Why are hexa airfoils used on rockets despite having more drag that diamond airfoils? I was doing a study on airfoils shape for a rocket. I tested the diamond and the hexagonal airfoil with Missile DatCom, RasAero and the Shock Expansion theory and from my results it seems like the diamond is better (little more lift and noticeable less drag). Looking at other rockets design I found out that many actually uses hex airfoil, but I don't get why. Am I missing something? Any reason for that?

Also like 99% of rocket uses a sweep angle. If I remember correctly, having a sweep angle reduces the Mach number normal to the L.E., so using a sweep angle means that I'll have a subsonic flow normal to the L.E. even if the fligh Mach is supersonic. So, the L.E. should be rounded. Since all these rockets uses thin sharp airfoils, wouldn't the wing work better with no sweep angle?

A rocket stabilized by fins alone needs a certain amount of lift at the rear to ensure that if it is disturbed from a nose-first attitude, it returns and damps out the resulting oscillation.  Adding mass at the rear of the rocket increases the amount of lift (hence fin area) required, as well as increasing the inertia factor that counters damping.

If a diamond fine provides little if any more lift, but weighs more (as it most likely does) than a flat-sided hexagonal section, it's probably a net negative in this compromise.  The added mass makes it harder to damp oscillation, and requires more area, which adds more mass.  Drag, on the other hand, helps a little (since it's near the rear of the vehicle, it tends to pull the tail behind the nose).

End result, for a rocket, it's likely that both on a lift/mass basis, and in consideration of drag, the flat-faced hexagonal fin shape is superior for overall performance.


What is the phraseology when leaving a TRSA? When leaving TRSA what is the correct phraseology to tell ATC that radar service is no longer desired?

You can say "cancel radar service" (probably the most standard under ICAO), "cancel flight following," "request frequency change," or anything else that conveys the same general idea. If all else fails, plain English is always acceptable too.

Regardless of which you say, ATC's response should be "radar service terminated, squawk VFR, frequency change approved," same as in any other class E airspace.


Angle of attack difference between outer wing and inner wing during a descending turn and climbing turn I understand that during an ascending or descending turn the angles of attack of the inner wing and outer wing are different.

However, I don't understand why then ascending and turning, the outer wing has greater AOA than the inner wing but during descending and turning, the inner wing has greater AOA than the outer wing.

Clarification:
My confusion is that, for example, if the AOA is greater for the outer wing, then the AOA should always be greater for the outer wing regardless the airplane is climbing or descending.

Here's one way-- not the only way-- to look at the dynamics involved--

Imagine an aircraft in a 45-degree-banked constant-altitude turn.  Now imagine that the pilot gradually adds more and more power and the aircraft gradually enters a steeper and steeper climb until it is climbing almost straight up.  Can you see how to maintain a constant bank angle, the aircraft must actually roll toward the high wingtip?  As the climb angle gets steeper, the maneuver gets closer and closer to resembling a vertical rolling climb, with the direction of roll being toward the wingtip that was originally the high wingtip in the constant-altitude turn.

"Fly" through the maneuver with your hand or with a little hand-held model airplane until you understand this.

(Like this-- https://vimeo.com/128025851#t=157s -- video intentionally starts at 2:37)

Now, can you see how a rolling motion always tends to increase the angle-of-attack of the descending wingtip, and to decrease the angle-of-attack of the rising wingtip?  As the descending wingtip comes down through the airmass, the local relative wind blows "up from below" compared to the local relative wind closer to the aircraft centerline-- this is an increase in angle-of-attack.  Similarly, as the rising wingtip moves up through the airmass, the local relative wind blows "down from above", or at least blows up from below at a shallower angle than the local relative wind closer to the aircraft centerline.  This is a decrease in angle-of-attack. These changes in angle-of-attack create an effect known as "roll damping"-- a resistance to rolling.  This is why the roll rate doesn't just keep getting faster and faster as long as we hold the ailerons in a deflected position.

So that's the answer to your question. In a constant-banked climbing turn, the aircraft is continually rolling toward the high wingtip, so the high wingtip experiences an increase in angle-of-attack and the low wingtip experiences a decrease in angle-of-attack.

Note that while our thought experiment involved a continual increase in climb angle and climb rate, the basic dynamics we're talking about are present even in a climb at constant angle and rate. In a climbing turn, an aircraft must continually roll toward the high wingtip to hold the bank angle constant.  Otherwise the bank angle will increase.  It's not a matter of aerodynamics, but rather of three-dimensional geometry.

In a descending turn, everything is the same except that to keep the bank angle constant, the direction of roll must be toward the LOW wingtip, so the low wingtip experiences an increase in angle-of-attack and the high wingtip experiences a decrease in angle-of-attack.

"Fly" through the descending turn case with your hand or a little hand-held model airplane until you understand that the extreme case of a constant-bank descending turn is a vertical rolling spiral, with the direction of roll being toward the wingtip that was originally the low wingtip when the plane was turning with a constant altitude or with a less-than-vertical dive angle.

(Like this-- https://vimeo.com/128025851#t=128s -- video intentionally starts at 2:08)

As a footnote, you can see how aerodynamic "damping" in roll -- the tendency for the roll rate to decrease-- exerts a destabilizing influence in a climbing turn, tending to make the bank angle increase.  In a descending turn, aerodynamic "damping" in roll tends to make the bank angle decrease.  This is very noticeable in some applications, such as powered hang gliders and trikes.

As another footnote, understand that we are speaking of "ascending" and "descending" relative to the surrounding airmass-- an unpowered glider spiralling up in a thermal updraft is still in a "descending" turn for the purposes of this discussion.

As yet another footnote, we can observe that it is easy to see how the bank angle can change when we pitch up with zero roll rate, in some version of a chandelle or wingover for example. It is harder to see how bank angle can be constant and roll rate can be non-zero in a climbing or diving turn, but it's true, as illustrated in the video links given above.  Again, it's fundamentally a matter of 3-dimensional geometry, not aerodynamics.

In closing, here is a link to a diagram from John S. Dencker's "See How it Flies Website" that illustrates how a rolling motion creates a difference in angle-of-attack between the two wingtips.  The diagram is not dealing specifically with the constant-bank case, and also it is really aimed at explaining "adverse yaw" which is a separate issue, but it still may be helpful-- https://www.av8n.com/how/htm/yaw.html#sec-adverse-yaw


Is it possible to have the laminar flow above $Re=10^7$? For pipe flow I came across the information that the onset of turbulent flow occurs at approximately $Re=10^3$ to $Re=10^4$, while for boundary layers on the airfoil the onset occurs in between $Re=10^5$ and $Re=5\cdot 10^6$. Therefore, since the onset of turbulent flow ranges greatly, is theoretically still possible in some cases to have the laminar flow above $Re=10^7$ on the airfoil, disregarding the laminar sublayer in every turbulent flow above the surface?

Any reference to books would be highly appreciated.

The airfoil always starts with a laminar boundary layer; at some point on the airfoil surface, the boundary layer may transition to turbulent. In a uniform free-stream, two modes of transitions dominate:

Natural transition
Forced transition

a. Natural transition

Natural transition is the transition mechanism that we typically associate with Reynolds number. As flow moves along the airfoil, the local Reynolds number increases and any initial disturbances amplify. When the amplification increases past the maximum threshold that a laminar boundary layer can tolerate, the flow separates locally (laminar separation bubble) and reattaches as turbulent boundary layer.

The following graph (Ref. Drela, Flight Vehicle Aerodynamics) shows the growth of the local Reynolds number ($Re_\theta$) and the instability parameter ($\tilde{N}$) for a flat plate. Once $\tilde{N}$ increases past the critical value ($N_{crit}$), then laminar-turbulent transition occurs. Notice also how the point of transition is affected by the free-stream Reynolds number ($Re_\infty$): the higher the free-stream Reynolds number (which is what your OP is asking), the earlier the natural transition.

Image ref: Drela, Flight Vehicle Aerodynamics

Since the shape of the airfoil affects the pressure distribution, it also affects the boundary layer shape. You can modify the airfoil shape to delay the transition as much as possible in order to minimize skin friction drag. This is the design objective of Natural Laminar Flow (NLF) airfoils. But even on NLF-0215F at a $C_l$ of 0.65, for example, transition occurs at 61% chord on the upper surface, at a free-stream Reynolds number of 5 million.

b. Forced transition

Forced transition occurs when there is irregularity or protuberance on the airfoil surface. This can be due to manufacturing tolerances, contamination, or by design. Contamination can be due to rain, ice-buildup or even collision with insects.

Thus in practice, actual transition would occur much earlier than predicted via natural transition.


Why did the crashed TAM Airlines Flight 3054 veer off the runway only near the end? For the accident, why did the aircraft veer off the runway near the end of the runway, instead of the moment it touched down (where the left engine went into reverse thrust and the right engine powered up to climb throttle)?
The aircraft managed to maintain a (relatively) straight path for most of the runway length. I thought asymmetrical thrust that significant would immediately send it off course

Right Engine thrust

The engine takes about 12 seconds to spool up from idle to full thrust.

Auto-throttle had held both engines near idle during the approach to touchdown. The throttle levers should both be retarded from "climb" to "idle" position prior to touchdown. But only in the last two seconds before touchdown, after the aircraft emitted a warning, was the left throttle retarded - but the right throttle lever was not moved from the "climb" position.

When the left throttle lever was retarded, this disengaged auto-throttle, so  the right engine started to spool up to "climb" power setting as commanded on the right throttle lever.

So immediately after landing the right engine wasn't producing any thrust.

The thrust only developed gradually during the following 12 seconds as the aircraft traveled down the runway.

Rudder authority

At landing the aircraft might be travelling at 140 knots. At this speed, deflection of the rudder by the pilot can still have significant effect and can counteract asymmetric engine thrust.

As the aircraft traveled down the runway, airspeed would have reduced and rudder authority gradually diminish at the same time as the right engine was spooling up to CL (climb) power.

The aircraft ran off the runway at about 90 knots.

Nosewheel steering

When using the rudder pedals for nose wheel steering, the steering angle starts to reduce at 40 knots and progressively reduces to zero degrees at 130 knots.

According to the accident report,

  When the accident happened, the volume of precipitation was 0.6 mm.

So a combination of speed and a wet runway may have reduced the effectiveness of nosewheel steering.

I don't know, but I suspect that nosewheel steering may not be able to fully compensate for the yawing effect of left engine at idle and right engine at climb power.

Differential braking

  The FDR also recorded the use of the rudder and the differential braking by the pedals as the aircraft veered to the left (probably in an attempt to maintain the plane on the runway and stop it).

It seems that the crew really needed to shutdown or idle the right engine to complete a landing within the boundary of the runway.


Why did the later versions of AeroVodocody L-39 Albatross find much market success? The Aero L-39 Albatros had great success in the past.

Why didn't the later versions of AeroVodocody L-39 Albatross find much marketing success in the post-cold war modern aircraft market, like Aermacchi M-346, BAE Hawk, Korean T-50 golden eagle, Hongdu JL-8, and so on?

It was, although it's not in widespread use.

The L-39 was developed into the L-59 and from that into the L-159 Alca. It's radar-equipped, can carry just over 5,000lb (2,340 kg) of air-to-air and air-to-ground weapons, and is in service with the Czech Air Force. According to Wikipedia, 72 were built between 1997 and 2003.

Given that it's an aircraft designed in the former USSR's influence, it's not unsurprising that it didn't get a lot of customers. Russia prefers to buy Russian; Russia's friends also prefer to buy Russian. America's friends are strongly encouraged not to buy anything that isn't American. And thus a small Czech single-seater is not likely to become very popular.


Would a airfoil move backwards if you rotate it vertical Lets say i have a wing with an engine attached to it like a propellor.
And now i point the nose of my airplane up untill it is vertical.

Would the wing still generate lift because of the air flowing past it. Resulting in a backwards movement of the entire airplane?

EDIT I am suggesting that the plane is hovering vertical not gaining or losing any altitude.

This may sound very vague, so here an image hopefully to make it clearer:

So just to clarify, the brown thing should resemble a propellor.
the yellow line the horizontal normal orientation of a wing.
and the red arrow the resulted direction of the airfoil.
and the green lines the airflow.

As you may have guessed i am not an expert when it comes to planes and the physics behind it all. So pls let me know if more information or clarification is needed.

A practical example of your question is when a model aerobatic aircraft with a conventional aerofoil profile (ie, not symmetrical) is fitted with a sufficiently powerful motor that it can be made to hover in the vertical position. This is quite a common trick.

The answer is yes, there is a force in the direction of the red arrow.

The model might drift in that direction, although there are other aerodynamic forces, torque, centre of gravity & thrust vector issues that will affect the balance, and these will change as power is increased and the model goes from hover mode to vertical flight mode.


What is the purpose of the air inlets on an A320neo's pylon (LEAP-1A)? What is the purpose of the air inlets on an A320neo's pylon (LEAP-1A)? Passive cooling, air bleed like in the 707, or something else?

It's not unique to the LEAP. You can find similar grills on the CFM56-5 and Trent 700, for example. That grill is the PCE's (precooler heat exchanger) air outlet.

Compressed (hot) air is taken from the engines (before combustion) for pressurization and air conditioning. This air has to pass through a PCE (cooled by air from the fan) before heading to the PACKs at about 200°C. The PCE is typically located in the pylon due to space constraints.

  CFM56-5 (A320) bleed users; source: slideplayer.com.br

The largest of turbofans don't have the PCE inside the pylon, and instead have them in the cold bypass stream (as shown below), as does the 737 due to its short pylon (or almost nonexistent pylon on the -3/4/500 series).

  Source: Boeing via leehamnews.com


Why is this chart called a Short Field Effort Takeoff Ground Roll and not simply a Short Field Takeoff Ground Roll? What does the word 'effort' mean in this context?

I think it is used in the same meaning as the maximum effort takeoff/landing (similar to @mins comment above). Maximum effort takeoff is used to reduce the ground roll/obstacle clearance distance. Maximum effort landing (or assault landing, as it is called) is used to reduce the ground roll after landing. This is mostly used for military aircraft, which may have to operate from small, improvised forward air strips.

This is alluded to in the PA-44-180 manual:

  In certain short field takeoff efforts when the shortest possible ground roll and the greatest clearance distance over a 50 ft. obstacle is desired, a flap setting of 25° is recommended.

This can also be figured out from the charts themselves. For Pressure altitude of 680', OAT of 8$^{\circ}C$, 8kt headwind and 3430 lb TOW, the normal TO roll is 920', while the short filed effort TO roll is only 800'. For the same specifications, the total distance over a 50' barrier using normal procedures is 1750', while using short field effort, it reduces to 1280' (All figures from the manual).

You can see a C130J demonstrating max-effort TO and landing here.


How can a Boeing 747 take off from Princess Juliana 7,546 ft runway? I recently read this article that talks about 747s taking off from Princess Juliana International Airport in Sint Maarten.

The Princess Juliana runway is only 7,546 ft, but according to Wikipedia, the 747 needs more than 10,000 ft of runway for take-off.

How can the 747 take off from Princess Juliana?

(Source: Boeing)

The approx. 10,700 feet Wikipedia figure is for a fully loaded 747 at sea-level. The lighter the plane, the less runway it needs. The 7,500-foot runway at TNCM allows a takeoff at 84% of the maximum takeoff weight. (Not taking into account any climb restrictions, such as the big hill over there.)

And as Terry pointed out, "ambient temperature also enters in. The cooler the air is, the more you can lift." And vice versa for a hot day.


How does a national ATC make money? I was reading last week of the public listing of the Italian ATC provider.

In the article it is said that

  If successful, the IPO would mark the first listing of a European national air traffic controller, although not the first privatisation.

and this got me wondering: how do they make money? Usually private companies are there to make a profit, do airlines have to pay the ATC providers?

It made me wonder also about possible impact on safety and security: I assume that this is in accordance to EASA rules, but is there any specific mention of "private ATC", or is it permitted simply because it is not forbidden?

In Europe, airlines pay so-called route charges for flying through national airspaces. EUROCONTROL, the European aviation organisation, collects route charges from their Central Route Charges Office, CRCO, and then distributes the money to the member states, who in turn will distribute them to the national air navigation service providers (ANSP's) - including private ones. The advantage of collecting route charges centrally, is that airlines only have to pay to a single organisation, in a single currency.

The charge for individual flights is calculated based on distance flown and aircraft weight, which are multiplied by a unit rate. The unit rates are determined by the individual countries - they are not the same across all of Europe. Unit rates are based on the actual costs for providing air traffic services, such as ATC, communication facilities, navigation equipment, meteorological information, aeronautical information service and so on.

Route charges do not apply to aircraft weighing less than 2 tonnes, state and government flights and search and rescue flights. Some states also exempt military flights, training flights, test flights, local flights, VFR flights, humanitarian flights, police flights etc.

You can read more about the CRCO here, and about how route charges are determined here.

Regarding your second question, I fail to see why a private ANSP should be any less safe than a government one.


Can TS-1 fuel be used in an aircraft that takes Jet A? Reading up on some airports in Russia I noticed that some only supply TS-1 jet fuel (see point 7) instead of Jet A. I tried to find out more about this fuel, but only saw that it has a lower freezing point and a higher flash point. What I couldn't figure out was if this fuel is "compatible" with Jet A. Could a plane that usually flies with Jet A operate with TS-1 instead, or vice versa? My guess is yes, but I couldn't find anything authoritative about this.

The answer is maybe.  You would have to check the Fuel System Limitations in the Operating Limitations in the AFM of the aircraft in question to find a table or list of the approved fuel types, which may or may not include TS-1, and if it doesn't you're kind of stuck.

For example, if I look up the allowable fuel grades for the CRJ700, it includes several worldwide standards (American, British, Chinese, NATO etc), and a fuel type is listed as "RT" under CIS (Russia's official name - Commonwealth of Independent States I believe).  But there is no listing for TS-1, so unless RT and TS-1 are the same thing and you have official documentation confirming that, it can't be used in the RJ (I'm retired and the pilot reference handbook I'm using is quite old and out of date so perhaps TS-1 is listed in current ones, but in any case you get the drift).

You can't use wide cut fuels in the CF-34 family (gasolene-kerosene) but if TS-1 is equivalent to Jet A there is a good chance it's approved for a particular airplane, but don't be surprised if there is a temperature limitation or other restriction.


What are the equations of motions for parafoils? I want to use the following equations so as to describe the motion of parafoil
$$\left[ {\begin{array}{*{20}{c}}{\dot x}\\{\dot y}\\{\dot z}\end{array}} \right] = {V_a}\left[ {\begin{array}{*{20}{c}}{\cos ({\gamma _a})cos({\chi _a})}\\{\cos ({\gamma _a})sin({\chi _a})}\\{ - sin({\gamma _a})}\end{array}} \right] + \left[ {\begin{array}{*{20}{c}}{{w_x}}\\{{w_y}}\\{{w_z}}\end{array}} \right],
$$
where ${\gamma _a}$ is a flight path angle, and ${\chi _a}$ is heading angle in horizontal plane.

$${\gamma _a} =  - arcsin \frac{{{V_{az}}}}{{{V_a}}}$$
and also

$${\gamma _a} =   arctan \frac{{{-1}}}{{{L/D}}}$$
The equations for lift force and drag force lool like these

$${\displaystyle L\,=\,{\tfrac {1}{2}}\,\rho \,V_{a}^{2}\,C_{L}\,A}$$
$${\displaystyle D\,=\,{\tfrac {1}{2}}\,\rho \,V_{a}^{2}\,C_{D}\,A}$$

according to paper https://lib.dr.iastate.edu/cgi/viewcontent.cgi?referer=https://www.google.ru/&httpsredir=1&article=1629&context=etd

But why the reference area $A$ and speed is similar for both cases? I think its projection should be rather smaller for drag force than for lift one.

But then on can make assumption that
$${\gamma _a} =   arctan \frac{{{-1}}}{{{C_{L}/C_{D}}}}$$
I don't understand why this is valid for parafoil

Anyway, I don't want to sink in rigid body physics and it will be comfortable for me to stay on next level of abstraction.

For my case the maximun lift-to-drag ration
$L/D = 4$ and the only information i know is the area of parafoil.
It's enough to characterize the simple model but i can't describe the change of speed caused by the change of lift-to-drag ratio due-to symmetric motion of control handles (breakes, srtopes? I'm not sure what defenition is correct). What is the equation that is responsible for the dependence of lift-to-drad ratio on symmetric motion of handles? Or is there other way to write down variation of velocty due-to handles lengths that allows not to consider forces? It would be appropriate if you know how it was done in X-38 parafoil.

In my opinion the shoud be the law like this
$${\gamma _a} = {\mathop{\rm artan}\nolimits} \left( {\frac{{ - 1}}{{L/D}}} \right) = f(\delta )$$ where $\delta$ is symmetric lenghth of each of two  control handles. But as I said I have only area of parafoil that is 400 ${m^2}$ and mass a few ton.

I don't want to sink in rigid body physics and it will be comfortable for me to stay on next level of abstraction.

Then I'm afraid you will stay stuck at your current level.

Your first equation is only a coordinate transform for the airspeed vector.

The reference area is just an arbitrary area. It makes sense to use the same area for all force components, and the wing area has been universally agreed for this. You will note that c$_D$ is quite a bit smaller than c$_L$ - why should the area be different?

When the same area and speed is used, you can calculate with coefficients just as if they were the real forces. This makes comparison between different speeds and different aircraft (or parafoils) much easier.

Regarding the effect of pulling on the risers (yes, that's the proper word): This changes both the load distribution and the local shape of the parafoil and is not easily expressed in a simple equation.


What are the pros/cons of ram air turbines? Commercial aircraft are equipped with ram air turbines that can be deploy to provide power in case all other sources of power are lost. Ram air turbines have the benefit of providing power as long as the aircraft is moving through the air. However, aircraft are almost always designed with internal generators, driven off of the engines.

There is a limited case of adding generators to older aircraft. But they are also used to power large accessories, like the jamming pods on the EA-18 Growler. The EA-6B, which the Growler replaced, was also a modified attack aircraft using jamming pods with ram air turbines. Larger aircraft that are modified for the electronic warfare role don't seem to go this route though.

Obviously the turbine will add drag, and it seems like internal generators are more efficient, since almost all aircraft are designed to generate power that way.

So my question is: what are the benefits or drawbacks of using ram air turbines to generate power? While they are generally saved for emergencies, what makes them more useful in cases like jamming pods, compared to other options?

You have kind of answered your own question. The down side to ram air turbines is they cause drag.

The up side is that they provide power outside the internal generating capacity of the aircraft (e.g., in emergencies when there is no power).

In the case a of a jamming pod, having its own power source eliminates/reduces the need to rely on internal power. That makes the pod modular. If the pod did not generate its own power, there would need to be a generator inside that sits there regardless of whether the pod were attached.


What is the definition of "Sideline" in reference to aircraft noise? The FAA has measured external aircraft noise levels and published the results in the Advisory Circular:

AC 36-1H - Noise Levels for U.S. Certificated and Foreign Aircraft

In the appendices, noise levels are listed for Takeoff (TO), Sideline (SL) and Approach (AP).

I understand the concept of Takeoff and Approach, but what is "Sideline"?   It is not defined in the document, nor does it show up in a search of the  Code of Federal Regulations.

The definitions are specific.
(They are defined in FAR Part 36).
I'm writing also the Take-off and approach noise definitions just for your information.

  Sideline noise: is defined and measured 1476 ft (450 m) from the runway centerline at a point where the noise level after liftoff is greatest.

  Take-off noise: is defined as the noise measured at a distance of 21,325 ft (6500 m) from the start of the take-off roll,
  directly under the airplane.

  Approach noise: is also defined and measured under the airplane when it is at a distance of 6562 ft (2000 m) from the runway threshold.

For each of these conditions the maximum noise level is a function of maximum takeoff gross weight, and for the take-off case the limits depend also on the number of engines.


Is it safe to fly ultralights at 6-7 weeks pregnancy? Are there regulations or official guidance regarding pregnant women flying ultralight aircraft at 6-7 weeks pregnancy (amenorrhea weeks)?

Ultimately the decision of whether or not a pregnant woman should be piloting an aircraft is between her and her doctor, and you shouldn't take the commentary of strangers on the internet as medical advice ("I am not a doctor, and even if I were I am not your doctor").

That said while I'm not sure what EASA has to say on the subject I know the FAA does not consider pregnancy to be a "disqualifying medical condition" for operations requiring a medical certificate, so it would logically not be disqualifying for operations which do not require a medical certificate (gliders, balloons, or ultralights) either.

Ultimately much of the advice out there comes down to "you can fly through the second trimester, and shouldn't fly in the third trimester" - assuming a normal and uncomplicated pregnancy, with the arguments against flying in the third trimester largely focusing on the onset of labor, obstruction of the flight controls, or difficulty with the aircraft's restraints (seatbelts).

Some specific concerns that have been identified for pregnant pilots include:

Inability to get full range of movement on the flight controls
If the pilot's "baby bump" is large enough to obstruct the free movement of the flight controls they probably shouldn't be flying an airplane.
This is a concern for all pilots with larger-than-average abdomens, but as pregnant women tend to enlarge quickly it's something they need to be aware of on each flight.
Onset of labor
All the women I know who have given birth have lead me to believe it would be rather difficult to simultaneously fly an aircraft and give birth, so it would be sensible to avoid single-pilot operations (including ultralight flying) late in pregnancy where this might be an issue.
Blood Clots
Sitting in the same position for long periods of time increase the chance of blood clots. This is a problem for all pilots, but pregnant women can be more susceptible to blood clots so flights should be kept short if possible.
Hypoxia
Mom is breathing for two, and physiologically the fetus has a priority claim on oxygenated blood. As a result pregnant women may require oxygen at lower altitudes, but this is not likely to be a concern for ultralight pilots as you won't be climbing that high.


Why $\frac{\Delta p}{\overline q}$ is depending by weight, flap deflection and other parameters? Which are other parameters? As you can see in this link (Roskam, Airplane Aerodynamics and Performance, Chapter 2.5.3 Airspeed corrections) ...

... in the first and second line of page 30 Roskam tells that, in hypothesis of incompressible flow $$ \frac{\Delta p}{\overline q}=\frac {\frac{1}{2}\rho_0V_c^2-\frac{1}{2}\rho_0V_I^2}{\frac{1}{2}\rho_0V_c^2} $$ " depends on factor such as weight, flap deflection and other airplane parameters ". Why does it depend on weight, flap deflection?

Which "other airplane parameters" do affect $\frac{\Delta p}{\overline q}$ ?

Note: for completeness of definitions, above in the same link, page 27  Roskam is defining:

"[...]  $V_I$ (IAS) is the indicated airspeed corrected for instrument error, $\Delta V_i$, only:

$V_I=V_i+\Delta V_i$      ________________$(2.54)$

$V_c$ (CAS) is the calibrated airspeed. It is equal to the indicator reading corrected for position error due to incorrect static port location $(\Delta V_p)$ and also corrected for instrument error:

$V_C=V_I+\Delta V_p$      ________________$(2.55)$ [...]"

The formulas deal with the relationshop between calibrated airspeed and indicated airspeed. The difference is due to two factors:

instrument errors: these errors occur within the airspeed indicator instrument when transforming the pitot pressure to a speed indication.
position errors: these errors are caused by the position of the pitot tube on the airframe causing the pitot pressure from being different than the freestream pitot pressure.

Since the pitot tube is usually close to the fuselage of the aircraft, the local airflow around the pitot tube is influenced by the aerodynamic properties of the aircraft itselfs. The pitot tube's location is chosen such the the local flow characteristics deviate as little as possible from the freestream characteristics but there will be a measurable difference in pressure between the freestream total pressure and the pitot pressure. The pressure differences depends on airflow around the aircraft which is infuenced by the angle of attack (and thus weight) flaps, slats, gear, turn rate, side slip angle etc.

In order to analyse the position errors during a flight test programme, test aircraft are often fitted with additional pitot probes protruding ahead the airframe and/or trailing cones (for static pressure measurement) far behind the aircraft.


How close to the envelope and the ideal was US1549 on ditching in the Hudson? I assume that for "water landing" an airplane should be configured for the lowest possible stall speed, and then flown to that speed before impact to minimize the energy to dissipate on impact.

What is that configuration for a plane like the A320?  E.g., full flaps?  Was UA1549 so configured?
How close did UA1549 get to the stall speed before impact?  If I understand this answer then the A320's fly-by-wire protection would not allow a pilot to stall the airplane, meaning that the Pilot Flying could pull full aft to nail that speed (without either pilot calling airspeed to avoid a stall, which I assume would be the procedure for a plane without a self-protection computer).
Was the ideal pitch for a power-out water landing known by the plane and/or the pilots?  Normally we "pitch for speed," and it would seem an unlikely coincidence for the stall pitch to match the ideal impact pitch.  Which pitch was higher?
If impact pitch was higher did the Pilot Flying have to account for this, flying above stall speed in order to permit an increase to impact pitch immediately before impact?

The configuration of the A320 for ditching with no engines running is CONFIG 3. I don't know how familiar are you with the flap configurations on A320, so I will start from the beginning. The flap lever has five positions: 0,1,2,3 and FULL (two configurations correspond to position 1-> CONFIG 1 and CONFIG 1+F).
In the CONFIG 3, which is the preferred method for ditching, the slats are extended to 22 degrees and flaps are down by 20 degrees. Config FULL, has slats down to 27 degrees and flaps down to 40 degrees. Look at the difference between flap deflection in CONFIG 3 and CONFIG FULL, that's 20-degree change in flaps. The 20-degree change will make a lot of impact on the drag of the aircraft and its vertical speed at the moment of impact. Therefore, CONFIG 3 is preferred. I must note that CONFIG FULL will not decrease the stall speed by a large amount: from my experience, it will decrease it by about 5 knots or a maximum of 10 knots. But definitely not more than that. The US airways flight 1549 had flaps down to CONFIG 2, below the ideal state.

If the ditching is performed with engine thrust, the suggested configuration for ditching is then, obviously, CONFIG FULL because we can trade engine power for the lowest possible approach speed which, for flight 1549, was not the case.

Flight 1549 was pretty close to the stall speed. On the video below you can see the approximate speed at the moment of impact. The exact touchdown speed was 125 knots.

With dual engine failure on Airbus A320, the aircraft will revert to alternate law, but due to the captain's fast reaction to turn on the APU, aircraft remained in normal law, assisting the pilot to not stall the aircraft. This does not mean that if the pilot pulls all the way back at such low altitude that no stall will occur. Upon landing/touchdown normal law goes gradually out and the FBW system introduces a nose-down pitching moment, so the pilot will not balloon the aircraft. In the last seconds before touchdown, the computer gradually returns to direct law, giving the pilot more feeling over the pitch. In this abnormal scenario, it is difficult to judge exactly what the FBW would do since this "reverting the pitch control to direct law" thing is characterized by the FLARE mode on the FMA, and I am not sure if the FBW system met requirements for that mode. If normal "reverting to direct law" occurred then the pilot would have been able to stall the aircraft just before the touchdown. If it did not occur, due to all abnormalities that occurred to the aircraft, the pilot would not be able to stall the aircraft.
The plane definitely does not know the correct pitch for ditching, neither what the crew was attempting to do. In ditching, the best pitch attitude for A320 is 11 degrees. In the answer that you linked, I can see that for 11-degree pitch attitude, the aircraft at the given weight is descending at -1 degrees, which makes the angle of attack equal to 12. Look the accident flight, angle of attack was 13 degrees, by the same analogy. That means that the aircraft was slower than ideal although the speed was 7 knots higher (due to the takeoff weight of the aircraft). The point is, given its weight the aircraft should have flown faster (than 125 knots) and the pilot should have pitched the nose of the aircraft higher, to match the preferred attitude of 11 degrees.
Stall pitch should be higher than the actual pitch for the ditching.


Is this legal for transportation in the US? (video in description) I wanted to make something like this, but I don't know if this is legal for transportation.

In class G airspace provided proper separation from people and buildings you should be good to go. The airspace you are in can be determined by geographic location and altitude using the FAA's charts you can find here.

  legal for transportation.

This is a somewhat broad term. The FAA may require you to get it set up as an experimental aircraft but thats up to them. If you plan to do more than hop around empty farms and over a pond you may want to contact your local FSDO for a ruling on what you can do. You can also reach out directly to the FAA for a ruling on a specific question.

The FAA as per

  § 1.1 General definitions.

  ....

  Aircraft means a device that is used or intended to be used for flight in the air.

does define what you show as an aircraft and would most likely see it as falling under their purview.

Note that since he is over open water he has a life jacket on board (although he is within the required 50 miles and technically does not need one). He also has a chute presumably for emergencies.


Does downwash increase or reduce lift generation? I’m wondering about the impact of downwash on lift generation. I've read that, because downwash creates lift according to Newton's third law of motion, increases in downwash due to greater AoA (especially when augmented by devices such as slots and slotted flaps, which use various aerodynamic effects to increase the amount of downwash generated) result in increased lift. But I've also read that ground effect increases lift by decreasing downwash, so I'm confused how this works. Can someone clarify the effect of downwash on the amount of lift generated and tell me whether I've got it right or not? Thanks!

Downwash is behind the wing and is the result of pressure differences between the top and bottom of a wing.  Although the energy conservation bookkeeping says the plane goes up and the air goes down, the main driver of lift is pressure differential.  True to Bernoulli, the angled bottom wing slows and increases air pressure beneath the wing.  This is "bottom lift" that even simple flat plates have.

Airfoils also deflect air upwards and away from the top of the air foil, creating additional lift above the wing.  Downwash is created by the movement of air from higher to lower pressure as the wing goes by, filling the void where the wing was.  This constant process is known as circulation.

Ground effect may not be directly related to downwash, but may be indirectly, as the ground and the downwash stream may create enough of a "fence" to slightly raise the pressure under the wing.  A Cessna 172 has a wing area of $174 feet^2$.

$174 feet^2 × 144 inches^2/foot^2= 25056 inches^2$

A pressure increase of 0.01 psi from ground effect adds 250 extra pounds of lift!

Ground effect is also said to be caused by the wing tip vortices being disrupted by their proximity to earth.


Is there a minimum level of lighting required for a runway to have an instrument approach? Is there a minimum amount or type of lighting, in the form of runway or approach lights, that must be present for a runway to have an instrument approach? I'm curious to know in the context of both the FAA and ICAO.

I have no idea about ICAO but as far as I can tell from the FAA's TERPS, there's no general requirement to have any runway or approach lighting at all (see below for an example), although some specific approach types (like CAT II/III ILS) do require it. Where there is lighting, it's used to reduce the visibility minimums, but the calculations assume no approach lighting by default.

This is from 3-1-2(c) (emphasis mine):

  Approach lighting systems extend visual cues to the approaching pilot
  and make the runway environment apparent with less visibility than
  when such lighting is not available. For this reason, lower
  straight-in (not applicable to circling) visibility minimums may be
  established when standard or equivalent approach lighting systems are
  present.

The TERPS concept seems to be that the approach minimums can be reduced depending on the lighting type available. Section 3-3-2 has an example of calculating visibility minimums when there are no approach lights available.

As for a specific example, MDO/PAMD (Middleton Island, AK) has three approaches (2 RNAV (GPS), 1 VOR) but - as far as I can tell - no lighting of any kind. The chart supplement says:

  Rwy 02–20 marked with rwy cones. Rwy 13–31 marked with cones and OTS
  lgts. Many missing.

As you might expect, the approaches are not authorized at night :-)

Finally, part 121/135 passenger flights can't land at night unless the runway is lit (121.590, 135.229), so any airport that handles those flights will have runway lighting at least, and almost certainly approach lighting too.


What kinds of jobs could a senior in high school get at a small local airport? Is there anything a senior in high school could do for a small regional airport in Utah?

Sure! When I was a senior in high school I had a job as a line boy at a local FBO. We refueled aircraft, cleaned aircraft and moved them in and out of hangars. Not the most glamorous job but it was the beginning of the never ending learning process of aviation.


How are special flight paths coordinated with ATC? I assume they have to enter a flightplan for this or do say just say "it's a test, please clear airspace for us around the complete US"?

Still flying and completing the right wing.

I would appreciate it with a 747-8, harder to draw :)

Rules for ATC in the US are laid out in FAA JO 7110.65.

  The primary purpose of the ATC system is to prevent a collision between aircraft operating in the system and to provide a safe, orderly and expeditious flow of traffic, and to provide support for National Security and Homeland Defense.

It's up to ATC to use their best judgment as to how to accommodate the requests of the pilots while keeping the system safe and expedient for everyone. Pilot requests can always be denied, but of course the pilot has the ultimate responsibility for the safety of their flight.

Since ATC is specifically required to support National Security, the military already has reserved areas charted, called military operations areas, or MOAs, and Restricted Areas. The military has priority in a MOA, and when Restricted Areas are in use non-military aircraft need special permission to fly there.

For civilian flights, they are less likely to get a completely reserved area. ATC needs to know where the aircraft will be so they can keep them separated from other traffic. If pilots want a block of airspace for testing, where they can turn, climb, and descend without asking permission every time, they typically need to find some airspace where they can stay out of the way of other aircraft. Companies like Boeing may have agreements with ATC about certain areas that are available for this kind of usage, often out over the ocean

For special tests like the one in the question, the pilots have to plan out their route. The filed route uses GPS waypoints to complete the pattern:

  KBFI SEA NORMY J70 MLP GTF 4632N/08706W 4626N/08908W 4301N/09715W 4352N/09907W 4358N/09958W 4306N/10033W 4245N/09958W 4229N/09834W 4122N/10101W 4254N/10552W 4312N/10730W 4314N/10848W 4302N/10919W 4235N/10907W 4157N/10820W 4112N/10654W 3932N/10210W 3717N/10133W 3757N/10243W 3803N/10323W 3702N/10401W 3633N/10320W 3604N/10117W 2827N/09937W 2652N/09820W 2814N/09844W 3438N/09829W 3538N/09819W 3745N/09715W 3610N/09249W 3533N/08953W 3148N/08837W 3126N/08754W 3503N/08731W 3457N/08616W 3539N/08713W 3809N/08411W 3820N/08458W 3642N/08915W 3804N/09148W 3935N/09604W 4143N/09442W 4230N/09354W 4601N/08829W 4631N/08706W KBFI

The pilots must stay on their cleared routing and ATC will do their best to accommodate them. Of course if safety becomes a concern ATC may have to deviate them from their pattern. But knowing the flight path ahead of time, ATC should be able to have other flights in the area out of the way without much trouble.

This flight in particular was done overnight, when air traffic is lightest, which would have made separation much easier. Also, a lot of the path is in the western US, which also has less air traffic. Towards the end of the flight, once more fuel was burned off, the flight climbed to FL400 and higher which would have taken it above most other traffic. All of these factors would make ATC more likely to accommodate this sort of strange routing.

There are many other examples of this sort of thing:

787 and Boeing
logo
737 MAX
747
747-8
Seahawks
Gulfstream
Cessna


What are those in the belly of a 747? In the next picture what are the items circled in red?

Photographed by Adrian Pingstone in August 2002 and released to the public domain.

The forward ones are a ram air inlet (NACA duct) for the Environmental conditioning System (ECS) and what looks like an antenna. The aft one is an exit louver for the ECS.


What type of airfoil do low-supersonic aircraft use? I understand that supersonic airfoils have better performance supersonically, but it seems at if they are not always used for any aircraft that goes supersonic and that supercritical airfoils are often used instead. What Mach number or other quality determines whether a plane will go with supersonic or supercritical airfoils?

Normally, supersonic fighter wings for which airfoil information is published use a very thin NACA 6-series section with very little camber, such as
Aircraft                root airfoil      tip airfoil
McDonnell Douglas F-15  NACA 64A006.6     NACA 64A203
General Dynamics F-16   NACA 64A204       NACA 64A204
Lockheed-Martin F-22    NACA 64A?05.92    NACA 64A?04.29

This information is from The Incomplete Guide to Airfoil Usage by Dave Lednicer. As you can see, the F-16 uses camber throughout, indicated by the 0.2 design lift coefficient of the airfoil, while the F-15 uses an uncambered root airfoil.
Those airfoils are chosen because flow around them at supersonic flight speed is still heavily influenced by subsonic flow characteristics* as long as wing sweep allows for a subsonic leading edge. This produces nose suction which is very helpful to keep drag down. Delta wing aircraft enhance this nose suction by cambering the outboard leading edge (conical camber).
Common to all supersonic wings is their minimization of wing thickness, because wave drag will grow with the square of thickness. Typical sections use a relative thickness between 4% and 6%. In case of the F15, thickness varies between 6.6% at the root and 3% at the tip.
Supercritical airfoils work best in a narrow Mach and angle of attack range and are used for transsonic designs (flight Mach number between 0.7 and 1.0). Fighter aircraft with their wide variety of speeds and angles of attack will rarely profit from using them. The strongly negative pitching moment of supercritical airfoils (resulting from rear loading) makes them unsuitable for most fighter designs.
Supersonic airfoils are reserved for designs with a supersonic leading edge, like the F-104 or X-15 wings and tail or the XB-70 canard. They are only used if top speed exceeds Mach 2.2 and the sweep necessary for a subsonic leading edge would be too high for decent subsonic performance.

* For those with a severe problem of reading comprehension: Of course the flow over a swept wing is supersonic when the airplane moves at supersonic speed. Only the behavior of the flow is like that at subsonic speed as long as LE sweep is higher than the Mach cone angle.


Is there a standard term for "3D groundspeed"? Does the term "groundspeed" always refer only to the magnitude of the horizontal component of an aircraft's velocity vector with respect to the earth, or does it sometimes include the contribution from the vertical component of the aircraft's motion?
If the latter, what are some examples (from outside sources) of the terminology being used this way?
If the former, is there a standard term for the magnitude of the aircraft's full three-dimensional velocity vector with respect to the earth, including the contribution from the vertical component of the aircraft's
motion?

The former is correct; an F-16 climing straight up has 0 groundspeed.
"Inertial velocity" would accurately describe the 3D motion you're describing.


Is Fluid Structure Interaction considered in aircraft design? Fluid Structure Interaction (FSI) causes an  aeroplane’s geometry to change and hence the forces on the different surfaces of an aeroplane become different than the forces expected according to initial calculation.

Is this Fluid Structure Interaction considered while calculating
forces (and hence the final design) of aircraft while finalizing
the designs for aircraft?
If it is considered, what are the available software packages which could be used to analyse this?

Just one example: Good designers put the aileron pushrods away from the elastic axis of the wing to enable the deformation of the wing to create a damping deflection of the ailerons. This is especially helpful for high aspect ratio wings:

When the wing flexes, the pushrod will not be compressed, so will become relatively longer than the surrounding wing structure. This will create a negative aileron deflection which works against the lift force which flexes the wing in the first place. Doing this is particularly helpful in damping wing flutter.

Generally, the engineers make sure that every aircraft component works as intended even when the structure is deformed. Another example: To compensate for differences in the thermal expansion of different components, pushrods in glass fiber fuselages have two halves, connected by a pivoting lever, so that changes in their length will compensate.


How do splayed wingtips work? I need to know more about the "splayed wingtips" design made by Airbus in their latest conceptual design "birds of prey".

How would wingtip vortices work on this plane? How are they reduced by the splayed wingtips or the feathered tips?

Splayed wing tips are like .... Fowler flaps.  Totally useless for cruising flight unless .... you want to try the "coffin corner" at perhaps 60-70,000 feet.  The best wing for cruising remains the high aspect albatross style.  However, they may wish to fold them back in cruising flight.
The writer had imagined this for the Etrich Taube.  Unfolding them on approach would greatly reduce the probability of tip stall and make lots of drag.  Strictly a low speed gimmick.  (By the way, slats also do this very well, actually helping high AOA pitch control).

However, the design does hold some interesting concepts:  no vertical stabilizer AND a high wing mount.  Sort of a fuselage mounted on a flying wing with an Hstab for better control.
These concepts, along with engine mount location, bear further study.  The rest is for the birds.


Where are the circuit breakers on the 787? (787 left, 777 right)

Normally found aft of the overhead panel, where are they on the Boeing 787?

The cockpit is clean and uncluttered thanks to the absence of the large circuit breaker panels that we’re used to in traditional types. Almost all circuit breakers are ‘virtual’ and are accessed via the forward Multi-Functional Display (MFD).
— flight.org

The 787 and its contemporaries have moved away from physical CB's and use virtual CB's instead.

One of the more dramatic simplifications of the 787 flight deck is a result of the 787’s “more-electric” architecture. Remote power distribution allows for the use of electronic circuit breakers, eliminating hundreds of physical circuit breakers from the flight deck. Flight crew awareness of system state is enhanced with visual information on every circuit interruption device, including those remotely located, via multifunction display (MFD) screens.
The reduction in parts and improved design means lower operating costs and higher reliability. For example, the 787 requires just 13 line replaceable units (LRUs) to provide a full complement of flight deck display, communication, navigation, and surveillance capability. That’s about half as many LRUs as other models require for the same capability.
— boeing.com

(Click image to enlarge) Example of CB sorting by system and different states.


Where can I get a picture of a specific aircraft by registration? I'm actually building a website where I want to display pictures of a specific aircraft. So I have the registration and I would like to show a picture next to each registration. For example I have the registration: A7-BCW

I want to get the picture in a way like this:

website.com/a7-bcw.jpg

Is there any site where I can do this and where I'm allowed to use the pictures for my site (watermarks are OK and I would also display the copyright information)? Of course there is no site where I can look up every aircraft around the world, I just need it for the common airlines like Qatar, Emirates, Singapore Airlines, Delta, United and so on.

Have you checked what data is used at flightradar24.com (http://www.jetphotos.net)? Probably only commercial airliners, though.


What are the requirements of ferrying a spare engine? It was not uncommon in the 60s and 70s to have B747 ferrying a spare engine.

(source: Australian Aviation)

Was that allowed only on aircraft specifically designed with a pod, or was that possible to add the equipment on any B747. What is the regulation applicable? (in the US for instance).

Additional question: is this still commonly used today in civil aviation?

It's a manufacturer option on some larger planes - basically adding a bit of structure and some attachment points. And it's expensive enough that airlines think about it.

Today's engines are much, much more reliable than the ones used in the 1960s so the need to move engines around by bolting them on to the next thing going that way is not what it once was. There is also a larger air cargo market, and it's likely cheaper in general to put the replacement on a pallet rather than under a wing.


What drives the compressor before the turbine provides power? I understand that the power extracted from the turbine is used to drive the compressor which sucks and squeezes air sent to the combustion chamber, and the cycle continues.

But initially the compressor has to suck in air! What drives it at this stage before the turbine takes over?

Turbine engines are spun up to idle speed using a starter.  This is typically in the form of an electric motor for smaller turbine engines and APUs and pneumatic powered starters for large turbine engines.  Once the gas core is spun up to a minimum speed, typically around 12-20% maximum core speed, fuel is introduced and ignited, causing a self sustaining combustion and the engine core spins up to its idle speed, typically about 50% - 60% maximum speed, before the starter cuts out.  Care has to be taken not to introduce fuel to the engine prior to reaching these speeds as the engine can overheat during startup and be seriously damaged (this is about the only disadvantage of aviation gas turbines).


How can I find out what time an airport was closed due to weather? Where do I find at what time an airport was closed, due to inclement weather, on a specific date? I completed the first leg of my flight, which was one hour from take-off to landing. When I arrived in my connecting city, my final destination airport was closed due to weather conditions. Why did they not cancel my entire flight before I departed on the initial leg of the flight?

The best way to get that information would be to call Airfield Operations at the airport in question.  They can tell you what time the airfield was closed, IF it was the airport itself that was "closed" in that situation.  Oftentimes, however, the field itself isn't technically closed, but the weather was simply so bad that nobody was getting in, and that gets discussed as "the airport is closed" due to weather.  Not technically accurate, but close enough for discussions of "can flights get in there or not."

As for what happened before you left for your connecting city, all sorts of answers are possible.  Perhaps the weather wasn't that bad initially, and it looked like your connecting flight had a good chance of going.  Or perhaps "the system" slipped up, and they should have notified you that the connecting city was as far as you'd be likely to get, and they didn't.  Or perhaps there were PA messages made to that effect that you didn't hear. (It happens.)

Also, an airline wouldn't cancel the flight to the connecting city, since some passengers presumably were trying to get there as their destination, and others had other connections to make to cities that weren't affected.  What could happen if they knew early enough that your second flight wasn't going to go, and recognized soon enough that "this passenger won't get where they're going today", is they'd advise you of the situation, and offer you the option to cancel your trip, rebook the next day, or get to the connecting city so you're that much closer when the weather has passed & flights resume.  Depending on multiple factors, any of those might be a reasonable choice for a passenger to take, so they offer the options, rather than unilaterally cancelling your ticket.

It's also possible that the airport itself made some sort of call that "we're closed" at some point after your first flight had taken off, surprising the dispatchers at the airline.  In that case, you are, plain & simply, out of luck.  Not desirable, but in the millions & millions of airline flights and hundreds of millions of passengers flying every year, it sometimes happens.

Reviewing the weather reports for that timeframe from someplace like Weather Underground might shed light on just how bad the weather was, and when the forecasts were amended.  Making sense of that would require some familiarity with aviation weather reporting formats, though.


Are aircraft transferable between companies with different Air Operator Certificates? Can Company A use Company B's aircraft if the two companies are not on the same Air Operator Certificate (AOC)? Company A will provide the crew. This would be a transfer of equipment use with no transfer of ownership.

The aircraft in question happens to be a medical emergency helicopter.

The answer to this will depend on what the two company's Operation Certificates allow and forbid in the Operation Specifications (Ops Specs). All Ops Spec examples provided below represent FAA examples, are examples only, and may differ from those in any specific situations.
Considerations will include:

Aircraft Authorization
Operational Control
Maintenance
Crewmember Requirements

The Ops Specs will specify in A003 which aircraft and configurations are authorized for use, for example:

A003 . Aircraft Authorization
The certificate holder is authorized to conduct operations under the provisions of Title 14 CFR Part 135 using aircraft with the approved configuration and operations described in the following table:
[table omitted]

If the available aircraft is of a type and configuration authorized for use, then it may be possible to use it. This will most likely be the case if the aircraft is of the same type and configuration, and in the same class/category of operation as those aircraft which Company A already operates.
Ops Spec A008 will probably specify that the certificate holder shall not:

Engage in any arrangement with an aircraft owner, lessor or any other person or entity [...] which allows the use of an aircraft for operation under these operations specification without a complete, effective and sustainable transfer of operation control to the certificate holder for all Part 135 operation conducted under these operation specifications.

The lease agreement must provide Company A with complete, effective and sustainable operational control of the aircraft.
Additionally, the aircraft must conform to the extensive maintenance requirements required by Part D of the Ops Specs.
The flight crewmembers must also be trained and approved for the aircraft. However, if the aircraft is of the same type and configuration as those already listed in A003, this requirement may be easily met.


Why does TCAS not issue turning commands as Resolution Advisory? The TCAS (Traffic Collision Avoidance System) is capable of issuing RA (Resolution Advisory) when a mid-air collision is imminent by telling the pilots to "climb", "descend", "increase climb" etc.

Why does the system only issues commands in the vertical direction, but not the horizontal direction? It seems an oversight in the design of the system to not make use of all available maneuver options to resolve a traffic conflict. Why can't the system tell the pilots to "turn left", "increase right turn" etc.?

TCAS gets fairly accurate altitude information from the same source as the transponder. Thus any extrapolation from this information can yield a fairly accurate prediction of whether two aircraft may collide, and provide more certainty that changes in altitude will avert any conflict.

Range information is obtained by measuring the round trip time of the interrogation and response. This will also be fairly accurate.

Direction information is obtained by using the TCAS antenna to detect the direction of responses from other aircraft.

These values are then extrapolated to provide an expected path of other aircraft. Most airliners are required to use TCAS II which only provides the vertical guidance. TCAS III was envisioned to provide horizontal guidance as well, but:

  it was judged by the industry to be unfeasible due to limitations in
  the accuracy of the TCAS directional antennas.

Even if TCAS can be accurate to 3 degrees in direction, this translates to over 300 feet of uncertainty at 1 nmi.

TCAS IV was planned to use more accurate GPS information, but with ADS-B becoming more widely adopted, this development was stopped in favor of some future system that can use existing ADS-B technology.

Another point is that airplanes are generally larger in the horizontal plane than the vertical, and thus would need to change course more horizontally to avoid collision than they would need to vertically. Especially as planes get larger, they also tend to be more maneuverable in pitch than in turns.


What military aircraft has six propeller engines? Today, in south-east Scotland, I saw a plane that looked a bit like a Hercules but had four pods on each wing. I'm pretty sure that three of them were propeller engines and the end one was something else. They all looked a similar size. Height was lowish but not very low and it did not show up on flightradar24.  I could not discern colour. I didn't get much of a look as I rushed in to get binoculars and it was well past and banking to the right when I got out again.

You've probably seen a tanker variant of the C-130, like this KC-130J:

Source: https://www.thedrive.com/the-war-zone

On each wing there is an extra fuel tank and the pod containing the air-refueling hose.


What would happen if I had a type rating for an Airbus A320 and applied for an airline that has an A320 and other aircraft? Let's say I have a type rating for an Airbus A320 and applied for lets say delta. So we know that Delta has an Airbus A320, Airbus A330, Boeing 737, Boeing 777, etc. Suppose I have an Airbus A320 type rating and I applied and passed the interview and everything, will they automatically assign me to the Airbus A320 considering I already have an Airbus A320 type rating , or not? (By Airbus A320, I mean the Airbus A320 family which include the A318 A319, A320, A320 neo, A321, A321neo)

No. You'd take the same initial course as everybody else, learning that airline's procedures & checklists for that aircraft.  Having a type rating shows the hiring people that you're able to pass the training course & checkride for that level of aircraft, and that's good to have. But beyond making the aircraft systems part of the syllabus easier for you, having the type won't change your training.

It also probably won't affect which aircaft you initially get. Those are based on where the airline needs pilots, and then (typically) on some sort of bid process. The airline presumably expects all its new pilots to be able to complete whichever training course they get, so your type and/or prior experience is unlikely to drive your initial assignment.

For a new, small airline in need of hiring captains off the street, things might well be different.


Why are landing fees at large airports based on weight? KORD airport for instance charges domestic vs international arrivals differently.

I could see that this may have something to do with imports/taxes/tariffs etc, but why are the landing fees measured in \$ per 1,000lbs?

From Anne Graham's book, Managing Airports:

  This charging mechanism uses the ‘ability to pay’ principles, since
  airlines using larger aircraft are in a better position to pay higher
  charges. Some costs such as runway wear and tear do increase with
  weight and also larger aircraft require vortex separations, which can
  reduce the number of aircraft movements during a certain period.
  Overall, however, there is not a strong relationship between aircraft
  weight and airfield cost. A flat rate landing charge for all aircraft
  types may be more appropriate, particularly at congested airports.
  This is because the cost of occupying the congested runway is movement
  related and independent of aircraft size. Each aircraft movement will
  consume the same resource.


What is the cost of the engine Boeing 747 Model 400? What is the cost of the engine Boeing 747 Model 400?
Including what component of the cost of the aircraft engine Gies

The actual prices paid for an engine are likely to not be released publicly. However, list prices are advertised, and other sources may help give an idea of the price range for such engines. The 747-400 model has three engine options available: PW 4056, GE CF6, and RR RB211. These engines are also used on other aircraft, which will help in finding the prices.

The CF6 engine has a list price of about $11 million (from an A330 order in 2009, higher thrust version; \$12.2 million in 2015 USD1).

The PW4056 engine has a price of $5.8 million (from a 1994 report; \$9.3 million in 2015 USD).

I haven't found good pricing for the RB211. An older, lower thrust version was priced at £340,000 in 1971 (\$4.8 million in 2015 USD2), or you could buy one right now for $35,000 (the seller hopes it can be put on display, mentioning "very high end art displays" but also "top dollar in scrap").

The list price for a 747-400 was about \$240 million, which means that 4 engines at a list price of \$10 million each would be about %17 of the cost of the plane.

1Inflation calculator
2exchange rate


Where can I find regulations in different countries for flight level rules based on direction of flight? I'm from Brazil, and here we use the West/East rule, so we use an odd flight level when we fly between 0/360 - 179, and when we fly between 180 - 359 we fly in an even flight level.

But what should you do in other countries? Where I can find those rules?

I've heard that in Europe it's totally different, and that in some countries in Asia they use meters, instead of feet.

Where can I find this information?

Every country's Civil Aviation Authority issues an Aeronautical Information Publication (AIP) as part of their Aeronautical Information Services (AIS) which contains the information you are looking for. Most likely the information about Flight Level rules will be contained in the GEN (General) or ENR (En-Route) section. For Europe, most information from the AIP's can be found through the European AIS Database


What scientific evidence is there about the effectiveness of pre-flight walk-arounds? As a student pilot, often on my walk-around, I get the impression that there are any number of hazards that could pass me by, simply because I can look at every part on the checklist but I wouldn't necessarily recognise a problem with that part. This idea seems more plausible when I speak to more experienced pilots of the same type, and each of them warns me about checking one thing in particular that's not on the checklist, because they once saw an accident that was caused by a failure there - and crucially, each of them warns me of a different thing.

At the same time, when I read the monthly accident report bulletins, there are several every month where the cause was some part failing in flight, and they either imply that the failure should have been caught in a pre-flight inspection, or they explain why it might not have been visible. In one local incident a few months ago, a pilot made a hard landing and thought he made an extra-careful inspection afterwards, but made a subsequent flight without noticing that both blades of the prop had been shortened and the firewall was crumpled. More generally, taking off with your pitot cover still in place is the stereotypical example of a bad inspection.

Pre-flight inspections seem very error-prone, on the face of it. What evidence is there about how error-prone they are, and what fraction of defects they detect? I'm asking for either scientific experiments under controlled conditions, or statistical analyses of aircraft grounded after unsatisfactory inspections vs. failures in flight. Turning the question around, you might instead answer about how much less safe we would be in GA or air transport if we didn't have pre-flight inspections at all. This related question is pretty relevant, but focuses on checklist items which are forgotten completely: I'm hoping for a more general answer which also includes defects that are not detected even if the checklist is performed correctly.

First off you are required by the FAR's to preform a preflight check,

  Sec. 91.7

  Civil aircraft airworthiness.

  (a) No person may operate a civil aircraft unless it is in an airworthy condition.

  (b) The pilot in command of a civil aircraft is responsible for
  determining whether that aircraft is in condition for safe flight. The
  pilot in command shall discontinue the flight when unairworthy
  mechanical, electrical, or structural conditions occur.

Don't forget the Preflight is also about making sure the aircraft is legally airworthy (VFR or IFR minimum equipment) as well as being physically airworthy.

Here is a brief from the FAA on the matter. It has at least one example of an accident that occurred as a result of a bad preflight. According to this Flying Magazine Article 15 accidents have been the result of a bad preflight in the past 10 years (from the publish date of that article). Here is another example as well. Clearly it has lead to accidents in the past but you may have an issue finding any data on times that it has found things and potentially saved lives (as that is often not reported to anyone but the mechanic).

Nasa conducted a study on checklist usage (preflight included) which is along the lines of what you may be looking for.

Here is another FAA article on preflights and has some more specific stats on what you are looking for.

  Consider this: NTSB aviation accident data show that in the last 10
  years, poor preflight inspections caused or contributed to 156 general
  aviation accidents and resulted in 41 fatalities.

You can compare that to the total number of other GA accidents for an approximation of how important it is in causing a crash. of When it comes to the FAA a great deal of analysis is carried out on accident data not necessarily preemptively. One of the other analysis issues here as mentioned in the comments is much of the reasons that planes get grounded does not get reported to any official authority (aside from the mechanic) so the data may not be public or easily accessible.

If we include preflight checklists and walk arounds in the same category. Following the Northwest 255 accident that was the result of misunderstanding/misusing pre-flight checklists the NTSB did do a study on preflight (and all checklist) procedures. You can find the study and results report here which includes some stats.

  This idea seems more plausible when I speak to more experienced pilots
  of the same type, and each of them warns me about checking one thing
  in particular that's not on the checklist, because they once saw an
  accident that was caused by a failure there - and crucially, each of
  them warns me of a different thing.

This may be more a case of correlation over causation. If you are involved in aviation long enough (especially the older generation that has flown when laws and planes were much different) you see lots of things. Some of the issues they talk about may have been covered by AD's since they encountered them (if you are flying a common airframe like a 172 or PA-28).

As for not finding stuff this will come with how well you know your plane. As you start to fly the plane more and more (you should be training in one plane or at least only one type of plane). Eventually you will begin to know whats where, the POH can help with that, and you will be able to recognize if something is out of place.

I can speak from personal experience that I have delayed many flights due to things I have found on the preflight. I had a cracked cowling bracket, countless low gear struts that needed air, many fuel calls in the rental planes, a fuel vent issue, and one breaks issue.

Of course you will always have human factors present in manned flight.


What is the relationship between STARs, IAPs, and feeder routes? From what I understood, if I want to do some approach procedure, I need to get to the waypoints marked at the STAR chart, and then I go to the IAF marked at the IAP chart through the feeder route. After reaches to IAF, I can make the approach as published.
Is the relationship between STAR, IAP, and feeder route correct?

Definitions
From the FAA's Pilot/Controller Glossary, an instrument approach procedure (IAP) is:

A series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing or to a point from which a landing may be made visually.

A feeder route is:

A route depicted on instrument approach procedure charts to designate routes for aircraft to proceed from the en route structure to the initial approach fix (IAF).

A standard terminal arrival (STAR) is:

A preplanned instrument flight rule (IFR) air traffic control arrival procedure published for pilot use in graphic and/or textual form. STARs provide transition from the en route structure to an outer fix or an instrument approach fix/arrival waypoint in the terminal area.

So you can see that a STAR and a feeder route serve the same general function: to allow IFR aircraft to transition from the en route structure (meaning Federal airways, the Victor, Tango, J- and Q-routes) to the beginning of an instrument approach procedure. The major difference is that STARs are published for busier airports to make things easier and more predictable from ATC's point of view; a STAR can contain any number of waypoints/fixes and, more importantly, can have altitude and speed restrictions pre-published at those fixes so ATC doesn't have to issue them to each individual arrival.
Example
Let's look at the ILS Runway 11 approach into Portland International Jetport (PWM). We can see that there are three Initial Approach Fixes: Kennebunk VOR/DME, BUXTO intersection, and PARSO intersection. If you can somehow navigate to any one of those three fixes, you can follow the approach procedure to safely get down to the ground (or at least pretty close to the ground).

Now say, for example, you're navigating via V93 from the southwest. When you reach CON you could continue to follow V93 to ENE and start the published approach by flying on the ENE030 radial to BUXTO and performing the hold-in-lieu-of-procedure-turn. But that takes you rather out of your way, so if you could you'd rather start the approach at PARSO and avoid having to perform a procedure turn.
Well, PARSO is on V3, so you could fly CON.V93.SATAN.V3.PARSO. But that still isn't the most direct route.
Happily for you there's a published feeder route starting from CON! When you arrive at the VOR/DME you leave the airways and navigate on the CON067 radial directly to PARSO. Hooray!

Enroute L-32 IFR chart

This plan might work if you were flying a Skyhawk at 5000 feet. But say you're flying Southwest 1982 from Baltimore, descending out of the flight levels at 250+ knots. ATC would rather have you flying a certain procedure that's the same as all the other jets coming in to Portland, and your dispatcher knows this—so they've filed for, and ATC has cleared you via, the SCOGS THREE arrival.

Some time before you reach SAACO, and probably long before then, ATC will tell you to expect Runway 11. Therefore, when you reach SAACO, you will make a left turn towards BIDDE and continue following the published route until you reach BUXTO. By this point ATC has cleared you for the ILS Runway 11 Approach, so you transition from the STAR directly onto the instrument approach. Note that you arrive at BUXTO on a track of 081, meaning you only need to make a 29º turn to intercept the localizer (track 110).
A different example
The SCOGS arrival is designed to get you from the enroute structure down to the ground with little-to-no ATC intervention. But at many even busier airports, the arrival will not smoothly transition onto an instrument approach. Instead, you will depart the final fix on a published heading (likely the radar downwind heading) and expect vectors to final from ATC. This allows ATC to give you extended vectors, or shortcuts, as necessary to account for the mixing of different arrival streams. The arrivals into Charlotte/Douglas International are like this, for example the CHSLY FOUR:

If you're landing Runway 23 the arrival has you navigate to JEPHS, the initial fix for the ILS approach for that runway. But if you're landing Runways 18 you come off the arrival on a heading for a left base, while if you're landing Runways 36 you're on a heading for a right downwind.


Why do DC-4 landing performance charts have different values for the intended and alternate destinations? I am studying the landing performances of the old Douglas DC-4 and there are a lot of different landing performance charts available. The pilots can use different flap settings during landing like 45, 35 and 25 degrees. For these different flap settings there are different charts. But there are also different charts for the Intended and Alternate destinations. Can someone explain to me why there are different charts for these?

How can the landing performance be different just based on intended vs. alternate? For example, in the charts for intended destination it says 60% of runway length and for the alternate destination 70% of runway length.

Runway length = landing distance / 60%

For the DC-4 there are two sets of landing performance charts. The first one is the landing distance. The other one is the minimum effective runway length, for the intended and alternate airports separately.

From a 1982 NTSB safety recommendation:

  The Safety Board recognizes that changes in the landing distance demonstration procedures during certification could result in penalizing the operational specifications of the airplane as they are presently determined using the existing minimum landing distance procedures. For actual line operations on dry runways, a safety margin is currently provided by the operational limitation of 14 CFR 121.195 which requires that the minimum effective runway length be the airplane's landing distance as determined during certification divided by 0.6 (or multiplied by 1.667). The Safety Board's accident investigation experience has not indicated to date that the actual runway lengths used in line operations for dry runways do not afford a proper level of safety. Safety Board recognizes that a change in the aircraft certification criteria specified in 14 CFR 25.101 and 25.125 will necessitate a corresponding review of the operational limitations in 14 CFR 121.195 so that operational specifications are not unjustifiably penalized. Of course, we are not suggesting that current runway length requirements be compromised to the detriment of present levels of safety.

The rules have changed since the DC-4 days. The related regulation I found applies to turbine aircraft, see: 14 CFR 121.195.

The 60% and 70% are an added factor of safety, which as the above text shows, limits the operational capability of the aircraft.

Dividing by 0.7 reduces the effective length required for the alternate compared to the intended stop, my understanding for the shorter runway length is to allow an easier selection of alternate airports, especially when the fuel maybe running low and the nearest airports are not of particularly long lengths.

The effective length charts make it clear that the 0.6 or 0.7 are already accounted for and need not be applied again. They would be manually applied if the crew are using the landing distance charts.

The crew would start by the expected landing gross weight. It will be heavier at the intended stop due to carrying the alternate fuel. Then the pressure altitude, and finally via the reported headwind, the required effective length is known.

Related: How to calculate the DC-4 landing distance with this graph?


Why is the de-icing fluid sprayed on jets coloured orange? On a cold night or if it's been snowing, jets are sprayed with orange de-icing fluid:

But why is it orange?

If it's to see where's been sprayed and where you've missed a bit, black would be the most contrasting colour on white; while yellowy-green is the strongest/most visible colour to the human eye; and blue is the least affected colour for colour-blind people.

Just curious as to why orange.

There are actually two types of de-icing fluid, one is orange and one is green. According to a product safety sheet for one brand:

  The dye is intended to indicate which parts of the  aircraft have been
  treated and to differentiate between fluids (Type I fluids are orange,
  Type IV  fluids are green).

As to why orange and green, presumably they aren't easily confused with other liquids used around aircraft. Black would look like oil or another fluid if it pooled on tarmac, hydraulic fluids or oils are often yellow/green in colour and blue is a very common colour in aircraft painted liveries. So I guess that orange and green were sort of the ones 'left over' after all the other obvious colours had been considered.


How do I make a simple model to simulate a banked turn? I'm attempting to make a game similar to Ace Combat, and I'm still confused about banked turns, namely the speed of bank turning depending on the aircraft's roll.

Can I assume, for simplicity's sake, that it's something like $Rgy = K * Rz$, where $Rgy$ is the rate of turning on the global Y axis (the banked turn's angular speed), $Rz$ is the roll angle of the aircraft, and $K$ is a constant? And if I can do so, how do I calculate $K$?

It's computed with centripetal force:

$$F_C = m \cdot V \cdot \omega $$

m = aircraft mass [kg]
V = aircraft speed [m/s]
$\omega$ = rate of turn [rad/s]

Centripetal force is a function of bank angle $\Phi$ and lift, or mass and flight path. For a coordinated, level turn:

Vertical lift $L \cdot cos(\Phi)= m \cdot g$ and turning lift $L \cdot sin(\Phi) = F_C$, so in a steady turn

$$ F_C = m \cdot g \cdot tan(\Phi)$$

$$\omega = \frac{g}{V} \cdot tan (\Phi) \tag{Steady Turn}$$

A more general equation, also valid for 90 degree bank angles and not concerned with the aircraft staying up in the air, can be found by considering horizontal forces only:

$$ \omega = \frac {L \cdot sin(\Phi)}{m \cdot V} \tag{always} $$

And then if you assume that lift L is still equal to weight $m \cdot g$ which means the aircraft is losing altitude in this turn, you're almost back at the Steady Turn equation but now with a sin instead of a tan.

The above is for SI units. For aircraft units with feet and knots, please check this answer, and here is one that introduces lift coefficient into the equation.


What does it mean when a track "straddles north"? Have heard a couple controllers taking note of a track that "straddles north".  What do they mean?

According to Google, the definition of the verb straddle is to extend across or be situated on both sides of.  Cannot see how this would relate to a track.

So the problem is that cruising altitudes are assigned based on heading E or W. If the desired track is within a few degrees of north or south, the heading needed to maintain the track could 'straddle' north or south. With some tracks/wind combinations two aircraft flying the identical route at different airspeeds could fall into opposite hemispheres. Traffic in the reverse direction has the same issue, possibly resulting in opposing traffic at the same altitude. So which altitude do you assign/use?


Why do airlines have geographical names in them? Why do airlines name themselves for example "Cathay Pacific" or "Virgin Atlantic". Aren't they indirectly limiting themselves to always fly over "Pacific" or "Atlantic"? It would be weird if Virgin Atlantic flies over Pacific and vice versa.

In a lot of cases it's because they started serving a specific region.

Lucky tells the story of Cathay Pacific. Virgin Atlantic was started specifically to fly from Britain across the Atlantic. Lots of US airlines started in a specific region, like Southwest. Westjet started serving the west of Canada.

It doesn't make sense to change a well-known name just because the reach of the airline is extended.


Cockpit vs Flight Deck? Is there a distinction between a cockpit and a flight deck on an aircraft, or are the terms interchangeable?

Boeing refers to the flight deck The new Flight-Deck Displays and Airbus refers to the cockpit Passenger Aircraft>Cockpits

Based on this image,

would the B-2 be described as having a cockpit or a flight deck, or is there not enough information in this image?

They refer to the same thing, but there is some separation between the terms, especially in the military. A cockpit is a hole with a seat that you strap into for the entire flight. A flight deck is a larger version of a cockpit, where you can at least leave your seat and walk behind it.

The traditional nautical term "cockpit" referred to a fairly small steering station at the top of the ship. Boeing introduced the term "Flight deck" post-WWII for their larger aircraft, to indicate the difference, and it has spread somewhat. A heavy's flight deck is still a cockpit, and can be referred to as such, but a "pointy's" (jet fighter) cockpit is very unlikely to be called a flight deck in speech.

In general and civil aviation, the terms are pretty much interchangeable. Still, a Ultralight Aircraft's cockpit is not a flight deck, so there is a strong connotation of a flight deck actually being a deck.

The B-2 has a flight deck, so do some fighters like the Su-34. Both can be called a cockpit as well. Basically, solo or tandem seating with entry through the canopy = "cockpit". Side-by-side seating with side door or bottom hatch entry = either "flight deck" or "cockpit".

This distinction is largely English-specific. Powered flight was being concurrently developed in France and Russia, and many languages ended up following their convention ("Piloting post/cabin" and "Crew cabin" respectively), where no term distinction was ever created.


How is a Flying-V more efficient than current fuselage-over-wing designs? It's claimed the plane will use 20% less fuel than the Airbus A350-900 while carrying a similar number of passengers -- the Flying-V will seat 314, while the Airbus A350 seats between 300 and 350. The design also mirrors the A350's 65-meter (213 feet) wingspan, enabling it to use existing airport infrastructure.

Source: CNN

All the efficiencies in recent years have come from better & better engines, huge high-bypass turbofans.  This fuselage looks like it'd be a lot draggier than existing fuselage/wing structures since there is so much more frontal area.

If you have a window seat, that window cover better be open if I'm in that row!

I always ask myself the same question when I read such claims. Only that I am concerned about the huge wetted surface - frontal area is less of a problem here.

When I get hold of such studies, they invariably use projected future technology and compare that with current standards. As you correctly observe, most progress in fuel consumption over the last half century has been due to better engines with higher bypass ratios. Improved aerodynamics contributed maybe 30%, helped by higher aspect ratios and better surface quality made possible by using composite structures.

Another trick: BWBs (Blended Wing Bodies) with their wide fuselage are assumed to need less time for embarking and disembarking of the self-loading cargo. That will make them more productive but the complication of emergency egress from this wide fuselage (remember - all on only one side, within less than 90 seconds!) are waved aside. Also, structural penalties for a flat pressure vessel are assumed to be ridiculously low, so the BWB is even claimed to be more efficient structurally. Which it is, if you look at the spar weight alone. But skin surface area has weight, too -  but not in those studies.

What also helps is to fly more slowly. That improves engine efficiency especially with high bypass ratio engines and allows thicker airfoils which certainly are needed in order to spread passengers over more than half of the wingspan. What is saved on the ground is then used up in the air, and the result is indeed a more efficient operation. If we were not bound by that magic number of Mach 0.85, new designs could indeed be more efficient still.

Remember that the A380 also was claimed to be 20% more fuel efficient? After being overweight (no wonder if scaling laws are observed, something the base of this claim conveniently forgot) what is left of that claim today? In reality, the competition uses the same technological progress and the comparison has to be made on a level playing field, with real data. Then those claims quickly collapse.


What is the reason for the detour flight route from AUH to BEY? I recently flew from Abu Dhabi to Beirut and I was intrigued by the flight route. Instead of simply avoiding Syrian airspace (as would be expected) and flying across KSA, Jordan and Israel, we flew almost to Alexandria in Egypt before hanging a big right and approaching Beirut from over the Mediterranean.

Source: FlightAware, text added

Before the Syrian war the flight used to take 3.5 hours, now it's more like 5 hours. Can someone explain to me why the flight took this route? Is it because Sinai is now considered a no-go zone? If so why not fly over Israel? Is this because it's not allowed?

It's for political reasons.The flight is clearly avoiding Syria and Israel. To fly a direct route between the two you must overfly either Syria or Israel.

Looking at the flight paths from the last week or so of the two airlines that service that route and it becomes very clear. The flight in question is (as it would appear from flight paths) Etihad Airways, the flag carrier for Abu Dhabi. All flights between the two from Etihad take this same circuitous route. The reason is that they can't fly over Syria or Israel. The UAE (of which Abu Dhabi is a part of) does not recognize Israel as a state. Israeli citizens are not even allowed in the UAE. Etihad does not serve Israel nor are Israelis allowed to fly on it. Many Arab states do not allow El Al to overly them so it's a safe bet Etihad is not allowed to overly Israel's territory.

In the past that would just mean flying over Syria instead. But Abu Dhabi is a member of the Arab League which has invoked sanctions against Syria. This would make it risky to fly over Syria and is most likely prohibited by the sanctions. So their only option is to go the long way around.

On the other hand, the Lebanese carrier Middle East Airlines/Air Liban also serves this route. Although Lebanon is a member of the Arab League, Lebanon refused to be party to the sanctions on Syria. Due to this they are still able to fly over Syrian airspace, so they have a much more direct route.

And it would appear that Etihad is still avoiding flying over northern Sinai since the Metrojet 9268 crash.


Can a completely drained battery be recharged via ground power on an airliner like the B737? When accidentally leaving the battery switch or something powered by the hot battery bus on over night, an aircraft's battery could completely discharge. Normal startup, where the battery is switched on first and then external power is connected, would no longer be possible.
Is it possible to somehow connect an external power unit to the aircraft such that the drained battery is being recharged? Or would maintenance have to swap out the battery or charge it in some other way?

Details for the Boeing 737 are below, but answers for other airliners are welcome:
On the Boeing 737 NG, the batteries are charged via their own transformer rectifier units:

Battery Charger Transformer/Rectifier
The purpose of the battery chargers is to restore and maintain the batteries at full
electrical power. The main battery charger is powered through AC ground service
bus 2. The auxiliary battery charger is powered through AC ground service bus 1.

(Boeing 737 NG FCOMv2 6.20.12 - Electrical - System Description - DC Power System)
These ground service buses can be turned on independently of the main aircraft AC buses:

Ground Service
For ground servicing, a ground service switch is on the forward attendant’s panel.
The switch provides ground power directly to the AC ground service busses for
utility outlets, cabin lighting and the battery charger without powering all airplane
electrical busses. The ground service switch is a momentary push button and is
overridden when both AC transfer busses are powered.

(Boeing 737 NG FCOMv2 6.20.2 - Electric - System Description - Electrical Power Generation)
This sounds like the battery chargers could be powered via ground power in ground service mode. It is however not clear to me, if this push button would even work without any battery charge left.

My one experience with this was in a 737-300 that had the battery charger die, and the battery depleted while in flight.  The Battery Bus was still powered by TR3, but the Hot Battery Bus died (interestingly, not a scenario I'd ever seen in the simulator).  We got to the gate & couldn't start the APU and couldn't connect ground power, so when we shut down both engines, we immediately had "one blue light" -- i.e. ground power is plugged in & available, but NOTHING else -- dark airplane.
I don't recall how longer after that it was, but we eventually were able to connect ground power, probably to the ground service bus first.  Then, with the ground service bus powered, the battery would recharge.  I don't recall if we were able to get anything beyond the ground service bus powered after that.  (Presumably, if the battery recharged enough, we could have gone back to normal routines.)
As a practical matter, though, our maintenance does exactly as John K mentioned: if the battery has been depleted, it gets replaced.  How much of that is a matter of what happens during charging, and how much of that is concern about damage to the battery itself, I don't know, but in practice they won't use the aircraft's battery charger in the manner suggested in the OP.  (The battery charger brings it back up to full charge after things like starting the APU or running on battery power for the time between initial power-up and when APU or ground power are connected -- but that's a long way from being fully depleted.)