanic ash while flying?

As mentioned in the comments BA flight 9 is a thorough example of why ash can be a huge issue.
Relevant points of that incident
One issue that ash creates is it cannot be seen on radar so it can be hard to track at night and must be reported by other means. This is deceiving as you would physically see what appears to be a cloud yet weather radar would not show anything.
Inside the cabin, this depends on the granularity of the ash. Some of it will be filtered by the plane's air filters as any particulate matter would. However, ash can be extremely fine and what does make its way through the filters will present itself in a smoke like manner. This may cause alarm in the cabin and a false indication of a fire.
When it comes to the exterior of the plane there are a few issues. The fine grains hitting the plane at that speed will act like sandpaper. The windshield may become scratched to the point you can't see through it (which is not actually as big of an issue as some may assume). The paint will be effectively sanded off which in the short term is not a huge issue. More importantly it could affect your instrument inputs by clogging things like the static ports and pitot tube creating erroneous readings in the cockpit.
The engines were the main issue that arose on BA 9. In short the ash entered the engine, was melted and began to adhere to the blades of the jet. In turn this blocked the engine airflow and caused an engine stall. In the process BA 9 lost all four engines; however, when they began to descend the solidified ash cooled and broke off the engine allowing a restart.
Air crash investigation covered the BA incident nicely in season 4. You can watch it here.
Other risks that BA 9 did not have
For a piston plane ash could potentially clog the air filter and starve the engine of air. Any super-fine ash that could get through the filter runs the risk of being ignited and causing detonation issue with in the engine. Likewise the sanding/grinding issue could have adverse effects on the propeller shape reducing its efficiency or even overall ability to act as an airfoil.
There is a nice wiki on it here and it appears that as of 1991 centers called "Volcanic Ash Advisory Center" have been set up to help track these very issues.


why does it cost so much just for an hour of training? I'm currently in the process of becoming a pilot and the question I keep asking myself is why does it cost so much for just one hour?

You've not specified how much you consider "so much", however it's unlikely to matter too much to the answer. What you're paying for is (at least) twofold, and probably consists of

The rental of somebody else's aircraft. Every hour you fly this aircraft takes it an hour closer to an expensive maintenance window. There are costs involved in running an aircraft much like there are costs associated with owning/maintaining any vehicle. Also, fuel isn't free - its is often rolled in to the cost of rental for aircraft.
The time of an instructor, who himself has spent time/money learning his craft, and quite possibly does this as his job (as in, its his sole purpose to earn money from teaching you to fly). He has skill and experience, and like all jobs, the more his skill/experience the greater fees he can charge.

You may have missed the first rule of purchasing a service - shop around. Is your flight school/instructor of a comparable price to others in the locality? Is the instructor you're using a senior CFI, or a new CPL hour-building to get a job with an airline? You will potentially get a different level of service depending on price, but this may suit your wallet better while still giving you the skills you need to get your own pilots license.

Anectote: When I was training for my PPL (circa 2001-2002) in the UK I paid roughly £150/hr. This included the hire of a C152 and a pretty experienced instructor. From memory the instructor was £80/hr and the remainder was the aircraft. When I got sick of being cramped in a C152 with another 6'2" guy, I paid more to fly a C172 - probably added about £40/hr to the cost.


How are arriving aircraft assigned to runways? A similar question to this one was asked before, however my question is not about who assigns runways to arriving aircraft, but what the reasons behind those decisions are.

As an example, let's look at Frankfurt EDDF with four runways (map here). 18 is only used for departures. Of the three parallel runways 25L/07R, 25C/07C and 25R/07L, one is usually also used for departures, leaving two of them for arrivals (from my experience, usually 07L/25R because it's for landings only, and then 07R/25L).

Besides runway length (as discussed in the above referred question) and width, what factors into the decision of which of the two arrival runways an arriving aircraft is assigned? (and other than that it is regulated that certain types may not land on 25R/07L such as A380, B747).

Can airlines / pilots request a runway? In particular, landing on 25R in Frankfurt should be pretty unpopular due to the long taxi time to the terminals.

Arrival and departure runways are mainly assigned due to airport flow. Each airport has its own set of plans of which runways to use, how to taxi to these runways etc. If everybody is moving in the same direction, things go smoother.

Pilots and airliners can request a specific runway, but the request may be denied unless the aircraft has an emergency. Generally the reason is to shorten taxi time, and ATC may grant the request if traffic volume is low. For example, in an airport with a parallel runway configuration, a cargo plane may request the one closer to the cargo terminal.

At some airports, a runway switch may be performed fairly late during the approach. For example, the visual approach to 13L/13R at JFK is largely the same - the only difference is timing the final turn*. Occasionally you will hear pilots requesting the other runway on ATC recordings on YouTube.

For specifics such as which runway goes to which airline, they are local to the airport in question and outside the scope of this answer.

*occasionally, the pilots got it wrong and line up for the wrong runway


Does an active pilot based outside the US require a flight review to maintain FAA currency? If a pilot is a holder of both Canadian and FAA commercial pilot certificates and is flying regularly in Canada, does this pilot still require a Flight Review to maintain currency of their FAA certificate?

FAR part 61.56 ( [U.S.]Flight Review ) requires a U.S.flight review (or authorized alternative - see below), for anyone operating an "N" numbered airplane within the U.S. (when using a U.S. certificate/or U.S. certificate based on a foreign certificate), even if that person is current in another country for which he/she also holds a certificate.

See also, FAR 61.75 (Private pilot certificate issued on the basis of a foreign pilot license.)

See also this FAA Legal Interpretation which relates to your question:
need for Flight Review for holder of U.S. cert based on foreign cert in accordance with FAR 61.75

NOTE: In accordance with FAR 61.56 there are various types of  pilot proficiency checks or practical tests, etc. that may be substituted for a flight review (i.e. see FAR 61.56(d)-(f))


What is the difference between en route and airway? I am studying about airway now. But there are multiple terms that mean airway like enroute or air route. I don't know exactly what the difference is between them.

Airway, en route, air route, air path

I want to know the difference of meanings or definitions between above terms. Please tell me in detail.

Enroute: An aircraft that is on its way to its destination.

Air Route: A specific route that an aircraft takes, just like a car route, taking specific highways and roads to get to your destination. Planes do not go a straight line from their origin to destination.

Airway: A highway in the sky. That is what planes fly in their route. So for example 2 planes flying the V23 Airway would have them flying the same path on the airway specifically.


Can a private jet take off without notifying anybody and land on private land in another country? If you have a friend in the USA who owns a lot of land that is suitable for landing a plane, and you own a private jet with 2 pilots in Norway, can you take off in private property without notifying anybody on what you have on the plane and where you are going or anything like that and fly to the USA and land on the property of your friend? Is that legal to do?

No, you would need to arrange for customs as you are crossing an international border.


Do all GA autopilots use cable "clutches"? In researching General Aviation autopilots it seems to me that most commonly the way control surfaces are affected is via a servo that attaches (via a clutch) to the control cable. References here and here.

Are there any autopilots that have a servo that directly attaches to, and actuates the control surface(s) as opposed to indirectly via the control cable?

From the Approval of Flight Guidance Systems AC-25-1239-1C document:

  30. Override of the FGS.

  a. General. An override of an engaged FGS function is defined as an action taken by the flightcrew intended to prevent, oppose, or alter an operation being conducted by the FGS function without first disengaging that function.

  b. Autopilot override.

     (1) With automatic disengagement.

         (a) Override force. The autopilot should disengage when the flightcrew applies a significant override force to the controls. The applicant should interpret “significant” as a force that is consistent with an intention to overpower the autopilot by either or both pilots. The autopilot should not disengage by minor application of force to the controls, such as a pilot gently bumping the control column while entering or exiting a pilot seat during cruise.

(Page 37)

It goes on to say that 25lbs of force has been determined to be a significant override force level for "other than approach" operations. This may be difficult to measure using a system that just looks at the force on the control surface since normal operations may cause force feedback through the surface. There would have to be a way to measure the pilots force in conjunction with the control surface force and determine if the pilot is trying to override the servo.

GA aircraft are not normally equipped with all the "bells and whistles", autopilots are typically optional equipment. This means that the autopilot system needs to "fit in" to the existing control system architecture. Adding bosses, actuators, connection points, holes, etc to an airframe to accommodate an autopilot is a "significant modification" that may require a new type certificate or an STC.

The easiest way around this is to use servo controls with clutches that move existing control cables. This way the pilots force is directly measurable on the control system. Using magnetic clutches the autopilot can easily disconnect itself, worst case, by popping the autopilot breaker (although this is not an acceptable disconnection procedure).

I can't say that there are no GA aircraft that don't use a different mechanism, but I've never heard of one.


How do we calculate top of descent (TOD) in flight? What is the in-flight trick?

I know how to calculate it in theory, but how can I calculate it fast? For example, I know I can use this formula for calculating the rate of descent:

[ground speed + add 0]\2

I'm trying to find a formula like that for TOD.

Any approximate method is going to vary for different types of plane, depending on their speed, altitude and descent rate, but here's how I figure it for my Cessna 172.

I know I'm traveling around 2NM a minute (actually a little slower), and I like to descend around 500 fpm.

So if I have to drop 5,000 feet to pattern altitude, the TOD is 10 minutes out (5,000 feet / 500 fpm).   At 2NM a minute, that is 20 miles out.

So if I have my GPS / DME set to my destination airport, I am looking for both ETE: 10 min, and also Dist: 20 miles, then I start my descent.

Its approximate, but its pretty close for planning purposes.
Its always just:

[Altitude Drop] / 500 = Minutes
Minutes * 2 = Miles


Where to find information on the Daimler-Benz 606/610? There seems to be relatively little information regarding either of these engines on the web. Anyone have an idea where I can find more info?

Each of those is two V12 engines coupled together.

The 606 is two 601s:

  Two DB 601 F or G coupled to work on a single propeller shaft for use in early Heinkel He 177As - 2,700 PS (1,986 kW) at sea level with a mirror-imaged starboard component engine supercharger, and derided as "welded-together engines" by Reichsmarschall Hermann Göring in August 1942, from the problems they caused with engine fires in the He 177A during service from their inadequate installation design; such problems were not present in either the Heinkel He 119 and Messerschmitt Me 261 which also used them.—Wikipedia

The 610 is two 605s:

  Two DB 605 "coupled" (geared together) as a "power system" (71.53L / 4364.8in3), to work on a single propeller shaft for use in Heinkel He 177, up to 2950 PS (2,909 hp) for take off, 2788 PS (2,750 hp) at 2,100 m. Mirror-imaged starboard component engine supercharger.—Wikipedia

The "engine difficulties" section of the Heinkel He 177 Wikipedia article discusses the story of both engines. The 606 was notorious for catching fire when installed on the He 177, and later it was replaced with the 610.

You can get more information by looking up 1) which aircraft they were installed on, or 2) the 601 and 605 base models.

(Image source)


Has someone with no experience at all ever taken off in a plane? Could they? I was watching Mystery Science Theater 3000 and their showing of 1970 TV movie/pilot San Fransisco International.  One of the plots in the movie involves a twelve (or so) year old boy, who, alarmed about his parents' imminent separation, wanders across the tarmac, hops into the cockpit of an Aircoupe, and flees his mother by starting the plane and taking off before anyone quite knows what's happening.  After he unsteadily flies it a bit (the best part of the movie is some stunt pilot making the Aircoupe swerve through the air like a drunken eagle), Bonanza's Adam Cartwright talks him through a safe landing.

Plenty of questions have been asked about the possibility of planes being landed by someone with no experience at all, and, of course, talk-down landings are a real thing, even if they're rarely done by anyone with zero experience.  But I'm curious about the first part, where the kid turns a key, taxis away, and is up into the California sky without even having played Microsoft Flight Simulator.

Naturally, a civilian getting into a cockpit at SFO without being stopped seems patently absurd in the security-conscious present, but times have changed.  Has anything even similar to this ever happened?  And if not (if this doesn't over-broaden my question) could a layman get a plane, single-engine or otherwise, into the air without any experience?

The Aviation Safety Network has an article listing 11 airplanes that crashed after being stolen by a non-pilot. The most recent was the Horizon Air Dash 8 that was stolen by a ground service agent in August 2018.

There are more interesting stories such as:

The guy that tried to crash a Cessna 150 into the White House (with minimal experience and training)
Ground crew member that stole and crashed an F-16 in Norway
Mechanic that accidentally took off in an English Electric Lightning
Mechanic that took off in an F-86 Sabre
15-year-old that stole a PA-34 and took off with 4 passengers, later crashing

Whether these qualify as "amateurs" is a matter of opinion. Most of them were mechanics/engineers. It would be difficult (but not impossible) for a person not familiar at all with the aircraft to get it started and manage to take off.


Fly-by-wire vs hydraulic systems So, the great old argument, flyer-by-wire systems vs conventional hydraulics. I was wondering which one was better and why. Which one is safer? Pros and cons in terms of safety? Basically, I just wanted to know roughly the pros and cons of both systems.

I was wondering which one was better and why.

When done equally right they are equally good.

However, FBW makes it possibly to improve the quality of control beyond what's determined by the aerodynamics (e,g, making unstable airplanes stable, or making hard-to-fly airplanes easy to fly), and making the airplane robust against malfunctioning components (e.g. stuck actuators or control surfaces), or and adverse conditions (neutralizing turbulence, wind gust, etc).

Giving computers some authority also enables the computer to correct for human error (stalling, overloading, etc), hence improves safety as well.

Which one is safer?

FBW is extremely hard to design, tune, test, and validate. Although the benefit of FBW could make the flight safer in a lot of ways, the risk that a premature FBW system could introduce is quite significant as well.

In general, although it is hard to state that an airplane equipped with FBW is inherently safer than one with conventional controls, and often times the reverse seemed true in history due to early bad track record of some FBW equipped airplanes, yet if an airplane is designed with safety as priority, FBW could offer a lot of benefits, again, if done right.


Why does the Pratt & Whitney 747 have an extra engine on the right side but not left side? What’s the purpose of this design, and why only on one side?

It's an engine testbed aircraft. In this particular picture, the tested engine is probably one of the PW1X00G series (mainly used by Airbus A220, Airbus A320neo, Embraer E-Jets E2, Irkut MC-21, Mitsubishi SpaceJet) and the aircraft is one of two Boeing 747SP testbed aircraft owned by PW.

Engine testbed aircraft test the engines in-flight, with parameters and conditions that can not be tested in a static test on the ground (for example, low temperatures and non-static thrust).

Engine testbed aircraft often end up in unusual configurations. Other examples include (but not limited to):

General Electrics Boeing 747 testbeds: 1 2
Honeywell's Boeing 757 testbed: many pictures with different engines, even turboprops.


Is there an FAA-published handbook for Aviation Physiology? The FAA has many handbooks, but I don't see one in the list dealing with aeromedical or physiology information.  Does such a handbook or advisory circular exist, or is this information only available within other handbooks such as the PHAK?

I found this Introduction to Aviation Physiology on the FAA web site.


Why wasn't the 737 MAX's landing gear lengthened enough to mount the engines under the wings, rather than in front of them? The reason Boeing originally added the MCAS to the 737 MAX was to compensate for a slight pitch-up moment generated by the engine nacelles at very high angles of attack.  This pitch-up moment occurred because the LEAP engine used on the MAX series is larger and longer than the CFM56 used on the 737 Classic/NG, so Boeing mounted the new engines further forward and higher up to fit them on the plane; the larger, forwarder nacelles added more planform area to the front part of the aircraft, causing the MAX's center of lift at high attack angles to be slightly forwarder than on the Classic or NG, causing the MAX to pitch up slightly more at high attack angles.

However, the reason the Classic and NG have their engines mounted in front of the wing is that the 737 originally used the much slimmer JT8D engine, allowing it to use a very short landing gear to make it sit lower on the ground and ease the process of loading baggage and other cargo by hand.  When the Classics came along, Boeing decided to keep the 737-100/-200-length landing gear, which forced them to use a smaller-fan variant of the CFM56, move all the engine accessories from the bottom to the sides, and mount it in front of the wing (instead of directly below it) in order to give the new, larger engine sufficient ground clearance; with the NGs, which use a CFM56 variant that is essentially the same size as that used on the Classics (with a diameter all of one inch greater), they simply kept the same nacelle, pylon, and landing gear designs as those used on the Classics.

The MAX, in contrast, has a longer landing gear than all other 737s (handloading of baggage not really being that much of a thing anymore at most 737-served airports); given that they were giving the MAX a longer landing gear anyway, why not make it long enough to let the engines fit under the wings and finally eliminate the engine-mounting kludge inherited all the way from the 737-300?

The main gear sits between the wings and retracts inwards, such that the wheels will rest in the lower fuselage. Lengthening the main gear would either require to shift the gear attachment points outward or to retract one leg a bit forward and the other a bit backwards, such that both wheels will sit behind each other instead of side-by-side, as they do now - see below (source).

Shifting the gear attachment points out is clearly feasible but results in a major wing redesign. That would cost money so Boeing management decided that a software fix would be the better solution.

Placing the wheels in tandem would equally be a major and costly modification. A lot of systems would need to be relocated and all modifications would require testing. Boeing management cleary did not want to pursue this option.

Another quick fix is shortening the gear upon retraction. Decompressing the oleo strut in order to shorten the gear upon retraction is already standard in many fighter jets. Another solution is to add another hinge such that the gear leg will fold inside the gear bay. Such a solution was used on the Grumman F-8F Bearcat and is pictured below (source).

From what I understand, this particular solution was applied to the longest 737 version to allow enough tail clearance for rotation, but added weight and complexity. Of course it could be applied to the rest of the 737 MAX fleet as well, but again Boeing management tried to save money and weight by implementing a software-only solution.

But the engine location would be fine if a larger horizontal tail would be added, increasing stability at high angle of attack and making a quick software fix unnecessary. Again, this would add cost and weight and make the aircraft less competitive.


Has reversing the active runway direction ever led to lined-up aircraft taxiing to the other end of the runway? I was in an aircraft yesterday waiting for its turn in the departure queue on the taxiway and noticed that the windsock was showing a direction approximately 30 degrees but directed along the direction we were entering the runway in. i.e. The parallel component would point in the take-off direction & not against it.

Made me wonder: Are there instances when lined up aircraft have to be made to taxi to the other end of a runway due to a last minute wind direction reversal?

Never happened to me, nor seen it mentioned in any ATC conversations / videos online so made me wonder.

Of course, if the parallel component is smaller than the allowable tailwind for the aircraft then  I guess it does not matter?

What you are describing does happen. The runway change is a major event at a big airport and it usually occurs once a day. This becomes a major transition because landing aircraft have to be switched to the other end. AND, areas served by a single approach control, the change has to be coordinated with the other airports. Note that lines of aircraft waiting to take off rarely occur unless the airport is very busy and has few runways.

Thus, the runway change generally occurs over time (half an hour).

If there is a sudden, unpredicted wind change, generally, aircraft that are already at the "wrong" end of the runway are allowed to continue using it if they are able to do so.

So yes, aircraft will on occasion have to move to the other end of the runway.

I have seen this more frequently at busy general aviation airports than at commercial airport.


What is the minimum power system required to fly a commercial aircraft? I heard of a A320 landing, no lights, both generators out, RAT deployed, and with only 28VDC(battery power),  made a successful landing. Is this possible?

I heard of a A320 landing, no lights, both generators out, RAT deployed ... , made a successful landing. Is this possible?

Yes

  A United Airlines Airbus A320-200, registration N409UA performing flight UA-497 from New Orleans,LA to San Francisco,CA (USA) with 109 people on board, was in the initial climb when the crew reported smoke in the cockpit, levelled off at 5000 feet and returned to New Orleans. The crew reported before joining downwind that they had lost all instruments and requested to be talked down by ATC via Precision Approach Radar (PAR). The crew descended to 600 feet where they got visual contact with the water of Lake Pontchartrain and continued visually for a landing on runway 19 about 10 minutes after departure. During landing the aircraft blew both right hand main gear tyres, went left off the runway, stopped with all gear just off the paved surface north of the intersection with runway 10/28, and was evacuated via slides.

  A number of passengers needed medical attention due to smoke inhalation.

  Post landing photos showed the RAM Air Turbine (RAT) deployed. Runway 01/19 was closed for about 10 hours.

  The crew told passengers that they had lost all electronics and were flying on minimal backup systems, landing would occur overweight with minimal braking and minimal steering ability.

From http://avherald.com/h?article=43a6bc08

  Early on, NTSB investigators suspected a faulty fire-warning sensor in the cargo hold. And they tentatively concluded that the cockpit crew had skipped a portion of the pre-flight checklist then failed to restore power to some equipment, making it more difficult to carry out the emergency landing

From http://www.nola.com/traffic/index.ssf/2013/05/united_497_emergency_landing_i.html

Basically it seems there was nothing wrong with the aircraft apart from a faulty smoke sensor. The crew missed this in their preflight checks, noticed it after take-off and then turned off all the electric generators (they were supposed to turn one back on according to the checklist - they didn't). Anyway, they landed the plane OK on emergency power from batteries and RAT.

  with only 28VDC(battery power)*

On the A320 the RAT supplies the ESS bus, not main buses 1 and 2. It powers both the AC ESS bus and the DC ESS bus through the ESS TR (transformer rectifier). So that's not just 28V DC but AC too.

In the interval after both main generators failing and APU being unavailable, I believe the DC batteries power the DC ESS bus until the RAT is deployed and providing power (which should happen automatically and quickly). So in this short interval there is only DC power on the DC ESS bus.


Is there a minimum altitude for ejection seats? Is there generally a minimum altitude for ejecting in order for the sequence to function reliably (all the way to opening the chute, and slowing down to a survivable descent rate)? I've seen ejector seats test being done on the ground, don't know if there were actually test pilots in those seats though.

I assume all bets are off if you're not wings level (obviously a low-level inverted ejection has a 0% chance of success).

It depends on the ejection seat.

Modern zero-zero ejection seats are designed to be usable at zero speed, zero altitude.

Older ejection seats had different minimums which varied from model to model.

On a side note, the early F-104 ejection seats required quite a bit of altitude to deploy properly, since the pilot exited through the bottom of the aircraft. This was done because there was some concern that the pilot would hit the F-104's T-tail with a standard ejection seat.

EDIT

It appears that it may actually be possible to eject from an inverted aircraft. According to Wikipedia (bold added for emphasis):

  The minimal ejection altitude for ACES II seat in inverted flight is
  about 140 feet (43 m) above ground level at 150 KIAS. While the
  Russian counterpart - K-36DM has the minimal ejection altitude from
  inverted flight of 100 feet (30 m) AGL. When an aircraft is equipped
  with the Zvezda K-36DM ejection seat and the pilot is wearing the
  КО-15 protective gear, he is able to eject at airspeeds from 0 to
  1,400 kilometres per hour (870 mph) and altitudes of 0 to 25 km (16 mi
  or about 82,000 ft). The K-36DM ejection seat features drag chutes and
  a small shield that rises between the pilot's legs to deflect air
  around the pilot.


How are the glide polar and L/D ratio charts related? We know from other questions and answers that airplanes and gliders in particular can have their performance described in terms of glide polar and Lift-to-Drag ratio.

As it appears from the images in the first linked answer (included below), the two are connected to each other.

Despite my research I couldn't find a source on how to derive one curve given the other (the polar given the ratio or the ratio given the polar).

Is it possible to do so? I have heard from friends that are glider pilots that the glide polar curve can be described as a parabola, but I haven't found any reference.

L/D ratio

Glide Polar

Images from this question

Let's look at what exactly is shown by each curve:

The glide ratio curve plots glide ratio (horizontal distance divided by vertical distance) against airspeed.
The polar curve plots vertical speed against airspeed.

The x axis (airspeed) is the same for both plots, but the y axis is different. To convert one curve to the other, we need to convert glide ratio to vertical speed and vice versa.

  Note: I'm going to make a slight simplification here and assume that airspeed is the same as horizontal speed. This is not true when climbing or descending. A more accurate answer will require some trigonometry to calculate horizontal speed from airspeed. But the error introduced by this simplification is very small.

Vertical speed is simply airspeed times glide ratio.
Glide ratio is simply vertical speed divided by airspeed.

So, to make one curve out of the other:

To plot the polar curve, take a glide ratio curve and multiply it by the x coordinate (thus converting glide ratios to vertical speeds). Conceptually, as you travel outward on the x axis, you are magnifying the curve by x.
To plot a glide ratio curve, take the polar curve and divide it by the x coordinate (thus converting vertical speeds to glide ratios).

You mentioned parabolas. The polar curve is a "parabola" only in the vaguest sense that it is shaped like a parabola. It is not a precise mathematical parabola. Its exact shape is determined by extremely complicated aerodynamic factors.

All this being said, if your airplane has a published polar curve, use it, instead of deriving your own. Its values were measured and verified during flight test and you're better off using those than something you produced yourself using other data.


Can SID/STAR have shortened names? I have a strange naming difference for a SID in a route. The route is:

  DOME4W DOMEG Y841 ANAVI DCT NVO UM170 KENUM UM615 IDOSA UN857 RESMI
  UN491 DITAL UN872 DIDAK UZ15 ARDOD A5 VALAX VALA1A

I am bothered by the DOME4W departure (Paderborn Lippstadt, EDLP). The actual name is DOMEG 4W.

Is it allowed to have shortened SID names? In the FMS, I see this as well as DOME4W, but the SID description name it DOMEG 4W. Why this difference?

According to the Jeppeson chart legend[pdf] those are database identifiers. I'm presuming that's what would show on a menu in the FMS.


How is the wind direction and wind speed measured in flight? Most large aircraft have a wind direction and wind speed indicator. How is this measured? The vector difference between TAS and ground speed? How accurate is this?

In the below picture (taken from this question) it is displayed in the top-left corner of the top-right quadrant (just below the TAS and GS).

Indirectly, as the difference between true air speed and ground speed.
Since aircraft cannot measure true air speed, several steps are needed to arrive at the correct wind speed:

The pitot tube (big aircraft have several of them) gives the stagnation pressure of the air, which is the sum of static and dynamic pressure.
The static ports (again, big aircraft have several of them) give the static pressure of the ambient air, so the dynamic pressure can be isolated.
With the static pressure and the ambient temperature the air density can be calculated.
With the density it is now possible to calculate the true air speed from the dynamic pressure.
From the compass you get the heading of the aircraft, so you know the direction of the true air speed.
The ground speed and track direction can be calculated by repeatedly measuring the location of the aircraft and dividing the distance by the time between measurements, or with modern aircraft it can be read directly from the GPS display.
Wind speed and direction can be calculated by subtracting the true air speed vector from the ground speed vector.

You will notice that there are a lot of possible sources of error in this procedure. All instruments involved have their own bias and scaling error. However, if everything is carefully calibrated and corrected, the result can be very accurate.


Post MH370, are there developments to improve the tracking of airliners? Post MH370, are there developments to improve the tracking of airliners? Is there any technology being developed that would utilize the smartphones of the passengers?  MY question include smartphones and inflight wifi being standard or at least looking to be standard in the near future

No, no technology has been developed that utilize the smartphone of passengers because the airplane is at a location where it is outside the connectivity of any smartphone during the entire flight, except for maybe the first and last few minutes.

A smartphone needs a cell tower to establish network connectivity, which typically has a range of a few hundred meters or at most a few kilometers. Once a plane takes off and climbs to around 5000 feet (which takes only a minute or so), it is out of range of all cell towers. There are departure and approach paths which flies over populated areas, but most flies out to rural areas for noise reasons. And if a plane is over a populated city, you don't need smartphones on board to track it anyway.

The only hope of communication in the middle of an ocean is a direct connection to a satellite. Smartphones are not equipped with the necessary hardware to do that, and I doubt they will in the near future. To connect to a satellite, you will need to know where it is in the sky, which in turn means you need to know your location to a reasonable accuracy and an antenna to point the signal at the right direction.

Your idea about inflight Wi-Fi is an interesting one. Theoretically, if someone's cellphone is configured to report its location once in a while (to help in a situation where the phone is stolen or lost), and that cellphone is connected to internet, it can be used to track a plane's location. However, bandwidth onboard is limited to the Mbps to Kbps range, since it is a satellite connection. In fact it is so limited that you have to paid (quite an expensive price) for it.

Moreover, this solution does not solve the connectivity problem, because the phone needs to rely on the plane's satellite connection to establish connectivity. But there needs not be a phone - the mere act of connecting to a satellite is already enough to track a plane's location.

However, there are changes in the aircraft systems that will allow airliners to be tracked more accurately. For example, ICAO recommends that by November 2018, all aircraft over open ocean should report their position every 15 minutes.


How should time as safety pilot be logged? Let's take a classic example. An instrument rated pilot is flying a C-172 and wants to maintain instrument currency. The pilot goes flying and performs some approaches, holding and intercept/tracking to maintain that currency, all while under the hood. In order to maintain a safe condition, a safety pilot is brought along to maintain VFR conditions.

The question is, how should the safety pilot log this time? In this condition the safety pilot is a required crew member, but is this time technically SIC or is it PIC?

The rules for safety pilots are spelled out in 91.109c but don't specifically state how the safety pilot should log the hours.

However, the common consensus I've heard from friends is that you can indeed log safety pilot time as PIC time. The August 2015 Flight Training magazine had an article about this actually. Here is what they said:

  What is implied but not specifically stated in the regulation is important. Because safety pilots are responsible for determining the safety of the flight, they can log their right-seat time when the left seat pilot is wearing a view-limiting device as PIC time. This transforms time spent serving as a safety pilot into a truly valuable educational experience that will also expand the flight time totals in your logbook

Edit: I did some more research into this.

PIC time is defined in Part 61.51(e). Safety pilots can qualify as PIC under bullet iii:

  (iii) When the pilot, except for a holder of a sport or recreational pilot certificate, acts as pilot in command of an aircraft for which more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is conducted

There are some other things to be aware of when logging PIC time as a safety pilot (in addition to the requirements of 91.109c):

The two pilots must agree that the safety pilot is the acting
PIC.
PIC time may be logged only while the other pilot is
"under-the-hood."
If something goes wrong you are the one that will be held responsible. I wouldnt take the responsibility lightly.
The pilot logging instrument time must record the safety pilots name in their logbook under 61.51(g)(3)


What is in the A320 Smoke and Fume checklist? What does the "Smoke and Fume Checklist" for the Airbus 320 series look like?

Is it a printed item or is it on the ECAM screen?

I'm resuming this old question because no answer was given.
It depends on where the smoke is detected (if automatically detected). The following abnormal procedures exist:

SMOKE FWD(AFT) CARGO SMOKE
SMOKE LAVATORY SMOKE
AVIONICS SMOKE
SMOKE/FUMES/AVNCS SMOKE + REMOVAL OF SMOKE/FUMES

The checklists 1, 2, 3 have the corresponding ECAM message automatically triggered when smoke is detected, while the checklist 4 is a long checklist which guides the pilot in identifying the source of the smoke and taking the necessary actions (and has no corresponding ECAM message).
Checklist 1 instructs the pilots to close the air isolation valve and discharge the agent(s).
Checklist 2 instructs the pilots to punch the guy smoking in the toilette contact the cabin crew.
Checklist 3 instructs the pilots to perform the relevant part of Checklist 4.


Why is the nose cone of Russian fighters pointing slightly down? Let's take SU-30 as an example:

The nose cone is clearly pointing a bit downwards with respect to the level of the engines and wings. Why is this? How can this kind of a banana even fly properly?

Here's the profile an F-18 for comparison:

The nose cone position depends upon the mission profile of the aircraft. Su-30 is a multirole fighter for all-weather, air-to-air and air-to-surface deep interdiction missions, since its air-surface with deep interdiction it needs to have a view of the ground while targeting ground troops/equipments/artillery. This nose down config helps it to have that view. F-18/F-16/F-15 are air superiority aircrafts. Yes same cannot be said for F-18 but then F-18 has many variants, F-18D which has air-ground support is slightly elevated pilot view for better ground view. Same can be seen in Eurofighter Typhoon and A-10 Thunderbolt.
While Su-15, Su-24 and Mig-27 where interceptors and bombers, they have straight nose just like their companions from the west.


What is the highest a helicopter can fly? What is the highest theoretical and current flight a helicopter can achieve?

This (and more) is quite easily answered by Wikipedia

Highest altitude without payload
12,442 m (40,820 ft)
Aerospatiale Lama

Highest level flight altitude
11,010 m (36,120 ft)
Sikorsky CH-54 Tarhe

Altitude with 40-tonne payload
2,255 m (7,398 ft)
Mil V-12

Visit the linked Wikipedia article for more records and sources.


What does the "blue" callout mean in the cockpit of an Airbus? So from watching many videos in the cockpit on YouTube I have noticed that pilots will say stuff like "Loc Blue" or "2500 Blue" but what does this 'blue' mean and are there any other colours?

These images are form this video at 3:43 and 4:25.

At the top of the Primary Flight Display (PFD, the one with the artificial horizon in the center), there is a so-called Flight Mode Annunciator (FMA) with several columns indicating currently active and armed modes of flight guidance:

The first line shows active modes (in this case: SPEED, ALT, and HDG) in green color. The second line has additional information about armed modes in blue color, which will become active later, for example LOC (localizer) mode will become active instead of HDG upon localizer capture.

The callout from the pilots like "LOC blue" serves to remind themselves of the current flight guidance modes, and to maintain awareness of mode changes. This is also to ensure that their mental idea of "what the aircraft will do next" is up to date and fits to the current flight situation.

However, I'm not sure about the "2500" you mentioned.

On youtube you can find videos like this one explaining a bit more about the FMA. (screenshot taken from there). As the comment by @DeepSpace mentions, the screenshot and video mostly apply to Airbus aircraft. Other aircraft may have similar displays about flight guidance modes, but I am not aware of their specific color codings.


How is the Dash 8 Q400 so fast? The Q400 has a cruise speed of 360kts, and on flightradar24 most Q400s that I looked at reached similar speeds during cruise. The ATR 72 has similar specifications yet only flies at 280kts. I'm currently designing a regional turboprop as part of a university assignment and I can't find a drag polar that gives 360kts as anywhere near the optimum speed for L/D ratio, 244kts was the cruise speed for my initial configuration. Is the Q400 likely flying at a much higher, less efficient speed? Why would this be done? Or has better technology allowed it to fly efficiently at this speed?
Edit: According to a pilot on this flight sim forum they used to cruise at around 200kts. This video shows Flybe (budget airliner) cruising at 240kts, FL240. Maybe the flights I've seen on flight radar are operating under different parameters at the moment, with fewer passengers and lower oil prices maybe 360kts is the best speed.

Here are the cruise performance tables for the Q400 at the heaviest and lightest weight (click to view larger):
Source: from the Dash-8 Q400 performance manual, which came included with a simulator product I purchased. They probably got their data from a QRH (Quick Reference Handbook), which usually includes such tables in the In-Flight Performance section.
At ISA conditions at FL250, the long range cruise is flown between 209 and 188 KIAS (depending on weight) and the high speed cruise is flown between 230 and 243 KIAS. The corresponding TAS at FL250 (assuming ISA conditions) are:

188 KIAS: 281 KTAS
209 KIAS: 312 KTAS
230 KIAS: 343 KTAS
243 KIAS: 363 KTAS

That last value (for high speed cruise at light weight) seems to agree quite well with the max. cruise speed of 360 KTAS, which one usually find for the Q400. But best range speed at that weight would be around 188 KIAS (281 KTAS), quite a bit slower. At higher weight, the speed differences between best range and high speed cruise are smaller though.
At typical weights the Dash-8 will still be faster than the ATR 72-600. I don't have exact performance tables for that aircraft, but Wikipedia says cruise speed is 280 KTAS. So yes, the Dash-8 is built for higher speed. The biggest difference is the choice of engine: PW150A with 3782 kW for the Dash, but PW127M with only 1846 kW for the ATR, more than a factor two difference! While this difference probably causes a higher best range speed for the Dash compared to the ATR, in absolute fuel usage the ATR is still more economical.


What is this closed cabin / open cockpit biplane from the 1910s? This photo was taken when Lieutenant Marix RNAS visited his old school, Radley College in Oxfordshire on 30 May 1914. Marix was awarded in October 1914 the DSO for bombing the Zeppelin sheds in Dusseldorf which was the first successful bombing raid of the war.

Is there anyway of identifying the aircraft? Perhaps from the registration number 104 shown on the aircraft tail fin?

I submit the Sopwith Type D "3-Seater".

No.104 appears to be one of the first Sopwith aircraft produced for the Royal Navel Air Service (RNAS). The RNAS received at least three examples (No.33, No.103, No.104) one of them being the original prototype, known as the Hybrid that was later rebuilt and delivered to the RNAS. The Hybrid was made from combining the fuselage and tail of a Coventry Ordnance Works biplane and the wings of a Wright Biplane, the Type D retained the wing warping method of lateral control used in the Wright biplane until fitted ailerons after entry into service.  Wikipedia

Comments about No.104 found in the Kingstone Aviation page for 1914: (All bold formatting added by me)

  The Daily Telegraph leader sums it all up. “These aircraft represent an extension of our sea power; they are the scouts of the future.  A fleet of battleships unattended by aerial craft will be blind.  Cruisers even if able to steam at 30 knots will be inadequate.  Their range of vision is limited; their rate of steaming is insufficient.  The seaplane on the other hand is the fastest and handiest ship ever contrived by the ingenuity of man – with a speed of 70 miles an hour and a capacity for manoeuvring which defies competition.  In two years the rate of flight has doubled and no one can say that the limit has been reached.  A fleet without aerial squadrons will be robbed of the essential intelligence which is the talisman of victory – the foundation of successful naval tactics.  As we are forced to develop our sea fleet, no effort must be spared to build up the complementary air service.”

  It is no surprise then that the RNAS are upgrading their older wing-warping landplanes by placing orders with Sopwith for sets of ailerons for “Type D” biplanes No.33 and No.104 at a cost of £198.10.0d a set.

  On 25th July 1914 Sopwith get an order from the Admiralty to repair “Type D” No.103 and retro-fit with the ailerons recently ordered for No.104.

  On 2nd August 1914, reflecting the deteriorating situation in Europe,
  the Order of Battle is issued by the Royal Naval Air Service.  The
  RNAS now owns 95 aircraft:- “57 seaplanes, 34 aeroplanes and 4
  monoplanes”.  Only 46 of these are considered operational and assigned
  to the nine Naval Air Stations. Only 3 of the 15 aircraft supplied to
  the Admiralty by Sopwith over the last 19 months appear amongst those
  46 - “Type D” No.104 at Eastchurch, “Anzani Pusher Floatplane” No.123
  at Grain Island and their original Bat Boat No.38 at Felixstowe.

Comments about No.104 found in the Kingstone Aviation page for 1915:

  On 11th January the Sopwith “Type D” No.104 which has been at Eastchurch since early September suffers a failure of its 80hp Gnome engine.  Flt. Lt. I.G.V.Fowler manages a forced landing on mud flats by the River Blackwater but this ends the 17 month career of one of the earliest Sopwith machines still in naval service.

  There is news that on 20th January long-serving Sopwith “D1 Three-Seater” No.103 crashed on landing at Eastbourne but is probably repairable, unlike sister-ship No.104 nine days before.

Images found here: kingstonaviation.org


What is fly-by-wire? What exactly does the term "fly-by-wire" mean? Where did it originate? I understand that it refers to control systems. If an aircraft is not fly-by-wire, what is it? That is, what are the alternatives?

The fly-by-wire means that in the aircraft, the (pilot or autopilot) control inputs are fed to the (flight) computer, which processes them and determines the required control surface movements and transmits this by electrical signals (through wires, hence the term fly-by-wire) to the appropriate actuators.

This is in contrast with the mechanical system, where the pilot control inputs are directly transmitted to the flight control actuators, through push-pull rods or cables. The following figure shows the schematic of a mechanical and fly-by-wire system.

Source: euroaviasevilla.es

The first aircraft to use this mode of control was the Avro Arrow, which used a dual-channel fly-by-wire system made of analog circuits. The flight control mechanism on the Apollo Lunar Module was fly-by-wire, the Primary Guidance, Navigation, and Control System, which was referred to as PGNCS, pronounced 'pings'.

Later, NASA tested the fly-by-wire system in a F-8 aircraft, a schematic of which is shown below. Note that it uses Apollo flight computer.

Image from Computers Take Flight- A history of NASA's Pioneering Fly-by-wire Project

In civil aviation Concorde and A320 (which had a digital-fly-by-wire system) introduced fly-by-wire systems, while in military, it was the F-16. At present, almost all combat aircraft and large airliners use fly-by-wire systems.

As an extension, the system is called fly-by-light (or fly-by-optics) is the signals are transmitted through optical cables. If the wires are eliminated altogether, it is called fly-by-wireless.


Are all US fighter/combat aircraft constantly armed, even just in training? I remember hearing once upon a time that all US fighter/combat aircraft constantly armed, even just in training. If I recall correctly, it's because the pilots need to be ready at a moment's notice.

Is this true?

As a general rule, unless you are going to use ordnance e.g. training, alert status, or war, you are not going to have it loaded on the jet.  It's just another risk to personnel or equipment out on the line, in hangars, etc.  Aircraft returning with live ordnance are disarmed and unloaded after shutdown and the weapons defused and returned to the bomb farms on base or magazines aboard ship.


Why do helicopters and airplanes use different headset plugs? If the headsets and microphones for general aviation have the same impedance for helicopters and airplanes, then why do they have different connectors on them?

Is it simply to make more money from selling adapters and more headsets?

It's a holdover from the old days when microphone technology wasn't as advanced.  The military adopted "dynamic microphones" as the standard, which were less noisy than the alternative "carbon microphones."  Carbon microphones required a DC bias voltage to operate, and the dynamic ones did not.

Fast forward to current airplane microphones, which are electric, and still use a bias voltage, so if you plug a military dynamic microphone into a civilian airplane jack, the microphone would burn out from the voltage.

So what?  Well, helicopters were originally very military oriented, so they all were wired for dynamic microphones.  They used a different jack to avoid accidentally plugging the wrong type of microphone into the wrong type of jack.  Even though helicopters are widely used outside of the military now, the standard remains, and many emergency radio equipment (fire, medical, police, etc) still uses the dynamic standard.


Is there a downside to trying multiple flight instructors? My local airport has a Part 61 flight school and gives students the option of selecting among three Certified Flight Instructors. Farhan and others have posted excellent explanations of characteristics to look for in instructors.

Other than wasted time and money, is there any downside to doing an "Introduction to Flying" lesson with each of the three instructors and seeing which one I like best? Similarly, am I likely to offend CFI's that I'm "looking around" other options?

No. Definitely try more than one CFI and ideally, more than one school. This is the smart choice and one I recommended regularly when I was an active flight school CFI.

You're about to spend a ton of money - do the due diligence and spend more up front to make sure you don't waste time and money with someone whose teaching style or personality clashes with you as a student.


Do bigger aircraft make a bigger sonic boom? I was watching an episode of MythBusters where they were trying to break glass windows and cups using a sonic boom generated by a F/A-18 Hornet, flown by the Blue Angels.  In summary, they were unsuccessful at creating a boom that could shatter the windows, despite a mach speed pass within 200ft of the target building. In the last two passes they even flew straight at the building to focus the boom straight at the house, still no windows were shattered. **

But I've wondered, ever since, if they were unsuccessful because the plane was simply too small.  What if the sonic boom had been generated by a B-1 Lancer or perhaps Concorde, which are several times larger than the F/A-18?  Logically it seems that since you are displacing more air, the energy wave should have more energy.  Then again, the plane isn't going any faster, so perhaps the surface area of the wave would be larger (because of the larger plane) but you wouldn't actually have any more energy at any given point?

Anyone know if a bigger plan than the F/A-18 would have a higher energy sonic boom?  And could that cause glass to break?

Bonus point:
A mathematical formula showing why, I love those things.

For those curious about what a sonic boom is to begin with, here's a wikipedia article.

**Just to clarify, for those who have seen the episode.  A window is broken during the 200ft pass but they say that it only happened because the frame warped, not because the glass itself shattered.  Their reasoning is that only that one window broke (out of several windows and glass cups in the area), and it had a pretty cheap frame on it.

The short version is that yes, larger aircraft create bigger sonic booms, but you still have to be flying very low (less than 100 ft.) and really trying hard in order to damage glass.

A sonic boom is so complicated that you will not find a simple formula to determine the strength.  This article describes a modeling tool called PCBoom3 which can be used for sonic boom calculations.

According to several different sites, like this one and this one, the size of the aircraft does affect the intensity:

  Factors Affecting Sonic Boom Intensity

  The intensity of sonic booms are affected by:

  Weight, size and shape of the aircraft.
  Altitude
  Attitude—orientation of the aircraft’s axes relative to the its direction of motion.
  Flight path.
  Atmospheric and weather conditions.

  As the size and weight of the aircraft increases, the intensity of the
  sonic increases. This is because a larger aircraft displaces more air,
  and a heavier aircraft needs a greater force of lift to sustain
  flight. Thus creating a louder and stronger sonic boom.

and

  General Factors Associated With Sonic Booms

  There are several factors
  that can influence sonic booms -- weight, size, and shape of the
  aircraft or vehicle, plus its altitude, attitude and flight path, and
  weather or atmospheric conditions.

  A larger and heavier aircraft must displace more air and create more
  lift to sustain flight, compared with small, light aircraft.
  Therefore, they will create sonic booms stronger and louder than those
  of smaller, lighter aircraft. The larger and heavier the aircraft, the
  stronger the shock waves will be.

NASA says that a typical sonic boom for the F/A-18 is about 1.4 psf and a different NASA page goes on to say:

  Overpressure Sonic booms are measured in pounds per square foot of
  overpressure. This is the amount of the increase over the normal
  atmospheric pressure which surrounds us (2,116 psf/14.7 psi).  At one
  pound overpressure, no damage to structures would be expected.
  Overpressures of 1 to 2 pounds are produced by supersonic aircraft
  flying at normal operating altitudes. Some public reaction could be
  expected between 1.5 and 2 lb.  Rare minor damage may occur with 2 to
  5 lb overpressure.

  As overpressure increases, the likelihood of structural damage and
  stronger public reaction also increases. Tests, however, have shown
  that structures in good condition have been undamaged by overpressures
  of up to 11 lb.  Sonic booms produced by aircraft flying supersonic at
  altitudes of less than 100 feet, creating between 20 and 144 lb
  overpressure, have been experienced by humans without injury.

  Damage to eardrums can be expected when overpressures reach 720 lb.
  Overpressures of 2160 lb would have to be generated to produce lung
  damage.

  Typical overpressure of aircraft types are:

  SR-71: 0.9 lb, speed of Mach 3, 80,000 feet
  Concorde SST: 1.94 lb, speed of Mach 2, 52,000 feet
  F-104: 0.8 lb, speed of Mach 1.93, 48,000 feet
  Space Shuttle: 1.25 lb, speed of Mach 1.5, 60,000 feet, landing approach

They also include a graphic that shows the difference in sonic boom between the F-18 and the Concorde, with the Concorde having a much greater sonic boom at the same alittude:

This article specifically covers glass:

  Glass. Poorly mounted, undamaged glass in the greenhouse was chipped
  by impact against nail holding points at a sonic boom overpressure of
  12.1 psf. The same type of glass, which was already damaged, was further damaged at a designed overpressure of 7.9 psf. A large
  one-ninth of an inch thick window, intentionally precracked from
  corner to corner, was further damaged by booms of an average 6.5 psf
  overpressure.

So typical sonic booms generated by normal aircraft aren't going to create anywhere close to the 12.1 psf that they say is needed to chip "poorly mounted" glass, but the strongest sonic booms can get well over this.


Do fighter jet pilots ever use autopilot? I know that military jets have autopilot, but do the pilots actually prefer to use it?

I ask this question because, unlike civilian airplanes, military jets are more likely to come in a situation where the pilot may have to take quick decision and leave the designated path for some mission (e.g. to intercept a civilian jet flying on a wrong path). In such case, the autopilot may become a problem for quick maneuvering.

I'm not in the military, so you could say I'm talking out my rear end here, but based on my experience as a pilot: yes, military pilots use the autopilot all the time.

Here's my reasoning, in order of most to least convincing evidence:

Punching the autopilot off takes about a fifth of a second.  The button is right there on the yoke, for crying out loud.  The time it takes to turn it off is not a good reason not to have it on.
The autopilot is a labor-saving device.  When you're in an aircraft (and particularly when you're solo in one) there are times when you'd rather be paying attention to your chart or setting up the FMS or stretching or eating a candy bar instead of actually flying the plane. Also, when Air Force pilots fly long repositoning flights, the autopilot reduces fatigue between in-flight refuelings (the Navy uses carriers).
Times when you might have to leave the designated path for a mission happen a lot less than you think.  Again, not in the military, I'm just basing this on the realities of fuel and the number of military aircraft out there.  Maybe if you're flying close air support for teams on the ground or something, but remember that the military is first and foremost a logistics organization - it's a machine for moving people and things from one place to another.  Most of the time, military aircraft aren't on a hair-trigger moment's notice ready-to-engage posture, they're going from one airfield to another for training or maintenance or something.
In most aircraft, you can override the autopilot if you need to anyway.  Again, never flown a military fighter aircraft, but based on what I know about flying in general, even if you're chilling in your F-22 (with the autopilot on) if you grab the stick and yank, the airplane will move.  (I would be interested to know whether this is true of Airbus aircraft. EDIT: Question answered after 4 years!)


How do pilots "turn an airport around" at nontowered fields? Consider Homestead Airport, a fictional paved, non-towered airfield in the exurbs of Bigtown, USA that has become popular as a home field for recreational pilots. The airport's busy enough that addressing "Homestead traffic" on MULTICOM any given daylight hour isn't just talking to yourself; there will be at least one other plane in the pattern and a couple more on the ground, however there isn't enough traffic yet to justify hiring ATCOs to run the field. The sole runway is 13/31.

On the Saturday in question, there's a southeasterly wind at sunrise and so traffic starts the day using runway 13. However, the wind suddenly changes just after noon as a norther blows through, such that the five or six aircraft currently in the traffic pattern now need to use runway 31.

What is the standard procedure, if any, to establish the new traffic pattern at the airfield given the wind change? I'm especially curious as to how traffic already in a pattern for the now-downwind runway would be expected to maneuver to establish the new pattern, especially if the segmented circle or AFD indicate traffic should stay to one side of the airport regardless of runway direction (for instance a left-hand pattern on runway 13 but a right-hand on 31, to keep traffic away from a developed neighborhood to the southwest).

Bonus question: At the time a transition to the new runway direction is needed, there is an aircraft holding short for runway 13, with another behind him. These aircraft need to taxi down to the other end of the airfield, and quickly, or they'll be staring at the nosecones of exiting planes. There is a single taxiway, too narrow to 180 on especially with other aircraft using it, and the nearest runway exit is halfway down the field, so aircraft on the ground must taxi down the runway in the opposite direction to get to the correct end. What radio comms are recommended/required to advise traffic in the pattern that the runway has taxiing traffic?

Your example is too specific to be useful to others, so let's consider the general case instead.

At an untowered field there is no "active" runway - they're all active.
There is usually a "preferred" runway - the one best aligned into the wind - but any runway can be used by any aircraft at any time, subject to whatever safety considerations the pilots mutually agree on. (At untowered fields with intersecting runways that have a lot of training on the field it's not uncommon to have traffic on the crosswind runway intersecting the preferred runway when students need to practice crosswind landings. It can be coordinated safely with a little cooperation between the pilots involved.)

The runway is "changed" by pilots announcing they're using a different runway.  There may also be a unicom operator at the field who announces a change in the preferred runway and lets incoming aircraft know about it.
Usually pilots who are already in the pattern for the "old" runway will complete their circuit and land, clearing the runway as expeditiously as possible.
Similarly pilots waiting at the threshold when the wind shifts may elect to either make their takeoff from where they are, or taxi around to the new preferred runway.  (In a case where the aircraft must enter the runway to turn around, or where they must back-taxi on the runway this obviously needs to be coordinated with the other pilots. The standard phraseology to use for this is "N12345 back-taxiing on runway XX" )

To your specific example, the directions of traffic patterns don't really matter much: As I mentioned aircraft already in the pattern will probably complete their circuit and land on the runway they were lined up for. Even in the case of Left Traffic for 13 and Right Traffic for 31 and two aircraft maneuvering to enter the pattern for opposite runways the standard pattern entry (45-to-downwind) will tend to keep airplanes apart (they won't ever be heading at each other in the downwind leg if they enter it on the 45, and it should at least ensure they see each other in the opposite-direction 45 and can coordinate to ensure they're never flying at each other). One airplane will probably have to extend their pattern to allow the other to clear the runway safely before they can land, however.

  Traffic really should not really be arriving to both downwinds simultaneously anyway, particularly in your example with a single runway: Inbound aircraft should coordinate to arrive in the pattern for the preferred runway.

Aircraft already in the pattern have two choices: Land downwind if safe, or depart the pattern and re-enter it to land on the new preferred runway.  A downwind landing must obviously be coordinated with aircraft which may be preparing to depart in the opposite direction.
If landing downwind is unsafe (due to wind speed) or otherwise undesirable (e.g. due to other traffic) climbing above pattern altitude, leaving the area, and returning via a standard pattern entry for the opposite runway is usually the safest course of action.

Aircraft waiting to depart also have two choices: Depart downwind (which must be coordinated with aircraft arriving to the preferred runway), or taxi to the preferred runway end for takeoff. In cases such as you've described where back-taxiing is necessary this must be coordinated with pilots landing (in either direction) as the back-taxiing aircraft will be occupying the runway they need for landing.

The major complicating factor you didn't specifically mention, but which is implied by multiple aircraft "in the pattern" is closed traffic (aircraft making touch-and-go or full-stop/taxi-back landings and immediately taking off again).

Full-Stop/Taxi-Back landings are not a problem: Much like "regular" landing traffic they can land downwind, and upon exiting the runway taxi back to the preferred runway end for their next takeoff.
Touch-and-Go aircraft have two main choices: Land downwind as a full-stop and taxi around to the preferred runway end (which is probably the safest and most considerate thing to do), or complete a touch-and-go with the intention of departing the pattern and returning to set up for circuits to the new preferred runway.

Another important consideration are aircraft without radios (NORDO)- yes, these do exist). A visual scan of the traffic pattern is required at any uncontrolled field at any time to ensure you are not conflicting with NORDO aircraft.
These are often slower planes, so having one in the pattern landing "the wrong way" may require you to wait a while for them to complete their circuit before you can begin operations on the new preferred runway.


How does supercruise thrust compare with static thrust ASL? As I understand it, turbojet thrust decreases both with altitude due to rarefied air reducing massflow, and airspeed due to a smaller speed increase between intake and exhaust relative to the airframe. However aircraft designed for sustained supercruise such as Concorde or Blackbird had intakes that used various amounts of ram-effect pressure recovery, so I was wondering how much that would offset the effects of being fast and high i.e. what was Concorde's mach 2 max thrust compared compared to sea level dry thrust, and/or the Blackbird's mach 3.2 turboramjet thrust compared to take-off wet thrust?

For Concorde, takeoff thrust:weight was 1:0.373. At cruise, the Concorde had a lift:drag ratio of 7:1. At cruise, thrust = drag. So cruise thrust is 1/7 = 0.1429
So, cruise:ASL is 0.14(rounded down for climb fuel burn):0.373 = around  1:3.8
For the SR-71, takeoff thrust:weight is 0.44:1. Using the Kuchemann supersonic L/D formula, we get
4(Mach(=3)+3)/Mach(=3)
=1:8
Now this looks too high. And running this formula for Concorde gave 10:1. So, having no better option (yet), I simply took 1:6 as the value. This would give us a cruise thrust:weight of around 1/6:1 = 0.167:1
0.167/0.44 = around 1:3.8 (again?)
The figures for the SR-71 may well be wrong.


Was any Russian design feature incorporated in modern US fighters jets or vice-versa? US has bought or sourced many Russian fighter jets.

Was any Russian design feature incorporated in modern US fighters jets or vice-versa?

Three things come to mind:

Geometric shaping for stealth is based on the theoretical work of Petr Ufimtsev, a Russian mathematician who explained how to calculate the reflection of radio waves from the 1960s on.
The sight-controlled missile targeting which appeared in the MiG-29 in the 1980s. In combination with the wide off-boresight capabilities of the aircraft's radar and the missiles, it allowed to get a lock on aircraft flying actually behind it. When US F-16 met ex-GDR MiGs in exercises in the early 1990s, they were shocked to find how much superior the Russian design was and soon copied it.
The rotating collars which were used on the Yak-141 to deflect the engine exhaust straight down for vertical take-off have been used in the VTOL version of the F-35. Lockheed-Martin co-operated with Yakowlev in the early Nineties to learn how the Russian airplane works.

From a historical perspective you can add the Russian (actually, Georgian) aircraft designer Alexander Kartveli, who headed engineering at Republic, and the influence of Georgia-born Alexander de Serversky (actually of Russian descent) who propagated strategic bombing to win future wars, even though this concerns bombers, not fighters.


What are the methods of reducing vortex? I have tried reading the notes on the wing tip, but didn't understand well. How will the vortex be reduced on the wing tip.

Wing vortices  cannot be reduced. It is a byproduct of creating lift. The various wingtip shapes help to combine the airflow from the top and bottom of the wing and can make the wing act like it is longer and creating the same lift, but the vortex is still generated. The biggest vortices are created by the big airplanes when they are heavy, dirty (lots of flaps, etc. deployed) and slow (i.e. takeoff and landing).  Even my little 4-seat Cessna Cardinal creates vortices.

See Section 3.14 here
http://www.av8n.com/how/htm/airfoils.html#sec-vortices
of this great e-book "See How It Flies"
http://www.av8n.com/how/


What is the purpose of a movable inlet on a jet engine? I was reading that aircraft like the F15 and SR-71 have movable inelts. Whats the purpose of this?
I was also reading aircraft like the F-22 doesn't have a movable inlet. Why?

Jet engines require the air that flows into them to be subsonic. Supersonic air hitting the front fan would cause shockwaves inside the engine, with undesirable results.
So the job of the intake on a supersonic aircraft is to slow down the air to subsonic speeds. The intake is designed to set up a series of shock waves. The air will slow down to subsonic speed as it crosses these shockwaves.
The location of these shockwaves changes with speed: the higher the speed, the shallower the angle of the shockwave and the further the shockwave will reach down the intake duct. So if you have a fixed-geometry inlet, your maximum speed is limited: there is a speed at which the shockwaves will intersect the front fan.
Variable intakes avoid this problem: the movable vanes in the inlet aim the shockwave so it stays in front of the front fan at all speeds. This enable a higher top speed to be reached.
If you accept a lower top speed, you can avoid the extra complexity of a variable inlet. For the F-22, for example, a variable inlet would make it more difficult to maintain a low radar cross section, so the tradeoff was made to maintain stealth and lower the top speed.


How do airlines (or the government) retrieve information from the black box of an aircraft? When black-boxes are found, how is the information retrieved from within the data storage?  Is there a special kind of device used for this?

They send it to the manufacturer (or other lab) who knows how to get the data out.

Old black boxes stored the data on tape which they take out put in a reader and print out the data. Partially damaged tape can still be read, the result will be a data stream with holes in it.

Newer black boxes use solid state storage (like one of those 8gig memory cards). It will be put in a reader to read it out. The exact format of the data will be specific per manufacturer.

Then the analysts will make nice graphs of it for the investigators.


How fast do four Tire-Propellers have to rotate to lift 2000 lbs? I just saw this come out, Goodyear's Tire-Propeller Concept – a combination tire that can also act as propeller (well, more like a ducted fan I guess).

There's a neat video that goes with it, describing how the fan blades need to bend while being used as a tire. (Otherwise, one winter in New England would take them out!)

Any ideas how fast something with say four 18 inch diameter wheel/propellers, and 3-4 inch fan blades, would have to spin to generate enough downforce to actually get 2000 pounds off the ground?

The weight is the vehicle with 4 motors, 300 pounds of batteries, 600 pounds of passengers & baggage; comparable to my 2500 lb max gross weight airplane, but with weight savings of no wings or tail structure, and batteries vs fuel. 4 motor/fans, and allowing (requiring?) the lift off process to be from a stop, so that all 4 motor/fans could be rotated from road use to propeller use (vs rolling on 2 like the video shows). I imagine 14,000 RPM or some high speed would make quite a lot of noise, compared to the takeoff noise of my 180 horse power engine and 86 inch propeller.

Edit: This rim-driven propeller wheel doesn't look like it would have much total blade are for moving air. That would take even more speed, wouldn't it?

The Moller Skycar seemed quite noisy for a comparison.

Let's do a back-of-the-envelope estimate. As a simplifying assumption, assume that a propeller generates lift by accelerating air through an opening of a particular size, at one particular speed. The formula for the amount of lift generated in this case is:

$$\text{Lift} = \text{Opening area} \cdot \text{Air density} \cdot \text{Exhaust speed}^2$$

For each propeller, the needed lift is 500 pounds force, and the area of each opening is $\pi \cdot (\text{$9$ inches})^2$.

So we can calculate the needed exhaust speed using Wolfram Alpha: square root of (500 pounds force / (density of air * pi * (9 inches)^2))

The answer comes out to 230 mph. That's the speed that the air has to move downward through the rotors. I don't know how fast the propeller will have to move in order to make this happen, but it will be a comparable speed.

The amount of power required can be found by multiplying this number again by the amount of lift. According to Wolfram Alpha, that comes out to 307 horsepower (229 kilowatts) per rotor. So about 1,200 horsepower for the entire aircraft, if the rotors were 100% efficient.

Good luck with that.


What are the repercussions of flying an aircraft with an invalid N number on the side? I have requested a new N number for my airplane a few months ago. Thinking the change would come through I had my airplane painted with the new number. What will happen if I fly it without the number being authorized?

As a controller, if it's a correctly constructed N-number, I'd know nothing. and wouldn't do anything. If you file a flight plan, however, the N-number you use will go into the FAA's database. Keep in mind that if you ask a controller for flight following, a Mode C check, etc., there will be a record, even if it's only "on the tape".
I have no idea whether they would flag an unregistered number, but I can give you some history on an aircraft that flew with an INVALID N-number.
In 2006 (or so, why is this stuff so long ago?), I was working the high altitude sector in the LBF (North Platte, NE) area. I received a handoff on an aircraft with a call sign similar to, but not exactly "N1EP2D", which is an illegal construct (see https://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/forming_nnumber/)
I alerted my supervisor, who directed me to question the pilot. As it turned out, the pilot had filed this deliberately, and on a whim.
The FAA does not do "whimsical".
I instructed the pilot to submit the correct N-number, which he did, and I amended the flight plan. I also instructed the pilot to NOT use the invalid number, and to call our Operations Manager for further instructions.
I heard it was a six-month suspension, although I had no official follow-up.


Why this inertial regulator of dragonfly wing pitch reduces self-excited coupled flapping and feathering vibrations and improves gliding flight speed The pterostigma of insect wings an inertial regulator of wing pitch is linked in this answer to Why do dragonflies have these special little spots on their wings? (open access copy here)
The Summary of the paper includes the following points. I've highlighted some in bold.
Question: Is it possible to explain in simpler terms what "Inertial regulator of dragonfly wing pitch reduces self-excited coupled flapping and feathering vibrations and improves gliding flight speed" means, and why these small weights do it?

The pterostigma of insect wings usually is a pigmented spot close to the leading edge far out on the wing, having a greater mass than an equally large wing piece in adjacent wing regions.

In several dragonfly (Odonata) species the position of the spanwise torsion axis of the wings, the mass distribution of the wings, and the position of the chordwise centre of mass in chordwise wing strips were determined.

In the dragonflies investigated, the torsion axis of the wing lies ahead of the chordwise centre of mass of the wing except at the pterostigma (Fig. 1).

A wing having its mass axis behind its torsion axis is very susceptible to self-excited coupled flapping and feathering vibrations, making gliding flight above a critical speed impossible. Due to unfavourable, inertial, wing pitching tendencies, a still lower speed limit is set to active flight.

Due to its mass contribution and favourable location, the pterostigma tends to raise these speed limits by causing favourable, inertial, pitching moments during the acceleration phases of wing flapping.

The favourable pitching moment of the pterostigma is proportional to the distance from the wing base to the pterostigma, and to the distance of the pterostigma ahead of the wing's spanwise torsion axis. The pterostigma usually has an optimal position at the leading edge of the wing near the wing tip, just where the wing curves backwards. Further optimization of pterostigma mass localization has been obtained in different ways in various insects, involving both pterostigma position (Fig. 4) and form (Fig. 5a).

The function of the pterostigma of raising the critical gliding speed, at which self-excited vibrations set in, was demonstrated in dragonflies. Although contributing only 0.1 % (one pterostigma) of the total dragonfly weight, it raised the critical speed by 10–25% in one species.

The pterostigma is common among the insect orders Odonata, Neuroptera, Psocoptera, Hemiptera, and Hymenoptera. By passive, inertial, pitch angle control, the pterostigma probably makes the wing beat more efficient in slow and hovering flight of small insects, while its raising of the critical flight speeds probably is of more importance to larger insects. The ability of active pitch angle control in many insects does not detract from the value of the pterostigma, since it contributes passively, without power expenditure, towards an efficient wing stroke.

Figures from the linked paper (click for full size):

Images from the linked question, click for full size:

Short answer:
Adding a mass ahead of the elastic axis of the wing tends to increase the critical flutter speed of the wing, thus allowing a larger flight envelope. Above this critical speed the wing would experience vibrations of increasing amplitude that could lead to its destruction (or to a limit-cycle flutter mode, which is also bad but less so than rapid unplanned disassembly).
Flutter is a destructive aeroelastic phenomenon that can be described (in a simplified way) as a combination of two natural vibration modes of a wing. These modes are torsion around a spanwise axis and bending with respect to the root. Each mode will have a natural frequency, and the flutter speed will have a minimum (not guaranteed to be a global one, btw) when both of these frequencies are the same, because then they will reinforce one another.
The distance between the center of mass and the elastic axis of the wing is very important for the torsion response of the wing, simply because the wing will twist around this elastic axis, and a center of mass far away from it will give high inertial moments.
By adding weight to the leading edge, the dynamic behavior of the wing is modified in a way that moves the critical flutter speed upwards, extending the safe flight envelope. This technique can be seen most often in helicopter blades, many of which have some trim or balance weight at the leading edge.
Long answer (math ahead):
WIP - The analytical treatment is quite long so I am trying to decide which results are actually worth typing into MathJax


Why is the IFE only available after take-off and shut off before landing? Every time I fly in an airplane that has an In-Flight Entertainment System (IFE) that consists of screens embedded in every passenger seat it is only turned on a few minutes after take-off and turned off a few minutes before landing? Why is this?

My limited knowledge of the system tells me that it should not interfere with any of the other on-board systems and thus it should not matter whether the system is running or not. The only reason I can think of is safety, similar to the question of why lights are dimmed during take-off and landing.

They do this for the same reason they make you put away all electronic devices during that period of flight. The first minutes of a flight (take off and climb out) as well as the last few (approach and landing) are the most critical and statistically the time that if things are going wrong they will go wrong. As such airlines shut down the IFE systems and ask users to shut down personal devices so that they can hear, and more importantly respond to any emergency directions that may be given during this critical time.

2019 Update: Since this original answer was posted some airlines now allow the use of "small personal electronic devices" in all phases of flight.


Do paper airplanes fly like normal airplanes do? After a while of researching, I found that nobody actually knows how paper airplanes work and after experimenting myself, I can't really find much about it. If anybody does, have a good answer and has a better researching angle, please tell me.

No that’s wrong. Paper airplanes fly by the same physics that allows a 747 to fly.


Why do the GS and LOC indicators blink? So, the question is in the title. Specifically referring to this video. At around timestamp 2:10 in the video, you can see the GS and LOC indicators blink. Why does it blink?

From this copy of the flight manual for the 737:

  Glide Slope Pointer and Deviation Scale

  ...

  At low radio altitudes, with autopilot engaged, the scale turns amber
  and the pointer flashes to indicate excessive glide slope deviation.

  Each pilot’s deviation alerting system self-tests upon becoming armed
  at 1500 feet radio altitude. This self-test generates a two second G/S
  deviation alerting display on each attitude indicator.

And for the localizer

  Localizer Pointer and Deviation Scale

  ...

  At low radio altitudes, with autopilot engaged, the scale turns amber
  and the pointer flashes to indicate excessive localizer deviation.

  Below 1,000 feet AGL, with LNAV engaged and LOC armed, the localizer
  scale turns amber and the pointer flashes if the localizer is not
  captured.

  Each pilot’s deviation alerting system self-tests upon
  becoming armed at 1500 feet radio altitude. This self-test generates a
  two second LOC deviation alerting display on each attitude indicator.

What is interesting is that the pilot seems to be right on slope and right on the localizer so I would presume it is NOT flashing as a result of excessive deviation.


How is non-standard OAT accounted for? This pdf from Airbus has a chart from ICAO showing the amount of correction to be applied to altimeter readings for temperatures below 0°C.

Do aircraft with flight data computers automatically correct for this?
In the US, does ATC account for this correction when assigning vectors?
How does a pilot know if they are or not?

We all know the saying "From High to Low, Look out below"  Some were taught that this only applied to pressure differences and thus were instructed to get a new altimeter setting every 100NM or so.  This is a good recommendation.

Temperature differences from standard also causes errors with the altimeter.  The same saying above holds true with temperature variations.

An altimeter setting is defined as: (ref. Pilot/Controller Glossary)

  The barometric pressure reading used to adjust a pressure altimeter for variations in existing atmospheric pressure or to the standard altimeter setting (29.92).

We also know there is a direct correlation between pressure and temperature and thus an altimeter setting is corrected for both pressure and temperature.  This means one thing, the altimeter error is zero at the field elevation.  As the aircraft gets climbs higher above the field, the altimeter error will increase.

There is a table in the Aeronautical Information Manual (7-2-8) that lists altimeter error due to temperature as a function of altitude (AGL) and temperature.

Here is the formula that will give you this table.  The formula can be found in Canadian Aeronautical Information Manual (RAC section).

The United States Air Force has a PowerPoint that discusses this topic.

The FAA has recently come out with Info 15002 which requires pilots (after 9/17/2015) who fly into "Cold Temperature Restricted Airports" to correct their altitudes for colder than standard temperatures.  To determine if your airport is part of this program you must go to the Aeronav FAA website and search for Cold Temperature Restricted Airports.  There should be a link at the bottom of the page.

Here is a graphic showing all the airports in the United States that were part of the program in February 2015.

Because Lnafziger wanted Alaska.

Not only is the pilot required to correct for the segment but they are also required to inform ATC of the new altitudes they will fly.  This is to ensure traffic separation with other airplanes who are not temperature correcting their altimeters.

Pictures taken with permission from All About Airplanes blog.  All rights reserved.


How likely is it that there is someone knowledgeable about piloting in a flight control room? I saw a reasonably looking video about a non-pilot trying to land a plane with the help of a flight control tower (in a simulator):

             (it is in French).

I believe that this was an ideal case where the plane was compatible with the airport so that the landing was almost automatic (they showed a short version of (successfully) trying to land without the automatic mode).

The person in the control tower was extremely knowledgeable about the plane, explaining exactly where to press, where to look etc.

Assuming that the whole exercise was realistic - how likely is it that there would be someone handy who could, by heart, explain via the radio what the exact steps to take are?

Note: I realize that the situation will be different between a large airport (where they could make an announcement "we are looking for a Boeing 747 pilot, please contact the reception desk if you are one") and smaller ones. In the video, they started from a cruising altitude and it took minutes to go from "there is nobody in the cockpit" to "listen to me carefully, I will guide you". It is more the realism of time which I am trying to assess.

The answer depends a lot on the type of plane being flow.  While plenty of air traffic controllers are also pilots on the side, it is highly unlikely that anyone on duty at the time would happen to have a type rating in a large complex turbine aircraft, and/or enough knowledge to talk through checklists.  They may be able to offer very generic advice such as "See the handle that is shaped like a wheel?  Push it down and that will lower the landing gear."

For simpler GA aircraft they might offer some basic assistance on how to control the aircraft, slow down, deploy flaps, etc. but there is a lot of muscle memory and technique honed by hours of practice needed to perform a "good" landing.  Just explaining the exact steps to take over the radio isn't going to be enough, there is a lot more to it.

Think about the first time you drove a car with a manual transmission:  Did the person telling you to push in the clutch, shift gears, then let it out smoothly while adding gas help you to do it smoothly, without stalling the engine, jerking, or racing the engine?  Probably not!

About the best they could probably hope for is to help the non-pilot maneuver into a safe airspeed envelope to survive a controlled crash landing at the airfield where emergency services will be on hand to provide immediate help.


Is there anything wrong with this more symmetric aircraft design, and why isn't it used? I imagine a fixed wing airplane design that's a lot more symmetric than what I see today. This symmetric design has wings in the middle of the fuselage (neither high wing nor low wing), and the empennage is a symmetric cross. Two vertical fins, one on top and one on bottom, and two horizontal stabilizers. The tail fuselage would taper symmetrically too, instead of the underslope with flat top we usually see today. This would make the fuselage closer to a Sears–Haack body, which I believe is ideal.

In other words, it would look a lot like the XB-42 Mixmaster:

Ignore the weird engine. AFAIK, this design could use an engine anywhere. BTW, this is the only aircraft I know with the middle-wing and symmetric cross tail design—whether experimental or production aircraft.)

The reason I imagine this is so the control surfaces are much more aligned with the center of mass. So the rudders, elevators, and ailerons will not produce any adverse torques when used. I think this will be more efficient, especially when using trims, and also is a simpler design as far as I can tell.

To get around the problem of tail strikes, I imagine a single tail wheel attached underneath it. For small aircraft it might not need to retract. For larger aircraft, I don't know how or where it would retract to, but maybe instead some kind of aerodynamic shield can enclose/open around it, like a prolate or oblate spheroid shape.

(An alternate symmetric design would be an X-shaped empennage—same shape, just rotated 45 degrees. I think for a given yaw, the combination of control surfaces would produce more drag though, but it's a way to increase ground clearance.)

(A more exotic alternate might be to forget about takeoff rotation entirely, and just increase takeoff speed and the length required to literally lift off without pitching up the nose. This might not be feasible for large commercial aircraft though.)

(But maybe best is to add canards with their own elevators, or all-moving canards, which will push up the nose and pivot at the wheel.)

To me this symmetric design seems simpler and versatile. By versatile I mean it looks like it could be used for small and large aircraft, whether prop-engine or jet engine, military or civilian, and not really mattering where the engines are located either.

Is there anything wrong with this design? Why is it not used more often? In fact I do not know of a single production aircraft with this design.

If anyone knows of any aircraft in this configuration, whether experimental or production, please provide a link so I can read more about it and maybe discover some reasons for its success or failure.

The biggest single problem with this is the location of the main spar - across the middle of the fuselage. This might not be a problem for single seat military or sports aircraft but would be a major headache for almost any other design. Imagine trying to load 100+ passengers with 50% of them having to clamber over or under a major obstruction in the cabin.

Yes, you can engineer around this but the resultant solution is likely to be heavier and more complex than simply moving the wing up or down and out of the way.


Why is a straight-in approach not allowed to RWY 07 at Cluj (LRCL)? Here's a VOR approach for runway 07 at Cluj (LRCL).

On the lower left side of the chart you will see the "Straight-in" OCA(H) as N/A and then a "Circling" OCA(H) of 2540 (for category C). There is only a 6 degree offset between the final approach course and the runway, and as far as I can tell below 30 degrees (or maybe 15?) the approach is considered straight-in.

So why are straight-in approaches not allowed but circling ones are?

It is allowed.
Runway 07 has a published GNSS straight-in instrument approach as of 10 Nov 2016.

Download link here, or click image for full size.
For non-GNSS equipped planes, there are no published straight-in instrument approaches for runway 07. Only the circling VOR 07.
However, in VMC the crew may request or likely be given a visual straight-in approach to 07.
As to why there aren't published minima for a straight-in VOR approach to runway 07, I can think of two plausible reasons:

VOR accuracy being not good in that quadrant, maybe due to terrain interference, or interference from the tall church on short final.
Winds almost always favor 25, so no effort was made to certify a straight-in approach using VOR for 07.

When an aircraft intends to land on a runway for which no instrument approach procedure exists, it may descend on the instrument approach to another runway and, provided the required visual references are established at the circling MDA/H, maneuver visually for landing on the desired runway. This procedure is used when landing on the instrument runway is undesirable, due for example to wind conditions or work in progress.
[...]
A circling approach is the visual phase of an instrument approach to bring an aircraft into position for landing on a runway which is not suitably located for a straight-in approach.
— skybrary.aero


During which phase of the mission profile, the airplane fastest? In a mission profile, there are various phases such as Climb, Cruise, and Descent (excluding other phases). My question is during which of these phases, the Mach number of the airplane is highest? Is that Mach number more or less than critical Mach Number?

Mach number is likely to be highest when the aircraft is highest.

Mach number is related to true air speed (TAS) while the power required is related to the indicated air speed (IAS). As a plane flies higher, the air becomes thinner. Typically a plane will fly at a constant IAS, so the aerodynamic forces remain constant, but the TAS (and ground speed, and Mach number) increase.

As a plane burns fuel and gets lighter, it can fly higher, so just before the descent could be the highest Mach number.


Why do children need to leave the plane during a refueling operation? On a flight at the end of the 90s,  the plane --  most likely a 747 -- made a stopover at an airport to refuel.

In my recollection, during the refueling process all of the children needed to leave
   the plane. What is the reason for this procedure?

You can find interesting lectures about the refueling in a Airbus Flight Operation Briefing Note or in the CAP 748.

When they have children leave the plane, it is probably a company thing! There are no such rules that all passengers have to deboard a plane during refuel (with JetA and similar). But, as you can see in the Airbus FOPN, there are some requirements that need to be met. Each manufacturer as well as each company probably has its on way of interpreting  of the rules and regulations issued by the CAP and the FAA.

Summing up, it is basically by the pilots and therefore the company's discretion what to do with the passengers (or children) on board during refueling as long as saftey requirements are met!


Partial panel power on stall under the hood What do you use for control and performance instruments while demonstrating power on stall under the hood with attitude and heading indicator covered (No vacuum instruments in 6 packs ) ?

Same as any partial panel work.  Altimeter is primary for pitch attitude.  Airspeed is secondary for pitch attitude (its indications complement the altitude data, and in a climb/descent it becomes a primary pitch indicator) and also for power setting in concert with RPM/MP.

VSI is generally considered too laggy to use for assisting in fine pitch control when partial panel and is only useful to confirm a stabilized climb/descent, because its indication might be 2-3 seconds behind what is happening at any instant.

Then it's turn and bank or turn coordinator for roll and away you go.

If you were told to do a power on stall in level flight it's pretty straightforward, just hold the altitude by altimeter watching the speed decrease, decreasing the power to get on the back side of the power curve than increasing it along with pitch to hold the altitude until the stall occurs.

If you are told to do a power on stall with a high power setting in a climb, it's a bit trickier because you have to try to judge that your pitch attitude increase is not excessive by the rate of change in altitude and airspeed.  In that case you might use the VSI to establish the stabilized rate of climb at the start of the exercise, then add just enough increasing pitch to get a gradual speed decrease from that climb state, adding pitch to maintain that decay rate of speed until the stall.