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Continental TurboProp crash inbound for Buffalo

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Continental TurboProp crash inbound for Buffalo

Old 14th Feb 2009, 02:49
  #161 (permalink)  
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Could it have been...

Asymmetric flap deployment?
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Old 14th Feb 2009, 02:59
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I would expect the flap system will stop the flaps if an asymmetry is detected over a certain amount. It can happen bu the airplane would probably not become uncontrollable.
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Old 14th Feb 2009, 03:06
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I'm not a Dash 8, or icing expert. But I'm wondering...

The posted photo of the Q400 tail shows the fairing, which projects forward of the intersection of the H and V stab leading edges, and it is not apparently deiced.

25 years ago, I had a terrifying experience flying a quite new Cessna 303, whose H and V stab leading edges form a cross at the intersections of their leading edges, which on that particular aircraft was not deiced (though the aircraft was known icing certified). We were flying in icing conditions, and accumulating ice, which the boots were handling fine. After a while, the aircraft seemed tempted to swap ends in the pitch and or yaw axis (roll was perfect). As I slowed down, it got very much worse very fast. I sped up, it got better. After finding warmer air, the ice melted off, and we lived. The aircraft had no ice upon landing, and flew perfectly. The AD on the c303, which addressed this design shortcoming of the aircraft, made reference to complete loss of control (in pitch I'm betting), and resulting in flight break up, with fatal results.

Could something similar be happening here? I've got to think that this has been addressed during icing certification of the Q400, but it was overlooked during the initial icing certification of the C303, and only found after accidents....

My contribution to the speculation for the evening....

Pilot DAR
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Old 14th Feb 2009, 03:13
  #164 (permalink)  
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For you Dash-8-Q400 guys;

Is there a way to monitor the output of the deicing system? If you had tear in one of the boots would you get any notification in the cockpit telling you a boot didn't inflate properly?
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Old 14th Feb 2009, 03:21
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Boots and Icing only mix when

Boots and icing only mix when you are wearing the boots on your feet while doing a walkaround inspection looking for ice.

IT IS NOW TIME TO GET RID OF BOOTS in all planes or severely limit those types to trace or light icing exposure for less than 2 minutes.

WHILE Icing can bring down any plane, it seems that heated wings/airfoils are the way to go.

OR make the airfoil so robust aerodynamically as not to need anti-ice.

I guess there should be a ice detector on the tailplane!!!!!!
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Old 14th Feb 2009, 03:27
  #166 (permalink)  
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press conference, via BBC

BBC NEWS | Americas | 'Ice build-up' on crashed plane
-------excerpts follow------

The crew ... noticed "significant ice build-up" on its wings before it crashed, investigators say

"Analysis of data recorders recovered from the scene shows the plane made a series of severe pitches and rolls seconds before plunging into a house. ..."
"... aircraft's cockpit voice recorder captured the crew discussing landing the aircraft at Buffalo and noting snow and mist. At 16,000ft they said conditions were becoming hazy and asked for permission to descend to 12,000ft.
After that they were cleared to descend to 11,000ft.
The crew subsequently discussed "significant ice build-up" on the windshield and leading edge of the aircraft's wings, Mr Chealander said.
The official added that before these comments were made, the plane's de-icing system had been switched on.
'Severe pitches and rolls'
One minute before the end of the recording, the plane's landing gear was put down. Twenty seconds later the crew repositioned the aircraft's wing flaps to slow it for landing.
Within seconds of the flaps being moved, the aircraft experienced a "series of severe pitches and rolls", Mr Chealander said.
Just before the recording ended, the crew tried to raise the landing gear and reposition the flaps, he added.
Other pilots had reported ice forming on the wings of their planes...."
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Old 14th Feb 2009, 03:28
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Is it time for little video cameras mounted on the tail, or something like that?

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.

I fly a G4 that has cameras everywhere exterior. Uplocks, downlocks, tail looking aft, top of T-tail looking forward, you name it. The only useable one in the airplane is near the skeg, looking aft, and it shows the coffee going out the heated drain, and the mains, if they get to antiskid on rollout.
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Old 14th Feb 2009, 03:31
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Asymmetric Icing - the Cause and the History

Quite obviously (IMHO) due to the asymmetric build-up of icing caused by both engine's props rotating in the same direction (think it through). I'd be amazed if it was due to engine failure.

They now need to put a scale model in an ice-distributor wind tunnel with the engines being electrically driven i.e. electric motors to drive the props at proportionate (to model-size) speeds) - and see just what the asymmetric ice loading effect becomes over time (in terms of aerodynamic drag differential (L to R), asymmetric lift and weight). By having the flight control loads monitored, they'd be able to determine what the increased stall speeds become and thus the much higher speed at which control is lost (i.e. the inevitable spinning auto-rotation onset speeds-whether on autopilot or not).

All of this was apparent after Roselawn Indiana and the ensuing icing crashes - but no-one bothered to look into asymmetric wing, tail and fuselage ice-loads induced spanwise by "same direction" prop rotation. Maybe now they will..... but wouldn't be surprised if they didn't.

Like wiring-initiated fires, all icing crashes lose their critical evidence post-crash. The problem with rain-ice or freezing rain (or SLD as it's called less alarmingly by the fAA/NTSB) is that it "hits and sticks". It hits (and sticks) more on one side than the other due to prop slipstreaming. That asymmetry is insidious. It's particularly lethal if the autopilot is left to quietly "soak up" that asymmetric ice-loading. Ultimately the autopilot will run out of compensatory trim-loading and be itself over-powered. That can happen quite quickly even in cruise - as the stall speed rises very rapidly in the latter stages of ice build-up. But the REAL problem is that the stall speed difference between the LH wing and the RH wing can be as much as 25 knots - all due to the spanwise distribution of the ice (both its mass centroid and its aerodynamic drag increment on each wing) being so different, left to right. Once that RH wing stalls, the aircraft will roll rapidly and the instinctive pilot input of opposite aileron (to counter the roll) will only embed the aircraft in the then inescapable condition of autorotation (i.e. spinning).

You have to wonder how many turbo-props approach that terminal condition each day, across the globe. The few that reach it and fail to recover just become another non-specific "control loss" statistic. It's less about the Dash-8 and more about the vulnerability of any turbo-prop type that is licenced to operate in icing conditions.
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Old 14th Feb 2009, 03:59
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compare the NASA video to the flight data -- wow

The descriptions in the NASA video, especially of the feeling and behavior the pilots observe leading up to the actual tail stall, sound very much like the description from the flight recorder. The video deserves careful watching, especially toward the end after you've understood the information in the earlier part. Tell us what you think after putting these two together, eh?
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Old 14th Feb 2009, 05:56
  #170 (permalink)  
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There have been times when I felt that the British style slow and academic type of tuition is best. With enough time, One can become very knowledgeable on a given science. There are other times when I think the fast, clear, American-style tutorial, as in the link, are absolute tops. Very good, unequivocal video training pertaining to a specific threat.

One of the worst months in my 40 plus years in aviation, was suffered in Toulouse on an ATR course. It was bizarrely awful, with colleagues leaving with horrendous confusion in their knowledge of the systems. The exams were passed, at least by all the people that I asked, by learning parrot-fashion from the Q&A book. I took another month to sort out the information, and re-write it in a meaningful manner. Despite the course being at the manufacturer's factory field, there was not a single lesson containing the vital information that we see in the NASA link.

I left there without any knowledge of the specific type-anomalies that this film, for example, would have given me. That is unforgivable.

I happened to have years in command of medium weight turbo-props, and T-tailed jets, but some of my colleges were looking forward to their first command. The inferences are obvious.
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Old 14th Feb 2009, 07:05
  #171 (permalink)  
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For you Dash-8-Q400 guys;

Is there a way to monitor the output of the deicing system? If you had tear in one of the boots would you get any notification in the cockpit telling you a boot didn't inflate properly?
Yes there is, each boot has a relevant light on the Deice panel which illuminates each time the boot is inflated, it's always tested on the ground before departure. If, for instance, a boot isn't inflating because it's got an 'ole in it (Not uncommon) you will get a caution on the MWP (Can't remember what it says) and you'd probably see the relevant boot light flickering or not lighting up in the sequence.

Edit to add the Flap Assymetry protection will stop the flaps moving if there is more than 1 degree (?) difference between each flap.
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Old 14th Feb 2009, 08:14
  #172 (permalink)  
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Raw Aerial Of Crash Site; Continental 3407

Aerial footage taken from a news helicopter shows the full extent of the damage from the plane crash in Buffalo, New York State.

LiveLeak.com - Raw Aerial Of Crash Site; Continental 3407
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Old 14th Feb 2009, 08:30
  #173 (permalink)  
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NO aircraft is certified to fly in severe icing conditions.

Having flown the Dash 8 100/300 and Q400 for a couple of thousand hours:

Parts of the Q400 windshield become coverd with ice some times when cruising at very cold temperatures at cruising levels.
BUT when your (heated!) windshield gets frozen up so close to ground (at temperatures around freezing level = rather warm) that would alert me a lot.
I would consider this severe Icing conditions beyond the certified limits.

Interesting to know, that Bombardier considered to modify the Q400 to be equipped with bleed air anti/deicing and getting rid of boots at all.....
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Old 14th Feb 2009, 09:02
  #174 (permalink)  
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IT IS NOW TIME TO GET RID OF BOOTS in all planes or severely limit those types to trace or light icing exposure for less than 2 minutes.

WHILE Icing can bring down any plane, it seems that heated wings/airfoils are the way to go.

OR make the airfoil so robust aerodynamically as not to need anti-ice.

I guess there should be a ice detector on the tailplane!!!!!!
Jet icing is a complete different aspect, different aerodynamics, different ice build up, a complete different beast when dealing with a sweapt back wing. In many jets, you rarely use wing anti-ice - Especially on the big ones. I've only used the wing anti-ice maybe twice in 4 years flying the 744. Mostly as a precaution after retracting LEDs after slushy TOs.

When you are dealing with jet speeds you also tend to use ram rise in temp for your advantage, not to mention that you can usually climb out of conditions pretty quickly, where as the turboprops tends to hang arround them longer and at slower speeds.

I really don't think that they have enough extra capacity from the engines to operate heated wings. the wing is also ussually much thicker and has a different ice accretion profile than a jet's thinner airfoil. Technically, ice builds on smaller surfaces quicker than on bigger ones. That is why wipers, window frames, temp probes are all good indicators, and that is why really really large planes like the C5 galaxy don't have wing anti-ice. Proportionately, the turboprop airfoil is thicker than a jets.

Besides, heated wings or inflatable boots, they both only de-ice the same region. I don't think the method matters.

Icing can be quite a challenge in that region (great lakes region, KBUF, KSYR, KROC), and having flown a turboprop arround those parts, it can certainly be challenging in the winter months. I remember buggin the cruise speed, then blowing the boots when you dropped about 20 to 30 knots below that. Used to keep us out of trouble.

Having moderate or greater icing during the time on the approach when you are slowing down and exposing un-protected aerodynamic surfaces would have really perked my ears up. That is what has done most turbo-props in during icing conditions, regardless of what the effect was (aileron reversal, tailplane stall, whatever). Just by looking at anti-ice equipment on most planes you gain a sense that it is designed and placed at the exposure points during cruise speeds. It really is not meant for prolonged, slow configured flight. Prolonged being dependant on rate of accretion. Even light icing will do you in if you spend enough time in it flying slow.

You can spend ages in even moderate icing as long as it is at cruise speeds, in which case, correctly functioning ice protection should keep your airframe very clean. I don't think it would be profesional or prudent, but I would certainly not be as concerned as I would when flying slow.

Regardless, a sad end to many lives - RIP.
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Old 14th Feb 2009, 09:15
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Other aircraft were reporting that the ice was coming off at the level at which the loss of control occurred.

What tests are carried out in the certification process to determine the effects of asymmetric shedding of ice?
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Old 14th Feb 2009, 09:38
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It is a weird accident.

The aircraft fell 2.200 feet in a matter of seconds, and the pilots appeared to have lost control.

From pictures of the wreckage you can see, that the aircraft did plunge to the ground in a vertical position. The tail is in pretty intact condition, and eye witnesses reports of a 20-25 degrees nose down attitude. The pilots may have been recovering from, whatever upset attitude, they were in - but eventually ran out of altitude.

The question of icing springs into mind, since icing have caused several accidents involving turboprop aircraft. This might have been the case, but the ice protection system of the Q400 is very conservative - due to the Roselawn accident. Furthermore, the aircraft had not been holding or asked to reduce speed, while approaching the airport.

The Q400 has an ice detector, that will sense any ice, and you have spigots on the wind shield wipers, where the pilots can ciearly see ice building up. If the pilot get ice detection caution/warning, he pilot should immediately apply wing de icing, and turn on the "increase ref." switch that will increase the stall floor with 20 knots. You should then increase any bug speeds with 20 knots. From what I have heard, that will allow the aircraft to carry 3 inches of ice on the wing tips - and still be safe.

The check lists calls for immediate application of wing anti ice, when detecting ice. You should not wait for half an inch of ice. Recent NASA studies have disclosed, that ice "bridging" are not likely to occur under any condition. Ice bridging is a myth.

In case any of the boots does not inflate properly, the pilot will have "de ice pressure" caution. Cycling the wing de icing system, you can detect what boot is causing proplems. In case of a pressure leak in the boot system, you can split the system, but this requires you to exit icing conditions immediately, since you wiil have asymmetric wing de icing.

Therefor, if icing plays a part in this accident, it propably also involves faulty use of the ice protection system.

Best regards


PS - If you have the "increase ref" switch on and forget to ad 20 knots to the bug speeds - then you will stall at a speed, that is 20 knots higher than normal. This might be an issue to look into as well.
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Old 14th Feb 2009, 10:08
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ice bridging

As a professional engineer designing ice-protection systems, I would be very interested to see documentary evidence of any regulatory authority claiming ice-bridging to a myth. I know ice-bridging is fact, I have seen it in wind-tunnel tests, and many many design hours are spent trying to avoid its occurrence in flight.
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Old 14th Feb 2009, 10:13
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In Jan 1977 a Viscount went in vertically from 1100ft on approach to Bromma, Sweden in icing conditions. Subsequent investigations showed that a horn shaped build-up could occur on the tailplane leading edge which coupled with full flap selection would cause the tailplane to stall with catastrophic results. I think also the airframe de-ice had been switched off as per the landing checklist.
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Old 14th Feb 2009, 10:21
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The NTSB says here in this recent alert (Dec. 2008):

Ice bridging is extremely rare, if it exists at all
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Old 14th Feb 2009, 10:33
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Interesting to note from the NASA video that signs of a tail plane stall are reduced when using powered flying controls like the Q400's elevator system and that the possible only sign will be an unusual trim setting which could easily be missed as has already been pointed out previously.

Not sure if it's been answered in a previous post, but:
The Q400's autopilot will trim the forces in pitch. The yaw damper will to a limited extent help reduce yaw. The roll is held by the roll control actuators, excessive trimming of forces is indicated on the PFD, but no trimming is done by the autopilot. A manual pitch trim will disconnect the autopilot. A manual roll trim will not disconnect the autopilot, although the correct method is to manually disconnect the autopilot and trim out stick forces. However it is possible to trim in roll until the message goes away
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