Continental TurboProp crash inbound for Buffalo

[BOAC]

Originally Posted by PT6

These actions are incorect for both a normal stall and the tail stall.

- I have no experience of T-tail icing but I do believe that sentence is in direct contradiction to the advice on actions following a tailplane icing 'stall' (NB correct on power) - you might wish to review? There is a good video from NASA here and you will see that the forward 'snatch' of the stick needs to be countered by a hard pull back (around 17 mins on the video) and the flaps should be re-raised.

[merlinxx]

Try this

FRONTLINE: flying cheap: watch the full program | PBS

[mary meagher]

Reading back through February, found this discussion the most fascinating to be found on PPRuNe, with contributions from wise old birds as well as those comfortable with automation....

One of the basic lessons we teach in gliding is knowlege of and RECOGNITION of the stall. DC8 retells his story of how he wised up his instructor that it might be a good idea to react to the symptoms, instead of waiting for the stick to shake. Stick shaker and stick pusher are gadgets designed to wake up the dozy pilot who fails to recognise promptly what is going on in his real world.

Symptoms of approaching stall: nose high attitude, decreasing airspeed, tailplane buffet, sloppy controls.

Symptom of actual stall, the elevator (so named because it ELEVATES the NOSE of the aircraft) does not work in the normal sense. As your glider is diving toward the terraine, and you are pulling back madly on the stick to raise the nose, it don't work. Not easy to push the stick forward under these circumstances. That's what training is about.

[Dont Hang Up]

Stick shaker and stick pusher are gadgets designed to wake up the dozy pilot who fails to recognise promptly what is going on in his real world

In many cases stick shaker and stick pusher are introduced precisely because the aircraft has aerodynamic characteristics that do not give good pre-stall indications.

Symptom of actual stall, the elevator (so named because it ELEVATES the NOSE of the aircraft) does not work in the normal sense.

Actually the elevator does work in the normal sense. It is just that pitch-up elevator will be further increasing the angle of attack of the wings and is not the correct technique for stall recovery.

[PT6Driver]

BOAC
To clarify I was refering to all the actions taken being incorect for either stall recovery.
Normal stall - increase power, reduce pitch (push forward)
T stall - Decrease power, increase pitch (pull Back), Reduce flaps.
The 2 recoveries are mutually exclusive.

The captain in this case did neither of these 2 distinct actions rather a combination of both. He did not command flap retract.
His actions as can be seen in the NTSB video are one of almost panic. He was I believe unaware of the speed / configuration environment and was desperatly trying to maintain altitude, then aware of the lowering speed aplied power, after that he was simply fighting the controls.
I do not believe he recognised any type of stall nor reacted corectly to the clues in front of him.
The dash8 400 has powered controls and is not a candidate for tail stalls (according to the guys who make it)

[BOAC]

PT6 - yes, that wording is better.

"The dash8 400 has powered controls and is not a candidate for tail stalls (according to the guys who make it)" is of course a two-part statement - powered elevators do not prevent tailplane stalls, they merely change the symptoms- I believe it is the tailplane design plus boots) that renders the D8 'immune'.

[chuks]

Something interesting...

You are all aware of how "duff gen" seems to persist, such things "everyone knows" such as flicker vertigo when flying into the sun or leaving the strobes on in cloud: Old wives' tales that we just cannot get rid of, somehow.

Well, I just did an AOPA/Jeppesen online CFI renewal course when there was our old friend, the tailplane stall in the section about icing! There was no careful qualification of how "this may not occur with all aircraft so make sure you know your type," just a brief presentation that would leave the less-informed with the idea that it is ever-present as a risk to be dealt with "so."

Too, there is that NASA video out there, the one with the experimental test pilot crew in a specially-equipped Twin Otter when they do encounter a genuine tailplane stall which they then examine in detail and speak about at some length. Perfectly valid for the Twin Otter, yes...

Put these two things together and you have a real trap for the unwary and complacent, the half-informed who think they know all about flying so that they stop learning.

[apatity]

Please help

The simulated stick shake and stick pusher on this type of a/c in combination with absense of airframe shake (did airframe shake at 135 knots?) and the powered controls (not much of a feedback from elevator with or without autopilot) would qualify for the T-stall as opposed to W-stall according to the video link above.

Then the power could be increased by the pilot just to stop speed dropping any further, and not applied fully as the full power would deteriorate the t-stall. Then the flaps retracted - could be, again, as part of t-stall recovery proc.

I guess, even if this was not the case (the pilot actions as I described it here), then something like that could happen to us with that shaker and pusher and otherwise powered controls, after that NASA video.

How would you diagnos the W vs T stall in the a/c like that? What would be your actions? As a studen PPL, I was shocked when I watched the NASA video. And now, after watching this video, I am not sure what I would do in the Buffalo situation. My instructor has 3000 hours, but in GA, which is not exposed to icing or fake yoke shakers and pushers. So, can someone more experienced clarify the correct set of actions and reasoning.

For example if airframe shakes, then I push the yoke and power up. If it is only yoke that shakes (and airframe is still and speed = stall speed + 33), then I pull the yoke and power down. Then again, if speed trend is going down to critical and yoke shakes only (not airframe) then I recover from t-stall, but want to increas the power just to stop speed bleeding or I will get into W-stall. But then I think that would not be right, cause this could be the Baffolo case.

Help me here if you can.

[p51guy]

Apatity, I flew my whole long career without hearing about a tail stall before this incident. Unless you are flying an aircraft with known tail stall incidents don't deviate from your wing stall recovery procedure. It will save you from 99.9 percent of all stalls. The Buffalo crash was proof of that. Two low time pilots took an airliner from a stick shaker to a full stall by doing everything wrong.

[Mansfield]

The ice contaminated tailplane stall phenomena remains remarkably misunderstood, partly because the aerodynamics involved are not often taught in primary flying.

The center of lift on the wing generally resides somewhat aft of the center of gravity. This generates a pitch down moment that can often be quite powerful. The horizontal stabilizer exists to create a balance force; thus the stabilizer must generate a lifting force in the downward direction. It operates as an inverted wing. The relationship between these pitching forces forms the basis for longitudinal stability. From the accident investigation standpoint, the main spars will almost always fail in a downward direction, due to negative G, following the inflight separation of the tail structures. Indeed, the sound of the main spars failing has been documented in both witness reports from the ground and on the CVR. It sounds like a large caliber rifle shot.

Thus, if the stabilizer is ice contaminated and actually stalls, the nose is going to pitch down. A stall, of course, is not the same thing as the inflight separation of the tail. Although stalled, lift is always still being produced to a limited extent, and the pitch down is not likely to exceed the structural capacity of the main spars. The occupants, however, may involuntarily test their seat belts.

That said, the typical ice contaminated tailplane stall rarely reaches this point. During the Twin Otter work, the tail was fully stalled only accidentally. What happens prior to the stall is an initial separation of the flow over a portion of the stabilizer. This was well documented by NASA through the use of flow visualization tufts. The flow separation seriously degrades the aerodynamic balance of the elevator, long before the tail actually stalls. When the aerodynamic balance is altered, the elevator control forces may lighten, leading the pilot to displace the control much farther than he intends for a given attitude ajustment. This gross displacement often leads to a PIO in pitch, which almost inevitably exacerbates the problem. Eventually, the elevator (or aileron, as in the ATR scenarios) will “snatch”, or violently displace into the region of low pressure. At the tail, this would a trailing edge down displacement, creating a nose-down pitch for the airplane. The tail is not yet stalled, and the elevator is fully functional aerodynamically. But the control force balance has been destroyed.

Control snatch is only possible with an aerodynamically balanced control surface. A fully powered, irreversible surface is not susceptible to this. (Reversible/irreversible refers to the ability to make the control wheel turn by manually moving the control surface from outside the airplane. If you can do this, the control is reversible. If you can’t, perhaps because there is an actuator between you and the control wheel, it is irreversible.)

The response to elevator snatch is to muscle it back into a trailing edge up position, which re-cambers the stabilizer and causes the flow to re-attach. This can require considerable force; NASA demonstrated 170 pounds of pull force required on the Twin Otter. The next step is to retract the flaps one notch, which reduces the downwash angle off the main wing and thus reduces the AoA at the tail, restoring normal pressure distribution and thus control force and stability.

If you have a powered control, it won’t lighten or snatch because the force used to position it far exceeds the airloads under nearly all circumstances. If the stabilizer were to stall due to ice accretion, a powered control allows the pilot to easily re-position the elevator to a camber that un-stalls the surface.

Thus, the Q400 does not have the snatch problem since it uses a powered elevator. The DC-9/MD-80, on the other hand, has experienced this type of problem, since it uses a spring/servo/geared/flipper/thing-a-ma-jig but, eventually, manually operated elevator.

The Twin Otter work also went a long way toward supporting the new certification requirements involving a 0.5 g pushover maneuver to investigate tailplane stall susceptibility during certification. The Q400 met these requirements; many, many older designs have not.

ICTS has been identified in accidents and incidents involving the Jetsream 31, DC-4, Convair 240 through 580 series, Viscount, YS-11, DC-9/MD80, DHC-6, Saab 340 (prior to mod) and others. There is no requirement that it be a T-tail design. It is fair to say that it could be a problem for most designs, if equipped with reversible flight controls and enough flap deflection. The question is whether the designer has properly optimized the tail area and stall margins with the flight control design and flap configuration. Most have; in cases where they have not, this has often been corrected through modification or flap restrictions. You should be able to get educated on this with respect to your airplane during training.

For a good look at the possibility of the flight crew misinterpreting a shaker/pusher event as an ICTS events, look at the Atlantic Coast accident at Clumbus, Ohio in 1993:

http://libraryonline.erau.edu/online...s/AAR94-07.pdf

There is no doubt in my mind that this crew did mistake the shaker and pusher for ICTS. Needless to say, if they had correctly interpreted their new-fangled tape display airspeed, they would have improved their mental model substantially.

I can currently identify 18 events involving ice-contaminated stalls of the main wing in which clear evidence exists of the pilot pulling the nose up in response to stall indications. There is a good case to be made in each situation that the stall indications could be mis-interpreted due to the mental model operative at the time. So the Colgan captain’s response to the shaker/pusher does not, in itself, indicate that he believed the elevator had snatched, although that remains a possibility.

On the other hand, the first officer of a Mid-Pac YS-11 at West Lafayette, Indiana in 1990 did actually retract the flaps without the captain’s command. As it turned out, this was the correct thing to do, so no one made an issue out of his “insubordinate” initiative. As the NASA video was far in the future at that time, I suspect that he reacted just as the Colgan first officer did…by re-configuring to the last known point of safety. The Roselawn crew attempted this as well, but were outmaneuvered by the automation.

To date, tailplane stall events have never been documented without a) ice accretion, and b) full landing flaps. There has not been a documented case of ICTS in transport airplanes for quite a few years, but who knows why that is. The manufacturer’s procedures must be followed, whether it be the Twin Otter’s flap restrictions in icing or the MD80’s tail deice requirement before landing flap extension.

[p51guy]

In the mid 80's our airline purchased 7 MD80's and several pilots in icing conditions neglected to push the tail deice before selecting landing flaps and the nose pitched down so they reselected the approach flap setting and landed after pushing the tail deice switch. Until the Buffalo crash I didn't know that was a possible tail stall. Since the pilots neglected to push the tail deice switch they probably didn't write it up for obvious reasons. They probably don't know today what happened because no training program I have ever been in has taught it. They still recovered easily because they were good pilots and knew what was working on the approach and went back to it. Confusing pilots with tail ice stall procedures might cause more problems than it fixes. Explaining it in ground school would be fine but teaching it in a sim might not be a good idea if it confuses them when it comes to a simple wing stall recovery.

[AirRabbit]

I've been involved in DC-9/MD-80 training on and off for more years than I'd care to divulge ... there has ALWAYS been part of the training program devoted to tail de-ice problems and procedures. It seems to me that if there is a known problem (that there is a system to prevent the problem or to correct the problem - it shouts that this is a "known" problem) the flight crew members that might be exposed to that problem should be given all the information they need to be able to deal with it should they ever encounter it ... and that should include flight (i.e., simulator) training.

[p51guy]

AR, you could be right if you are flying an airplane that is prone to tail stall but don't teach pilots to reduce power and flaps and pull up if the yoke shakes indicating some kind of stall. Let the 90+% use normal stall recovery and don't confuse them.

[apatity]

These are from NTSB final report (for those who did not have time to read this 299 pages report):


The accident flight crew had seen a NASA-produced video, titled “Icing for Regional and
Corporate Pilots,” during winter operations training in initial, transition, and recurrent ground
school. The video was intended to enhance a pilot’s ability to assess hazardous icing conditions
and understanding of icing effects on an airplane. The video also discussed tailplane stalls and
wing stalls as a result of icing conditions. In addition, the video stated that pilots needed to
properly diagnose icing problems (while maintaining airspeed awareness) because the
differences between a wing and a tailplane stall were subtle but the recovery techniques were
different.

Postaccident interviews with Colgan pilots about tailplane stalls produced varying
responses. One captain stated that the video about tailplane icing made a big impression on him,
and another captain stated that the video got his attention. Some pilots indicated that they would
apply the tailplane stall procedure if they had clearly identified the symptoms of a tailplane stall,
whereas other pilots stated that it would be difficult to determine if the airplane was in a
conventional wing stall or a tailplane stall. Some pilots thought that the Q400 might be
susceptible to a tailplane stall, some pilots were not sure about the airplane’s susceptibility, and
one pilot (a check airman) stated that the possibility of a tailplane stall in the Q400 had “never
crossed [his] mind.”
Nevertheless, the
NTSB concludes that the inclusion of the NASA icing video in Colgan Air’s winter operations
training may lead pilots to assume that a tailplane stall might be possible in the Q400, resulting
in negative training.





Mansfield posted a link to a 1993 case, where the pilot acted in the same way as Buffalo pilot in the similar situation. What drew my attention was that in both crashes the pilots were converted from a/c known for t-stalls and had a few hours experience on the new type.

[protectthehornet]

colgan was a new airline (comparatively) with a new type of plane. its pilots were low time upon hiring, depending upon the airline to train them, instead of bringing a wealth of experience with them.

a calculus of this might be included in the equation to develop airline safety.

When I was hired at my first, tiny commuter airline, flying Cessna 402's...I had an ATPMEL also CFIIMEI and about two thousand hours...many in actual IFR flying those awful ''bank checks''.

Colgan hired people with less experience to fly more advanced planes and payed them poorly.

Nothing beats a great pair of legs

The most important thing in flying is a well trained, experienced pilot.

[p51guy]

PTH, we know that so I guess the first positive step is the new ruling of 1500 hrs to be an FO with an airline. Wouldn't we have loved those requirements when we were trying to be airline pilots in the 70's. Only flight instructors could get hired with 1500 hrs. 5,000 with 1,000 turbine for airline jobs. I barely qualified for my little airline and had several hundred hours of 4 engine jet time. I felt very lucky to be selected and could have landed that 737 on my first day with no help because they hired captains, not student pilots paying for training, to fly their airplanes.
I prefer the way we went through making it to the airlines. It was fun, wasn't it.

[protectthehornet]

yes my friend (p51guy) it was fun...and yes, the first day on the line, we were a valuble part of the cockpit...not like now...its almost like flying a two engine jet, knowing full well that one of the two engines isn't ''right''.

be well...don't worry, soon enough the planes will be flown by remote control! (ha)

[p51guy]

I hope the remote control thing never happens. I still need to fly a couple of trips a year hopefully flown by competent crew members. Hopefully they will know if they get a stick shaker they just have to lower the nose a tad and add some power to be flying fine again. Please don't decrease power, reduce flaps and pull up on our flight because of your tail stall training. I would rather go with the traditional method of stall recovery.

[twochai]

Please don't decrease power, reduce flaps and pull up on our flight because of your tail stall training. I would rather go with the traditional method of stall recovery.

p51guy: Forget about "T-stall" or "W-Stall". Just follow the Approved AFM - there's good reason to suppose it offers the best advice required to operate your aircraft safely because these things have been well thought through during aircraft development and type certification!

[protectthehornet]

heck with stall recovery, you shouldn't even get close to a stall while airborne...and even touching down at 1.25 to 1.3vso is as slow as you should ever get. (ok, V2 is 1.2 etc)