How often are (quickie?) stalls in commercial airlines? Other query on 737 simulator

General Questions
#1
  1. Just watched this 18-min run through of data only ILS simulations–what does that mean? ILS by definition is data “only,” I thought.

http://youtu.be/u_HwuuXKfYg

  1. But the co-topic of the little vid is stall and stall recovery. Now, I always had this image of a stall where the captain either breaks out in sweat (or is cool and debonair) grimly attempting to handle this life and death situation, as rare as it is dangerous.

I understand the video focuses on stalls, but the correction seems 1,2,3: stick shakes, do this, five seconds max. Obviously, when all hell is breaking loose, five seconds is more than enough time for disaster.

But how often do quickie situations of a stall arise in real life? And no doubt, quickie situations stay quickie because of skill and everything else going right. But situations like in the vid.

  1. About the simulator’s machinery vs. real life: below and to the side of the thrust levers (is that the right word?) two flywheel-like contraptions clank around and spin briefly, making the sound of an old-fashioned adding machine advancing the tape. It first crops up about 3:00 min in, and towards the end is constantly in camera shot.

What the heck is that?

#2

I’m not a pilot so I can’t answer 1 and 2. But i do watch enough youtube videos that I know the answer to 3.

Those clanky spinning wheels control the horizontal stabilizer trim. You can move the wheels manually, and you can also cause them to move quickly using buttons on the control column.

#3

Stalls are actually pretty gentle. Accelerated stalls can be more more problematic. Aircraft can stall at any airspeed, as the stall happens when the air flowing over the wing is interrupted. High speed dives (as in WW2 diving on a target) can result in stalls when trying to pull out. In that situation, the captain would have sweaty palms for sure

With respect to general aviation aircraft, stalls are pretty much taught from probably lesson 3 or 4 on. Stall recognition, recovery, and avoidance is stressed and practiced. Approach stalls, and departure stalls (one with little or no power, the other with full poser) are taught in preparation to soloing the student because take off and landing are the 2 times that stalls can be fatal. That said, stalls are typically gentle and docile. Worst I’ve ever done (unintentionally) is dropped a wing, and that’s nothing to worry about. Then you get a little cocky, and try to hold the aircraft in a stalled condition, using the rudder to try and keep the plane level.

Where stalls become “oh shit” moments, at least in general aviation, involves a stall/spin accident. This happens typically, when the pilot overshoots his turn to final (the part of the landing where the airplane aligns with the runway) and tightens his turn. Steep bank angles increase stall speed at a time when the airplane is already going much slower than normal, and the pilot adds a little more rudder to tighten the turn a little more. One wing stalls, the plane rolls inverted and you have just enough time to see if Jesus is watching before you make a big mess on the ground.

Now, someone with experience stalling large commercial aircraft can tell you about stick shakers, flying in the coffin corner, etc. I’ve never been there or done that.

#4

http://www.aopa.org/asf/ntsb/stall_spin.html
This article, analyzing 9 years of data, indicates that stalls (and spins) make up 10% of aircraft accidents, but it isn’t broken down into commercial v. general aviation. I’m guessing it is very rare for commercial flight crews, as they spend more time training and flying than most dentists with a Mooney. Over the years I’ve read more than a dozen NTSB reports of GA pilots who are circling an airport or coming in at a right angle for the runway (on base leg) and they pull back power to slow down, or raise the nose a little to extend their point of touchdown farther down the runway or bank too hard to make final while at a slower speed. The NTSB site isn’t set up (that I can see) to see how many stalls occur each year presently, but it’s not a super-rare occurrence in non-commercial flying.

#5

This sort of stall appears to be what happened to the B-52 that crashed in 1994: at low altitude, pilot banked hard to avoid restricted airspace, inboard wing stalled, plane banked past 90 degrees and crashed. Video here, impact at 0:51.

#6

Didn’t watch the OP’s vid; not worth my 18 minutes today. So no comment on “ILS data only simulation”

As to stalls …

Short version: Stalls in big swept-wing airplanes are a different matter than in small slow aircraft. Stalls at high altitude are very different maneuvers than stalls at low altitude. Stalls by definition represent a piloting goof; somehow the aircraft state got to someplace the crew would never want it to be. And they would not have let it get to that state if they’d been paying the right amount of attention to the right thing. So by definition they either weren’t paying attention at all, or were paying attention to the wrong thing. Recovering from that startle / surprise / shock can take more slack time / space than is available. Having airplanes that spend 99.9% of the time flying themselves doesn’t help this.

#7

Back when I got a private pilots license, many many moons ago, IIRC the US flight training did not include spin recovery, just stalls; Canadian training included both. The key was that spin recovery is counter-intuitive. If you do what you would normally do to recover in a non-stall situation, you only make the spin worse.

Smaller general aviation planes are usually pretty forgiving - in fact, given enough height, a Cessna 150 would recover from the problem on its own… Given enough height - that’s the problem, often stalls happen during takeoff and landing maneuvers when you don’t have the necessary recovery height.

In a previous thread on the Air France crash (I think it was) a for-real pilot mentioned that stalls in large airliners are not pretty; the craft shakes and rocks violently as it approaches the stall and enters it.

#8

Wasn’t it that Air France flight that disappeared on a flight between Brazil and France that, as they later found out, was caused by the pilots not recognizing the aircraft was in a stalled condition? Point being that even the best pilots, with the best training, and the best equipment can screw up.

#9

There was a lot going on there, including:

-a copilot who put the plane into a deep stall and kept it there by inexplicably pulling back on his control stick for most of the descent. The other guys in the cockpit didn’t notice this because his stick was out of view from them. When they finally noticed and told him to stop, he stopped for a bit - and then inexplicably resumed pulling back on the stick for the remainder of the descent.

-The visual indicator on the dashboard indicating how the inputs from the two control sticks were handled didn’t catch the eye of the pilot. Had he noticed it, he might have realized earlier that the copilot and he were fighting each other by inputting opposite control inputs.

-the stall was so deep (very high AoA), and the airspeed so low, that the computer/software thought to itself, “holy shit, this can’t possibly be a stall; I’ll shut off the warning horn.” So when the pilot pushed forward on the stick to try to recover, and the AoA and airspeed once again appeared plausible to the software, the alarm began sounding again. This confused the pilots: they were doing the right thing to get out of a stall, but doing so caused the warning to happen.

In other words, these were not the best pilots, and the equipment was not the best.

#10

I was told the FAA took it out because it was really pointless. Intentional spins are totally different than the stall/spin accidents that GA aircraft are involved it. As you said, when that happens, there’s no room for recovery. IIRC, it took about 600 feet to recover from a spin if you initiated recovery as soon as the aircraft entered the spin. And you’re right, that turn to final is where many of these stall/spins happen, and that turn is made usually around 400 or less feet AGL.

Here’s a short (1.5 min) YouTube video on the classic stall/spin if anyone wants to see what this is all about. This was intentionally done and at sufficient altitude so recovery was possible.
https://www.youtube.com/watch?v=jj4rG_m4rdo

#11

The OP was interested in airliner stalls. There are really two scenarios: high and low altitude.

The standard high altitude stall is caused by an auto throttle / auto pilot problem. They’re cruising along Zen-ing out while arguing Union politics and somehow end up with too little thrust. Slowly but surely the airspeed decays while the autopilot continues to hold altitude. The slower they get, the more quickly they decelerate. It might take 10 minutes to lose 20 knots, then 5 minutes for the next 20 knots, then 2 minutes, then …

Eventually they get real slow. Like instead of doing ~280-300 knots indicated speed it’s more like 180. About then shit goes from a little quieter than normal to batshit crazy. The autopilot gets to the end of its authority and disconnects, sounding its alarm. Meantime the airplane starts pounding like a car at 40mph on a washboard dirt road. They still haven’t fully stalled, but they’re nibbling at it.

The standard knee-jerk remedy is full power & lower the nose. Full power takes 4-8 seconds to come in. And on jets with wing-mounted engines mostly forces the nose higher, rather than increasing speed. So now the pilots have to be pushing like mad to lower the nose. If they let the power push the nose up they’ll probably get a bit slower. If that happens they enter wing rock. And about then the stall warning noisemakers finally trigger adding to the confusion.

Wing rock is not something straight-winged airplanes do, but swept wings are real good at it. The airplane starts to wallow, yawing left & right. As it does so, first one wing or the other abruptly drops off 20-30-40 degrees. Then snaps back to level and the airplane rolls off the other way. Lather rinse repeat.

With a well-developed stall you can fall a couple *miles *getting everything back under control. And perhaps sling off an engine, further adding to the confusion. This event will require a pretty complete cabin overhaul to get all the poop & vomit out.

OTOH, if the pilots are a bit more awake, at the first light rumbles before the washboard really starts they stuff the nose down, add power only at the rate they can keep the nose coming down and the airspeed rebuilding. Do that right and most of the folks in back may never really get excited. It still takes a long time to get back up to a safe speed since at altitude even full power is not that much more than it takes just to maintain cruise speed, much less offset the much greater drag at low speed. You absolutely need to supplement the power with a pretty good descent in order to get the airspeed back up.

The bad news is they’ll still lose 3 to 5000 feet doing all this. Which means slicing across other airlanes that might have airplanes in them at just the wrong place.

The two big differences with low altitude stalls is that:

  1. Engine power is vastly more and if you can offset the much larger power-induced pitch-up with enough nose-down input you can power out with little or no altitude loss.
  2. The stall warning systems should trigger earlier in the process, alerting the pilots before, not after, the aerodynamic pounding & rocking starts. Recovering from slow-but-not-yet-stalled is much better / easier than recovering from half-or-fully-stalled.
#12

It all started with the pitot tube icing up so the autopilot had no valid airspeed data and so it guessed until it was too late.

And also, the sticks have no tactile feedback or coordination, apparently. So the pilot was pushing forward with no indication that the copilot was pulling back on his stick; and the Airbus apparently averaged the two instead of indicating a problem.

#13

It’s “raw data ILS”. The aircraft ILS receiver sends information to your primary flight display (PFD) or equivalent instrument. You see two dots, one indicates where the correct course is and the other indicates where the correct glide slope is. Keep both of those dots centered in their respective displays and you are on course and on slope. Follow it all the way to the ground and you will hit the runway in the middle of the touchdown zone. Have the presence of mind to look out the window and flare just before you hit and you will land instead. That is raw data, the pilot interpreting the raw ILS data and manually flying the plane in response to it.

There are a couple of other ways you can fly the ILS. First, you can turn the flight director on and tell it that you want to fly the ILS by pushing the approach (APP) button, or perhaps the LOC and GS buttons, it depends on what you are flying. Now the aircraft clever bits will interpret the ILS data and present to you, on your PFD, a couple of bars or perhaps a chevron type thing that is called the flight director and it will tell you exactly where to put the nose of the plane so that you accurately track the ILS until you hit the runway touchdown zone. The raw data is still there, but you don’t have to interpret it anymore, you just do what the flight director tells you to do.

The final option, and by far the easiest, is to turn the autopilot on. Now the flight director interprets the ILS raw data as before and presents a display to direct you how to stay on course and on slope, but this time the autopilot flies the plane in accordance with the flight director’s commands while you sit back and watch. If it is a good autopilot, and the ILS is correctly certified, and there aren’t any big hunks of metal sitting close to the ILS antennae, it will even look out the window and flare for you.

#14

Purely anecdotal, but I had my first stall training 1.5 hours into my flight training. In that case it was in an ultralight. When I moved over to private pilot training we started stalls on lesson two according to my logbook. The fact that my instructor knew I had prior flight experience, including stall practice, might have moved that up a bit, but really, speaking to other people, my experience of getting an introduction to stalls around the second time I’ve gone up isn’t unusual, at least in the US.

#15

I was a passenger on an airliner taking off out of San Diego Int’l Airport, and the pilot pulled up a bit too steeply deploying the auto slats, a safety feature to protect against stalls. The pilot pulled around into the pattern and we landed for a brief maintenance check, then were on our way again.

When I was training to fly the KC-10 (DC-10-30CF), we practiced approach to stalls in the jet. In level flight, we’d slowly decelerate until onset of stick shaker, then recover. The exercise was a bit unsettling in such a big plane; a year or so after I left the KC-10 for another assignment, the USAF stopped doing approach to stalls in the jet and made it a simulator only thing.

#16

When our BAe146s come out of heavy maintenance they get a check flight that includes an approach to the stall until the stick shaker goes. I have done it and it is very much a non-event, but I’m not a fan of the idea. It is a hole in the cheese.

#17

Am I the only one who keeps on mis-parsing the question in the subject? When I first saw the thread, I thought it meant semi-enclosed chambers on board an airliner wherein one might join the Mile High Club.

#18

[quote=“Morgenstern, post:10, topic:748542”]

I was told the FAA took it out because it was really pointless. Intentional spins are totally different than the stall/spin accidents that GA aircraft are involved it. As you said, when that happens, there’s no room for recovery. IIRC, it took about 600 feet to recover from a spin if you initiated recovery as soon as the aircraft entered the spin. And you’re right, that turn to final is where many of these stall/spins happen, and that turn is made usually around 400 or less feet AGL.

Here’s a short (1.5 min) YouTube video on the classic stall/spin if anyone wants to see what this is all about. This was intentionally done and at sufficient altitude so recovery was possible.

[/QUOTE]

YEs, out spin training involved (if I recall) doing a stall, power most of the way back/off and pulling back to reduce speed, while turning. As others mentioned, a real spin typically involves turn during takeoff or landing with the engine on significant power. The prop under power then just helps trying to flip the plane and you want to pull power off ASAP if I recall procedures correctly.

#19

@Chronos: In that regard I always thought the “quickie stalls” were called “lavatories” by everybody else.

#20

Back to the OP: How frequent are stalls in big jets?

Full up stall and fall from the sky seems to be about one every couple years industry-wide. Some are pure goof-ups, others have a lot of help from aircraft malfunctions.

The more minor incidents of airspeed excursion to near stall then uneventful recovery don’t make headlines or get into publicly searchable databases. But they’re also pretty darn rare. A handful per year industry-wide would be my WAG, but that’s definitely an anal-extracted WAG, not a calibrated WAG.