In fighter aircraft, we know that they have good enough of maneuverability. But in case of a passenger airplane, if a stall happens is the aircraft maneuverable enough to recover from it?
$\begingroup$ This question may be related, although it's about spins, not stalls $\endgroup$– PondlifeJan 16, 2015 at 15:26
1$\begingroup$ Manoeuvrability normally means how sharp turn an aircraft can make and how quickly it can roll into and out of it. Stall and spin recoveries are rather independent of that. $\endgroup$– Jan HudecJan 16, 2015 at 15:26
2$\begingroup$ I think this may be off-topic because the basis of your question is flawed: maneuverability and stall recoverability are not normally linked. $\endgroup$– CGCampbellJan 16, 2015 at 19:06
2$\begingroup$ @CGCampbell Well, not directly, but they are somewhat correlated... negatively. :) I don't think the question of whether an airliner can be recovered from a stall is off-topic, though. Also, stall recovery does usually involve a maneuver (though it's a pretty trivial one,) so the question isn't entirely incorrect, though it does use 'maneuverability' contrary to its normal meaning within aviation. $\endgroup$– reirabJan 16, 2015 at 21:00
5$\begingroup$ @CGCampbell Also, I'm not sure that a false premise in a question actually makes it off-topic. It's not unusual for someone not familiar with a field to have false assumptions about it (or even for someone familiar with a field to have false assumptions about some more obscure parts of it.) The underlying question - whether an airliner can be recovered from a stall - is perfectly answerable and on-topic - and has been answered. $\endgroup$– reirabJan 16, 2015 at 21:46
The main thing that is required for a stall recovery is just the ability to drop the nose to decrease angle-of-attack and regain airspeed (and, of course, adding power helps, too.) Except in the case of deep stall, there is still sufficient air flowing over the horizontal stabilizers (and, thus, the elevators) in an airliner to push the nose down during a stall. Furthermore, most airplanes (including nearly all, if not all, airliners) are designed with a center of gravity forward of the center of lift. In normal flight, the air flow over the horizontal stabilizers actually pushes the back of the plane down, which holds up the nose. During a stall, this airflow is reduced (still present, but to a lesser degree,) which will cause the nose to tend to drop by default during a stall condition, even if the pilot (or autopilot) gives no additional control inputs at all. As such, normal (e.g. not fighters or aerobatic planes) will recover from a stall on their own with no additional control inputs, given enough altitude.
As already mentioned, some altitude is also usually required for successful stall recovery. This is because the recovery procedures involve dropping the nose which will briefly result in some descent. The lack of sufficient altitude to recover was the main problem in Asiana 214, which crashed just short of the runway in San Francisco. The aircraft was already too low and too slow to recover before the pilots acted. If I remember correctly, they started attempting a go-around only about 7 seconds before the aircraft impacted the seawall. At that point, there was nothing they could do. A small, piston-engine aircraft probably still could have recovered from that situation because piston engines spin up much, much faster than jet engines and could provide the power needed to recover much faster. Pushing the nose down alone would still technically have recovered the plane from the stall condition in this case, but that wouldn't have been very helpful, since it would have meant a nose-first impact into either San Francisco Bay or the seawall, which would obviously have been a much worse outcome.
Another problem that can happen (though is very, very unlikely on an actual airline flight, but much more likely on cargo flights in airliners) is for the cargo to shift to the point that the center of gravity is too far from where it's designed to be for stall recovery to be possible. This is what happened on National Airlines Flight 102, a 747 cargo flight departing from Bagram Air Force Base in Afghanistan. Very shortly after takeoff, the cargo shifted to the back of the aircraft, preventing the pilots from being able to lower the nose enough to keep the plane from stalling. It stalled and crashed before ever leaving the property of the airfield.
In general, pitch stability (more precisely known as longitudinal static stability) is what makes an aircraft capable of stall recovery, not maneuverability. While it may seem counter-intuitive to those not familiar with aerodynamics, it's likely actually easier to recover from a stall in an airliner than it is in a fighter (and almost certainly easier to recover in, say, a Piper or Cessna than a jet fighter.) This is because more maneuverable aircraft (such as fighters and aerobatics aircraft) are usually less stable than less maneuverable aircraft like airliners and normal GA aircraft.
The answers to this question give a thorough explanation of stall recovery which I would recommend reading. Its answers apply to how stall recovery is performed in any normal airplane, not just airliners. That question isn't specifically about whether airliners can recover from a stall, though, which is why I didn't mark this one as a duplicate.
An airliner certainly has the ability to recover from a stall, given sufficient height and power. Moreover stall recovery isn't about maneuverability as such. A fighter jet is more difficult to recover from a stall than a Cessna 150, but the Cessna is much less maneuverable. (That is one among many reasons people learn to fly on Cessna 150s and not on fighter jets.)
It's also not a given that a fighter jet is easier to recover from a stall than an airliner.
4$\begingroup$ Well, that and the fact that a Cessna costs around 300K while a fighter jet is at least 30M. $\endgroup$– OctopusJan 18, 2015 at 5:47
2$\begingroup$ @Octopus And that's the new price. The used planes that a lot of people actually train in (myself included) can be more like \$20-\$30k. $\endgroup$ Jan 19, 2015 at 1:27
Yes and no.
If a stall happens while the plane is low to the ground without sufficient power to maintain altitude, there may not be time to recover.
At altitude, there is plenty of time for a plane to recover from a simple stall, and yes the plane has the maneuverability to do so.
Other conditions, like severe icing, may render the plane unable to recover.
All this assumes a plane without mechanical problems. Air France flight 447 had airspeed sensor problems and the pilots were presented with confusing information, they stalled the plane at altitude and rode it down into the ocean. All aboard perished.
Can a large passenger aircraft recover from a stall?
Here's what Boeing & Airbus say
this article was written jointly by Airbus, Boeing Commercial Airplane Group, and Douglas Products Division. The article focuses on Airbus and Boeing airplanes that do not have electronic flight controls, commonly known as fly-by-wire. However, when a fly-by-wire airplane is in a degraded control law (mode), the recovery techniques are appropriate.
An airplane stall is characterized by any one (or a combination) of the following conditions:
- Lack of pitch authority.
- Lack of roll control.
- Inability to arrest descent rate.
These conditions are usually accompanied by a continuous stall warning. A stall must not be confused with the stall warning that alerts the pilot to an approaching stall. Recovery from an approach to stall is not the same as a recovery from an actual stall. An approach to stall is a controlled flight maneuver; a stall is an out-of-control, but recoverable, condition.
In all upset situations, it is necessary to recover from a stall before applying any other recovery actions. To recover from the stall, angle of attack must be reduced below the stalling angle. Nose-down pitch control must be applied and maintained until the wings are unstalled. Under certain conditions, on airplanes with underwing-mounted engines, it may be necessary to reduce some thrust in order to prevent the angle of attack from continuing to increase. Once unstalled, upset recovery actions may be taken and thrust reapplied as needed.
A Bloomberg article: Does Your Airline Pilot Know How to Escape From a Stall? says
When planes do crash, the No. 1 cause is pilot loss of control. From 2001 to 2010, 1,756 people died in 20 such disasters. About half of these accidents involved aerodynamic stall,
Although this article suggests more training of pilots in stall recovery, the emphasis is properly on preventing a stall.
The Air France tragedy was partly that according to the flight data/voice, and some other impingent facts of note. Very high altitude, near the limit of the type for both altitude and air speed (actual air speed ~ 250 kts !!), also due to high air temp, less power, and non-stall velocity/AOA envelope was then very small. The pilot at the controls saw (typical for equatorial mid atlantic nights) severe weather ahead, and wanted to get on top of it. He really wanted altitude. Then the pitots iced, and he was suddenly a fish out of water, and he started to try to climb more, putting it into a stall regime, but he didn't seem to realize. They got into worse shape (up to 45 deg bank excursions) and the Captain was awakened and came to the flight deck, but apparently never touched a control. in just a short time, the ice cleared, the pitots were good. the plane that hit the water was a 100% functional machine. Then the problem seemed to be language - although all French, when co pilot suggested he get "more" he meant airspeed, but didn't say put the nose down. The first pilot continued to try to put the nose up ("more altitude". those two pilots went back and forth, verbally and override=preempting control of the control system from each other. Mean while, the flight deck annunciator for "STALL" had shut it self off after a while cuz it was given an "impossible" angle of attack as input, and gave up. It was so far nose up, the software disregarded it as a broken signal. Speculation is this reinforced the "climbing" pilots conclusions. This all went on as it plowed thru the air for several minutes, from +40K ft to the predicted last chance at 13Kft, when in theory, they could have still gotten the nose down enough for lift velocity then pull up before the wave tops that killed them. They never began a real stall recovery (other than to NOT roll over into an inverted dive or spin). They continued to argue and be confused, and unmanaged. My source for all of this was a good, detailed treatment in VOGUE, a few months ago. The plane most certainly could have been flown home, but not in boxes and bags, as it was.
It was capable of recovering, given the most altitude any pilot might ever get to start an emergency. I sit next to a SW developer from the 777 project (did flap control), and he was bemoaning the fact ...yes, Airbus went too far in expecting lesser trained crews to save the plane via auto systems, vs the perception that Boeing style designs were more likely to let a good pilot know what the plane is doing, and not doing, and get on with flying it.
2$\begingroup$ This answer seems to focus on the story of the Air France accident instead of the question (over 70% screen space). $\endgroup$– kevinJan 17, 2015 at 7:52
3$\begingroup$ This would be a good answer to "what happened to AF447 in 2009?" but it doesn't directly address the question above. Since AF is large and long established there have inevitably been several "AF tragedies" (AF4590 in 2000 is also notable) - it would be better to identify the specific event at the start. Also, wall-of-text: paragraphs aid reading. P.S the official report might be a better reference than Vogue magazine. Some edits to this answer could make it a higher scoring answer. $\endgroup$ Jan 17, 2015 at 10:32
It depends on the aircraft type. For instance, Tu-154 cannot recover from stall unless a special stall-recovery parachute is installed in its tail. The parachute normally is only installed during development testing, and never on the regular airlines.
1$\begingroup$ That's interesting. Can you provide a link for a source on that? The wiki article doesn't seem to contain anything about either the inability to recover from a stall or the parachute. I'm curious why it would be unable to recover from a stall. Is its design aerodynamically unstable? That would be very unusual for an airliner. $\endgroup$ Jan 16, 2015 at 20:57
2$\begingroup$ @reirab there are several reasons. First, its tail is overloaded because of 4 engines (3 main and 1 aux) inside. There is no way to lower the nose after stall. Second, the wings shadow out the engines and the elevator at high attack angle making encreasing engine power and elevator useless. Third, at high attack angles the turbulent air from wings reaches the engines often triggering surging, and at even higher angles air hunger in the engines (due to wing shadowing) starts, making increasing power impossible. Engines just go off. The parachute is meant to rise the tail to reduce the angle. $\endgroup$ Jan 16, 2015 at 21:22
6$\begingroup$ That sounds like a deep stall. Is it possible to stall a Tu-154 without entering deep stall? If so, would such a stall be recoverable by normal means? Also, it would probably be good to add that information to your answer rather than just having it in the comments. A source would be great for those of us interested in further reading, too, if you can find one. $\endgroup$ Jan 16, 2015 at 21:32
1$\begingroup$ @reirab from deep stall Tu-154 cannot recover even with a parashute... Stall longer than 2-3 sec means certain death for a regular liner. $\endgroup$ Mar 26, 2015 at 20:27
Yes an airliner can recover from a stall. The question of the pilots abilities to recover from that stall come into play.
Most modern airliners (Boeing, Airbus, Candair) install "stick shakers/ stick pushers," which are designed to alert the pilot to a stall and attempt a recover from the stall before it happens. If the pilot were to push the airliner into a stall, there is a possibility that the jet would not recover "nose down" as previously stated because of the aerodynamics of an airliner. This requires a stalled horizontal tail surface as well; a highly unlikely situation. In this case, if a tail-down command occurred, the pilot would need to press full deflection on the ailerons, possibly supported by spoilers, to either side to bring the aircraft over.
Pushing forward in a stall situation would result in one of two scenarios:
- the airflow over the horizontal stabilizers would not be sufficient to bring the nose down and the stall would continue,
- the tail gets lifted, the angle of attack decreases and the airplane recovers.
So with the aileron at full deflection the aircraft would roll and bring the nose down, and once level or below the horizon the pilot could then begin to gain airspeed and roll the aircraft out of the high roll angle and begin a normal stall recovery with positive G-forces.
Edit: According to Boeing, my previous comment is not totally supported. This answer is based on a "nose high, wings level" situation. Per Boeings website, they state-
"If normal pitch control inputs do not stop an increasing pitch rate, rolling the airplane to a bank angle that starts the nose down should work. Bank angles of about 45 degrees, up to a maximum of 60 degrees, could be needed. Unloading the wing by maintaining continuous nose-down elevator pressure will keep the wing angle of attack as low as possible, making the normal roll controls as effective as possible. With airspeed as low as stick shaker onset, normal roll controls -- up to full deflection of ailerons and spoilers -- may be used. The rolling maneuver changes the pitch rate into a turning maneuver, allowing the pitch to decrease. Finally, if normal pitch control then roll control is ineffective, careful rudder input in the direction of the desired roll may be required to induce a rolling maneuver for recovery.
Only a small amount of rudder is needed. Too much rudder applied too quickly or held too long may result in loss of lateral and directional control. Because of the low energy condition, pilots should exercise caution when applying rudder."
Hopefully this is the support that was asked for. I personally came across the aforementioned answer during aerodynamics class in college.
$\begingroup$ Hello Flyboy128, welcome to Aviation.SE. $\endgroup$– DeltaLima ♦Jan 17, 2015 at 11:51
$\begingroup$ You're right about the presence of the stick shakers. As far as your statements about the aerodynamics of an airliner, do you have any sources to back that up? It would be especially nice to have a source for your second scenario. Dropping a wing is certainly a way to get out of a stall, but dropping the nose is usually the recommended way when it's possible. In most airplanes (including most airliners,) the nose will drop on its own in a stall, due to decreased effectiveness of the horizontal stabilizers. The primary exception to this is a deep stall. $\endgroup$ Jan 17, 2015 at 20:44
$\begingroup$ @reirab: I edited the obvious nonsense out of the answer. $\endgroup$ Jan 19, 2015 at 7:17
Your premise is flawed. It is easier to recover from a stall in a passenger jet than in a fighter jet. An airliner (glide ratio 15:1) is much more buoyant than a fighter (glide ratio 8:1). When a fighter stalls, it drops like a brick and pray it is not in a bad attitude when that happens.
2$\begingroup$ This is totally wrong. $\endgroup$ Jan 16, 2015 at 20:41
$\begingroup$ Ease of stall recovery is determined mainly by stability, and to a lesser extent by design features (eg. T-tail vs. conventional tail). Glide ratio is almost entirely irrelevant. $\endgroup$– MarkJan 17, 2015 at 4:04
$\begingroup$ LOL Anixx, what are you even doing on this site? Are you like stalking me? As for Mark's comment, while that is true, can you name a better metric for stability? $\endgroup$ Jan 17, 2015 at 4:13
Stalls occur more frequently than you may think. A stall is basically when there is no lift being generated due to lack of air moving past the wing. In fact, when an airliner takes a somewhat steep turn, the outer edge of the wing starts stalling before the inner tip of the wing due to a slight tilt in the airliners wings, called a wash-in wash-out. This way, the pilot still has some control of the aircraft in order to correct it. So yes, the answer is that an airliner can indeed recover from a stall. In situations where the stall angle is too high and the speed is too low, the airplane may not be able to recover, as it most likely would be falling down like a rock, but majority of the time, given enough altitude and speed, it is possible to correct the stall. There have been many cases where pilots have recovered from stalls without crashing.