Why isn't the point you begin descent part of the flight plan? In This question there is discussion about how to determine when to start the descent from cruise. There are several factors at play and it is usually calculated for maximum fuel performance.

Would this calculation not be done ahead of time, especially for aircraft cruising in class A airspace (presumably by dispatch for part 121 ops)? Why is this not included in the filed flight plan? Wouldn't ATC want to know when to expect this, especially if you lose coms?

Because the Top of Descent (TOD) is calculated in flight based on current weather data, STAR/Transition assigned, directs received during the cruise portion of the flight, vectors received taking you off your planned route, etc.. The FMC does the calculation for you with higher precision in flight.

For regular ops, ATC can use the rule of thumb 10.000ft / 30 NM to calculate an estimated TOD. In most cases, they will not need to do that however, as they can give instructions to aircraft to plan a certain STAR entry gate at an assigned flightlevel/altitude.

R: DLH123, when ready descend FL240 to be level\to reach at ARPEG

During lost comms, you are expected to maintain your filed or last assigned flightlevel/altitude until you reach the clearance limit. From there you will begin your lost comms procedures which usually include holding at the Initial Approach Fix (IAF), descending at the IAF to the approach altitude, and commending the standard approach procedure for the active runway.


How to calculate the shear centre of a wing? How is shear centre of a wings calculated? i.e. how can I calculate the wing shear centre of a two spar wing with main spar at 0% of wing chord and rear spar at 75% of wing chord? (Assuming the two spars have the same stiffness.)

I implemented a program using Matlab for S.C calculus purposes (I'm actually involved in an aircraft project and, fortunately (or not), I'm the structures guy. I have based the code and the theory in a PDF bibliography that is linked w/ the .zip folder. You'll notice two matlab codes:
-One is named "Load_Airfoil_Coordinates_using_MATLAB.m". It loads any .dat file (i.e., if you have your airfoil points, you can plot it using this code);
-Another is named "Matlab_script_for_the_shear_center.m". It calculates, beyond your airfoil's C.G (Xcg,Ycg), the shear center (Xsc,Ysc) - probably you'll need to change some of the inputs to agree with your problem, specifically. Despite I've commented the most part of this code, I recommend you to follow Perini's theory (PDF bibliography) to understand the steps.
To download the .zip folder, please click my OneDrive link: https://1drv.ms/u/s!Aqqj-vTtH2vbomM9cVTInsHp7dbn?e=PMFudZ.
If you're just focusing on the theory, I recommend you some bibliographic references, such as:

T.H.G. Megson - Introduction to Aircraft Structural Analysis

David J. Peery -  Aircraft Structures

B. K. Donaldson- Analysis of Aircraft Structures
Hope I was helpful.

Best regards,
João Cioffi


What is the definition of "geometric height" referred in the ISA Model? The International Standart Atmosphere document always mentions the "geometric height" (along with the geopotential hieght) in their calculations. I predict that it means orthometric height, which is the distance from a point in the atmosphere to the Geoid (as an approximation of the Mean Sea Level). My questions are:

Is it actually  the same as orthometric height? Is there a reliable source with the definition? I need to be certain because I am going to be using these formulas in a critical setting. There is no definition I could find in the document and other sources that I found have been unreliable.
If they are the same, why don't they use the term "altitude" instead of "height" since they're referring to the distance to Mean Sea Level and not to the Earth's surface?
If they are not the same, how are they different? And again, is there a reliable source that has the definition.

Thanks in advance.

In the ICAO Standard Atmosphere model, as described in ICAO Doc. 7488, the geometric height is equivalent to the orthometric height.
The ISA model uses a hydrostatic equation to calculate the pressure differential over a geopotential height difference.
The reference height (0 meters) of the model is the mean sea level. It furthermore assumes a standard acceleration due to gravity, conforming to a latitude of 45.32'33". This $g_0 = 9.80665$ m/s2 is used to convert between geopotential height $H$ to geometric height $h$.
For this purpose the ISA model assumes a non-rotating earth with uniform mass distribution, so that only Newton's gravitation law can be used to obtain the relation between $H$ and $h$:
$H=\frac{rh}{r+h}$.
with $r = 6356766m$ the radius of the nominal (spherical) earth.
Now to orthometric height.
The orthometric height of a point is the distance H along a plumb line from the point to a reference height (typically the mean sea level).

Image source: ScienceDirect: Evaluation of the various orthometric height systems and the Nigerian scenario – A case study of Lagos State
The plumb line however, is not a straight line. Due to rotation of the earth and gravitational anomalies due to an irregular mass distribution in the earth, the plumb line curves.
Within the ISA model, orthometric height and geometric height are the same, because the model assumes the earth is uniform, spherical and non-rotating. Therefore the plumb line in the ISA model is straight.
In the real world however, the orthometric height (measured along the curve of the plumb line) is thus not equal to the geometric height (which measures along a straight line).
The difference are extremely small; for practical purposes this can be ignored in most fields and orthometric height is usually said to be the same as geometric height.


Is passenger weight distribution important on a commercial flight? This is something I've wondered about for a long time.  On really large airplanes, like a 747-400 or A380 for example, I would assume that the weight of the passengers on board is a significant to the flight characteristics of the plane. And it seems like it would be pretty easy to put all the passengers in an odd place (like all at the front or back) and as a result significantly change the flight characteristics of an aircraft.

So, assuming I'm right (tell me if I'm not), how do commercial aircraft counter this problem? Do they do their best to distribute passengers throughout the craft with seat assignments? Or do they have ballast they can move around (like fuel ballast)?  Or is the weight shift not significant enough to warrant anything along these lines?

On the EMB-145 the passenger cabin was split into 5 zones and we were given passenger totals in each zone from the flight attendant prior to leaving the gate.  If balance is off (this happened quite rarely for us) you would tell the flight attendant "I need 2 passengers from zone 5 moved to zone 1" or "I need a passenger from zone 3 moved to zone 2" or some other similar instruction.  The flight attendant would solicit volunteers and if no one did, they would instruct someone to move.  The move was only for takeoff and once airborne they could go back to their normal seat.

After moving passengers we would re-calculate the weight and balance to verify we were in the envelope and set takeoff trim.

Similar methods are used in larger airplanes with the cabin split into zones.

The only time we would use ballast is when we had a full cabin and not enough bags in the cargo (not common).  In those cases we would ask ops for ballast and they would put something in the cargo.  They would try to make it useful if an outstation needed something else they would just load 50 lb bags of sand.


What is the maximum age limit for getting a pilot licence? Can I do pilot training courses even after age 26 ?

As far as I know there are no maximum age restrictions on getting a pilots license anywhere in the world. Many countries have a minimum age restriction for getting a license, that usually does not prevent pilot training from taking place. 26 is fine, in fact 76 is fine as long as you pass whatever medical is required.


What is the difference between active tip clearance control system and passive tip clearance control system in turbine? What are the main differences between turbine active tip clearance control system and passive tip clearance control system?

This is kind of half an answer, but the difference between active tip clearance control and passive tip clearance control is in the definition of “active” and “passive”. An active system has some way of determining the clearance, and then making adjustments to achieve a desired gap. So, it has a feedback loop in the control system. A passive system has no feedback, it just operates “blind”.

Turbine blade tip clearance is usually achieved by blowing cool or hot air onto the turbine casing, to make it contract, and move closer to the blade tips (when cool air is being used), or expand (when using hot air). A passive system will just blow x amount of air at temperature y, during a given portion of the mission (say the climb), without actually knowing what the actual clearance is.  It was up to the designers to make sure the values for x and y result in the right tip clearance. In comparison, l expect an active system has some feedback so it modulates the flow to achieve a desired clearance.

Here is a scientific paper that describes a concept for active tip clearance. The paper uses the term “open loop” to describe a passive system. An active system would be “closed loop”, because there is a signal going back to the controller, telling it how well it is achieving its target tip clearance. It appears in this paper, this signal is not an actual measure of the tip clearance, but rather a prediction from a thermal model of the casing & blade.


How can an inexperienced pilot tell if the weather is good enough for flying? When I look at weather in the morning of my flight, it looks good. However, the actual determination can be made later during the day closer to my flight time.

Being a student pilot, how can I efficiently make a decision about flight based on weather? Is there a particular way which can help me?

My flight is at 2PM. When I check weather at 8:30AM using this website I get the METAR for my closest airport as shown in these pictures:

There are a few details available. I want to know how can I make an informed decision at 8:30AM about my flight, instead of waiting until around noon time?

I'm a UK PPL of 14 years, I fly out of North Weald which is on the opposite side on London to Farnborough, so I'm well placed to give you some tips here. First, use the Met Office aviation portal for your planning, most of the services a PPL will use are free. Metars are useless for planning as they only say how the weather is right now, TAFs are good for planning, however they only get you so far as they show you the forecast for one location. The Met Office portal gives you access to the low level forecast charts and spot wind charts, these give the big picture for the whole UK and Europe, including fronts, and forecasts in specific zones. These are published 4 times a day and are good for about 18 hours each.

The weather in the south east of England is very hard to predict accurately, it's getting better as they throw more computing power at it but it's still a challenge. When I do my weather planning I look at the low level chart and spot winds, then I look at the TAFs throughout the area. Heathrow and Gatwick both have 24 hour TAFs, and Farnborough is snuggled between them I'd look at them both and assume the worst from each.

Read the TAFs and look at the briefing charts every day you can until you get a feel for it, experience will give you confidence.

Next set limits. In the SE of England there ain't much topography but you don't want to cruise below 800ft in most places, back before I got an instrument rating I typically set a limit of 1000 ft ceiling, anything below and I wouldn't fly except for circuits, and even than that's pushing it. Wind-wise you need to know your crosswind limit for your airplane and yourself. It doesn't matter if your airplane's rated for 20 knots if you can't hack it, so don't put yourself in a bad position.

Lastly, UK TAFs have a funny quirk. You'll often see PROB for probability in a TAF. The only 2 figures you'll ever see in a UK TAF are PROB 30 and PROB 40, the numbers are for percentage likelihood. PROB 30 means it's unlikely to happen, whereas PROB 40 means it probably will happen. In other words a 40% probability does not mean 40%, but about 60-70%, don't ask me why. So if you see PROB 40 consider it likely.


Where and when would a 737-700 be taking off at an altitude of 19 kft? Another question triggered by reading the 737 technical site; according to this section of the page on the 737's pressurisation system, the 737-700 comes with an option that allows it to safely take off and land at altitudes of up to 19 kilofeet AMSL (my emphasis):

High Altitude Airport Operations System
Is a customer option for operations into airfield elevations of up to 10,000ft (all NG), or 13,500/14,500ft (-6/700 series only). Changes include: Addition of high altitude landing selector switch to transfer to the high altitude mode, cabin altitude at warning horn activation is increased, an extra hour of emergency oxygen (bottles stored in aft cargo compartment), 10 minute take off thrust if engine inop; winglets, carbon brakes and fwd Cof G options are recommended. For the 737-700 the takeoff envelope is increased to 19,000 ft & 0.50Mn. The option is usually taken with increased MLW, carbon brakes and RNP

Yet even the highest-altitude airport in the world - Daocheng Yading (DCY/ZUDC) in western China - is only 14,472 feet AMSL.
What justified providing the 737-700 with the ability to operate from a completely hypothetical airport over 4,500 feet higher than any existing in the world?

As Ron points out in the comments the question is not so much where as it is when. Aircrafts see the density altitude of the air around it not the true altitude they are at. On a very hot day at a very high altitude airport the density altitude may very well be higher than the true altitude by a significant amount which affects takeoff performance. The FAA provides a nice overview of density altitude here. SO even though there are no airports at 19,000 MSL a lower altitude airport that routinely sees very high temperatures can yield the same situation.


Can a convergent nozzle be used for a supersonic jet engine? Can a supersonic fighter incorporate a convergent nozzle or does it always have to be a convergent-divergent nozzle?

Short answer: Yes.

A convergent nozzle will not allow supersonic exit speeds of the combustion gasses, but due to their high temperature their speed of sound is considerably higher that that of the surrounding air. For example, at 700°C the speed of sound in air is 625 m/s. Since thrust is mainly determined by the difference in entry and exit speeds of the air flowing through an engine, a higher speed than flight speed is required for positive thrust. Low supersonic flight speeds are entirely possible with a convergent nozzle.

Long Answer: Better not.

Once the aircraft crosses the sound barrier, drag increases only slowly since the drag coefficient actually drops. If the design is meant to fly supersonically, which implicates a lot of design adaptions, it makes sense to go for higher supersonic speed; however, this requires both an adjustable intake and an adjustable convergent-divergent nozzle. Both increase efficiency, dramatically so at higher Mach numbers. The simple pitot intake of the F-16 is just good enough for Mach 1.6 (above that its efficiency becomes outright awful), but still its F-110 engine has a con-di nozzle.

With an adaptable convergent nozzle the exhaust gasses can be accelerated up to their speed of sound, but not more. A narrowing of the flow path will accelerate subsonic flow, but only to the speed of sound. Only a divergent flow path will then accelerate the flow further to supersonic speed. A convergent nozzle will be shorter and lighter, but means throwing away a good deal of useable energy with the hot exhaust gasses. In most cases it would be more efficient to convert the pressure energy of the exhaust gasses into more thrust by accelerating them to supersonic speed.

Convergent nozzles only make sense if the aircraft is designed only for short, limited supersonic dashes, but will spend almost all flying time at subsonic speeds. Examples are the Northrop F-5E or the Panavia Tornado.


What is the exception applicable to basic VFR weather minimums in FAR 91.155? Question applies to operating an Airplane.

The part 91 regulation regarding Basic VFR weather minimums in Class G airspace states (in the FAR 91.155 chart):

For aircraft other than helicopters:

Day, except as provided in 91.155(b): 1 statute mile and clear of clouds.

When I refer to 91.155 (b) I don't see any exceptions pertaining to airplanes operating in Class G airspace during the day.  The exception noted for airplanes only pertains to night time.

Is there some reason this regulation indicates that an exception does exist for daytime operations?

CFR 91.155(b)(2) has the exception:

  (2)Airplane, powered parachute, or weight-shift-control aircraft. If the visibility is less than 3 statute miles but not less than 1 statute mile during night hours and you are operating in an airport traffic pattern within 1/2 mile of the runway, you may operate an airplane, powered parachute, or weight-shift-control aircraft clear of clouds.

So if the visibility is less than 3 statute miles (not less than one statute mile at night), you can operate in Class G as long as you are clear of the clouds and within 1/2 mile of the runway. It does not mean that the entire exception applies at night, only that at night, you need to have at least 1 mile of visibility, otherwise during the day you can operate down to nothing as long as you are clear of the clouds.


Why does the Comet's horizontal stabilizer have so much dihedral? The Comet's horizontal tail has a noticeably extreme amount of dihedral compared to that of, say, a 707:

(Image by MilborneOne at Wikimedia Commons.)

Note how the Comet's tail has about twice as much dihedral as that of the 707 in the background, especially considering the Comet's quite low wing dihedral.

Why such a large amount of dihedral on the Comet's tail?  Does this have anything to do with the Comet's tail being unswept (whereas most later jetliners have horizontal stabilizers that have almost as much sweep as the wings, if not more)?

As mentioned in this question, the two major factors are:

Lifting the tail plane out of the jet efflux area. Placement of the stabiliser root is structurally optimal when at fuselage mid, dihedral can then lift the surface out of the efflux stream. Note that the Comet has a relatively straight aft fuselage cone, which is better for low drag. And like @DaveGremlin mentions in his comment: the jet engines on the Comet are higher than those of the B707 and need to be lifted up higher.
Reducing sudden main wing wake effects: with a pronounced dihedral, there is always some of the tailplane sticking out into a less affected streamline.

The tailplane dihedral does contribute to roll stability, like main wing dihedral does as mentioned in this answer.


Why must the throttle be moved slowly? User 'Calphool' writes:

  For example, in a real plane, if you jam the throttle forward too quickly, you can kill the engine or make it backfire. This may sound like a trivial detail, but people have died on takeoff because they never learned proper throttle technique.

Why and how?
What accidents were caused by mishandling of the throttle levers?

There are a few ways rough throttle handling on a propeller airplane can get you into trouble:

Gyroscopic yaw and torque: a rotating prop creates yaw 90 degrees to its spin which are offset by control inputs (mainly rudder), throttling up or down requires changes to these control inputs. Quick changes require bigger changes, slower changes give a pilot more time and allows smoother transitions. This isn't that big a consideration on lower-powered aircraft but it is on high-performance aircraft. In the first case that comes to mind an inexperienced P-51 pilot rammed full throttle in on a go-around and it flipped the aircraft on its back. At low airspeed it's possible there wasn't enough control authority to manage the forces even if he had been prepared for them
Pitch changes: most aircraft will have a pitch change when the throttle is increased or decreased, again quick changes require coarser changes in controls while slower changes mean smoother and better controlled inputs. Again more applicable to higher performance aircraft
Engine and carburetor: The engines in most light propeller-driven airplanes represent the pinnacle of 1950's technology. Fuel mixture, priming, and throttle control are all completely manual - there are no electronic systems to help smooth things out during throttle changes. Many airplane engine carburetors do not have an accelerator pump to shoot extra fuel to prevent the engine stalling during a quick throttle up. Given that an engine stall when airborne is a life-threatening emergency it's in your interest to make smooth, controlled changes

Although not usually a safety issue wear and tear is also a consideration. Smooth, gentle changes are better for the levers, plungers, and cables in the engine control system. Less wear and tear means better reliability and less costs.


Do any regulatory bodies require ISO 9001 QMS certification from airlines or service providers? As the aviation industry is transitioning to SMS approach, is having ISO 9001 certification required from any civil aviation authority? Similar to how IATA requires IOSA certification and certain airline /  airport authorities require ISAGO certification for ground handling companies. Note this question is not trying to debate the advantages or disadvantages of ISO 9001 certification towards achieving safety, but rather the presence or non-presence in the regulatory landscape.

No, there are no civil aviation authorities that require QMS implementation.

ICAO documentation (Document 9859) discusses the integration of other systems, such as quality and environmental management systems. There are advantages of integrations, such as facilitating data management and reducing redundancies.

For example, a QMS has many of the same documentation requirements as an SMS, so an integrated system is logical. However, not all operator benefit from an QMS, especially the smaller ones.


Is joining the air force a good way to become an airline pilot? I've always loved the air force. However, my main goal is to become an airline pilot. Would joining the air force affect becoming a commercial airline pilot?

I am asking because if I join the air force, I am committed to seven years of service. Would this put me behind other pilots? Or, do airlines like pilots with military backgrounds?

Honestly, every U.S. Air Force pilot I know, who wanted to retire to the airlines, got hired on with no problems.  The ex-Air Force pilots I know have all gotten immediately put into the big planes: A380, 747, 767, 787, etc right from the start.  This is because the airlines know that an ex-military pilot has had some of the best training and experience in high pressure situations.

That being said, in the USA it is very hard to become an Air Force pilot.  You have to contract with the Air Force before they even let you know if you can go to pilot training.  That means, if you don't make the cutoff for pilot training, you have to spend at least 4 years in the Air Force.  If you do make it through Air Force pilot training you have to contract for 10 years after you finish flight school, which means about 12 years from your date of commissioning.  This will take a good 16+ years out of your life, including the time spent in college.  However, you will progress from your first flight all the way to potentially flying F-22s in under two years - a rate of progressing you won't see anywhere else.

Bottom line is, if you don't want to join the military then you shouldn't.  By joining the military you are expected to give your life for people you may not know, or even care about.  That aside, there's no point in spending a minimum of 16 years doing something you don't like, or fighting for a cause you don't support just to become an airline pilot.  If you can find a good airline cadet program, or scholarship, you can become a great airline pilot, it will just take a longer time to progress from one aircraft to another.

Just a little tangent.  That being said, I'm currently an AFROTC cadet, and I had no military background.  I love AFROTC, the US Air Force, and the USA.  I'm currently applying for a pilot slot in the U.S. Air Force, but if I don't make it I would be vary happy taking other jobs, too.  The key is to have small, achievable goals that you can take one step at a time.

I wish you the best of luck.


What is the procedure when an aircraft with an emergency can't land due to a blocked runway? This is a hypothetical scenario, but I'm interested to know if there are any regulations/guidance for what ATC should do in this situation.

The hypothetical nightmare scenario:

The runway is blocked by a crashed airliner and can't be cleared quickly.
The airliner is full of injured passengers who will take time to move.
The next aeroplane in line to land has an engine failure and is gliding to the runway (so can't go around).
You're in a hilly/built-up area so other options for landing are limited.

Clearly, you can't have one aircraft landing on top of a crashed aircraft, so what should ATC do?

Some of the options I can come up with (in roughly ascending order of how crazy they sound):

Switch him to a different runway e.g. LHR has two parallel runways (but if he's close to the airport making the sudden move across to another runway might be dangerous without power?)
Empty a taxiway (but you'd probably struggle to empty it fast enough at a busy airport?)
Point him towards a grassy bit of the airport
Allow him to land, but aim to land before or after the crashed aircraft (crash is probably at start or end of runway, so might just work)
Wish him good luck and tell him to find somewhere else to land (you know that's possibly going to result in him crashing, but at least he won't crash into the already crashed aircraft).

So is there any advice for the controller and if so what is it?

Note the source of this question was listening to a recording of the ATC when BA38 crashed at LHR. The controller asks the next aircraft to go around - it made me wonder what would happen if they had said no!

What's the procedure? The procedure is, be creative to save as many lives as possible!

Really. The procedure is to determine a course of action which will likely result in the best outcome for everyone, utilizing all resources and given all constraints. Period. It is as simple as that.

There are infinitely many scenarios, and one cannot be trained for everything. However, pilots and controllers are trained to remain calm. When we look at the accident report years later, reading the document, we can easily say "if the pilots had done that, people would have been saved...". The important thing is that the people who were responsible at the time had to remain calm enough to look at the big picture instead of focusing on a particular problem, otherwise they can easily overlook a solution.

During training, it is common to throw multiple failures / emergencies together. The purpose is not to train the trainee to react to this exact combination of failure, since that is rather unlikely. Rather, the purpose is to simulate a stressful environment, under which one has to make sound and logical decisions.


What are these thermal spots on this infrared image of an F-16? In this question, Hephaestus Aetnaean posted the following cool movie:

which showed the following still:

As indicated by the red circles (the yellow marking can be ignored) there seem to be a few hotspots visible on the IR image. What are these hotspots? They seem to be rather random, so I'm not sure what they exactly are.

In this picture from Wikipedia it can be clearly seen that the two along the bottom of the fuselage are both heated air data probes, as Federico pointed out. The probes are heated to prevent ice from forming and blocking air flow to the sensors. The forward one is a pitot probe, and the aft one is a total temperature probe. The AOA sensor can also be seen as a much smaller hot spot above the forward pitot probe.

I agree with Ron Beyer that the top area is probably the sun reflecting off of the canopy. The lower area is probably a sun reflection as well, off of the external fuel tank. You can see in the video that these areas are not always visible, and move as the F-16 flies past, consistent with a reflection.


Does zero-lift angle of attack depend on Reynolds number? In this post I read that, due to viscous effects, the $C_{l}$ at a given angle of attack increases slightly with the Reynolds number but it seems that it just happens near the stall angle of attack.

I am performing some wind tunnel experiments at much lower Reynolds than those of the figure of the linked post (150,000 and 300,000) with the same profile, NACA 4412. My question is if at the mentioned Reynolds, can there be a small variation in the angle at which $C_{l}=0$, and therefore my $C_{l}-\alpha$ curves at Re=150,000 be noticeably below the Re=300,000 ones.

The aerodynamic coefficients  $c_l,c_d,c_m$ are in general functions of the angle of attack $\alpha$, Reynolds $Re$ and Mach number $Ma$. For your experiments, since you are operating in a very low $Re$ regime, assuming incompressible flow, your lift, drag, moment curves will largely depend on viscous phenomena (i.e. $Re$ number). Generally, as $Re$ number drops, the boundary layer thickens. For this reason, you will expect a lower $c_l$ number (due to viscous decambering) and a higher $c_d$.

You may also discover non-linear behaviors even on operating angles due to laminar separation bubble forming/bursting on the suction surface and this is very dependent on the turbulent intensity of your wind tunnel so the stall angles and post-stall behavior may not be the same for flight conditions where turbulent intensity is very low.

Finally, you can confirm with Xfoil that for $Re=300k \Rightarrow \alpha_{L=0}=-4.33\ deg$ while for $Re=150k \Rightarrow \alpha_{L=0}=-3.64\ deg$ for the NACA4412.


Why is the nose landing gear of a Rutan Vari Eze up during parking? I recently saw a Rutan Vari Eze parked at the airport and I was wondering why the nose landing was up during parking. How does it work for a pilot to get in? Can the pilot put down the landing gear while sitting in the cockpit or has the pilot to put it down while standing outside? And what's the idea behind such a construction, why isn't there just a normal landing gear?

Rutan Vari Eze during parking, with the nose gear up

Rutan Vari Eze before takeoff, with the nose gear down

For getting in, the nose has to be physically raised before the pilot can board the aircraft:

When the aircraft is parked, the NLG is retracted and the aircraft rests on the bumper at the front of the aircraft, in what is described as the 'kneeled' position.
Extension of the NLG requires the front of the aircraft to be physically raised, after which the NLG extension system is operated from the cockpit.
To begin the NLG extension, a handle in the cockpit is turned in he extend direction. This handle is connected to a shaft that turns a worm gear and crown wheel, and the rotation of the crown wheel drives the actuating rms of the NLG in the down direction.  When the NLG is extended, an extra 1.5 turns of the handle causes the crown wheel to drive the actuating arms over-centre, which locks the gear in the fully down position.

After this, the pilot boards the aircraft. On some aircraft, linear actuators seems to have been fitted for this purpose:

In recent years the application of general purpose, 12 volt, linear actuators came into use for electrical actuation of the nose gear with the airplane loaded.
With the linear actuator the airplane can be parked nose down for stability, boarded (in the nose down position) and raised by the push of a button.

As noted above, this design has been adopted for stability- As the engine is on the rear, if the pilot is not in the aircraft, it can tip backwards, damaging the propeller. This also acts as a parking brake.


What would happen to the rudder on an A320 if both FAC systems failed? What would happen to the rudder of an A320 if both Flight Augmentation Computer (FAC) systems completely failed during mid-flight? Would the auto pilot immediately pass control back to the pilots or if they  failed would that be it? Would it be impossible for the cockpit to communicate with the mechanisms which control the rudder or is manual operation possible in an A320?

Also, I know this maybe a more difficult/impossible questions but what would cause the malfunction of one of the FAC computers? Are there any likely scenarios or previous cases?

The A320 has a mechanical link from the rudder pedals to the hydraulic rudder actuators. Computer-generated rudder commands for yaw damping and turn coordination are added to the mechanical signal from the rudder pedals, but in the event of a two-sided computer failure the rudder can still be controlled.

The elevator trim wheels are also mechanically connected, so rudimentary control of the aircraft remains even in the event of a total electronic failure, as long as there's hydraulic power.


Why were there passengers allowed on Concorde's route proving flights? Based on this site, Concorde needed to fly 750 hours to prove its airworthiness and be used in regular service. Air France and British Airways flew two Concords (F-BTSC and G-BOAC respectively) on a total of 254 flights, with... 11180 passengers combined! How come there were passengers allowed to be on the plane when it was doing flights to get its airworthiness certificate?

Bear in mind that these tests weren't to prove the safety of the aircraft per se, just to show that it would work as an airliner. It had to be loaded up with an appropriate complement of passengers and luggage to prove this.

However proving flights may not generate revenue from passengers - they are either selected through an application process or chosen at random, and take part in the proceedings free of charge.

CAA AIRWORTHINESS INSPECTOR‘S HANDBOOK (Page 2, point 3)


Would solar panels on the wing of an aircraft increase drag? If a small scale UAV (wingspan <2 metres) was to be fitted with solar panels on its wings to have more power available, would the addition of these panels cause an increase in the drag coefficient, and consequently aircraft drag?

Though wind tunnel testing would be required to ascertain the exact change in drag, can one theoretically anticipate a change in drag on account of these solar panels? Furthermore, will the minimal variation in surface thickness on account of the panels result in the same?

The solar panel thickness is of the order of micrometres.

No, assuming the wing geometry and the coefficient of friction of the material on the surface of the wing do not change. So, swapping a section of aluminum or carbon fiber skin on the wing for a section of Plexiglas or silicate glass under which you place the solar cells will, all other things being equal, have a negligible effect on drag.

However, doing something like this, all other things are not necessarily equal. First off, the border between the normal skin material and the solar cell cannot be a perfectly smooth transition; at some level of magnification, there will be a noticeable seam which will reflect as an increase in the surface "roughness" of the with with solar cells compared to the one without. While nonzero, it's likely negligible if the parts of the wing are well-fitted.

Second, there will likely be a change in mass when removing a thin layer of aluminum, carbon fiber or polymer sheathing, and replacing that with Plexiglas with solar cells underneath (plus the power wiring, converters and other additional components that otherwise wouldn't need to exist). Classically, that has no effect on drag, but it will change momentum calculations which affect how much the drag matters, and also as was stated, heavier masses require higher angles of attack to increase lift and counter weight, which increases induced drag as the effective shape of the airfoil slicing through the air changes to present a larger cross-section. Wing stress moments will also be affected as the weight distribution of the plane between fuselage and wings has changed, and this can change the amount of effective dihedral due to wing loading under various conditions.

Lastly, there will be a nonzero difference in surface roughness between the majority of the skin or sheathing and the solar cells. For instance, a matte finish as some aircraft have is rough by definition to provide different reflective planes to scatter light. You want a highly polished surface on the solar cells to minimize energy loss through the outer layer. Even if most of the aircraft is finely polished, there's a difference in how fine a polish various materials can take; the harder the surface, the easier it is to take a fine polish.


Has a commercial passenger airliner ever had its cockpit fully upgraded? In an earlier question What are the barriers to feasibility of stratospheric cruising for commercial air travel? (i.e. Concorde?) it was suggested that Concorde was not properly maintained as its analogue flight deck had never been upgraded.

Concorde production ceased in 1979. Fourteen Concordes saw commercial service. By end of operation in 2003 there were nine Concordes in use.

Excluding the military, has any airline or manufacturer ever retrofitted a new design of flight deck to an existing fleet of old commercial airliners?

While many times an upgrade is not economical for older airplanes, sometimes the new features make it worth the cost.

Two examples I found were Southwest upgrading their 737-300 fleet, and Delta upgrading their MD-88 and MD-90 fleet. The second article also mentions American and Icelandair 757 and 767 upgrades. The Southwest and Delta upgrades involve over 100 aircraft in each case, which probably helped to make the upgrades more economical.

In both cases, a major factor mentioned was the ability to perform required navigation performance (RNP) procedures with GPS and other modern features. As the FAA works to implement the NextGen ATC system in the US, these upgrades will offer more benefits for the operators.

Also, I'd like to comment on the following statement:

  Concorde was not properly maintained as its analogue flight deck had never been upgraded.

Proper maintenance and technology upgrades are not always the same thing. Aircraft with older systems can be maintained just as well as newer planes. We have airplanes that are 50 years old or older, like the DC-3, which are still flying. While technology upgrades certainly have benefits, aircraft with analog cockpits are still operating just fine around the world. They may not be the most modern machines out there, but proper maintenance is what has kept them flying this long.


Why does this analysis show very high stress in a propeller? I have been trying to evaluate the stress on aluminium propeller:

Diameter: 78", 2600RPM

Have fed load numbers from here, applied distributed mass model onto the blades.

Static Thrust (2600 rpm):
MT 2-blade, 83" composite, 920 pounds
MT 3-blade, 80" composite, 900 pounds
McCauley 2-blade, 82" aluminium, 860 pounds
McCauley 3-blade, 78" aluminium, 825 pounds

The results are rather scary - 30 MPa out of 55 max, for 6061 class Aluminium (the visual deformation is increased 20x for better representation),
resulting in +-1cm vertical bending.

Is this normal?

Is there any info on industry's practice for safety margin (numbers show its less that 50%)? Or any kind of test procedures applicable to manufacturers?

The shear stresses are negligible - 150 Pa out of 150 MPa

The two propeller case is really scary looking
Below is a distributed mass (375Kg) - 80% of Max. yield stress

And centrifugal force - over-stressed by 200%:

Finally, a combined non-Linear analysis (incl. torque) - over-stressed by 250%:
(notice that everything not in blue will bend and likely crack, with only the blade tips surviving the torture)

The plots of your propellers seem to use a regular airfoil all the way to the root. Real propellers become almost cylindrical there, however. Also, aluminium propellers are hollow, so the outer part is only a thin shell, saving mass and reducing centrifugal loads significantly.

After all, real aluminium propellers work, so there must be a way to keep the stress in operation below the yield stress. FAR 23.907(c) even demands that a non-wooden propeller must be life-safe:

  The applicant must perform an evaluation of the propeller to show that
  failure due to fatigue will be avoided throughout the operational life
  of the propeller using the fatigue and structural data obtained in
  accordance with part 35 of this chapter and the vibration data
  obtained from compliance with paragraph (a) of this section.

Below is a drawing of a wooden propeller, but the outer shape of a metal propeller is not much different.

Drawing of a wooden propeller for the Fokker D VII (picture source)


Is VOR identification automated in modern avionics? Is the VOR identification via audible Morse code automated in modern autopilots / avionics?

Or does a pilot in an A380 still sits in there, listens and compares the .-. .. -.. to her charts?

Modern air transport and bizjet avionics do decode the audio ID and provide it digitally on the data output bus. This data is displayed on the Nav display or RMI (depending on Mode) along with the frequency. It's not as common for general aviation radios to have this capability.

VORs that comply with ARINC Characteristic 711, VOR MB Receiver, output the ground station ID in two ARINC 429 Labels.  The first and second characters will be in Label 242.  The third and fourth (if there is a fourth) characters will be in Label 244.  Characters are coded in ISO 5 format.

Since all modern radios are DSP based, detecting and decoding the audio tones is a fairly straightforward process.  The radios also provide an analog audio output, so the crew can select the VOR radio on the audio panel and listen to the Morse code if they desire. (I'd be surprised if you found a pilot that did that routinely.)

ILS is similar. The ILS ID is contained in Labels 263 and 264.


Load factor and how does velocity affect it? An aircraft initially flying level with a velocity of 130 m/s pulls
into:

a turn of radius 300m at constant altitude (i.e. a horizontal circle) with constant velocity;

a loop (i.e. a vertical circle path) of radius 300m, where the thrust is varied to equal the drag at any point (hence, any change in
velocity is entirely due to gravitational effects).

Determine the load factor for (1.) and (2.) when the aircraft is a the 90, 180- and 270-degrees position within the loop.

I have been trying to understand the question, however, I don't entirely understand what they mean. 90, 180 and 270 don't seem like banking angles and specially for part b, does it mean that at 90 degrees it has travelled 300 m vertically and its velocity will decrease based only on the gravity? Also, does the question assume 0 banking angle?

b) means straight up into a vertical loop with a 300m radius, with the load factor calculated at the 9 o'clock position as velocity is decreasing and G increasing on the up side, 12 o'clock position as velocity and G reach a minimum at the top inverted,  and 3 o'clock position as velocity and G is increasing on the down side, all due to gravity alone.  Bank angle is not a factor and can be considered "level" flight from that perspective.

a) means the load factor in a 300 m radius level turn, at whatever bank angle is required to achieve that radius at a constant 130 m/s.

The question should end with "loop and turn" instead of just loop and I would assume the 90, 180, 270 business also applies to the equivalent locations in the level turn in the case of a) (and I would presume to be the same number at each location in the level turn).

The question is pretty poorly done, but that's how I would interpret it to make do with what is presented.  Between the confusion over loop and turn and the typos like "id" for "is", the exam writer needs some remedial training.  So if you get the answer wrong, and it's important, I would protest it if that is feasible.


Why aren't contra-rotors used on the V-22 Osprey? The Osprey has 38 ft (11.6 m) rotors in a rotating nacelle on each wing. The rotors are powered via a gearbox as in usual turbo-pro fashion.

Is any reason that is obvious that smaller contra-rotating rotors wasn't adopted. It is noted on Wikipedia that the rotor diameter is currently 5 ft (1.2 m) below ideal, wouldn't a contra format be more compact on this front.

  Due to the requirement for folding rotors, their 38-foot diameter is 5 feet less than optimal for vertical takeoff, resulting in high disk loading.

Instead of having a set of contra-rotating proprotors on each side, if you're after decreasing the disk loading, a span increase would also do the trick, allowing wider proprotors. However the Wikipedia paragraph starts by saying:

  Due to the requirement for folding rotors...

The main contributor to its less-than-ideal size is the folding requirement to save parking space aboard ships, since the primary operators are the US Navy and the USMC.

Adding another set of rotors or increasing the span won't help:

(Source)


How does exceeding the critical Mach number of an aircraft affect its operation? If an aircraft exceeds its critical Mach number, does it affect the way the aircraft is handled? Are there any significant changes to performance or the safety of the aircraft when above this speed? What actually happens to the aircraft in the first place?

At the critical mach number, some part of the aircraft (usually the wing) will have air flowing over it at a speed in excess of mach 1.

If the aircraft is not meant to fly at transonic or supersonic speeds, shock waves will flow over the wing. This can either cause the wing to stall, the control surfaces to become unresponsive, or the plane to go into the mach tuck, which is very dangerous.

The mach tuck is a phenomenon first observed with the P-38 Lightnings and Spitfires in World War II. These planes were so clean that when dive bombing it was possible to exceed their critical mach number. When this happened the center of lift would move back on the wing. This would cause the plane to 'tuck'; the elevators stop functioning, and the plane's dive becomes steeper and steeper until the aircraft is actually partially inverted. Recovery can be attempted by lowering the gear, extending the dive brakes, and lowering the flaps.

In later versions of the P-38 a small 'speed bump' flap was added for diving which caused a more even pressure distribution on the wing, and decreased the chance of entering a mach tuck.


Are agricultural pilots allowed to use a highway as a runway? I lived not far from a spray pilot who had had a hangar in his yard in the country but right off the highway. Would he need some special endorsement to use the highway as a runway?

My answer is colored by having spent a couple of years as an ag applicator.

There is no endorsement needed to use the highway as a runway.

Practically, it is done less now than 30 years ago.  Also more states have codes now which prohibit operating aircraft off public highways.

Locally an operator used a paved road which terminated at an interstate, where all the houses on that road were owned by the same family. In 1978 that operator had to scramble, because the town decided to enforce a code prohibiting aircraft from using town roads for landing and takeoff.  The only other place I have seen it today is in parts of the northern mid-West. I am not familiar with their local codes or state codes.


Is there a database of airfoils for a given Reynolds number? I'm trying  to design my ultralight airplane. I know the basics of aerodynamics and airplane design, however, my question is
if there are any tools (online, software, database ) that suggest the best set of airfoils with best possible Cl/Cd ratio based on a given Reynolds number?

I think that the database  should have all airfoil graph data and not just the geometry information.

Reynolds Number is calculated as:  velocity × chord/kinematic viscosity of air

velocity is meters/second, chord is meters, kinematic viscosity of air is around $1.48 × 10^-5$

Then go to Airfoil Tools.
As you make your selections, you can see, in the polar diagrams, the effect Reynolds number has on the lift and drag properties of your wing.

A typical ultra light will have a Reynolds Number around 500,000 to 2 million.  A possible path to a solution may be to study aircraft of similar size and speed range.  These have been in existence for more than 100 years.

You may find a heavily cambered rectangular wing (Aspect ratio around 6-8) with a blunt rounded leading edge will give good low speed performance and very docile handling characteristics.  Variations at this Reynolds range will be mainly in amount of undercamber you choose,  depending on speed range you prefer and engine power.

The NACA 4418 may be a good place to start.


What is this equipment under nose of aircraft? From the news of Singapore Airline A330 nose gear collapse at Changi, I notice an equipment is under the nose part of aircraft and somewhat damage the radome when nose gear collapse. It looks like some ladder. What is it and what is it used for?

Note: it is during routine airline operation.

The report says the aircraft was undergoing a landing gear system check. The equipment looks like a trolley-mounted inspection ladder that could well have been used during such a check.


Why do some aircraft require type ratings to fly them? I know it might seem like a silly basic question, clearly some of these aircraft are awfully complex.  I doubt anyone questions the idea of a type rating for a 747-400.

But where is the line between, "sure, if you can fly you can probably fly this one" and, "you need to know how to fly this plane in particular".  What sorts of functionality cause that sort of distinction?

The FAA specifies the airplanes that require a type rating in 14 CFR 61.31:

  Sec. 61.31 - Type rating requirements, additional training, and
  authorization requirements.

  (a) Type ratings required. A person who acts as a pilot in command of
  any of the following aircraft must hold a type rating for that aircraft:

  (1) Large aircraft (except lighter-than-air).
  (2) Turbojet-powered airplanes.
  (3) Other aircraft specified by the Administrator through aircraft type certificate procedures.

So in short, large aircraft (meaning that they weigh more than 12,500 lbs.), aircraft having turbojet engines, or any airplane deemed suitable complex that it needs it by the FAA need a type rating in order to fly it as PIC.


Under EASA regulations, what constitutes loggable flight time? It wasn't too hard to find questions and answers here discussing flight time as defined by the US FAA.

However, I'm curious about EASA regulations, and if applicable specifically as implemented in Sweden.

Based on the relevant EASA regulations, at what point do I note the start and end time of a flight for the purposes of flight time logging?

I looked through the copy of the regulations that I have, but couldn't find anything relating to logging (of flight time or otherwise).

Citations, please!

According to FCL.050(g):

  Flight time is recorded: (1) for aeroplanes, touring motor gliders and
  powered-lift aircraft, from the  moment an aircraft first moves to
  taking off until the moment it finally  comes to rest at the end of
  the flight;

That seems to be the same as the FAA regulation.


What is this radar-like thing? A friend of mine sent me this picture, which Is somewhere in Miami. But I don't seem to recognize it

It is a wind tee; it serves the same function as a wind sock. It is designed to resemble an airplane from the air so that pilots overflying the field can more easily determine in which direction they should land. The top of the "T" is the front of the airplane and represents the direction in which an airplane should land.

When the wind hits the vertical tail surface it weathervanes. The tail points in the direction that the wind is blowing.

Unlike the wind sock, the wind tee does not provide wind speed information, only wind and landing direction.


What is the Mach Never Exceed number for a C-130J Hercules under ISA conditions (approximations are welcomed!) I am looking for the Mach Never Exceed number for a C-130J Hercules so that I can create an approximate 1g envelope.
Does anyone have any idea what this can be? I am trying to find the value for similar aircrafts so that I can make an educated approximation but I am having no such luck. Perhaps someone with more experience can provide me with an educated estimation.
Thanks!

The MMO for a C-130J is Mach 0.77 according to flugzeuginfo.net. Official values will be found in the AFM for the aircraft and may vary between production variants of the C-130.


Why would the fuel pressure decrease during a climb? When performing a climb in a SIAI-Marchetti SF.260 with a Lycoming engine, the fuel pressure decreased. Why would that happen?

The most obvious answer is "Gravity".

To some extent this is "normal" in a low-wing aircraft with a nose-mounted engine and a fuel pump drawing fuel from the wing tanks into the engine: As the nose pitches up the fuel needs to run "uphill" to get to the engine - that's more work for the fuel pump, which might not maintain full "straight-and-level" fuel pressure.

You can see something similar in a Piper Cherokee in an aggressive climb, particularly if you are only using the engine-driven (mechanical) fuel pump: The fuel pressure typically drops when you pitch past ~15-20 degrees nose-up. The drop isn't much, but it's noticeable if you're looking for it.

If the pressure drop makes you uncomfortable turning on the electric boost pump(s) may reduce or eliminate it, but as long as the fuel pressure remains in the aircraft's normal operating range it's probably not a cause for concern. You should however become familiar with how much the pressure tends to drop in a climb: A larger drop than "normal" may indicate a problem with the (mechanical) fuel pump which you would want to have your mechanic investigate.


How did this flydubai 737NG get Max winglets? I’ve seen this one on my way to the office in DXB. It’s clearly equipped with paired MAX winglets, however the engines are not curly. So judging by symptoms it’s not MAX. Was filming from a car, hence tail number is not visible. It’s A6-FEC, which, according to planespotters.net, is 737ng and 7+ years old. How did it get those winglets?

These are called Split Scimitar Winglets and they are offered as an upgrade for some existing Boeing 737 NG series aircraft:

Split Scimitar Winglets are offered by APB for the 737-800 and 737-900ER and came into service in early 2014. They are available as a retrofit to existing winglet aircraft.
A set of SSWs weigh 133kg (294Lb) per aircraft but give fuel savings of 1.6% on sectors of 1000nm rising to 2.2% on sectors of 3000nm. This equates to an extra 65nm range.
The modification requires a trailing edge wedge, strengthened stringers and ballast weight but no changes to any avionics or the FMC. The base price cost for an upgrade from blended winglets to SSWs was $555,000 as of 2014.

(b737.org.uk)
According to this article (in German), Flydubai is using this upgrade since 2019:

The low-cost airline from Dubai is equipping 30 Boeing 737-800s with so-called Split Scimitar Winglets. The scimitars on the wing tips save thousands of liters of fuel.
[...]
The first aircraft of the low-cost airline from Dubai - it bears the A6-FEC registration - has already been equipped with the split wing tips.

(translated by Google)
It is not exactly the same winglet as the MAX has (see also Why do newer 737s use two different styles of split winglets?) as you can see in the following images:

(Flydubai Boeing 737 NG, aerotelegraph.com)

(Flydubai Boeing 737 MAX, photo by Nabeel A. Hashmi)


How is thrust generated by a propeller? I get confused sometimes because I hear different theories of how propellers generate thrust.

One is that the propeller pushes air back to provide thrust.
Another is the blades generate lift creating a high pressure behind the blade pushing the aircraft forward.

Is it just one of these true or is it both? For you guys its the same way of generating thrust, but to me its two ways thats my confusion. And why does a propeller need to generate lift if it just accelerates air backwards to provide thrust. That question is my main confusion.

It's the same thing, it changes only the point of view, see Newton's third law: for each action there is an equal and opposite reaction, i.e. to create thrust, the engine has to push air backwards. Pushing the air backwards means that the air is pushing you forward and this, in the reference system of the propeller blade, is lift.


Do VOR's follow true north on a chart? Although VOR stations follow magnetic north, do VOR's on a chart follow true north?

As per the FAA's legend they are referenced to magnetic north

  Compass rosette will be based on the five year epoch magnetic
  variation model.


What is the tallest tower (AGL) identified on a sectional chart within the Class-E-to-surface airspace surrounding an airport in the US? What is the tallest tower (in terms of AGL) identified on a sectional chart within the Class-E-to-surface airspace surrounding an airport in the US?

For the purpose of the question, "within the Class-E-to-surface airspace surrounding an airport" means within the part of the sectional chart that lies within a dashed magenta line that completely encloses the airport and is not separated from the airport by another dashed magenta or blue line.  I.e. not including within Class-E-to-surface "extensions" that are separate from the Class-E-to-surface that actually surrounds the airport.

For simplicity, let's NOT include Class D or higher that reverts to Class-E-to-surface at night, etc.

"Tower" means any type of structure-- radio antennae, whatever-- that is depicted on the sectional chart with a tower symbol and has the AGL elevation of the top of the tower identified on the sectional chart.

Winslow-Lindbergh Airport (Arizona): Tower east of the airport is 356 feet agl.


What is a "round-robin flight", in layman's terms? I'm struggling to find a sufficient explanation of a round-robin flight, as it pertains to ATC.

Can someone explain, in layman's terms, what it is and the lifecycle of a round-robin flight? Graphic analogies are welcome.

It's simply a flight that returns to the original airport after stopping at one or more other airports.  ATC doesn't have a good way to code those types of flight plans in the computer, so the pilot will usually just tell the controller that he/she is planning to land at the intermediate stop for x amount of time.

The controller will then either close their flight following (or IFR clearance as appropriate) and have them reopen when they take off again, or just keep it open.  It depends on how busy their airspace is.  Often they'll just leave it open if it's in the middle of the night.


What precautions prevent 'insiders' from stealing a large aircraft, as in the Horizon Air Q400 incident? For those who haven't heard it yet, a ground worker stole a Q400 at SeaTac this week, performing an unauthorized takeoff and going for a joyride before eventually crashing into an island. The plane was empty and fueled at the time of departure.

My questions are:

How easy/hard would it have been for this mechanic to get on this aircraft alone and take-off without assistance or authorization?
What precautions are in place to prevent something like this?
And if I may ask a speculative question, what do people familiar with airport operations think will change as a result of this incident?

This is not a duplicate of this question because I'm asking about a) insiders who already have access to the aircraft, and b) large/transport aircraft like airliners.

As an aircraft mechanic at a major airline, I think I can answer this pretty well.

It wouldn’t be hard at all. All I have to do is wait for an aircraft move. This could be to bring a plane into the hangar or just to move it from one gate to another. I could simply volunteer to taxi the aircraft, which wouldn’t be unusual at all. At my airport, we have to cross an active taxiway and runway to do this sort of thing. We do it weekly, if not daily. I’d request fuel (if needed), and instead of proceeding across the active runway, I’d just hang a right and throttle up. By the time anyone knew what was going on, I’d be airborne.
There aren’t really many precautions to prevent this. Nor are there a lot of precautions preventing me from, say, throwing a bunch of screws into an engine or chopping a wire bundle in half. The truth is that I pretty much have carte blanche access to the airplane.
What will be done? Probably nothing. The efficacy of airport security is about what you’d expect from a $12/hour job. The focus is on making sure you don’t have a large tube of toothpaste, not whether I’m going to steal an aircraft. Most mechanics have often joked about how easy it would be to “steal” an aircraft. I’m so familiar with airport procedures and policies that even if you prohibited me from doing A, B, and C, I could simply do X, Y and Z. I am a mechanic after all. My job is to think outside the box with respect to “my” aircraft as well as to think about policies and procedures we have in place. I’m probably more lawyer than mechanic. I can find a loophole in everything long before security ever will.

Furthermore, we do a really good job at policing ourselves. My coworkers and I are like brothers (and sisters). We know when someone has an alcohol problem, a marital problem, a debt problem, etc. security is just focused on the four seconds they see you. As long as you’re not acting extremely strange, and you don’t have a weapon, they’re as good as useless.

Is it possible for this to happen? Sure. But, I wouldn’t bet on it being a new way for down and out aircraft mechanics to end their lives.

EDIT: Since my original answer, the media has reported that the person in question was a ground servicing agent. I think this is an interesting twist as, where I work, most of these agents do not come from an Airframe & Powerplant background. Even the ones that do generally don't have a background on the same fleet types. They may know how to do some things in the cockpit, such as operate the fuel panel, but most of them are not familiar with all of the controls.

I suppose anybody could download a flight simulator game and learn these things, to some extent, but there's still enough going on that it would be sufficiently difficult, if not very slow, to figure out how to do things like starting an engine (which generally requires starting the APU), release the parking brake, steer with the tiller, etc...

That said, I have heard of some airlines allowing these ground service agents to tow the aircraft. That would require knowledge of starting the APU, releasing the parking brake, etc. To my knowledge, none of them are allowed to taxi, so there's still the "problem" of starting the engines. That said, it's not like starting engines is really a big deal, it's just that it's another delay in the process. I'm going to go out on a limb and take a stab that he has had some prior "higher capacity" experience with planes before this ground servicing job.

I'd also like to note that now that I think about it: when I see planes being pushed back on the ramp, their engines starting, and them taxiing out, I rarely give it a second thought. It is literally not something I would even question. You just assume the people up there are qualified, know what they're doing, and you just go about your day.


If airplanes can't use reverse thrust in flight, what am I hearing? I've flown on a few commercial flights, and on several of them I recall a phase of the flight during descent when the engine seemed to go idle (or at least, the engine noise subsided substantially) and then all of the sudden, the engine got really loud and I could feel the plane slowing down substantially, as in, I felt the same as if I was in a car that was slowing down suddenly.  This seemed to last between 5 and 15 seconds, or possibly slightly longer, and then the engines got more quiet and the noticeable deceleration stopped.

Living under an incoming flight path for a few years I have also noticed many times that a plane will be going overhead by the fact that suddenly the engine will get few loud for about the same amount of time.

This seems to be rather common, and I always assume this was reverse thrust.  But today I am reading two separate questions: "Is it possible to use reverse thrust while airborne?" and "Why can't most jets safely use reverse thrust while airborne?", the answers to both of which seem to imply that using reverse thrust while airborne is very rare.

So what have I experienced / heard?  I'm pretty sure it's not an airbrake, because far as I can tell a speed brake is a more passive device that doesn't involve the engine, and it would seem to defeat its purpose to spool up the engine while using it.  I've never been in a seat where I could actually see the back of an engine to tell if a reverser was deployed, but I think at least in some cases the speed brakes were also deployed; from in front of the wing this made it impossible to see the back of the engine.

Update: Everyone is saying speed brakes... how long are these usually deployed for?

It is normal for engines to spool up during the approach. The initial part of the approach, from cruise level down to approximately 10 miles from the airport, is flown at flight idle power. This is the most efficient way to get down. In the final part of the approach, flaps and landing gear add so much drag that the engines need to be well above idle power.

At low speeds required for landing, the wing of the aircraft will not produce enough lift to sustain flight. To compensate for the low speed, flaps are extended. They do not only increase the lift, they also increase the drag. When the flaps are extended, suddenly the drag increases, resulting in a deceleration. Extending the landing gear has a similar effect.

Normally the flight crew will limit the time that they fly at low speed and high drag. The first couple of degrees of flaps deployment are relatively efficient;they do not add a lot of drag but allow the aircraft to fly slower. When the aircraft is about 7 to 10 nautical miles from the runway, the crew will transition the aircraft to landing configuration for the final approach. Often there is a horizontal segment before the aircraft starts a 3 degree glide path down to the runway. The crew will ensure that enough flaps (drag) is added before they start this final segment, otherwise they have difficulty reducing speed (they usually try to prevent use of speed brakes in that part of the flight).
Often there is a sequence of flap and gear extension before the final descent segment starts. This causes the aircraft to decelerate from the efficient high speed configuration (flaps 2 or less on the B737) to the landing configuration. At the end of that configuration sequence the aircraft has a lot of drag and is decelerating rapidly towards the final approach speed. To stop the deceleration extra power is commanded which spools up the engines and stops the deceleration. To reduce the spool up time of the engines, the engine control system (FADEC) will give a short burst of power. This what you hear while still decelerating. When the engines are spooled up they start to produce thrust which is the end of your deceleration.

This youtube video shows how it happens. When at 28:20, the aircraft (Boeing 737) is flying horizontally, flaps 2, and is about to start decelerating and descending for landing. Keep a look at the thrust levers(right bottom corner of the screen) and the airspeed (on the left of the artificial horizon).

It begins at 28:28 when the captain ask for flaps 5, and reduces the thrust in order to reduce to final approach speed. 15 seconds later he asks for gear down and flaps 15. The speed is now reducing rapidly. Starting at 28:50 the thrust levers are moved forward, until they are reduced again at 29:08. This is the power boost you hear. In 40 seconds the aircraft is transformed from low drag / low thrust to landing configuration.


Are there any runways that aren't labeled reciprocally to each other? Runways are generally labeled by their magnetic azimuth between 01 and 36. This means that runways are normally labeled on each end with a number that is reciprocal to the other by 180 degrees.

Do any runways exist where the approach ends aren't labeled reciprocally to each other?

Elk City, ID has runway 14/35 with about 30 degrees between reciprocal approach paths:


Turboprop vs Turbofan: How to compare Specific Fuel Consumption I understand that Turboprop engines have a lower Specific Fuel Consumption (SFC) than Turbofan engines, on average. I want to see this for myself by analysis, ideally by comparing values of SFC for typical turboprop engines vs turbofan. As turboprop SFC is usually given as the Fuel Consumption Rate / Power, and turbofan SFC is given as Fuel Consumption Rate / Thrust, it is tricky to directly compare them.

For a given airspeed and altitude, I want to show that a turboprop engine will require a lower rate of fuel consumption to produce a given amount of thrust. Is there a way I can show this without going into too much detail on things like blade pitch, thrust coefficient etc.

Ideally, I want to compare SFC of turboprop engines with that of turbofans, and show that the SFC for turboprop engines at a given thrust is lower.

Thanks

Well, propellers deliver thrust and turbofan engines deliver power to the fan axis, it is just a matter of choice.

Finding the thrust that a propeller generates at a specific airspeed and altitude, can be derived from the drag of the whole airframe in those conditions. Statistically, this sort of data can be found in reference books on pre-design of aeroplanes, such as Synthesis of Subsonic Airplane Design by E. Torenbeek. If we take a generalised approach:

$$D = C_D \cdot ½ \rho V^2 \cdot S \tag{1}$$
$$C_D = C_{D0} + \frac{{C_L}^2}{\pi A e} \tag{2}$$
$$C_L = \frac{2W}{\rho V^2 S} \tag{3}$$

So total drag follows from:

design factors weight W, wing area S, wing aspect ratio A, Oswald factor e.
environmental factors airspeed V and air density $\rho$

For the generalised $C_{D0}$ of aeroplanes, from Torenbeek page 149:

So you can use all of this to compute propeller aeroplane specific thrust. But the exercise will be futile, because:

The engine of a turbofan looks remarkably like that of a turboprop. In fact, they are both turbine engines, powered by the Brayton cycle. Similar size and design engines deliver very similar gas generator power to the [fan or prop] axis.
Turbofan engines tend to larger than turboprop ones, generating extra efficiency due to less boundary layer effect and more uniform internal flow.
Speed is of the essence: at turboprop speeds, turbofans are not very efficient. At turbofan speeds, turboprop cannot deliver enough thrust due to propeller tip drag divergence.
Turbofans utilise more of the hot exhaust flow for thrust generation due to the higher required flight speed. Lower efficiency, higher thrust.


Why would a jet engine that runs at temps excess of 2000°C burn when it crashes? Airline engines are designed to work at very high temperatures. Yet, when a plane crashes they're burnt (see below). Is it something in their design?

(bostonherald.com)

How The Jet Engine Works:

Inside the typical commercial jet engine, the fuel burns in the combustion chamber at up to 2000 degrees Celsius. The temperature at which metals in this part of the engine start to melt is 1300 degrees Celsius, so advanced cooling techniques must be used.

You can read more about some of those cooling mechanisms in How are temperature differences handled in a jet engine?
See also, How do you stop a jet engine melting?:

Neil - The normal melting point of the nickel blade alloys that we use in the turbine is typically about 12-1400 degrees. But what you do, and this is the clever bit, is you actually cool these blades. You have internal cooling passages, which effectively has air that flows through and it's about 7-800 degrees. And this cooling air then exits from small little minute holes that have been drilled on the surface of the blade and this air then forms a kind of a film on the surface of the blade, and this technology is typically called a 'film cooling.'
What you also do - you coat these blades and typically use something called a thermal barrier coating. The thermal barrier coating, effectively, is ceramic, typically about quarter of a millimeter in thickness, but they have got very, very low thermal conductivity. So, effectively, even though the gas stream is at a much higher air temperature, the effective metal that exists beneath the thermal barrier coating is much colder, and you get thermal grade of the order of about 100 degrees C between the hot and the cold surface. So all of this put together - this whole cooling technology effectively helps to keep the blade below its melting temperature.

The engine is designed to manage the intense heat in a controlled way, by restricting it to certain components, injecting cool air around the hot parts, and choosing different materials for different parts of the engine. If the engine is severely damaged, doused in jet fuel, and set on fire, none of those mechanisms function; the entire engine (or whatever is left of it), as opposed to just the portions intended to manage heat, will be hot, and none of the cooling mechanisms will be working.


How have fuel consumption and emissions per passenger/kilometre declined since the first jet airliners? The efficiency of jet aircraft has improved since the 1960s.

Is it possible to chart figures that show how consumption and emissions of pollutants and CO2, per passenger/kilometre, have declined since then?

Don't know where you can find those details (ICAO or some UN organization maybe?) but you could ballpark it by looking at the specific fuel consumption of a 1950s airliner engine and a modern one.

The JT3/J57 turbojet used on the 707 in the late 50s had a specific fuel consumption of .909 lb/(h lbf) at cruise, and the GE90 used on the 777 is .545.  This means the fuel burn per unit of thrust is about 40% lower on the GE 90 than the JT3. Since a jet engine is just a fancy oil furnace, without elaborate systems to reduce specific kinds of emissions like car engines, the SFC itself should be a good  proxy for overall emissions.

Being conservative by assuming the thrust per pax is roughly the same for modern aircraft vs old ones (I'm sure it's lower), you could use that comparison as representative of the industry and say emissions are at least 40% lower per seat mile now than in the 50s.


What is the busiest route of Turkish Airlines in 2017? What is the busiest non-domestic route of Turkish Airlines:

in terms of passenger number,
in terms of number of flights performed per year?

Is there a database that I can look for such kind of statistics for all other European airlines?

According to Turkish Airlines VP Ziya Taskent, they are adding a ninth weekly flight between Tel Aviv and Istanbul. He mentioned that:

  695,000 [passengers] flew roundtrip with the airline in 2014 [between
  Tel Aviv and Istanbul], 4.86% more than in 2013, making it the leading
  foreign airline in Israel

The largest number of airports served by the carrier is Germany with 14 destinations.

For other European carriers as requested, the Wikipedia article 'List of busiest passenger air routes' is a good starting point.


How do civilian pilots and ATC verify that other people on the radio are who they claim to be? I am interested in authentication - how identity is verified - in civilian aviation radio transmissions. I know that when someone is speaking on the radio he tells his call sign. But is there any other system that verifies the identity of the person speaking besides just the call sign that he claims to have?

I am interested not only in how ground ATC verifies which aircraft is speaking, but also in how aircraft ensure that they are speaking to a real ATC facility.

This is a reasonable question, and to an outside the simple answer of We don't / can't might seem a little bit jarring.

After-all, we live in a time of hacking, terrorism and so on and I can certainly see how this looks like a simple vector to create some havoc.

So, what's to stop somebody from setting themselves up with a Radio Transmitter and deciding to be Air Traffic Control for the day? Absolutely nothing. In fact, lower power handheld air-band transceivers can be purchased legally and cheaply by anyone. I have one near me - I could literally turn it on now and declare myself [Local Airport Tower]

However - the thing about Airband radio is that it's wonderful in its simplicity. At its core is AM radio which is basically unchanged since the early 1900's. This means a few things:

The strongest signal doesn't simply "win". Multiple medium strength signals will simply merge into a garbled mess. This means you don't simply get to "take over" ATC's transmissions - all you can do is ruin them.
Similiar to the above, there's no way (from outside) to stop the ATC signal. All you can do is stomp all over it - something which is totally noticeable.
Even if you do "win over" air traffic control for some aircraft, communications is a two way process, and airband radio is simplex. This means only one person can speak at a time - at some point ATC are going to key in.
Pilots aren't automatons. We listen and build up a picture, we learn normal procedures and can hear stress in somebodies voice. We also know who we were speaking to. Combined with a decent situational awareness, we don't just do things without thinking - you can't just pipe up on the radio and ask an aircraft to fly into the ground.
And even if you did, and they initially believe you, real ATC is going to hear your readback and ask what the hell is going on.

By way of analogy, imagine you've  snuck in on a conference call between an employee and a boss. And you start trying to speak on behalf of the boss - it's going to last all of 1 second before somebody realises something is going on. I think people tend to think of ATC as somewhat robotic, but it's still a human interaction and any good pilot will understand why they're being given instructions.

To attempt to interfere in Air Traffic Control in a way that is believable by the pilots is going to be incredibly difficult. You won't be able to use normal phraseology and cadence if you're attempting to step on real ATC, and that will concern the pilot. To do that for more than a few seconds and to to cause some kind of conflict with multiple aircraft is verging on the impossible.

The most likely outcome is more a denial of service, rather than some kind of spoof. It's not really a great vector to cause any damage. A nuisance, certainly and absolutely dangerous (and there's a reason it's very illegal!) but there are well established procedures for disruption in communications.

I've focused primarily on somebody trying to be ATC here, which is the way in which somebody on the ground would likely go about trying to make a mess. As for pretending to be a plane - firstly there are more technical difficulties because you'll be transmitting Ground -> Ground. I live within 2 miles of my local airport and often struggle to receive their transmissions when I'm at home.

Pretending to be a real plane that currently exists in the sky poses the same problems as above and any facility with RADAR is going to know something isn't right. Again, it might cause some initial confusion but you're unlikely to persuade somebody of something.

You could, in theory, pretend to be a light aircraft with no (or a faulty) transponder but really to what end? I guess you could cause a little disruption before somebody realises you're having a laugh but we're more into the realm of 'pranks' (Not that it's funny) now rather than serious risk.


How do pilots manage to keep aircraft on centerline during taxi? Cockpits usually seem to have windows that are high up and it doesn't seem from pictures that they would allow a pilot to look down so easily while sitting in their seat. Please correct me if that is wrong because that is the basic assumption of this question.

Then how do pilots know where the centerline is on the taxiway and runway? They always seem to taxi with nose wheel almost always on that line even when turning. Are there some instruments that help them? Or its the same logic as in a car as to how you find out where the lines are?

Aligning yourself in the middle of a straight taxiway isn't a problem. On the 747, if you put yourself in the middle of the taxiway as you see it beyond the nose, you'll be in good shape. If you're the captain, you can hold yourself a little left of the perceived center, but not much, because you're looking at from an eye level over 30 feet up as I remember. If the taxiway has those little metal reflectors sticking up on the centerline, you can play games trying to keep one of the nose wheels hitting them. You can just barely feel going across them. Or, since the nose gear is two wheels, you can play with getting the reflectors between the two wheels if you're really bored.

Turns on a taxiway present a bit more of a challenge insofar as keeping the center line because the nose gear is behind you, but one develops a feel for it. A 90 degree turn from a narrow taxiway onto another narrow taxiway is a little challenging, especially if the taxiway you're on T's into the one you're turning onto. All you'll see out the front window as you start the turn is grass. Also, on narrow taxiways, you can't see the taxiway out the side window from your normal sitting position.

If you need to do a 180 on a runway, you need to remember that when you first get yourself on, say, the right side of the runway, the nose gear isn't there yet, and the wing and body gear have even further to go.  You have to run yourself along the side of the runway a sufficient distance so that the airplane is aligned with the edge of the runway before you start your turn.

Personally, I found taxiing a 747 one of the more fun things in life.


How can the fuel decrease evenly from both wing tanks when an A320 is running on APU only? I stumbled over this sentence in a training material about fuel leak:

"If the fuel quantity symmetrically decrease in both wing tanks and the fuel quantity in the center tank decrease, the fuel leak comes from the center tank or the APU feed line."

Regarding the APU feedline part, what I don't understand is if the APU is feeding from the left tank always regardless if it's by the fuel pumps or it's own pump (in case the fuel pumps are off) how can the fuel decrease evenly from both wing tanks?

If you look at the fuel leak checklist you will see that you will come to this point only after you have confirmed that there are no leaks from the inner wing tanks and engine fuel feed lines.
According to the checklist if there are no visual indications of fuel leaking near the engines, you are to ensure the fuel cross feed is maintained closed. Then you turn off the center tank pumps. When the center pumps are off the engines will be only supplied by the inner tanks. Then you are to monitor the fuel in the tanks for a total of 30 minutes. If one tanks depletes faster than the other tank by 300 kg you can assume an engine leak. So, you shut off the associated engine. If this stops the leak, engine leak is confirmed. If it continues to leak you can assume an inner wing tank leak.
Now, the checklist says, if both the inner tanks deplete at a similar rate, you can suspect a center tank leak (remember the pumps are off) or a leak from the APU feed line. I have highlighted the word similar, because the checklist says to check for similar readings, not same or symmetrical readings. Yes, with the APU on, the left wing inner tank will deplete faster than the right tank, but it should not bring a massive difference to the figures. The A320 APU burns about 130 kg of fuel per hour. The checklist says to monitor the fuel for 30 minutes. This means, at the APU fuek line a leak would happen at a lower rate. That is why it says to look for similar rates, because an APU fuel line leak is quite insignificant. But you cannot still assume no leaks at the APU fuel line. The fuel leak checklist is a very conservative checklist. It is all about trying to close off any possible areas where a leak might be possible.
The checklist also says that if you have a fuel smell in the cabin, to turn off the APU to prevent additional fuel loss. It uses the word additional because the rate of leak at APU fuel is insignificantly low.

The checklist says similar not symmetrical (highlighted).


How does a diffuser (in ground effect) accelerate the air in front of it? A diffuser reduces speed and increases pressure, so how does a diffuser accelerate air in front of it if we have an adverse pressure gradient situation?
Wouldn't be better that we put the lower pressure (instead of higher) on end which will "pull"/accelerate air in front of it?
Example of F1 diffuser in ground effect:

Even though this isn’t strictly an aviation question, it does involve aerodynamic principles.
To put it simply, the diffuser’s main purpose is to gradualize the transition from rapidly flowing air under the car’s body as it transitions back to the speed of the ambient air behind the car.
There is a high pressure zone in front of the car from air particles colliding with the vehicle, and a low pressure zone in the wake behind the car as airflow is attempting to rejoin on the other side. This high to low flow draws air under the car where space is limited. This limited space results in an increase in speed and a decrease pressure, thus increasing downforce as the pressure below the car is less than the pressure on the top and sides of the car. This is Bernoulli’s equation at work.
However, the rapidly moving air experiences adverse pressure gradient at the rear of the car and airflow separation results in significant turbulence. This turbulence not only increases drag, but limits how quickly air can be evacuated from underneath the car. By carefully shaping a diffuser, the airflow can be slowed more gradually, easing its transition back into the ambient flow, minimizing turbulence which increases the flow speed under the car, decreasing the pressure and increasing downforce on the wheels even further.
The diffuser is shaped to increase the airflow speed in front of this funnel to ‘push’ a low pressure zone in front of the funnel, more effectively drawing air into the diffuser.


What factors determine magnitude and orientation of induced velocity at propeller blade? • Magnitude
What factors determine magnitude of "Vind" (induced velocity)?
• Orientation
If we take analogy with induced velocity at wing,isnt "Vind" must be prependicular to Vr?
• Induced velocity is almost always neglected
I notice that blade theory very rearly use Vind into consideration.For example effective pitch and advance ratio not include Vind, pretend like blade is "ideal".
I can see that Vind increase axial velocity  and decrease circumferential velocity,this reduce real AoA what blade section see.
Is Vind very small compare to V and Vt,so this is reason why it is neglect in most cases?
Θ real angle of advance

Using Momentum theory (the french version known as Froude theory is much more detailed) and under several restricting assumption, we can find a relation between thrust ($T$), radius of the propeller ($S=\pi R^2$), flight speed ($V_0$) and induced velocity ($v_i$).
$T=\rho S(V_0+v_i)*2v_i$
A numerical example with $R=2.2m$, $\rho=1.225kg/m^3$ (air density in standard condition), $T=30'000N$ show the evolution of the induced velocity with respect to the flight speed.
$v_i$ as a function of flight speed $V_0$" />
As you can see the induced velocity is decreasing with flight speed. As we are designing propeller blades to be efficient at cruise speed, the induced velocity becomes in fact quite negligible when you are calculating the ideal twist of your blade.
On the other hand if you want to calculate the thrust available at takeoff you need to take the induced velocity into account as it will greatly decrease your propeller efficiency.
As for the orientation of the induced velocity, it has two component axial ($Uind$) and rotational ($U\phi ind$) velocity that are created by the propeller as clearly shown in your second picture. Therefore it is not exactly parallel to $V_0$. The rotational component is a direct energy loss and is therefore minimized during design phases. In the Froude theory there is an assumption saying it is equals to 0.


How are the BNR and BCD data formats identified in an ARINC-429 message? I'm a newbie in ARINC-429 standard. How does the receiver identify which data is in BCD format and which is BNR? I understand that labels indicate the message data carried information, but it does not indicate if the data is BCD format or BNR. If my understanding is correct, the BCD or BNR format used is dependent on the equipment ID. And that leads to my next question: how is the equipment ID embedded in the message?

The receiver has to be programmed.  It's important to remember that A429 is a unidirectional hard-wired bus with a single transmitter and multiple receivers.  Each connection is physically unique and the reason for all the pin-out diagrams and bus definitions in the ARINC Characteristics.

To help with data integrity and fault detection, each transmitter includes Label 377 on the bus which contains its equipment ID.  For each type of equipment, the label assignments and coding are fixed.

So, if you're building an LRU that's receiving GPS data, you would program the port assigned as the GPS#1 Input to verify the equipment code is 00B hex and the find the specific labels your LRU needs (it's likely to be a small subset of all data on the bus).  Since you know the source LRU and the Labels you're looking for, you know the individual label coding and can program the receiver to decode the data.

Most avionics companies have developed custom ASICs to act as the A429 UART.  It simplifies the design and saves costs.


Can anyone identify this 1970s Mitsubishi pushback tug? What's the original name and specifications of this probably 1970s pushback?  The bottom of this model is stamped "Mitsubishi towing tractor." Made by Tomica. Bought at a flea market in Kyoto circa 2010. Googling finds only the toy.
I'm particularly interested in what looks like an elevating cab, possibly at both ends.
Details from comments so far:  This model is 1:119 scale.  The pushback was in use at Tokyo's Haneda airport at least through 1976-78.  It's not a Hough T-500 Paymover.
Photos of other pushbacks show that this one is unusual in having four separate cabs, and wheel arches that are perfectly semicircular.

Sept. 2020 edit before the bounty expires:
The toy is from a box labeled
ジャンボエアポートセット ミニカー
which translates as Jumbo Airport Set Minicar.  The UPC code is 4904810 26441 5 (or 8 instead of 5).
These sets are sold at the Japanese
ebay.
Can a Japanese speaker glean any clues from the back of the box?  (I can guess at the kana, but not the kanji.)

I Have found out this Mitsubishi pushback tug in real life at Haneda airport, Tokyo. but I wasn't able to get the original model number but I belive Mitsubishi hasn't set one for it otherwise the TOMICA toy co. would have named it as the other toys.

This pushback tug was only associated to pushback the B747 only, since all the photos the tug was with B747 only! cheers

References:-
-https://aflyinghistory.com/search-aeroplane-photographs?query=tokyo+haneda+airport&page=1
-https://www.airliners.net/photo/China-Airlines/Boeing-747-132/2246060
-http://motorcade.weebly.com/mitsubishi.html


Do crew need visas when landing at airports in countries other than their own? If the crew never leave the plane, have they really entered the foreign country? What about if the crew leaves the plane, but not the airport? How do crews of international flights keep up with all of the visas they may need?

It all depends on the laws of the country that the crew is visiting.  Some do and some don't.  Many do unless they have a reciprocal agreement with the pilot's country, in which case they don't.

This would be a great question for a specific country pair, or even if you want to know the laws about a specific country (in which case we could give the actual requirements), but the best answer for a general question like this is "it depends".

In some cases, the crew isn't even required to clear customs unless they are leaving airport property.  Other times they have to clear as soon as they land.

Part of qualifying for a route with the airlines is making sure that you have the required visas.  Having two passports help a lot in getting multiple visas, because they can keep flying internationally while the visa application is in process.


Are there any drawbacks to requesting progressive taxi every time? Unless you know the airport like your own backyard, it seems like requesting progressive taxi would always be the safest option to essentially eliminate the possibility of taking a wrong turn or busting a hold short. Aside from the risk of slightly annoying the folks in the tower, are there any drawbacks to requesting progressive taxi as standard operating procedure?

Apart from appearing really unprofessional, the obvious drawback is a significantly higher workload, both for the pilot but especially for ATC. You're not the only aircraft moving around at the airport, and even if you are, the controller most likely has other things to do than focus entirely on you.
As a pilot, you will also have a lower situational awareness, since you are not actually keeping track of where you are, but just following turn-by-turn instructions. Are you 100% sure you are at the right runway? And that the runway is long enough? What was the departure procedure again? Is the aircraft correctly configured for takeoff? I guess you didn't have time to check the charts, do a departure briefing and run through checklists since you had to focus on the radio all the time.
A more subtle drawback is that the controller will trust you less and as a result may very well choose to delay you in some situations. This is not written in any books, but controllers do establish sort of a mental picture of a pilot's competence level while talking to them, and if someone repeatedly requested progressive taxi, that would certainly raise a red flag. If you're waiting in line for takeoff, and there is a gap between arriving aircraft just large enough to get you going, the controller is more likely to let you wait for a better opportunity if they do not trust you fully. What's to say an (apparently) inexperienced pilot won't line up and spend 30 seconds on the runway before applying power - forcing a go-around for the aircraft on short final? Best wait another few minutes until there is a larger gap.
Ultimately, if you are in doubt about where you are, PLEASE DO ASK the controller for help! But, if you plan on making a habit of it just for convenience, please know that you are abusing the system, potentially reducing ATC capacity and causing an unsafe situation for yourself or others.


Is it recommended to get a life raft for short overwater operations? I'd like to fly to Santa Catalina Island (AVX) from the mainland around Los Angeles.  There is a portion of this overwater flight where my Cessna 172 will be beyond gliding distance from land.  I know that people usually do this flight with only life jackets, but the water is about 64 degrees F (18 °C) right now and I'm pretty sure that if I needed to make a forced landing in the water I may have hypothermia before rescue arrives.

Is it recommended to take an aviation life raft?  They're pretty expensive - they start at US$1000 for a two-man raft.  I see that raft rentals are available, but that's kind of a big pain, especially because they are going to be shipped from some other location and there is the possibility of needing to reschedule the flight because of weather.

What are the recommendations of authorities? Is there any alternative equipment that would be as effective in this scenario?

I used to be a bush pilot flying Cessna 180s on floats. If you ditch in a 172 on wheels with a life raft in the back seat, it's going to flip inverted when it contacts the water and start to sink immediately, and getting your own carcass and your passenger out of the thing without drowning will be enough of a challenge.  Forget about trying to pull a life raft out of the back seat of a sinking inverted 172 after you just escaped.  It's gone.

If you are that wary of overwater flight, the normal practice, for things like trans Atlantic ferries, is to wear an immersion suit. With the water at 64F, you could get by on a warm weather immersion suit or a sailing dry suit plus life jacket, but even without, it takes quite a few hours for 64F water to kill you, and the Coast Guard is going to be there within 30 min.

In any case, a 172 has an L/D of about 9, which means from 10000 ft you can glide somewhere around 17 miles.  At mid point between between Long Beach and the island you are less than 15 miles from shore, so there's really no need to worry about ditching in the open ocean, unless you want to do the flight at a couple thousand feet.

Even if you only climb to 5000, you could glide to a few miles of either shore.  And the actual "risk exposure" time of the engine spontaneously blowing up in your face without warning, while out of gliding distance of land, is only a few minutes. The probability of this happening, that is the engine doing something like throwing a rod suddenly, in that little time window, is a fraction of the probability of driving your car off a bridge into the water on your way to the airport.