There are obviously a number of people contributing to this thread who have a limited practical experience of operating for sustained periods in moderate icing and who additionally have only a cursory knowledge of a/c anti/de-ice systems.

An a/c does not simply have a particular de-ice or anti-ice system that is switched on/off with a consistant result rather like a light bulb. Crew have to be aware of current icing conditions and when possible help alleviate the problem by altitude or route changes. In temperate latitudes ice accretion can be markedly reduced simply by climbing or descending 3000 ft. One crew may make a decision to climb or descend in cruise, the crew of a similar a/c following along behind may simply stay at their planned cruise altitude and experience problems that the first crew avoided. One crew having avoided icing by climbing may request a late descent to destination so as to avoid prolonged exposure to ice in the descent... another crew might not bother.

As for extending the boots through an auto-system that doesn't wait for any ice to build or making a decision to wait for a build up of 1/2 to one inch of ice.. this decision should be made in accordance with the a/c manufacturers advice... a/c boots operate differently on different a/c... the manufacturer carries out the tests, follow their advice.

Again, one crew may decide to continue a flight utilising the auto-pilot and another crew, correctly disengaging it and flying manually... auto-pilots disguise the onset of trim changes required to keep the a/c flying that would otherwise indicate to a crew that things are getting seriously out of hand. On disengaging the autopilot the crew can be in for a rude awakening.

Tail icing (as I posted earlier) needs to be recognised as such and the correct recovery technique applied... with tail icing column buffet will be experienced (as opposed to feeling the buffet through the airframe as with a conventional wing stall)... the column will have a tendency to move easily foward and be increasingly difficult to move aft giving rise to Pilot Induced Oscillations... if allowed to develop the column will move sharpley forward as a full stall develops... the recovery procedure is to pull back on the column (opposite of a conventional wing stall) though by this time the forces required may be so great as to prevent the crew from recovering, especially as this event is likely to occur during a configuration change at a lower level during the approach.

This crew appears to have followed the recommended procedure in 'undoing' the configeration changes that may have caused the initial upset by selecting flaps to their original position and gear up... all sadly too late to recover. The problem with icing accidents is that all too often the evidence is lost in the resulting impact/fire.

Hopefully the FDR will offer some clues... in the meantime let's all keep in mind that, as with wind shear, ice is something best (when possible) avoided.

Could someone knowledgeable please help out by describing what changes occur in the forces required from the stabilizer during the change to flaps 15?

To a simpleton like me it might seem that it must briefly supply up-force instead of the normal downforce, bringing the state of its upper surface (possibly more iced) suddenly into more critical play.

Doubtless this is total garbage, but if someone can slap my hand and put me right it would help with the question "if the stabilizer is badly iced, how would the effect of this alter on lowering flaps". A question which some here have hinted may be relevant ?

I'm trying to think back a few years but for anyone interested there are 2 automatic settings for the deice boots.

Each section of the boots inflates for 6 seconds and then the next inboard section inflates. Once the sequence gets to the inboard boot one side will inflate at the same time as the opposite side engine intake boot and then vice versa. On the SLOW setting there is then a pause and the whole process starts again 3 minutes after it first started. The sequence is the same for the FAST setting but the pause after the cycle is (I think) 24 seconds meaning the whole cycle lasts 1 minute before it starts again.

It is also possible to manually cycle the boots. This requires the non flying pilot to cycle through the process using a rotary selector, each boot should not be inflated for more than 6 seconds and drastically increases the work load.

fg32, there is obviously a force required on the control column during configuration changes but going from Flap 10 to Flap 15 I seem to remember it was minimal (there will obvioulsy be more current Q400 pilots out there to prove me wrong!). In fact you can take off with Flap 15 and clean up to Flap zero and still quite easily hold the out of trim forces. Haven't tried it in any kind of icing though. Any help?

Please MungoP!:ugh:

Flying in Norway, I can promise you, other than you have experience in ice.:*

And, former AE ATR captain.

Autopilot Trim
 

Does the autopilot on this type aircraft not trim the elevator so that there is no pitch up or down when the autopilot is disconnected?:confused:

Flaps and trim
 

Which way to trim when flaps are deployed depends on the aircraft. Some pitch nose up; others pitch nose down.

Amazing that we get such pertinent info from NTSB so quickly. In UK it would take months for AAIB to make anything public. Jumping the gun? or not?

Please MungoP!

Flying in Norway, I can promise you, other than you have experience in ice.

And, former AE ATR captain.


Empati, I in no way was suggesting that I was an expert (who is) on icing... simply attempting to enlighten some of the theorists of how things work in the real world.. I sincerely apologise if it came across in any other way.:ok:

Autopilot and Trim
 

Mungo:

I confess to not being a professional pilot, and my few experences in icing, many years ago, taught me to stay far away or go commercial. But my B36TC Bonanza maintains altitude on A/P by continuously adjusting elevator trim. So in general, turning off the autopilot hands me an airplane with perfect elevator trim for its configuration, although I am always holding on tight just in case.

Are you saying that on the Dash 8 the autopilot holds attitude/altitude by brute force and does not adjust trim?

Just curious.

Video I had to watch for the DH8 Typerating at Tyrolean Airways about Tail Icing/Tail Stall.
The common practice for flap extension near max flap operating speed is about the worst one can do concerning the risk for a tailstall.

especially interesting from 7'30 on....


Tailplane Icing

Thanks MungoP...I had a long day I guess.:}

From what I remember of the NTSB briefing, they had listened to the cockpit voice recording. He stated that the crew had done their approach briefing incl. a weather/ minima brifing and had mentioned ice buildup on the a/c after anti ice was selected ON. They verbaly selected it ON. NTSB did NOT speculate on anything! I do not think they would be ready this early to give out flight data readings. But who knows!?

The Q400, ATR and B737 etc are certified to fly in icing condition, with droplet size (freezing rain) up to 50 microns. After the Roslawn accident NTSB reported that day and place a size of 200 microns! Pilots obviously have no info of this inflight, other than visually checking ice buildup. I do not know if this crew was flying through freezing rain.

Scary stuff, I wonder how much of this info is passed on to operators of high-tail turboprops.

If it turns out this due to icing, maybe it's time to revisit where in the flight profile these kind of aircraft make their config changes for landing. Who wouldn't want some extra altitude when your ride unexpectedly noses over?

NASA has a very good video on tailplane icing. I did my undergraduate research project on the subject (tailplane icing) and learned a great deal from NASA. Im not attributing the blame to this accident on tail ice and subsequent stall, it is however a viable theory. I think all aviators and non-flyers alike, will find the video informative and educational on the basics of aerodynamics and the affects of ice accretion (especially on the tail). Fly safe.

Tailplane Icing

Ah, yeah, that's the problem sir! If an unusual amount of trim is being required you may not know about it until the trim runs out and you're handed (via autopilot disconnect) a serious out-of-trim situation. By then it may be too late.

Better to be flying manually in icing conditions so you know exactly what direction and how much trim is required to relieve the elevator forces.

Pitch trim on flap extension
 

Chesty - a general rule of thumb, from moments about the a/c lateral axis would be:

High wing: flaps down, nose down.
Low wing: flaps down, nose up.

There may be lots of exceptions, esp. if the flaps do not simply add lift and drag but also apply a torque.

I agree, the NTSB seems extra fast in this case - good job:D.

For anyone who's interested, here's a basic GA primer on flying into icing conditions. This should help answer some basic questions.

http://www.aopa.org/asf/publications/sa11.pdf

BTW, I thought the NASA map on page 3 was rather interesting for the Buffalo area. :eek:

THCROZIER... in answer to your Q

The advice in icing is to disengage auto-pilot. A/P will disguise subtle 'feel-back' to a pilot that otherwise would warn him of unnatural trim settings.. in a worst case scenario the A/P will ultimately give up trying to compensate for extreme trim settings and disengage itself leaving the pilot to cope with a hopelessly out of trim and possibly unrecoverable aircraft flight attitude. When a/c flight characteristics are steadily deteriorating due to steady ice build up (extra weight/ increasing angles of attack / disrupted airflow over critical lift surfaces and possibly under extreme conditions on some aircraft, less power available) it's far better for the pilot and a/c to be in touch with each other....

Gegenbeispiel, yes I'm aware of that. It was sort of a rhetorical question to a very general statement by Charv89. Afterall we are talking specifically about the Q400 and I was trying to find out what kind of experience he had on this type (I have some).

Anyway. I think that every pilot from a part time PPL to a 20,000 hour old boy should watch that video. The interesting part for me was the signs of tailplance stall/icing on powered flying controls: Unusual trim settings was one point the video made and the Q400 trim indicator is a crappy little thing often hidden behind yellowed, cracked plastic which makes it hard enough to see at the best of times.

Thanks Mungo and Fire, I get it now. Who knows, you may have saved my life! :8

Excellent video on tailplane icing. Thanks for posting that.

Flight Safety: A useful post that is well worth a read to any aviator. well done

Add a trim warning to the FMC ?
 

MungoP, Chesty : good points about A/P disengaging too late.

I wonder whether an FMC knows enough about AP and PFC output commands to have a "trim becoming unusual" monitor added to it which would warn the crew of, in this case, an extreme trim and approaching AP disconnect. You probably wouldn't want the additional code in the AP or PFC cos it would be an additional fault risk in a critical system.

That IS what you would want, and surprised if such warnings weren't built-in currently...

The AP systems I'm aware of don't retrim in the roll axis, but simply hold the force with the servos. They monitor that servo force and pop up a series of escalating warnings if the force becomes higher than normal, before the servo has to disconnect. The pitch axis does retrim, and there's no warning from the AP if the trim has moved "a lot" - only warns if the servo is holding excess force, which usually means the trim has jammed or failed, and the servo is now doing all the work. The trim would only generate messaging if you got to the end of travel, if then.

just remember
 

if you move something and things go to hell, try moving whatever you moved back to where it was

from the idiot's guide to flying ;-)

NASA video -- wow. Ten years old ...
 

two-tenths of a second, 40 degrees pitch down, 300' lost -- and that was the actual tail stall that occurred while they were in test flight intending just to creep up close to the problem! And the recovery procedure ....

Whew.

Is it time for little video cameras mounted on the tail, or something like that?

Mad (Flt) Scientist: right, so the monitoring software would need to look out for both extreme trim positions and unusual, near authority limit actuator commands.

Someone earlier in the day postulated a stall spin accident due to icing and configuration change, somehow the post was removed.

The Roselawn icing accident had similar pitch and roll excursions that began on approach when flaps 15 were selected. I realize that aircraft was an ATR, not a Dash.

Assuming that tail icing is the culprit; I just wonder if there are any data's on record in respect of the tail configuration, i.e T tail Mid tail or a conventional tail.

No! On the Roslawn accident the F/O 'deselected' flaps! He had selected flaps in the holding to stay under max holding speed (Mistake!). When he got the clearence to descend, he forgot flaps and got a flaps overspeed warning. He then reduced flaps, and the roll upset begun.

Yep, you're right now that I think about it. Anyway, the loss of control with the configuration change rang a bell when I heard that comms were lost in BUF at the marker.

Dash 8 Crash
 

I am extremely sorry for the loss of life. But what is it about supposed professional Pilot training? Even as a lowly and humble PPL/IR, I have read, had instilled into me, and studied the effect of ice. In as much as if you are getting iced up, dont use the flaps , you recalculate the landing distance available and if its too short, divert, unless you are certain that the tailplane is not a problem. Which must be impossible in a Dash 8. If the facts confirm this, it is another totally avoidable accident. Other causes could be a midair, but then there would be a debris path, not a entire aircraft crashed into a single house, there is not a another rational explanation No doubt I will be vilified for this comment, as usual, and told to wait for the official report, but reports of ice on approach and then a sudden fatal dive just when they went for the flaps over the OM all adds up. I am flabbergasted how this can happen, yet again and again and again, remember people died.

The lawyers have already read all the comments, so mine are not going to make an iota of difference. In fact I hope they sue the airline out of existence

Good video learning about tail stall due to icing:ok:

Lots of discussion following.

But how sure are we that it's indeed tailplane stall:confused:

Are there other possibilities with the information released to date?

That is a very profound comment.

I think it will turn out to be tailplane stall, but remember the ATR crash was aileron reversal, not a tailplane stall. I am nearly certain the crash is ice related, but it may not be a stab issue. I am sure in time the FDR will reveal the source.

Airbubba!

"Anyway, the loss of control with the configuration change rang a bell when I heard that comms were lost in BUF at the marker. "

Yes! I, too, had a flashback after hearing that!

dope05:

every single day around the world airline aircraft fly into ice, accumulate ice, and land safely. q400's build ice on the wings, tail and the deice system removes it and they land safely. these aircraft are approved for flight into known icing. you can't simply say "well they had ice so why did they try to land, divert!"

it is very, very likely that the crew had seen icing like that many times and had no issues with it at all, but perhaps something unique happened this time and fate arrived and luck ran out... hopefully just like after roselawn we can learn more to prevent this in the future, but it will never be as simple as avoid icing because in our environment, we can't... we can only manage the situation.

I mentioned this in the Barajas thread for a quick check-see of a/c config (and other useful things)... but they would of course need heating and lighting .

I would hope all new design a/c are given a good complement of cameras, long overdue.

Let us not forget the possibility of crew fatigue, it was 22:00 hrs or something, how many sectors had they flown yesterday?.
I was on a late-day/early evening commuter flight into Albany, New York 3 years ago, the one Flight attendant looked tired and I asked her how many sectors they'd had that day, and was this the last.
It was the last of seven, thats a lot !!, that possibility, and bad weather, end-of-the-day.
Whatever the circumstances, a tragedy.
f