Avoid Flying in Icing Conditions

[rcgldr]

I wasn't aware that the term "tail stall", isn't the same as a true elevator stall.

That would certainly explain the original disagreement. My apologies if I seemed condescending.

No problem, my fault for not looking up tail stall before posting. I never heard the term "tail stall" before, I have read a lot about aerodynamics (I also fly radio control gliders). I was aware of how icing can badly affect airfoil shapes, but was totally unaware that deploying flaps at speed, combined with icing effects, could result in tail stall. After looking up more web pages about this, some aircraft are subceptible to tail stall while others aren't (those others still have icing issues, but not the pitch down issue related to tail stall).

Anyway, it doesn't appear that "tail stall" was an issue. The pilot might have mistakenly though the aircraft was in a "tail stall" due to the auto pilot pitching the nose down and shutting off, and pulled back on the yoke in what is reported at a 2G manuever. The news is reporting that the aircraft pitched up 31 degrees (not down) and hitting a 2 g peak (1 g of this is gravity related). It's also possible that the pilot was trying to avoid a mid-air collision with what might have appeared to be another aircraft.

Aircraft pitched up 31 degrees, rolled 106 degrees, tail icing (tail stall) not an issue for this aircraft, but it was on the previous type of aircraft that that pilot had flown a possible reason that the pilot pitched the nose up so much. There's a animated mulitmedia link in the second photo on this web page describing what happened (airspeeds aren't known yet and I don't know why):

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

This web page includes more info, including some air speeds:

http://buffalopundit.wnymedia.net/blogs/archives/8070

It's really too soon to tell. Pitching the nose up 31 degrees from a nose down condition and pulling 2g's seems extreme, causing me to wonder if some type of mechanical failure was involved.

 

[Nick M]

Properly equipped aircraft pass through icing conditions all the time. The key phrase here being "pass through", and not sustained flight. Usually this happens when you're climbing through a layer of icing conditions to clear conditions at a higher altitude, or when descending through an icing layer to land. Even small personal aircraft equipped for passing through icing conditions have de-icing equipment like heated props, inflatable wing boots, and a heat-plate for the windshield so you have a small rectangle for visual reference of the ground. You can't make gear like de-icing boots automatic, because they only work when activated with ice build-up (you can actually make things worse by cycling them without a sufficient ice layer).

I would also question why the pilot didn't notice a change in the flight characteristics of the aircraft if it was indeed icing related. I have my Private Pilot license and a few hours of instrument training (read beginner), but even I can feel the difference between an aircraft at gross weight operating at a high density altitude, and one with just me in it with half-tanks on a cool morning.

Regional airlines kinda scare me anyways. Usually their ranks are filled with greenhorns working insane hours under intense pressure.

Of course it's still safer to fly than to get in your car and turn onto the highway.

 

[mgb_phys]

You can't make gear like de-icing boots automatic, because they only work when activated with ice build-up (you can actually make things worse by cycling them without a sufficient ice layer).

They only work for a certain rate of ice build up, they don't handle ice forming on the tail. Some pilots turn the wing boots on and off in the belief that it's more effective

I would also question why the pilot didn't notice a change in the flight characteristics of the aircraft if it was indeed icing related.

It appears that it was on autopilot. As with most of the low altitude turboprop+ice crashes - the pilot didn't know anything until the plane became unflyable

 

[rcgldr]

deicing bootsThey only work for a certain rate of ice build up, they don't handle ice forming on the tail.

Looking at the diagrams, the leading edges of the vertical and horizontal stablizer also have de-icing boots. The news reports claims that tail icing isn't an issue for this particular aircraft.

pilot not aware of problemIt appears that it was on autopilot. As with most of the low altitude turboprop+ice crashes - the pilot didn't know anything until the plane became unflyable

That isn't known. The aircraft pitched up to 31 degrees, generating 2g's of lift during the process so the wings were able to generate a lot of lift and the elevator generate sufficient downforce to pitch the noseup. What isn't known is why the aircraft pitched up to 31 degrees.

 

[edward]

pilot not aware of problemIt appears that it was on autopilot. As with most of the low altitude turboprop+ice crashes - the pilot didn't know anything until the plane became unflyable

That isn't known. The aircraft pitched up to 31 degrees, generating 2g's of lift during the process so the wings were able to generate a lot of lift and the elevator generate sufficient downforce to pitch the noseup. What isn't known is why the aircraft pitched up to 31 degrees.[/QUOTE]

The plane was on autopilot according to the FTSB. The 31% pitch up was a result of the pilots action. At this point we can only assume that the pilot reacted to the stick pusher by applying full power and pulling back on the yoke.

The stick pusher engages before a plane is actually in a stall situation.

 

[mgb_phys]

The stick pusher engages before a plane is actually in a stall situation.

It engages before the plane reaches it's design stall speed, if the ice changed the aerodynamics so that the stall speed of the new wing shape was higher it could have stalled before there was any warning.