Despite the lessons from DC-10 planes in 70s, why didn't Boeing ensure their cargo doors didn't fail even until the end of the 80s? In the early 70s, DC-10 planes had disastrous failures with cargo doors. It proved how massive a havoc faulty cargo doors can have on the planes. Despite those two incidents with Boeing 747 planes in the 80s prove that Boeing were not careful enough to avoid problem with the cargo doors. In fact, there is a striking similarity with what happened to DC planes in 1972(a warning) and in 1974(not learned from the warning) and what happened to Boeing 747 in 1985(warning) and in 1987(not learned from warning).

Why didn't Boeing learn from what happened to DC-10 planes?

Most probably because the failure modes were very different. In the DC-10 case the door could appear closed even though the locking mechanism was not properly engaged. On 747 that was not a problem; instead the electric motors opening the door had enough power to break the locking mechanism if electric power somehow made it around the switch that was part of the locking mechanism.

And then, 2 years are not really enough to analyse a problem like this, develop a fix, test it and deploy it. The NTSB investigations alone often take longer than 2 years.


Circa 1942 Republic of Ecuador - Can someone identify the aircraft in the background? Circa 1942 Republic of Ecuador - Can someone identify the aircraft in the background?

Looks like a Fairchild PT-19...
https://en.wikipedia.org/wiki/Fairchild_PT-19


The wing has a pressure gradient along the AB direction, is there a pressure gradient along the CD direction? The wing has a pressure gradient along the AB direction, is there a pressure gradient along the CD direction?

Yes, but a weaker one than in lengthwise direction.
You can observe the local pressure by comparing the distance between two stream lines. When they move closer together, speed goes up and static pressure goes down. As you move away from the airfoil, the distance between stream lines recovers to its value at infinity.

Stream lines around airfoil (picture source).
This effect depends on the Mach number of the flow. At very low speed, the recovery is rather quick because speeding up contracts the airflow so it is easy to make way for the airfoil. At higher (but still subsonic) speed, speeding up is coupled with a drop in density, so the contraction is less pronounced and it takes more height for the disturbance to die down. At supersonic speed, the pressure change is sudden (in a shock or an expansion fan), and the pressure rise of a shock reaches into infinity.


On a bypass engine does the bypass air travel faster or slower than core air? Using the convergent /divergent duct theory the low pressure cold stream bypass air would travel faster but I read on a web page that the bypass air travels much slower than core air. But again using the convergent / divergent duct theory core air is subject to higher pressures and temperatures therefore should theoretically travel slower?

Or is it because air is mixed with fuel and accelerated during combustion which makes the core speed faster and Bernoulli converging / diverging duct theory I stated above doesn't apply?

Hopefully someone can tell me if I'm thinking this incorrectly... Simple explanation please and not something over complicated.

Thanks!

The simple way to think of it is the bypass engine is kind of part way between a pure jet and a turboprop.   In a nutshell, the pure jet moves a little bit of air a lot; the turboprop's propeller moves a lot of air a little, relatively.  In other words, small mass at high velocity vs large mass at low velocity, to get the same push.

A bypass jet engine is somewhere in between.  It's just a fixed pitch non-geared turboprop with 30 or 40 blades, in a shroud, instead of 3 or 4 variable pitch blades in the open (geared turbofans get even closer to the "fixed pitch turboprop" thing).

The package of air being accelerated is smaller than a propeller, but much larger than a pure jet, so fan's exhaust velocity is also in between; faster than the wash of a propeller, slower than the exhaust of the core.


What does "500 and 1" mean? In this AVWeb article, numerous references are made to 500 and 1, with other references to 3,000 and 5.

Based on the statement The current observation was 800 overcast and four miles visibility (in the second paragraph), I would presume that 500 and 1 means a 500 foot ceiling and one mile visibility, is that correct?

Yes, 500 and 1 is 500 ft ceiling and 1 mile visibility.


Why do airlines not paint the wings on their livery? Why? Does anyone know why airlines do not paint the wings on their aircraft? What is the reason why?

Some do. However, paint is expensive and heavy. You may find that getting approval to paint a lift producing surface is more difficult to justify to the regulatory authorities. And also, why paint somewhere you can't see very well when it adds weight and therefore burn more fuel?


Is vertical separation based on geometric difference or altimeter difference? In the comments below one of the answers to this question about the influence of temperature on vertical separation, the question was raised whether ATC ensure 1000ft vertical separation based on geometric difference (true altitude) or pressure altitude difference.

In cold air, the true vertical separation will be less than 1000ft if the difference in altitude indicated on the altimeter is 1000ft.

Source: the other question

Is there an offical reference that gives the answer?

The short answer: "Altimeter difference"

The long answer:

From a pilot perspective, when issued an altitude to maintain by ATC, he/she will fly the altitude in reference to his/her altimeter, whether or not it's a "Flight Level" assignment (usually FL180 and above in North America), or "altitude" assignment (below FL 180).

For example, when the temperature is colder than ISA and one aircraft is assigned FL250 and another is assigned FL260 , the  actual (geometric/true) vertical separation between the aircraft would be marginally/somewhere less than 1000 ft. There is no ATC correction (in the U.S.) for actual "true" altitude being (probably slightly) less than 1000 ft. in this scenario.

Since there is not an automatic correction for colder than ISA (or warmer than ISA) internal to the altimeter, true altitude is different than what is being displayed to the pilot on his/her altimeter and being displayed to the controller on ATC radar.

This is only with respect to separation between aircraft.  Separation from terrain is considered both by the pilot and ATC, as necessary.  For example, at some locations during very cold temperatures, MVA (minimum vectoring altitude) for a specific area may be raised so that aircraft always have the necessary "true" altitude separation from the terrain while being vectored by the controller.

The pilot, while conducting instrument approach procedures at specifically designated airports, will make altitude adjustments for the IAF/IF/FAF/MDA/DA/missed approach holding, based on a correction value obtained either automatically from the onboard equipment, or manually from a cold temperature altitude correction table/chart.

On these occasions, the pilot has the obligation to notify ATC of the altitude adjustments being made. These adjustments will be made to the indicated altitude being flown for the purpose of obstacle/terrain clearance and the indicated altitude on the altimeter will be higher than published on the chart.


Having trouble reading some charts (SBMG-SBLO) I'm a flight sim user practicing instrument navigation with a short and apparently simple flight, SBMG to SBLO (South America). The distance between the two airports is 49.5 nautical miles (the simulator tells me). My simulator is X-Plane 11. The aircraft is the Cessna 172.

I've flown the mentioned flight a couple of times, but I'm afraid I am making mistakes. There are a couple of questions I'd like to make.

Let's start with this SBMG SID chart (these charts come from AISWEB). The path with red dots is the one I'm following.

(1) You see 096 > on the first 3 nautical miles? Does it mean I should track course 096 on the LON VOR right after takeoff, or is it just the heading I should be on for the first 3 nautical miles? You see, I'm having trouble figuring out what is the reference navigation aid for these headings/radials.

(2) After passing MG123, I start to track the 100 radial on the LON VOR for 47 nautical miles. After 47 miles I switch to the approach chart. Is that correct?

The next chart is a IAC for SBLO. It has a VOR/DME arc.

(3) I am still tracking 100 towards LON, but the nearest entry point for the arc is 090. After 47 nautical miles, I am too close to SBLO to change my course, and it's time to enter the arc already. I feel I missed something.

Interesting academic exercise crimson_king. I don’t think you would get cleared for or use this SID/IAP combo. The airports are too close together. You are basically using your destination airport’s NavAid as the beginning/start of your departure. You will overfly the airport before you get to the VOR that starts the procedure. Then, you would have to backtrack out to the arc, using LON as your IAF.
The plate that you referenced is just an instruction on how to get to the start of your departure. There is probably a textual ODP to go with it. If you were in IMC, you would remain under radar vectors and ATC control the entire time. They would probably give you instructions like: Fly runway heading climb and maintain 5000 radar vectors direct D270L cleared the VOR Z Runway 13. This is of course abbreviated since you would have a switch of ATC from tower to approach.
Based on the information provided, For the purposes of simming, your best bet is to:

Take off from the runway of predominant wind.

Remain in the traffic pattern and climb over the airport.

Climb until you are at 5000 feet or more. The reason for this is that the only altitude information I see on the plate are the Minimum Sector Altitude and the Maximum Elevation Figures.

Fly direct to MG123 using RNAV/GPS.

Switch to VLOC/VOR mode

Fly direct to D270L.

Begin your IAP
A second option is to just fly direct to LON using your Nav radio by the shortest route possible. Use MG123 as a fly over reference point. Maintain full throttle at Vx until 5000 feet. Once you are within 12 miles DME of LON. Start your descent down to 4100 feet. Join the arc wherever you happen to enter.

Celia is not marked as an IF/IAF. So, I would avoid going directly there. It would be a perfectly good option if you were being radar vectored and cleared there by ATC.


What is the best strategy for landing when a flock of birds is on the runway? At a controlled airport, the tower advises large flocks of small birds at the approach end of the runway.

I'm in a small trainer aircraft like a Cherokee or Cessna 172. Should I request to land the other way (Rwy 9 vs 27), proceed as normal but just expect them to only be a distraction?  What are the best options here?

I think the answer depends on what the birds are doing, but all options are basically "at the pilot's risk" - the tower is just advising you there are some birds hanging around the airport, but nobody can say how they're going to react to you trying to land there too.

If the flock is airborne and flying across the final (completely neglecting to coordinate their movements with tower, as birds are wont to do) you can request an extended downwind until they've moved on.
This has happened to me twice, and in my experience birds tend to be far less interested in airports than pilots. They're usually gone in a minute or two.
If they're sitting on the runway somewhere you can try a low pass over the field to scare them off, but my preference would be to ask the tower/unicom operator if they can chase them away for me with a ground vehicle (so I'm not near the flock in case they decide to disperse "upward" instead of "outward").
If they're just pecking around in the grass near the approach end of the runway looking for lunch Skip Miller & p1l0t have the right idea with a go-around or low approach/overflight to scare them off.
(This is part of why a low pass over an unattended uncontrolled field is often advisable -- you'll hopefully scare off any critters on the runway that you wouldn't want there when you actually land.)
If they're "airport birds" you might want to just land.
Some of the airports by me have resident flocks of birds that I'm convinced just sit there and rate people's landings - I swear I saw the same birds every day shooting touch-and-gos.
These are the kind of birds that aren't going to scatter when you do a low pass unless you hit them with your landing gear, so just be aware of where they are (in case they lose their minds and try to commit suicide by propeller) but they probably won't bother you.

I don't think I'd ask for a downwind landing because of birds (unless we're talking geese or hawks or something), but if it's a calm-wind day, the pattern is empty, and you're more comfortable with that idea go ahead and ask. The worst the tower can do is say "unable".


How would an aircraft fly PIKES ONE departure procedure of Denver Airport? I was examining FAA's departure procedures and I noticed PIKES ONE SID (chart and continuation) which serves Denver Airport.

In the description, it states:

  TAKEOFF ALL RUNWAYS: Fly assigned heading for RADAR vectors to assigned route. Climb and maintain 10000 or ATC assigned lower altitude. Expect filed altitude 10 minutes after departure.

  LOST COMMUNICATION: If no transmissions are received within one minute after departure, maintain assigned heading until 7000 feet, then climb to filed altitude via direct DEN VOR/DME, thence via assigned transition.  If filed altitude is above 10000 feet, cross DEN VOR/DME at or above 11000 feet.

What troubles me is that DEN navaid is (obviously) very close to the airport, so I am not sure how an aircraft would depart from the airport via a runway very close to DEN, for example 07/25, and have enough space in order to reach DEN. In addition, based on Lost Communication, an aircraft would climb until 7,000 feet and then go direct to DEN, even if it has already surpassed DEN (by departing, for example, via runway 17R/35L) and theoretically it can just follow the assigned route by skipping this navaid.

In other words, is the aircraft obliged to fly to DEN before following the assigned route under any circumstances and, if yes, what would be a possible flight path in case of a runway that is really close to it?

Let's treat the "normal" and "lost communication" cases separately.

  Fly assigned heading for RADAR vectors to assigned route. Climb and maintain 10000 or ATC assigned lower altitude. Expect filed altitude 10 minutes after departure.

The essence of this is that on departure, responsibility for navigation rests with the air traffic controllers, not the pilot. The controllers will issue headings and routes to fly in order to keep the aircraft separated from other departures, arrivals, and other traffic. Once clear of traffic, the controller will issue instructions on how and where to rejoin the cleared route. At this point the pilot takes over responsibility for navigation along the cleared route.

Usually, it goes something like this. The departure will be assigned an initial heading, often the runway heading: "runway 17R, fly runway heading, cleared for takeoff." The aircraft flies this assigned heading. The aircraft will then contact the departure controller. The departure controller may continue assigning specific headings in order to separate the aircraft from other departures, arrivals and other traffic. Once clear, the controller has some options. They can clear the aircraft direct to a convenient fix/waypoint or NAVAID on the aircraft's flight plan ("Proceed direct ADANE, resume own navigation") or they can say something like "Fly heading 130, join the Denver 159 radial, resume the departure." It's up to them, but they will issue some kind of instruction that results in the aircraft joining its cleared route.

  LOST COMMUNICATION: If no transmissions are received within one minute after departure, maintain assigned heading until 7000 feet, then climb to filed altitude via direct DEN VOR/DME, thence via assigned transition. If filed altitude is above 10000 feet, cross DEN VOR/DME at or above 11000 feet.

If communication is lost, the pilot should do the following in order once it is realized that communication has been lost.

Fly the last assigned heading until reaching 7,000'.
Turn (back toward the airport and the DEN VOR) and fly to DEN.
Comply with the crossing restriction (make sure you reach 11,000' before getting to DEN if your filed altitude is above 10,000').
At DEN, turn outbound on the appropriate (filed/cleared) transition leg.
Keep climbing to the filed altitude.

It is likely that some short amount of time will pass before it is realized that communication has been lost. The aircraft will travel some distance away from the airport during this time. The aircraft must also continue until it reaches 7,000'. So by the time it would become necessary to "proceed direct DEN," the aircraft will not be "right next to it" and a turn direct DEN is reasonable.

If you departed runway 25, your route might look something like this (not to scale!).


Does the FDR record data about the cockpit door lock system? Does the flight data recorder record whether the cockpit door lock was deliberately used to lock someone out?

While it is not on the required parameters list, it would not surprise me if it would be recorded- most FDRs record considerably more than the 88 mandatory parameters, and cockpit doors are of course interesting in accident investigations.

That being said, it should also come across pretty evidently on the Cockpit Voice Recorder if somebody was trying to get in. The normal request is a pretty distinct buzzer and the emergency request is the same buzzer for 5 minutes unless denied/ cancelled by the pilot. The door also locks quite loudly. Both should be able to be picked up by the general cockpit area microphone (CAM).


Why would a turboprop rev down just before going full throttle during takeoff? The only turbprop I've travelled is the ATR 72. I've noticed that the props' rev go down (for like a second, the sound also goes down) just before engaging full throttle in order to takeoff. I've included a video (video is not mine), this thing happens at 1:40. Why the RPM drops for a sec? Or is this just the sound?

Because the pilot is taxiing the airplane with the props in the beta range (turboprops turn into landsharks if you don’t do this and you end up really riding the brakes to keep the speed down), then on takeoff, the propellers move into a maximum power setting, the engine snarls and slows a bit under the increased workload.


Will the steep beta descent mode become illegal for new aircraft? The PC6 is a popular skydiver carrier due to its ability to use steep nose down beta descent to get back to the ground quickly, even beating free falling skydivers.

(YouTube)

FAA AC25.1155x (I only saw the draft) proposes that a "means to prevent intentional or inadvertent selected of reverse thrust or propeller pitch below the flight regime" be required, which cannot be overridden. The intention is to prevent several accidents resulting from said deployment. The lockout means must not degrade landing performance, so the intent is not to eliminate beta entirely.

Does this mean that no new aircraft can be certified that has a descent mode from altitude similar to the PC6?

I wouldn't call it a "descent mode from altitude".  It's considered to be a dangerous and foolish practice to operate an engine in ground beta (generally coming back into DISCING - blades flat) while in flight to get steep descent rates.  If the prop doesn't want to come out of ground beta, you are dead meat.

When the Twin Otter was in production, it was an open secret that demo pilots were using DISCING to get crazy steep approaches to impress customers.  After a couple exciting events, flight ops finally put an end to it.

Some airplanes already have ground beta lockout systems.  Is this a proposal to mandate a system for the PC6 specifically?


Would titanium be a better option for aircraft skin if cost were not a factor? If price was not an issue, would titanium be a better option to use as the skin of airliners as opposed to aluminum?

even assuming price would not be an issue, formability certainly would be. Ti is much harder to bend, drill and cut than Al so building a plane out of cheap Ti would significantly increase its manufacturing costs over Al. Ti retains its strength at high temperatures far better than Al but in subsonic aircraft like passenger planes, airframe heating is not a design limiter that would drive a choice between selecting Ti or Al.


What exactly causes pitch moment in the Phugoid mode? I am trying to figure out exactly what causes the pitching moment for the Phugoid mode? We know that alpha remains mostly constant, so what is causing the pitching moment? I thought maybe it is the trim point of the aircraft, but if trim was exactly neutral then how would the phugoid mode still proceed, since alpha is zero and at the design condition there would be zero tail load?
I guess my question then becomes what derivatives are responsible for causing the Phugoid mode or am I missing somehow that is just the dynamic response to the derivatives as a whole?

Everything. When we are talking about flight dynamics and stability in particular, it is the balance of forces or moments that we must consider. For simplicity of analysis, we often choose reference points that allow us to isolate some effects and make them independent of some variables, but if you are interested in the "physics" of it, then you should keep in mind that, in general, the forces and moments are everywhere, and they change.
Specifically, you seem to think that the tail load is zero in the trimmed condition. Not true. It could be true only for aircraft with neutral static longitudinal stability, which normally wouldn't display phugoid oscillations.
In the trimmed conditions, both the tail and the wing create moments (with respect to CG), but they balance out to zero. The essence of static stability is that upon the disturbance, the balance is offset such that it leads to restoration of the initial conditions.
In pure phugoid motion, the upset is airspeed but not angle of attack (AoA). Now, an airplane may have a tendency to have a pitch moment directly in response to speed, which we can designate $M^V$, or better as a coefficient $c_m^V$. This can be related to the nature of its thrust and/or moments from other parts. But this is not strictly required, and we can consider the simplest classical system of just a wing and a fixed tailplane. This system will not see a balance change simply due to airspeed. But consider what will happen:

Say, airspeed is suddently reduced due to wind shear. This is the only change, and AoA remains truly the same.
The moment balance remains the same, becuse lift of the wing and the tailplane changes proportionally. Thus no pitch change yet.
Lift will drop and will not sustain level flight anymore.
The aircraft will start accelerating down (while still in the same attitude!)
This acceleration has an effect of increasing AoA (due to the vertical component of speed). Notice that this angular effect depends on the absolute forward airspeed, which suggests that the effect will be lower at higher speeds.
Now the normal short-period static stability (the $c_m^{\alpha}$ or $c_m^{c_L}$ derivative) will cause a nose-down moment (if the system was stable) and will restore the original trimmed AoA.

This restoration effect normally happens much quicker than the speed change, especially for larger airplanes. So with a good approximation you could analyse just speed changes and assume AoA = const throughout the process. But physically this is not true, which, I guess, is the source of your confusion.

With the nose down, the aircraft will gain airspeed.
QED: the aircraft tries to negate the initial airspeed upset, which is the definition of static stability.
However, what happens next can be interesting. Due to high inertia, the aircraft will inevitably gain more airspeed than needed, and the process will reverse. Oscillations will ensue, and this is what is usually called "phugoid motion". The dynamics of this motion depends on several factors (absolute speed was already mentioned). Typically, this motion is much less dampened than the short-period AoA stability, and can even be dynamically unstable (i.e. have increasing amplitude). But this is not necessarily a problem: because the motion is slow, pilots can control it.

If you want derivatives, they have already been mentioned. Omitting derivation and with some simplifications, they combine to
$$\sigma_V = c_m^{c_L} - \frac{V}{2c_L} c_m^V$$
This $\sigma_V$ is the measure of static stability by airspeed. It is negative for stable aircraft. As can be seen, aircraft without direct speed-moment response ($c_m^V \approx 0$ - think gliders, for example) will have speed stability fully determined by the short-period AoA stability.


What is the area between the taxiway and runway shown in the picture below? Is this the Arresting area? I'm not too sure what you call this area

Additional information on the airport would have been nice, but from the markings it looks like it simply is a pad where two aircraft can be positioned at once.

This can be useful where you have a case of eg. one aircraft needing additional time to be ready for take-off while the aircraft behind is all set, or a larger aircraft in front being held back to allow a smaller aircraft to pass it and take off first.

Copenhagen Airport (CPH) has a similar layout at the end of one of the runways, as shown below, although this is using two taxiway stubs rather than one solid pad.


Can a runway turnpad be used as a runway holding position? Can a turnpad also be used as a runway holding position?

No, since you must have been cleared to enter the runway to be on the turn pad.  It is part of the runway.

From the point at which an aircraft is cleared to enter the runway, until it reports vacated or departs, the runway is occupied.


What control issues did the X-1 have to overcome to achieve supersonic flight? In Chuck Yeager's autobiography, he went into a little bit of detail as to why the X-1 was able to break the sound barrier safely where as the P-51D he flew during WWII could not have safely broken the sound barrier.  He mentioned it had to do with the controls... Something about flow separation, as I recall, and the elevator not working as a result in most aircraft before the X-1.

I was wondering if someone could explain this though?  What advances where made during X-1 development that made it stable at Mach 1?

The control problems are caused by a shift of the aerodynamic forces. In subsonic flight, they are mostly created in the forward part of the wing (the lift increase with angle of attack works at the quarter chord point of a wing, regardless of sweep), while in supersonic flow they work equally over the full chord. The center of lift in pure supersonic flow is at mid chord, and in reality the aerodynamic center shifts slowly back when the aircraft accelerates through Mach 1 and more of the surface is exposed to supersonic flow.

Since the c.g. position is mostly fixed (Concorde pumped fuel between tanks to shift the c.g.), this shift must be compensated with elevator deflection. The elevator must move trailing edge up, which creates a break in the airfoil contour, which in turn creates a heavy shockwave at high subsonic and supersonic flight speed. This shock causes flow separation and can lead to elevator reversal. Only when the fixed part of the horizontal tail can be moved, too, or you have a full-flying tail (the whole stabilizer is moved, not only the rear part of it) to create the needed lift change without a contour break, the aircraft can be trimmed for both subsonic and supersonic speed.

The benefit of the X-1 was a stabilizer with variable incidence, which the P-51 lacked. Sweep would have helped, too, but was not really necessary.


Are ATCs required to notify pilots when they use MVAs? I understand ATCs may use minimum vectoring altitudes(MVAs) when they deem it as appropriate. When they do that, do they notify the pilots of the fact that they are being radar vectored based on MVAs? Or are pilots expected to query ATCs when they find the newly assigned altitudes below the MEAs on the charts?

I'm not exactly sure what you are asking, but no, we do not notify pilots that we are vectoring in accordance with the minimum vectoring altitudes - because that is what we always do. ATC is responsible for terrain clearance during radar vectors, and pilots know this, so it is implied and understood that we use safe levels.

MVA's simply define the lower level for radar vectoring in an area - the lower level of our designated "box". Just like there is an upper limit and lateral limits as well, that we cannot cross during vectoring. MVA's are based on terrain and other obstacles, to ensure that terrrain clearance is always provided. You make it sound like MVA's are only used in special circumstances, which is not true. Vectoring at and above the MVA is completely routine and happens every day.

As for cross checking by pilots, MVA's are supposed to be published on a separate chart which pilots can use to cross check their assigned levels. The MEA is not used during approach, and pilots know this. In case of a radio failure during approach, if the flight is being vectored below minimum sector altitude (MSA), the pilot will climb to the MSA, even if the MVA is lower.

Further reading on SKYbrary.


Does lift coefficient vary with the wind velocity for a given angle of attack? I have this question in my mind. I have been trying to look for this in different books about aerodynamics and I couldn't find the answer. I know I could check the answer experimentally, if I had a wind tunnel or some advanced software, but I don't have access to any of them.

Let's say we have this plot (fig. 1) obtained experimentally by testing an airfoil at a low speed (subsonic) with a wind tunnel. If I were to change the wind speed of the wind tunnel, would the graph change or would it remain the same?

For instance, if the wind velocity was initially 15 m/s and then 25 m/s, would it change or is the CL-AoA relationship constant for a given airfoil?

I just need to understand this, I don't need any example with numbers (I just give the numbers to have an order of magnitude of the velocities of the testing. And assume the airfoil has a regular shape, for instance a NACA0012, which is pretty common for academic examples.

Yes, it does vary slightly due to viscous effects.

In inviscid flow, the flow speed would not affect the lift coefficient - angle of attack relation. However, increasing the flow speed will result in a thinner boundary layer and a slightly different shape of the airfoil - boundary layer combination as "seen" by the outer flow. This influence is captured by the Reynolds number. See below for a plot of the venerable NACA 4412 from Abbott and Doenhoffs collection of airfoil data (picture source):

Note that the lift coefficient is plotted for Reynolds numbers R of 3, 6 and 9 million.


Can I land a helicopter by controlling only power, not angle of attack? With full RPM on my rotor system, can I land my helicopter using only the throttle? That is, by just reducing power rather than reducing the blades' angle of attack?

Assuming you mean a manual thrust lever with out a constant speed regulator: yes that is possible but not optimal. Best is to keep the rotor blades at optimum speed and reduce AoA of the blades by lowering collective - if you do that the thrust needs to be adjusted otherwise the rotor overspeeds, but it is still better this way than reducing thrust/rotor speed first.

If rotor speed is slowed down first, the blade speed reduces and with the collective at the same setting, the blade AoA will increase. So the safety margin with stall AoA decreases, at a time when it is required most.

Possible - yes. Recommendable - no.


What exactly did this mechanic sabotage on the American Airlines 737, and how dangerous was it? An American Airlines mechanic sabotaged a 737 in Miami

An American Airlines mechanic accused of sabotaging a navigation system on a flight with 150 people aboard at Miami International Airport was denied bond by a federal judge on Wednesday after prosecutors suggested he may have links to a Middle East terrorist organization.
Abdul-Majeed Marouf Ahmed Alani, a 60-year-old veteran employee, told investigators after his arrest earlier this month that he disabled the system because he was upset over stalled union contract negotiations with the airline and wanted to generate some overtime for maintenance on the plane. He said he meant no harm to anyone, and the July 17 flight was aborted before takeoff after an error alert appeared on the navigation system.

His defense attorney said it wasn't as big a deal as they were making it out to be

But Alani’s assistant federal public defender, Christian Dunham, said the prosecutors were exaggerating the evidence. He pointed out that there was a second navigation system still working on the plane so his alleged sabotage could not have caused it to crash.
“We don’t believe he intentionally endangered the safety of people” on that flight, said Dunham, who sought a pretrial bond signed by Alani’s family members in California and Florida. “I think the government is blowing this out of proportion.”

What was it he sabotaged, and how serious would it have been if it had taken off?

It's a serious crime, but what that guy did, only affecting one system out of three, would be unlikely to cause a crash if the pilots were half way reasonably competent.  The take-off would be rejected as soon as the blocked side's speed tape failed to "come alive", well below 80kt (the pilot not flying checks that both speed tapes start to move as the airplane accelerates - this would be the first obvious clue and is a very basic action on a jet).


How can I rebuild my missing logbook after 20 years of not flying? I took flying lessons when I was a senior in H.S. in Illinois.  I got through solo and all of my x-countries (even the long one).  I was about a month away from finishing when we moved to Colorado and I started engineering school.  I intended to continue flying but school became the priority.  I lugged my log book and text books around for years (I can remember seeing my log book only 4 years ago).  I am about to finish what I started and go back and start the process again.  Now of course I cannot find my log book (I have turned my house upside down) :(

I want to state (because I know someone will make the point) that I am not looking for a short cut and I fully intend to make sure I get great training (its been 20 years) and plan on working my way through the requirements for a second time. I will defer to my instructor on what I need to learn and practice. I remember I had about 80 hours and I would like to get credit for them (if only to show the new school that I'm not starting from ground zero) as well as I plan on getting my instrument as soon as I can and the hours would help.

The flight school is no longer in business.  I remember the first name of my instructor (and have the first solo picture).  I thought I could contact him if I could find his last name and search some sort of data base?  I have searched the business records of the state and found a business record that for the old flight school that lists the owner.  I thought I would start there and see if I get lucky. If I can find the instructor's name I think there is a good chance he'll remember me and could provide documentation that would allow me to start a new log book with credit for my existing hours.

I found a local news paper article from the time period that mentions another flight instructor that worked there (AmCorp out of Lansing, Illinois in 1995) at the same time.  Is there a way to look them up in some sort of pilot data base to contact them and see if they remember my instructor's last name?

I remember filing my flight plans (I assume there is no record of that with the FAA because it's so long ago)?

Hopefully you get the idea of my quesition and hope you guys can give me any ideas on resources that I don't know of that may help me out.

You will probably not be able to recover any solo flight time you have completed to this point, but contact your previous flight instructors in Illinois.  They should have logged the training time they did with you on dual instruction, which will allow you to recover that flying time this way.

If you don’t have contact information on this instructor, you may be able to search them out, either on the FAA’s website or third party flight instructor directories like this one.

http://www.iflightplanner.com/FlightInstructors/

Good luck


Is there a modern day "replacement" for the de Havilland Beaver? Is there a modern day equivalent or replacement for the Beaver's Payload, STOL and floats capabilities? By replacement, I mean that it can fly into the same airstrips under the same weather with the same load.
Is there any modern (still manufactured) airframe that wouldn't leave a seasoned Beaver bush pilot wishing for their old Beaver back?
In all of the time since that plane was designed, has something else has been designed and continues to be manufactured that can be called an upgrade without getting "bigger"? IE, has:

floats
a shorter or the same takeoff and landing roll at the Beaver's
max useful payload
the same or less stall speed with fully extended flaps
a same or less wingspan (negotiable if it's within 2 or 3 feet)

The motivation for the question is that less than 10 years ago, I remember a float plane flight out of Juneau, AK that I was on was flown by a Beaver still running a radial engine. I was amazed that something designed so long ago was still apparently considered  the "best" option for that carrier. Of course, the Beaver is now one of my favorite airplanes, but I am still amazed by the challenge it must be to find parts and maintain an aircraft of that age in the corrosive saltwater environment of SE Alaska.

As an ex DeHavilland employee I'll admit I'm a bit biased, but I'd say there isn't really a "direct" replacement so far.  Two reasons:
The Beaver was designed in Canada around a bush operator survey.  Outside Canada (and to a smaller extent Alaska), "bush operation" generally means remote land operations into dirt strips.  In Canada, "bush operation" meant almost exclusively seaplane operations, (and to a lesser extent ski operations in winter).  The survey provided the Dehavilland Canada designers with a wish list of features provided by seaplane operators running Norsemans and the like (sadly, helicopters and gravel strips to provide land plane access remote areas have replaced most seaplane use as basic transportation, and today most seaplane operations in Canada and Alaska support the tourist trade).
So, unlike its modern contemporaries, it is specifically designed to operate on floats, and is optimized for being serviced and loaded from a dock.  The fuel tanks in the belly, the placement and shape of the main doors, the battery location, etc. Easy to load, easy to service from a dock.  The Beaver's modern contemporaries aren't optimized for float operations quite the same way so the "fit" isn't quite as good for a seaplane operator. On the flying side, the very long wings and full span slotted flaps (the ailerons droop with the flaps) allows it haul loads out of very small lakes, with a decent rate of climb.
The other big reason is the engine.  The R-985 is one of the only large piston engines over 400 hp that is still commercially viable, that is, it's still feasible to keep running reliably in a commercial operation.  A piston engine is far cheaper to operate than a turbine.  Bush operators operate on very thin margins and direct operating costs have a direct impact on viability of an operation, so turbines are out of reach for most.
With the Petersen Mogas STC you can run an R-985 on aviation automotive fuel (Mogas) (like all 80 octane engines it's much happier on Mogas than 100LL), and in Canada at least some bush operators do this (the operator I worked for in the early 90s switched to Mogas when the supply of 80 octane in Canada dried up - 80 was still in production in Canada for some time after it disappeared in the US in the 1980s).
Add in the overall reliability of the design and ease of repair, and there you go.
The Beaver is kind of a single engine version of the DC-3. Its combination of features came together so well that after nearly 75 years, it's still the best choice for commercial seaplane operators to use as a business tool to make money. On top of that, it benefited from a large military order by the US Army that took roughly half of total production, 970 units, which has kept up the supply of used aircraft to keep prices in check (the story of the Army's adoption of the Beaver followed a trip to Alaska in the company demonstrator to take some generals fishing, and included a bizarre flyoff against a range of ill-suited contemporaries after US manufacturers complained about foreign sourcing - get the book the DeHavilland Canada Story for an interesting read).


FAR 91.215 (b)(3)(ii) -- transponders-- does the "or below 10,000' MSL" clause have any practical significance? Here are some of the airspaces where FAR 91.215 requires aircraft to have transponders--

  (b) ...

  (2) All aircraft. In all airspace within 30 nautical miles of an
  airport listed in appendix D, section 1 of this part from the surface
  upward to 10,000 feet MSL;

  (3) Notwithstanding paragraph (b)(2) of this section, any aircraft
  which was not originally certificated with an engine-driven electrical
  system or which has not subsequently been certified with such a system
  installed, balloon or glider may conduct operations in the airspace
  within 30 nautical miles of an airport listed in appendix D, section 1
  of this part provided such operations are conducted -

  (i) Outside any Class A, Class B, or Class C airspace area; and

  (ii) Below the altitude of the ceiling of a Class B or Class C
  airspace area designated for an airport or 10,000 feet MSL, whichever
  is lower;

Question 1: May an aircraft with no engine-driven electrical system and no transponder operate at 10,500' MSL in the airspace 10 miles west of South Valley Regional airport (U42) near Salt Lake City, where the overlying Class B shelf has a floor at 11,000', and a ceiling at 12,000' MSL? (Link to sectional chart.)

Note that KSLC is one of the airports listed in the Appendix referenced in FAR 91.215(b)(ii)-- this is a reference to the Mode C veil.

Question 2: May the same aircraft operate at 17,500' at the same location?

Question 3: (only applicable if the answers to (1) and (2) are both "yes")-- Does the "or below 10,000' MSL" clause of FAR 91.215(b)(3)(ii) have any actual practical significance of any kind?  What is an example of some airspace where an aircraft with no engine-driven electrical system and no transponder may not operate, but would be able to operate of the "or below 10,000' MSL" clause were absent from FAR 91.215(b)(3)(ii)?

Note that FAR 91.215(b)(3) is simply an exemption to 91.215(b)(2), which appears to only apply up to 10,000' MSL, so it appears at first glance that the answers to the questions ought to be "yes", "yes", and "no".  Is this really correct?

See also related question FAR 91.215-- may an aircraft with no electrical system and no transponder overfly Wheeler AAF at 9500' MSL?

The answers to the questions appear to be "yes", "yes", and "no".  Neither FAR 91.215(b)(2) nor FAR 91.215(b)(4) have any effect above 10,000' MSL.
The "or below 10,000' MSL" clause in 91.215(b)(3)(ii) has no effect on anything at all and does not prevent an aircraft with no electrical system from operating above Class B or Class C airspace as long as it is above 10,000' MSL.
This is clarified in this 2006 interpretation from the FAA Office of the Chief Counsel.
It possible that the original intent of FAR 91.215 was to prohibit aircraft without electrical systems and transponders from flying above 10,000 MSL above any Class B or C airspace that lies within a Mode C veil; if so the regulations were inadvertently written in a way that did not accomplish this.  This has been rectified in FAR 91.225, pertaining to where aircraft without electrical systems and without ADS-B-out will be able to fly starting January 1, 2020-- these aircraft will no longer be able to overfly ANY Class B or C airspace, regardless of altitude and regardless of whether or not the airspace lies in a mode C veil -- see related question What additional airspace will be off-limits to an a/c w/ no elect. system or xponder under 91.225 (ADS-B) compared to under 91.215?


Why is polar curve of a glider dependent on flight load? This is my first question here.
I'm just a glider in education phase and not yet a pilot, but because I'm also physicist, I'm interested in some details more than other people.

My question is simple:

I know what a polar curve is. Why is this curve dependent on the wing load?
For my knowledge in aerodynamics the polar curve is a property of the airplane/wings, but not dependent on flight state. Otherwise I know from my flight instructor, that gliders are often filled with water to increase weight, which gives a better gliding ratio.

What I mean you see on this curve: why is the curve changing with wing load?
My only answer would be, that wings are flexed differently under different loads and that the different curves arise from (slightly) different geometries. Is there something else I have overseen?

Oh god- I made a terrible mistake: While $C_{lift}$ and $C_{drag}$ are really independent on weight, this is (of course..) not the case for the velocity polar curve. The two curves scale perfectly with weight and are just subject to a simple transformation. No magic behind and completely transparent.

Sorry: Question Solved ;-)


Has a fixed-wing aircraft ever been built that featured multiple turbines powering a single propeller? Has a fixed-wing aircraft ever been conceived, prototyped or built that features multiple turbines powering a single propeller? The concept of a twin-engine aircraft with a single propeller is intriguing to me. Picturing something like a Pilatus PC-12 with two engines under the hood and a single prop might have some advantages. I come from a fixed-wing background and know little about helicopters, but if something exists I suspect it is a rotor wing.

The LearAvia LearFan 2100 used two separate PT-6B to drive a single pusher propeller through a common gearbox.

LearFan 2100 in flight (picture source)

If you want to know why its official first flight date is December 32, 1980, read here.

LearFan 2100 engine arrangement (picture source)

This engine arrangement was the LearFan's eventual undoing when the FAA denied it a proper certification because of concerns that the single gearbox constituted a single point of failure.


How safe is the single engine taxi out for twin engine aircraft? Fuel conservation programs are leading to single engine taxi out, asking the crew to start the other engine near or on the position 2, where the ground crew cannot monitor the engine's status outside the aircraft.
How safe is this procedure? One example is the jet pipe fire during the start up.

I am not aware of mechanics watching civil aircraft start up. They usually have far better things to do. Aircrew are responsible for the aircraft at this point.

The question on a twin is about directional control not safety. How easy is it to taxi on one engine without losing control or stressing the aircraft or tyres in any way? I think this probably depends on the aircraft, some will be easier than others. Also if its a piston twin, you don't want to wait for the other engine to warm up when you are ready for departure. Some four engined aircraft might taxi on two engines - one either side but I've never heard of twins doing this routinely.


Why do some countries separate a transition level and a transition altitude? The US airway system uses a single transition level (or altitude), but some other countries like China separate a transtion altitude and a transition level with the transition layer in between.

Could anybody kindly explain why they use this type of separate transition system? I can guess it's there to prevent possible mid-air collisions between two aircraft using two different altimeter settings (QNH and QNE) but I don't understand how exactly that works.

By definition, the transition level is the lowest usable flight level above the transition altitude. So if there is a transition altitude, there is a transition level.

In the USA, the transition altitude is 18 000ft. If the QNH (altimeter setting) is higher than 1013.25 mbar then the transition level is FL180. This provides at least 1000 ft separation from aircraft flying at 17 000 ft (or 500 ft from the VFR at 17 500 ft).

If the QNH is lower than 1013.25 mbar then the transition level is FL190 or even FL200 to ensure there is at least 1000 ft separation from 17 000 ft.

The transition level in other countries is based on similar logic.


What does the phrase “turnouts approved” mean? What does the (apparently nonstandard judging by its absence in the Pilot/Controller Glossary) phrase “turnouts approved” mean when given in the context of a takeoff clearance?

When departing from a towered field pilots may request something other than a "standard" departure. As an example, consider the noise abatement procedures for my home field shown below:

When departing from Runway 14 the standard noise-abatement departure for light aircraft requires you to turn south (heading 190) when you pass the departure end of the runway.  This is obviously inconvenient if your destination is to the north, so you can request a northbound departure.
If the tower can accommodate your request they will clear you for the non-standard departure, usually with the phrase "left turn-out approved" or "northbound departure approved", and a heading if necessary.


How do airplanes maintain separation over large bodies of water? I have read that the oceans are big enough that ground radar stations only reach so far out. I assume that means after a certain distance from the coast they leave ATC services. Do airplanes employ any techniques to avoid traffic separation outside of ATC services aside from following their flight plan and the rules of the airway they are flying, and for an emergency backup the TCAS system?

To expand on DeltaLima's answer:
They use routes called the NATs (North Atlantic Tracks), which can be different each day depending on things like weather and wind speeds. Each track is a set of coordinates. A pilot will do a position report at each coordinate or every 10 degrees of longitude. The aircraft has to get special clearance to fly oceanic about 30 minutes prior to crossing the entry waypoint for the NAT. Each NAT is 60 NM apart.
To clarify a bit more, HF radio is used to communicate, since it has a longer range than VHF, but is much noisier. This is where systems like SELCAL come in, but I won't talk about that here. They can also do position reports over the radio or over text (CPDLC/ACARS), taking advantage of ADS B/C, which I also won't talk about here. These communication systems are pretty complicated, so I recommend you search it on the web or look at the sites I linked below.
Aircraft are required to be 1,000 feet apart vertically. Eastward flying aircraft have odd altitudes such as 37,000, 39,000, 41,000, etc, while westerly flights will be the opposite. They are also required to be about 10 minutes apart from each other.
Gander Radio (notice not "radar"!) controls much of the North Atlantic airspace from Gander, Newfoundland, Canada. Shanwick is another major Radio station. New York controls further south, along with Santa Maria having relatively small airspace.
There is a similar system over the Pacific ocean, with stations in Anchorage, Alaska, and Oakland.
Links:
I highly recommend you read this article about North Atlantic Tracks, and this one too.
You should at least watch this video, it's only 3 minutes, and it's summarized:

More about ADS-B
More about SELCAL
More about position reports
If you want to learn more about ACARS:


Does turning off WAAS turn off ADS-B out as well? I'm a CFII and for training GPS approaches with advanced students, I like to occasionally turn off the WAAS receiver on the 430/750/G1000/etc. when they are not looking, to simulate a WAAS failure and make them notice they need to change their minimums.

Now, ADS-B out depends on a WAAS GPS-receiver. When I intentionally turn off WAAS, does that turn off ADS-B out as well? Would I be technically non-ADS-B-compliant in 2020, when flying the approach without WAAS?

This depends on the ADS-B receiver that you have, but if it is still receiving position information, but the WAAS portion is missing, you will get a lower NAC/NIC/SIL in the broadcast message. If you disable the GPS completely, the ADS-B will continue to function however the SIL for position will be the lowest level (likewise for NAC/NIC). The ADS-B will continue to function (as in send messages) but the position reports will be unavailable.

It's important to note that your transponder is still a Mode-C transponder, even if the ADS-B fails (completely or partially). You should inform ATC that you have an ADS-B or GPS failure and they will inform you if you are cleared to continue or not.

Really though as far as this is concerned, creating an actual failure is very much not recommended. If I were you, I'd just say "let's pretend that you have a RAIM message about your WAAS, what are your new minimums?" Creating an actual failure is something like pulling the bulb out of one of the gear indicators. It might be a "teachable" moment at first, but really just creates a distraction that can be done in other ways. What happens if the circuit breaker fails and the weather actually drops? Now you have a real problem...


Why not make the touchdown zone of runways wider than the rest? Reasons:

Save money by making the rest of the runway narrower
Larger margin of error left and right
Easier to turn around, if necessary

And if the reason that it isn't done is merely for regulation/legal reasons: Is this something that would be practical if it were allowed?

Because most runways already are as narrow as safely feasible.

Let us look at your question piece by piece:

  Save money by making the rest of the runway narrower

You seem to be assuming we are currently deliberately wasting asphalt on making runways wider than needed, and could build them narrower. As they say on Wikipedia: [citation needed].

  Larger margin of error left and right

The touchdown zone is the whole runway, as long as the aircraft in question can stop afterwards, so if you start down this alley you'll find it cheaper to complete the runway in the same width.

  Easier to turn around, if necessary

This is already done by including turn pads, on top of the nominal width. For an example, see: OGZ


What are the advantages of using a ramjet in an air-to-surface missile? Which are the advantages of using a ramjet compared to a rocket engine in an air-to-surface missile? I suppose the cost rises a lot, so why do some countries use ramjets as a way of propelling ASM missiles?

A rocket-powered missile carries both fuel and oxidiser and oxidiser is the heavier part. For example a gram of jet fuel needs almost 3.4 grams of oxygen to fully burn! Increasing the fuel load requires also increasing the power, which means even more fuel and this limits the practical range of a missile.

Ramjets are air-breathing, so they don't need to carry the oxidiser, which means the same amount of fuel gives them significantly longer range. Plus the other constituents of air, and extra air, that get pulled along and heated in the engine add to the available reaction mass, further increasing the propulsive efficiency.

Longer range means the aircraft can fire the missile further away and avoid coming into range of the defenses placed around the target, which might make difference between being able to attack a heavily defended target and not, so it is worth the expense to have some in stock.

Also note that ramjet is only more complicated, and expensive, than a solid-fuel rocket motor. Compared to liquid-fuel rocket it is simpler, because it only needs easy-to-handle kerosene while liquid-fuel rockets either need liquid oxygen, or nasty stuff like peroxide or hydrazine. It is also simpler compared to a full turbofan or turbojet (a small solid rocket booster is usually used to get it up to speed).


What is "ACO transition"? In MSFS2020, I frequently hear terms like "Cleared to ACO transition" and I can set an ACO in my flight plan.  What exactly is an ACO and its obviously not a unique point because they seem to be everywhere?
It was for KCAK (Akron-Canton Regional Airport) but I thought I saw the same thing for KCLE as well, maybe I was mistaken. But the MSF2020 ATC says ACO transition.

A transition is a branch of a Standard Terminal Arrival Route (STAR) or a Standard Instrument Departure (SID). ACO is the identifier for the Akron VOR/DME, which is a a navaid. It’s not surprising then that you would hear of an ACO transition for both KCAK and KCLE.
I would provide a chart showing where these are, but I can’t find any plates for the older VOR navigation. All the ones I find are RNAV which use GPS rather than navaids. Although the ACO VOR/DME is still operational, they are slowly being decommissioned. The FAA may have eliminated the VOR SIDS and STARs and are now only using the RNAV routes. It’s likely that the sim is using outdated plates.
If you are unfamiliar with SIDs and STARs you can check out This question.


Turbines in jet engines I was reading this thread and in the answer, the person wrote "For example, the turbine blades are replaced after a set number of turbine cycles and/or after a set number of hours, which are lesser than the others."

What is the main reason for replacing the turbine blades?
is it the fatigue or deterioration of TBC?

Both, and it depends.  When a Hot Section Inspection is done, they are looking for mostly blade erosion beyond dimensional limits, and cracks.  Some cracks are allowed if the OEM's engineering determines they are benign (sometimes cracks form which fully relieve the stress that initiated them and the crack stops propagating - such cracks can be left alone, and the engine OEM will have clearly defined crack allowances and limits).

Erosion is mostly a function of how dirty the atmosphere is.  An engine running in the high Arctic that sees very little dust (outdoor dust close to the ground is mostly silica particles - sand paper without the paper) may run a very long time before significant erosion and the hot section might only have to be rebuilt due to burner can or blade cracking from operating cycles.

An engine running in the Middle East may only run half the normal TBO before blade erosion forces the engine off, made worse if an operator avoids using flex thrust to minimize engine demands on takeoff.

Then, some engines are more susceptible to erosion than others, depending on the compressor inlet design.  Turbofans with a stronger ram effect (good for overall efficiency and for windmilling after a flame out) suffer more than those with less.


Is it practical to intentionally stall an aircraft to execute a fast, controlled descent? An MD-11 had an onboard fire, but had to request more flying distance at least partly to execute a safe descent (and to dump fuel). It ended in tragedy.
In another accident, an A330 descended 30,000 feet in three minutes, in control (or at least in a recoverable state) during a stall.
Right now, airplanes in general, and particularly large jets, seem to be limited to 8000 fpm. So, I am wondering, can an intentional stall really accelerate this descent in a safe manner? The very high drag would keep the airplane from overspeeding, and there's no need to certify things like thrust reversers for deployment during flight. Heck - it could even be used to speed up the approach phase of a landing, saving time and airspace.

It isn't practical for a number of reasons:

Intentional stalls are inherently dangerous. Stall-spin accidents are a major cause of accidents, stall recognition and recovery are taught specifically to avoid stalls.  Some airplanes have docile stall characteristics, but even those can still bite you. A Cessna 172 will drop a wing if mishandled, especially when heavy. Stall behavior at high altitude can be very severe
Some airplanes with a t-tail can enter what is known as a 'deep-stall', where turbulent airflow masks the tail and makes the elevator ineffective and the airplane unrecoverable
Situational awareness: dropping like a stone with the nose up does not give pilots a view of the outside, or see what mountain they may be heading towards
It takes time to do a controlled stall. You have to pull throttle and maintain altitude, degrading airspeed until you enter a fully developed stall. This isn't instant, in a light airplane it will take 30 seconds or so, I'm not sure how long it would be for an airliner at cruising altitude, but I imagine it may take a minute for a fully developed stall to develop and to get that high rate of descent, whereas you can be in a dive with a steep rate of descent in a much shorter time

Consider an emergency descent from FL400 (40 thousand feet) to FL100 (10 thousand feet) using the 2 methods: A dive at 8000fpm and a 'controlled' stall at 10000fpm, where it takes 30 seconds to get into a developed stall and high rate of descent:

60 seconds: the diving airplane is at FL320, the stalling airplane at FL350
2 minutes: the diving airplane is at FL240, the stalling airplane at FL250
3 minutes: the diving airplane is at FL160, the stalling airplane at FL150
3 minutes 30 seconds: the stalling airplane is at FL100
3 minutes 45 seconds: the diving airplane is at FL100

So, by these calculations the stall option saves 15 seconds to lose 30 thousand feet because of the time penalty to get into a stall in the first place. That's really not much, and considering the risks involved from the potential loss of control and spacial awareness it's simply not worth it.
Not only is it not practical, it's not necessary to descend faster. A high speed descent is required for a number of emergencies, a cabin depressurization being the most prominent one, but there you have emergency oxygen supplies which will last much longer than required, so a few seconds will make little difference to survival. With an in-flight fire or other emergency where landing quickly is imperative the limitation is not descent speed, but proximity to landing fields which determines survival.


Why did my flight descend for landing then suddenly climb steeply and turn sharply? I was flying on a Vueling flight (VLG6251) from Rome, Italy to Orly, France on the 31st of December 2017. During landing, my plane went to a really low altitude as if it was about to land but there was no airport! I mean it was really low, and all of the sudden the plane sped up as if was taking off and it went to really high altitude really fast, while sharply turning to the left! Then I saw the airport. I checked the flight history of that flight and there was no history of it doing that.

Any suggestions on what was happening?

According to data recorded on Flightradar24 and the Planefinder App, that particular flight did not go around; however the turn to final approach was flown at lower altitude than some other flights that day (this seems different but not necessarily uncommon or abnormal, and happened for unknown reasons that cannot be inferred from the data).

Screenshot from the app:


How can this ACARS message be decoded? With regards to the text below, can someone offer either advice or a link to a website/document that would help decode ACARS messages.

I am ok with the following:

QU - ACARS "to" address
Q - ACARS "from" address
FML - data from left hand FMS
FI - Flight Identifier
AN - Aircraft Number
IGW1 - Iridium server identifier
130710 - date/time of data package sent
F57A - package identifier

So that leaves the DT QXT info plus the hex from ADS line.

QU REKASCC
.QXSXMXS 130710
FML
FI AB1234/AN G-INFO
DT QXT IGW1 130710 F57A
-  ADS.TF-
AMU0719603F0D994AFD09849D0D1B05B71C71CAFC85601FFFFF55554AFC800E0EB0F57FF40F0E29AA3FF4100EB11E0E8EFE

ACARS encoding is usually different from customer to customer.  Decoding it can be very difficult, even if you have access to the aircraft to have some idea of what is being sent.  Usually, the manufacturer won't share the details with anyone other than the original customer, expecting subsequent operators to pay for custom coding on the ACARS.  A general introduction to the basic standard codes can be found here; www.universal-radio.com/catalog/decoders/acarsweb.pdf .   The 'out return in' messages are pretty much standard.  No doubt there are enthusiasts out there who have decoded at least parts of the carrier specific/aircraft specific coding.  I worked with an ACARS equipped fleet where most of the messages sent were carrier specific and I never did manage to get the decode of the top of climb (TOC), cruise (CRZ) and top of descent (TOD) reports that were being sent automatically, despite the co-operation of the vender and the original customer, as the original customer had thrown that information away.

LIkely decode from the data you have supplied;

POSN70071W097007 = Postion North 70 degrees 07.1 minutes, West 9 degrees 00.7 minutes.

Sorry, it isn't much.  G-INFO isn't the registration either, it would seem.  Registration information is usually hard encoded in a custom plug for each aircraft's ACARS system.


Why there is a helicopter sitting north of madras, OR, , above the warm springs reservation every single night? Every night I see a helicopter light above the reservation sitting in a spot above my house, but way up that I can't see it closely, just the light.  Has to be a helicopter since it sits in one spot.

If you are looking up at a bright thing in the southwestern or western sky before 11 PM in March 2020 and you aren't also able to locate the planet Venus at the same time, then the bright thing is the planet Venus.

Venus is very high and bright in southwestern or western sky in the evenings these days.  Unless it is very near the horizon, it appears to shine with a white steady light.  With a clear distant horizon, it will set in the west about 23:30 PDT at your location.  (Calculated via this on-line tool.)

The star Sirius is also still prominent in the evening sky.  It can appear to flicker quite dramatically, flashing from red to blue, especially when near the horizon, but is nowhere near as bright as Venus.  With a clear distant horizon it will set in the southwest at about 2:50 AM PDT at your location.  (Calculated via this on-line tool.)

Does the object make a helicopter sound, or some other sound, or no sound?

Is the light steady, or is it definitely blinking completely off and then back on?  What color(s)?   What direction is the light from you?  Does it stay in the same direction from you if you drive 10 miles down a road and look at again? (I.e. does it appear to "follow" you as some observers have often said about such things?)  Is it so high that it could not be a tower?  Does it get nearer to the western horizon over the course of several hours? Can you establish what time it "sets" below the horizon, if it does? Is it still visible at midnight? Is it still visible in the pre-dawn twilight? If you have access to binoculars, does it look like a tiny round circle that is not flashing or flickering when seen through the binoculars?

Odds seem good that it is Venus, but the answers to these questions should confirm or reject this hypothesis.  Due to the path of the ecliptic, Venus may be well north of due west even near the spring equinox when the sun is setting nearly due west.

If it is definitely a flying vehicle, which seems unlikely, you can't assume it is not an unmanned drone/ UAV.


What is this partially disassembled aircraft in the desert? I found this plane on Google Earth. I'm guessing it is being deconstructed, as there are no factories nearby. What countries could it have originated from?

The coordinates are 35°54'10.9"N, 117°43'51.6"W. Here's the location on Google Maps.

The plane is about 41 feet long, and seems to have had a wingspan of about 30 feet.

Also, if it is possible, what kinds of planes could this be?

Sorry if this question is not really possible to answer. I'm a complete beginner at aircraft.

So, you found what looks like an F-8 missing a wing in the middle of the USN's Air Warfare Center at China Lake.

It resembles the F-8 a lot:

Image Source

As @Andrew said in a comment, the plane might be an F-11 which has a little closer resemblance to your picture.

Image Source


Is there anything in any airport called a "warm apron"? I heard a pilot said they are located at big airports like LAX. But I couldn't find any information about it.

A warm up apron is a portion of the airfield close to the runway entry, where the engine can be warmed up before taking off. It seems to be more frequently used in military documentation.

There are such aprons at Cairns Army Airfield:

Source

Found in FAA regulations, e.g. AC 150/5340-30:

  PAPI LHAs must not be located closer than 50 ft from a crossing
  runway, taxiway, or warm-up apron or within the ILS critical area.

But also in other not regulatory documents, here for synonymous of hardstand:

  ... construction of the RMP test section and warm-up apron (hardstand)
  at the east end of Runway 04-22. The RMP warm-up apron was
  successfully constructed and has been opened for traffic since October
  1992.

Source: Design, Construction and Performance of Resin Modified Pavement at Fort Campbell Army Airfield, Kentucky

A vintage post-card:

Source: eBay


What are the differences in design considerations for ground attack and air dominance aircraft? What parameters and types of performance are designers trying to maximize when building an air dominance fighter plane rather than a ground support fighter? What are the trade offs between them - what do I sacrifice to make a great fighter aircraft vs. a great ground support aircraft?

One thing to note is that 'pure' air dominance fighter or ground attack aircraft is not being developed anymore. Most of the combat aircraft developed recently/under development are multirole (or 'omnirole') aircraft.

In case of air dominance (or air superiority) fighters, which have the task of eliminating enemy air defense system especially fighters and securing aerial control for operation of friendly forces without harassment, the following are important design objectives:

High thrust to weight ratio, as it helps in maneuvers.
Stealth, as the enemy can't shoot what he/she can't see.
High maneuverability, for close combat situations and evasion.
High weapons load, as it enables engagement of a large number of enemy aircraft at once.
A good range, as it is better to engage enemy aircraft in their area rather than in friendly territory.
A powerful radar to track and engage enemy aircraft, as it enables them to shoot first.
Communication links to transfer data between the aircraft and between the AEWACS aircraft, as most of the aircraft today operate in an integrated battlefield.
Speed is also a very important parameter.

In case of ground support (or attack) aircraft, whose primary task is the destruction of enemy logistics and/or support for ground troops under fire, the designers look for similar yet a bit different set of characteristics.

Ruggedness, as the aircraft should be able take some amount of punishment and return home.
High endurance and Time on Target, as the ground troops may require support for an extended period of time, with corresponding weapons load.
Communication links between aircraft and ground troops for obvious reasons.
Precision targeting systems for situations where friendlies are in close contact with the enemy troops.
Ability to operate from forward operating bases is desirable.

Most of the present generation aircraft carry out their ground support duties using precision weaponry rather than any fundamental design decisions. Though there are still trade-offs, as in any aircraft design.

The weapon load of stealth aircraft is lesser their non-stealthy counterparts as external weapons carriage increases the radar signature of the aircraft.
For ground attack aircraft, a high subsonic speed is more than enough unlike the supersonic air dominance fighters.
Low altitude maneuverability is important for ground attack aircraft for quick ingress and egress from the combat area.

One aspect of aircraft design is that combat aircraft optimized for high altitude operations can face higher stresses when operating in lower altitudes (i.e. near ground). For example, when USAF switched B-52s from high altitude bombing role to low altitude penetration tactics, it caused increased stress in the airframe.


Why is it assumed on sectionals that the area outside of a 700 AGL Class E (Echo) transition area is Class E starting at 1,200 AGL? In this Bold Method article (http://www.boldmethod.com/learn-to-fly/airspace/class-g-airspace/) it is stated that anything beyond the hard lines of this examples 1,200 ft AGL Class E (blue) transition area is Class G (Golf).

So far so good.

However, further down in the article, it is stated that beyond the hard lines of the magenta 700 ft AGL Class E transition area that the airspace is Class G until 1,200 ft AGL at which point it turns into Class E again (think the blue Class E area that exists above this entire area).

Why is it assumed that outside the 700 ft AGL Class E transition area there lies 1,200 ft AGL Class E? It surely isn't represented in the screenshot. Couldn't it just as well be Class G until 14,500 ft AGL?

Take a look at the legend on the side of a VFR chart. (You can get them for free at https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/vfr/ )

Class E exists at 1200' AGL unless otherwise designated as shown above.


Where does the final approach begin if the glide slope is intercepted at an altitude above that depicted on the approach chart? The final approach segment for an approach with vertical guidance or a
  precision approach begins where the glideslope/glidepath intercepts
  the minimum glideslope/glipdepath intercept altitude shown on the
  approach chart. If ATC authorizes a lower intercept altitude, the
  final approach segment begins upon glideslope/glidepath interception
  at that altitude.

(FAA IPH, p. 4-53)

Does this paragraph imply that the FAF(FAP) for a precision approach fix (point) begins at the minimum glideslope intercept altitude when you have intercepted the glideslope at an altitude above that?

I always have thought the FAF for a precision approach begins wherever the glideslope is intercepted regardless of a glideslope interception altitude. Have I been getting it wrong all this time?

This question doesn't answer what I'm asking. I'm not asking where the FAF generally begins on a precision approach; I know where it begins and I've cited it above. My question is whether the FAF begins at the interception point even when the glide slope is intercepted at an altitude above the minimum interception altitude on the chart. The definition above from the IPH clearly says the final approach fix is the interception altitude when it's intercepted at an altitude below the minimum interception altitude but is silent on where the FAF begins if it's intercepted at an altitude above the minimum interception altitude.

The FAS begins when you've intercepted the GS, and are at or beyond (below) the charted GS intercept point (altitude).  So if your charted GS intercept is at BONGO at 3000' and you intercept the GS outside BONGO at 4000', your FAS begins at BONGO.  If ATC has you join the localizer at 2500' and you intercept the GS at 2500' inside of BONGO, then that point, where you intercepted the GS, is where the FAS starts on that approach that day for you.

There can be lots of ways to say that, some of which are less clear than others.  But that's the simple, and hopefully clear, answer.  And, maybe, going back to the FAA definition, you can see how what they put on paper matches this concept as stated here.


When pilots check in with a different controller, how to reference flight level? When pilots check in with a different controller after they are handed off, how do they report their current altitude in flight levels if they are in level flight or a climb / descent? I feel like saying "level flight level" could be misunderstood.

Can pilots omit the "flight level" phraseology in the examples below?

"(ATC Facility) Baron x-ray five x-ray sierra level flight level two-five-zero... " (level flight @ FL250)

"(ATC Facility) Baron x-ray five x-ray sierra flight level two-five-zero climbing flight level three-two-zero..."

"(ATC Facility) Baron x-ray five x-ray sierra flight level two-five-zero descending flight level two-zero-zero..."

The word 'maintaining' is used, not 'level'. Using your example it would be:

(ATC Facility) Baron X5XS level maintaining FL 250.

The pilot can say maintaining if they're expecting higher/lower, otherwise omit maintaining altogether:

(ATC Facility) Baron X5XS FL 250.

If climbing/descending:

(ATC Facility) Baron X5XS climbing/descending FL 100.

On the first contact with a radar service, for example going from tower to departure, the SID and passing altitude are also mentioned:

(ATC Facility) Baron X5XS on the STACK 1C passing 2300 for FL 60.

In a busy environment you may be asked to 'report call sign only', in this case:

(ATC Facility) Baron X5XS

Local guidelines should also be used if different. I couldn't find examples in ICAO Annex 10 and Doc 4444, but clear examples are in the UK's Radiotelephony Manual (click image below to view).


Why can a localiser be used without a glideslope, but not vice versa? An ILS consists, at its most basic, of two components: a localiser (to provide lateral guidance) and a glideslope (to provide vertical guidance).  The two are typically used together, for an ILS approach, but the localiser can also be used on its own, for a localiser-only, or simply localiser (LOC for short), approach (for instance, if the glideslope is inoperative or nonexistent, the aircraft lacks a functioning glideslope receiver, or the pilot is shooting a back-course approach).  For a localiser-only approach, the pilot uses a specified series of navigational fixes to mark off each segment of the approach; each of these segments has a specified minimum safe altitude (which is shown on the approach plate), and the pilot uses this information, and their onboard baroaltimeter, to maintain terrain clearance during the approach.

While localiser-sans-glideslope approaches are quite common, there are, to the best of my knowledge (feel free to correct me if I'm mistaken here), no examples of the reverse: a glideslope-sans-localiser approach, where the pilot uses the glideslope for vertical guidance but relies on ground- or satellite-based navigation fixes for lateral guidance.

What allows the use for an approach of a localiser without a glideslope, but not a glideslope without a localiser?

Adding to @J.Hougaard's practical reasons, there is one technical reason in the existing standards I can think of:

The identification signal (morse code) is provided by the localizer, not the G/S, so G/S-only approaches would be unidentifiable. (ICAO Annex 10 Vol 1 § 3.1.3.9)

Side note: I'm not sure if there can be a workaround for it using existing airborne equipment, since a G/S works on UHF (which is transparent to the pilot, i.e., the pilot only selects the LOC VHF frequency, and the G/S UHF frequency is simply paired).

The identification is likely one of the reasons behind the following:

  Inoperative localizer. When the localizer fails, an ILS approach is not authorized. (FAA AIM)

There is no mention of an operative G/S remaining. Whereas a failed G/S does not prohibit using the LOC for a LOC-only approach (after adjusting the minima).


More information on PanAm's first trans-Pacific flight I have came across this answer, about PanAm's first trans-Pacific flight (SFO-MNL route via HNL, MDY, AWK and GUM). For the text, I'm working on, I was wondering, if there is any source that can provide more information on this route.

Literally:

years of operation,
approx. times needed to flight each segment,
approx. break times (refueling?) times at each mid-point,
was passengers allowed to leave the airplane during each break?

I'm also interested in getting answer to a question that might be harder to answer (too broad?). How it was possible to service / refuel airplane on airports marked as uninhabited in the original answer (MDY and AWK)?

There are many sources of information about these flights that you can find by doing an Internet search. For example, I just used "panam clipper flight sfo to mnl".

The following links should get you started:

In addition to some aircraft information, this link has a schedule image about halfway down the page:
https://www.pacificaviationmuseum.org/pearl-harbor-blog/pan-ams-pacific-clippers/

This link has more Manila-specific info, with a video.
http://www.lougopal.com/manila/?p=1463

The following link, in the paragraph "Building Bases Across the Pacific" will answer your last question regarding MDY/AWK:
http://www.clipperflyingboats.com/transpacific-airline-service


Does the coriolis force have an effect on the direction in which an aircraft travels? Suppose an aircraft is flying from Kenya (which lies on the equator) to UK (which lies in the northern hemisphere). Does the Coriolis force veer the aircraft to the right? Do pilots have to correct their flight route because of this?

Yes, the effect is there, and (auto-) pilots have to compensate for it, but the direct impact of the Coriolis force is insignificant compared to the impact of any wind forces.

This has been discussed on Physics SE: Coriolis force on bullet vs airplane

On the other hand side, the Coriolis force (seemingly) deflects moving air masses and causes the global wind patterns as we now them. Through the resulting wind forces on aircrafts, the Coriolis force has a very significant indirect impact on aircraft travel.


Travelling at faster than mach 1, how sharp could Concorde turn to avoid injury to passengers? To avoid injury to passengers (too many G's) was there a max 'sharpness' of the turns it made when travelling at certain speeds?

All aircraft experience the same G force per degree of bank angle, so a 60 degree turn in a Cessna produces 2G just like a 60 degree turn in Concorde would produce 2G.

The difference is that a Cessna doing 100 knots could circle in 0.2 miles by using a 60 degree bank angle.

Concorde doing 1000 knots and 60 degrees would take up 19.5 miles to do the same thing.

In both cases the passengers would experience 2G which even so is pretty severe if you are a passenger and aren't used to it. It would get your attention let me put it that way.

I'm not an airline pilot. However I would think that the risk with higher speeds is in angle of attack or angle of attack combined with bank angles. At higher speeds its much easier to produce a whole load of G by pulling or pushing the controls than it is in your Cessna, and even that can be pretty severe.

So while you might not worry as much about bank angles you would be very careful not to pitch up or down too far especially at higher speeds because you could overstress the aircraft real easy.

Hopefully a pilot who knows Concorde and / or airliner systems can improve on this answer.


What causes descending aircraft to make a noise like a giant blown bottle? I've lived for years about eight miles NW of Boston's Logan Airport. Although I can't say we get a lot of aircraft noise, once in a while, due to winds or air traffic, there will be a long line of planes traveling right over my house, perhaps 6000-8000 feet up, descending into Logan. At night you can sometimes see three in a row, with a fourth one turning on its landing lights.

Most of the time the overhead planes sound mostly like a roar with some jet whine. However, once in a while a plane will suddenly start making a very strange sound like an enormous blown Coke bottle. Often the pitch will descend during a half dozen seconds, stay constant for a dozen seconds, and then rise again until the sound disappears.

My best guess is that the sound is caused by the pilot lowering the wheels during their descent, and that it only happens on certain models of aircraft. As the wheel well covers open, the air blowing across the wells sounds like that giant Coke bottle, with the pitch decreasing as the opening increases. On certain models, the covers will then close once the wheels are down, causing the pitch to go back up.

(Edit: it's been pointed out that gear isn't dropped until 2000-3000 feet, so in my case that isn't the sound. So, I've removed all those videos, cool though they may be.)

Is my guess right? What model/manufacturer of large jet would make this sound?

Short Answer:

The sound is caused by airflow across holes on the underside of the wings of certain aircraft.

Long Answer:

I too have noted the sound phenomenon that you describe. This video has a great example between 0:26-52 (link starts playback at 0:26 where the noise starts):

I will readily admit that this answer is mostly just a compilation of what I have learned researching this. Your question intrigued me and I've enjoyed learning about it!

As I discovered as I started researching this, many others are familiar with the noise as well. This article on Airliners.net had a lot of discussion about it, starting with a lot of interesting—but ultimately flawed—theories.

But, that thread led me to the answer to your question, which is: the sound is caused by the "circular opening used to equalise the pressure in wing fuel tanks", according to Euractiv.com

This article on AirportWatch further explains:

  The Airbus 320 series of aircraft, [...] have been known for many years
  [...] to have a particularly irritating high pitched
  whine. This is caused by air rushing across the under-surface of the
  wing, where there are Fuel Over Pressure Protector (FOPP) cavities.
  This generates noise, in the same way as blowing air over the mouth of
  a bottle. Every A320 series aircraft emits a signature howling noise
  while approaching to land. It is heard most when the plane is
  travelling at around 160 knots, and the frequency is around 500-600Hz,
  which is close to peak sensitivity of the  human ear.

That being said, there is apparently a fix to that problem, as both the aforementioned links describe. As Euractiv.com explains, the fix is a vortex generator:

  a 5-cm triangular piece of aluminium sheet metal upstream of the two
  vents on each wing, in order to divert the air flow and stop the
  whistle. A decade of research went into the vortex generator, which
  stems from efforts to mask a similar whistle produced when air blows
  over the gun ports of warplanes.

This image shows both the FOPP hole, and the VG that softens the sound:

[Image Courtesy of Lufthansa]

Read the articles linked, interesting stuff therein!


What does it mean when an aircraft is statically stable but dynamically unstable? I am reading this book: "Flight Stability and Automatic Control", second edition, Dr. Robert C. Nelson. In the chapter 2, page 42, the author wrote:

Note that the vehicle can be statically stable but dynamically unstable. Static stability, therefore, does not guarantee dynamic stability. However, for the vehicle to dynamically stable it must be statically stable.

I understand static stability, but I am not sure I understand dynamic stability. Can someone help me understand the above texts and give me an example of this case?

Static stability means that a deviation from a trimmed state produces forces which return the system to this trimmed state.
If these forces produce an overshoot which increases over time, such that the system oscillates around this trim point with increasing amplitude, the system is dynamically unstable. The long period oscillation (phygoid) of gliders is often unstable because their L/D is high enough to push them into unstable territory.
Dynamic stability means that the oscillations die down over time. Without static stability the system would simply leave the trimmed state without any tendency to return. This tendency to return is the prerequisite for the oscillation, whether stable or unstable.


About how much drag does a non-operating engine create? I think the drag of the engine is high, for most type of engine, e.g turbo fan, jet, ramjet... I guess the engine's drag is worse than a flat plate of the same area perpendicular to air stream because the engine slows the air and compress it, and also the engine has many components inside it that will interact with air.

A flat plate is very bad aerodynamically and so the engine. Even small landing wheel should be folded inside body for better drag. So an aircraft with engines turned off will have very high drag, but I can not find any estimation on this matter.

For example, an aircraft that has L/D about 15, how about its drag if engine is removed, e.g. for better glide ratio when engine failure?

Can you estimate this drag?

An inoperative engine creates much less drag than a flat plate of the same cross section. According to Sighard Hoerner's Fluid Dynamic Drag, the drag coefficient of a flat plate is 1.17. An engine nacelle has rounded intake lips which help the flow to stay attached while flowing around the nacelle. The closest of the generic bodies in the table below would be the sphere (drag coefficient of 0.47).

Figure 33 from Sighard Hoerner's Fluid Dynamic Drag, Chapter 3. Left column: Bodies of rotation; right column: Cross sections of 2D-bodies.

Much depends on the detail of flow separation at the forward corner, and here modern engines are rather good. If the flow stays attached, drag will be much lower than with the massive separation around and behind the flat plate. Air flowing out from the inside and over the corner of the flat plate will need some space to "turn around", effectively increasing the blocked cross section that the outside flow experiences.

Note that the reference area for all values here is the cross section of the body perpendicular to the flow, while the reference area for airplanes is their wing area.

Depending on the type, the diameter of one GE90 engine is 134 or 135 inches. Two of those power a Boeing 777 which has a wing area of 427.8 m². The ratio of engine frontal area to wing area is thus 1/23.335. The (estimated) drag coefficient of the nacelle of 0.5 would shrink to 0.0214 when referenced to the wing area. This would increase the total drag by about 50%, so instead of an L/D of 18 without engines, the airplane would have an L/D of 12 with inoperative engines.


Why is there so much movement of the sidestick during this takeoff? Watching a video entitled Airbus A330 Takeoff Sidestick View, there appears to be a lot of side-to-side movement of the sidestick, as well as a lot of pushing the nose down:

I was under the impression that movements on the control column should be smooth and not erratic — what is the reason for the side-to-side movement? As far as I can see on the MFDs, there is no heading change prior to 02:50 (which appears to be done by the A/P anyway). Is it turbulence?

Also, what is the reason for pushing the nose down? Is the plane naturally trying to pull up at too high of an angle?

This landing video appears to show even more erratic control. Is this normal?

One of the unique aspects of Airbus fly-by-wire aircraft is that the sidesticks provide NO feedback. Because of this, the planes have an automatic trim system. Once the aircraft is pitched to a desired attitude, the pilot will then release the control stick and the aircraft will continue to fly at the selected attitude.

Correspondingly, if a pilot desires to reduce the pitch, they must push the stick forward to do so. In an Airbus (unlike most other aircraft), a pilot doesn't manipulate trim at all (except in non-normal situations).

As an aside, in the normal flight regime, Airbuses provide automatic protections from unsafe attitudes. Thus, if a pilot desires maximum rate of climb (that is possible in the current configuration), he can simply pull the sidestick all the way back. The computer will automatically keep the aircraft from exceeding maximum load factor and/or critical angle-of-attack.

To answer the other part of your question, the lateral stick movement is likely due to turbulence. Control inputs in large aircraft tend to be more pronounced than smaller aircraft (due to slower aircraft reaction times).


Can you be paid to taxi an aircraft if you don't have a commercial license? From a strictly legal standpoint, in the US (I'm also interested in Canada) can you (not should you) accept compensation to taxi an aircraft if you don't have a commercial pilot's license? If I was a mechanic with just a private license, could I charge for my time while taxiing an aircraft?

Yes, as per 61.113:

  (a) Except as provided in paragraphs (b) through (h) of this section,
  no person who holds a private pilot certificate may act as pilot in
  command of an aircraft that is carrying passengers or property for
  compensation or hire; nor may that person, for compensation or hire,
  act as pilot in command of an aircraft.

A person taxiing an aircraft that is not intended for flight is not acting as PIC under this rule, and therefore can not only be a private pilot, but the person doesn't have to be a pilot at all.

There is no specific FAR that qualifies someone to taxi an aircraft, but aircraft operators and maintenance shops train and authorize mechanics to taxi and run-up engines.

Some individual airports have regulations that specify who may taxi and run-up an engine, such as Palm Springs:

  (a)      Only qualified persons shall start and/or operate an Aircraft
  engine at the Airport and/or taxi an Aircraft on the Airport.
  Qualified persons include a pilot, an airframe and power plant
  mechanic, or a qualified technician licensed by the FAA and qualified
  to start or operate the engine(s) and/or taxi that particular type and
  class of Aircraft.

and Whitman County Airport:

  14.20.130 - Who may taxi aircraft.  No person other than a mechanic, pilot, or properly authorized student pilot, certified by the FAA,
  shall taxi aircraft on any part of the airport.


What were the disadvantages of early prop driven blended-wing aircraft? I've been researching the history of pre-jet aircraft and I've come across several famous, and not so famous, blended-wing aircraft. The idea seemed to show promise but never really caught on, even for a limited span of time or confluence of technological factors e.g. weight vs engine power etc.

Just to be clear, I'm not interest in flying wing and/or tailless aircraft whose early problems are well known, but rather those designs that have tails but have a fuselage shaped to produced a significant component of lift.

Just a few of the designs I've stumbled across:

Burnelli CBY-3

Cunliffe-Owen OA-1 (Burnelli license)

French de Monge 7.4

Soviet LK-1 a.k.a. Fanera-2

There are quite a few more I don't have handy web links for. Junkers did a couple that would probably qualify.

The large number of designs from all over the world show that the basic idea offered promise but all the designs eventually went no where despite being tried in many countries, economies and even political systems. That in turn seems strange because in the 1920s-early-1940s, lift seemed more important than speed for larger multiengine aircraft i.e. just getting a load airborne at all was worth quite a few other tradeoffs. As engines grew more powerful that tradeoff lessened but for at least 15-20 years a high lift design should have been more desirable than a high speed one for larger aircraft.

The failure of many different designers over the course of three decades to make the blended wing work suggest to me that the basic idea has some inherent disadvantage/s that outweighed any gains. Unfortunately, none of the resources I have consulted offer any clues to why the designs did not "take off."

I suspect the designs showed some rapid onset of stall of instabilty but that's just an uninformed hunch on my part.

Any clues?

Generally, to create lift means to deflect the oncoming airstream downwards. How and where this is done in detail on an airplane is less important than doing it with a smooth spanwise lift distribution such that the wake behind the aircraft is trough-shaped.
A fuselage is disturbing this lift distribution, but not severely. The length of the fuselage means that it creates considerable lift at small incidences, even with the low lift slope of slender bodies. In case of the N-250 it was found that an incidence of 2° produces the lowest drag. However, this also means that the lift is only just right at one angle of attack, and when the aircraft is flown in different conditions, the fuselage can mess up the lift distribution quite easily, especially if it is wider than necessary.
During the 1930s and 40s, when this was understood in detail not only in academia, but also in the design offices, progress in engine technology pushed operating altitudes up until planes needed pressurized cabins to transport passengers comfortably. Pressurisation demands a round or nearly-round fuselage cross section to keep structural mass down, so any attempt at widening and shaping the fuselage would result in an unacceptable mass penalty. This ended the experimentation with lift-creating fuselages.
As for the N-250, the idea of fuselage inclination in cruise is correct in theory, but resulted in massive protests from the cabin crew which now had to push their carts uphill, ending this kind of optimization quickly. This is why it never caught on.