Comments on: NASA Tailplane Icing Video

By: sb

sb — Wed, 25 Feb 2009 03:38:54 +0000

Tailplane stall has been an issue on Embraer Banderantis, Vickers Viscounts, Twin Otters and some other aircraft however the cert rules have been beefed up in recent years to address it. The q400 was flight testedthrough extreme pitch maneuvers with simulated tail plane ice and showed no tendency for tailplane stall. Tailplane stall occurs usually at full flap and the Colgan aircraft did not get to full flap if I understand correctly. Also, the nose-down is sometimes caused by aerodynamic force reversal on the elevator which for a reversable flight control system can push the stick forward violently, causing the nose-down. The Q400 has a powered system – the pilot does not feel the actual aerodynamic forces on the elevator as the force comes from an artificial feel unit. The aircraft behavior, as described by the NTSB, is not consistent with a tailplane stall.

By: Gary D

Gary D — Fri, 20 Feb 2009 15:45:02 +0000

Is there a reasonable chance of recovering from an ice-induced tail stall at low altitude in a Dash 8, even if the pilot responds optimally? If not, shouldn’t pilots be trained to perform only a normal stall recovery at low altitude, rather than even trying to identify a tail stall? (Is that in fact the training that’s given?)

By: Jonathan Birge

Jonathan Birge — Fri, 20 Feb 2009 06:36:38 +0000

The problem with the theory that he was correcting for a tail plane stall, is that he didn’t raise the flaps. Also, it strikes me as implausible that a pilot who wasn’t doing well enough to keep the airspeed up would manage to even remember what a tail stall is. I’m not judging him as harshly is it sounds. I’m sure I’d do no better. When I was doing my instrument training, my biggest takeaway from the whole thing was that it was utter bullshit for people’s lives to depend on a pilot doing it correctly when the chips are down. I really think too much is expected of pilots flying hard IFR in any airplane that’s not fully automated. Yes, it’s manageable, but not with the kind of margin you’d like to see when a terrifying death is at stake, and the pilot is flying his first job since instructing in C152s. One’s ability to react correctly is shockingly bad when terrified, and I’m guessing the slow speed situation caught the pilots off guard and scared the shit out of them.

We live in a world where automation has advanced to the point where the space shuttle can deorbit and land itself. We’ve got cars with anti-skid brake systems whose computational power rivals a jet fighter’s. Why the hell are our loved ones flying in airplanes without autothrottles? Why is “drop out of the sky and kill us all” a member of the set of allowable control inputs on a commercial aircraft?!?

By: Bill McGonigle

Bill McGonigle — Thu, 19 Feb 2009 20:08:48 +0000

What’s the right way for a pilot to know the cause of his stall? In cases like this, it seems like he has an impossible task – to evaluate the data in time – leaving the correctness of his decision to chance, even if he makes perfectly reasonable decision. ‘Pilot error’, maybe, but if it’s luck, it’s hard to really place that blame when it doesn’t work out. I mentioned some algorithms that the inventors claim can deal with icing automatically here:

http://mcgonigle.us/bill/blog/articles/2009/02/15/how-up-to-date-is-your-autopilot

By: EDZ

EDZ — Wed, 18 Feb 2009 23:29:01 +0000

…and now, according to the NYT there is speculation along the lines of Tom’s comment #5 above:

http://www.nytimes.com/2009/02/19/nyregion/19crash.html

Apparently the captain had recently transferred from flying Saab 340s which are notorious for tailplane icing, and he may indeed have used the wrong recovery. But the article also says Dash 8’s are “not susceptible” to tail icing. I find that hard to believe; Dash 8s are great airplanes but that would require something more like magic.

And it still doesn’t explain to me why the stall warning would have happened right when they lowered flaps.

By: Hank

Hank — Wed, 18 Feb 2009 17:20:05 +0000

It would not surprise me if in the final analysis it is determined that the precipitating circumstances and events including mimicked signs of a tail stall close enough to mistaken for a tail stall. Icing conditions, onset of difficulty upon configuration change (flaps), and action of the stick pusher (simulating dramatic uncommanded nose-down pitch) might well have deceived the pilot into countering the forced yolk forward action of the stick pusher, as pulling back against the yolk is essential to tail stall recovery.

By: Gary D

Gary D — Wed, 18 Feb 2009 16:58:18 +0000

NYT this morning proposes an explanation for the pilot’s pull-back reaction: as Tom speculated, the pilot may have misinterpreted the downward pitch as a tail stall (though it had instead been caused by the stick-pusher in response to low airspeed).

http://www.nytimes.com/2009/02/19/nyregion/19crash.html?hp

By: Jonathan Birge

Jonathan Birge — Wed, 18 Feb 2009 07:10:41 +0000

Well, it’s now looking like it was a regular stall, according to the WSJ. From the CDR it appears, shockingly enough, that the airplane simply got too slow, the stall shaker went off, and the pilot inexplicably pulled back against the stick pusher, pulling the airplane up into an aggravated stall.

By: Bob

Bob — Tue, 17 Feb 2009 13:56:10 +0000

Miles O”Brian (formerly CNN) has some interesting and detailed information on icing.

http://milesobrien.wordpress.com/

By: Dave Wardell

Dave Wardell — Mon, 16 Feb 2009 19:16:40 +0000

What kind of control system does the Q400 have on the elevator is an important question. Is the elevator fixed leading edge, and is the pitch control power assisted or is it a aerodynamically balanced pitch control system.