Buffalo Q400 crash

In article ,
James Robinson wrote:

When the flaps are extended, and a tailplane stall results, the aircraft
immediately pitches down. There is no stall warning or stick shaker
activation.

In the case of the Buffalo accident, the nose did not drop, but the stick
shaker activated shortly after the flap setting was made. The stick
shaker is fired by low air speed, and is only a warning of impending wing
stall, with some airspeed margin. It is not an indication of tailplane
stall, or of an actual wing stall. Therefore, the correct action when
the stick shaker fired should have been to push the nose down to keep
speed up and reduce AOA. No question.

Further, the Q400 supposedly will never see a tailplane stall in icing,
but the crew may not have known that. The Saabs the captain previously
flew are subject to tailplane stall in icing, and he might have reacted
based on his previous training and apprehension about such stalls.

Ah hah, that makes sense. Given that the stick shaker had activated,
they should have known it was a regular stall and performed a regular
recovery. A tail stall would have happened abruptly with no stick
shaker. Is that about right? Makes sense if so.

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon

On May 14, 8:12 am, James Robinson wrote:

There was a theory on one of the other pilot forums that the captain
might have done all of his stall training when the aircraft was under
manual control, untrimmed, with the throttles cut until the speed dropped
below stall speed. He might have gotten used to having some backpressure
on the control column to avoid altitude loss under those conditions.

He might never have experienced stall training where the AP had ratcheted
the pitch trim toward its maximum, and was caught by surprise with the
sudden pitch up when the AP kicked off.

The FDR shows his immediate reaction to the stick shaker was to apply 20
lbs backpressure, which he immediately let go of as the aircraft pitched
up. He never pushed on the control column, however the wild
left/right/left/right rolls pretty well made controlling pitch a moot
point.

Those rolls were made harder to get out of by the fact that the
captain let
the aircraft get all the way down to 80 kts at one point, and at such
low
airspeeds, the ailerons have much less effect, which he would have
known
if he had simply paid attention to his flight instructor.

James Robinson wrote:
wrote:
Standard practice is to wait until you have a positive rate of climb
before raising the flaps. Raising the flaps if the airplane was on
the verge of a stall would be a big mistake. Lowering the nose and
applying full power would be the best course of action, and once a
positive rate of climb could be achieved, then the flaps could be
raised.

There is some debate about that. For a wing stall, you are correct,
however, some have pointed out that the PIC's experience was recently on
Saabs, which can see tail stalls in icing conditions - the Q400 isn't
subject to tail stalls. A tail stall is most often first seen when the
flaps are extended, and the effect is for the nose to drop. The reaction
to a tail stall is to retract the flaps, and pull the nose up. Was that
what the captain was reacting to?

Perhaps, but even that doesn't make sense either. The airplane stall
warning system/ stick shaker was activating. This would only indicate a
stall condition is imminent for the wing. The stall warning system does
not indicate anything about the tail, so the only corrective measure to
take for a stick shaker would be a conventional wing stall recovery,
such as full available power, prop forward, pitch down, don't bring up
the flaps until a positive rate of climb is achieved.

I'm not familiar with the specific stall recovery for that type, but you
get the idea. If the pilot pushed the stick over to recover from a
non-existent tail stall, that was a bad move. I haven't seen anything
to suggest that happened however.

xyzzy wrote:
On May 13, 2:14 pm, Ron Garret wrote:
In article
,



bod43 wrote:
On 13 May, 12:57, Robert Moore wrote:
James Robinson wrote
The drop in airspeed was unnoticed, and the stall seemed
to catch them completely by surprise.
I wonder what the stall warning was doing all of this time?
Bob Moore
It appears that it was the stall warning (stick shaker) that the
captain (pilot flying) reacted to.
The reaction was to immediately pull back pretty hard
quickly precipitating an actual stall. 80% power was also
selected immediately. The stick was held back pretty much
until impact.
This boggles my mind. I'm just a PP but throughout my training I've had
it drilled in to me to lower the nose on an impending stall. How can
any pilot not know that, let alone one who is getting paid to fly
passengers?

It may boggle the mind of a PP like you (or me for that matter) who
seldom or never flies in icing conditions. However in icing
conditions a tail stall is possible, and the recovery from that is
exactly what this flight crew did. Yes, I know the Q400 is alleged
not to be suspectible to this but the captain had just come from a
type that is, and the FO spent a good part of the five minutes before
the crash chatting about how she feared icing, had never experienced
it before, and how would she handle it, etc. So then after chatting
and worrying about icing, they got something that felt/looked like it
could be an ice-induced tail stall and since it was on their minds
they did the recovery from that. They acted on instinct and it was
the wrong instinct. IMO.

Perhaps that is exactly what happened. But their indication was the
stick shaker (aircraft stall warning system), which only indicates wing
stalls, not tail stalls. Regardless of type, the only correct response
to the stick shaker/stick pusher was to perform normal (wing) stall
recovery. Instinct should lower the nose immediately when the stick
starts shaking.

Mike Ash wrote:
Ah hah, that makes sense. Given that the stick shaker had activated,
they should have known it was a regular stall and performed a regular
recovery. A tail stall would have happened abruptly with no stick
shaker. Is that about right? Makes sense if so.

The thing though, at least according to the FAA video on tail stall thing
(it's on video.google.com, search for 'Tailplane Icing') it seems that
tail stall also manifests itself by odd pitch feedback on the yoke... I am
really wondering if there is any clear cut way to identify tailplane stall
from main wing stall as easily as you make it sound...

--Sylvain

"///" wrote:

On May 14, 8:12 am, James Robinson wrote:

There was a theory on one of the other pilot forums that the captain
might have done all of his stall training when the aircraft was under
manual control, untrimmed, with the throttles cut until the speed
dropped below stall speed. He might have gotten used to having some
backpressure on the control column to avoid altitude loss under those
conditions.

He might never have experienced stall training where the AP had
ratcheted the pitch trim toward its maximum, and was caught by
surprise with the sudden pitch up when the AP kicked off.

The FDR shows his immediate reaction to the stick shaker was to apply
20 lbs backpressure, which he immediately let go of as the aircraft
pitched up. He never pushed on the control column, however the wild
left/right/left/right rolls pretty well made controlling pitch a moot
point.

Those rolls were made harder to get out of by the fact that the
captain let the aircraft get all the way down to 80 kts at one point,
and at such low airspeeds, the ailerons have much less effect, which
he would have known if he had simply paid attention to his flight
instructor.

They immediately dropped to 80 kts when the aircraft pitched up. Think
of a Russian Sukhoi fighter doing the cobra manoeuver. The low speed and
wild rolls meant the chances of recovery at that point were pretty slim.
The initial pull up, combined with the overcorrection to the rolls pretty
well made the accident inevitable.

Pushing the control column forward when they were rolled 100 degrees from
level wouldn't have done much to help.

Jessica wrote:

James Robinson wrote:

wrote:

Standard practice is to wait until you have a positive rate of climb
before raising the flaps. Raising the flaps if the airplane was on
the verge of a stall would be a big mistake. Lowering the nose and
applying full power would be the best course of action, and once a
positive rate of climb could be achieved, then the flaps could be
raised.

There is some debate about that. For a wing stall, you are correct,
however, some have pointed out that the PIC's experience was recently
on Saabs, which can see tail stalls in icing conditions - the Q400
isn't subject to tail stalls. A tail stall is most often first seen
when the flaps are extended, and the effect is for the nose to drop.
The reaction to a tail stall is to retract the flaps, and pull the
nose up. Was that what the captain was reacting to?

Perhaps, but even that doesn't make sense either. The airplane stall
warning system/ stick shaker was activating. This would only indicate
a stall condition is imminent for the wing. The stall warning system
does not indicate anything about the tail, so the only corrective
measure to take for a stick shaker would be a conventional wing stall
recovery, such as full available power, prop forward, pitch down,
don't bring up the flaps until a positive rate of climb is achieved.

The question is what to do when everything happens at the same time?
That is, after the flap setting is increased, the stick shaker stall
warning fires, and the nose pitches down. What would you do then? The
stick shaker is only an indication of an impending stall, and there are
probably a few MPH margin left, but the increased flap setting might have
started a tailplane stall, on aircraft that have that tendency.

Immediately retracting the flaps might be the best course, along with
either level flight with increased power or slightly pushing the nose
down to keep the speed up. Pulling on the control column likely wouldn't
be a good idea, unless the pitch down was extreme. I don't know.

I'm not familiar with the specific stall recovery for that type, but
you get the idea. If the pilot pushed the stick over to recover from
a non-existent tail stall, that was a bad move. I haven't seen
anything to suggest that happened however.

The FDR shows moderate backpressure (20 lb, 40 lbs total) momentarily
applied to the control columns on both sides in response to the stick
shaker. This causes the aircraft to pitch up. When the aircraft pitches
up, the pressure is relaxed, to be reapplied by the left side when the
stick pusher is fired as the speed drops and the wing stalls.

Clearly, pulling on the control columns was the wrong thing to do, so why
did they both do it? Pushing should have been the instinctive reaction
to the stick shaker. I'm trying to figure out what else might have been
in their minds to generate the opposite reaction.

Mike Ash wrote:

James Robinson wrote:

When the flaps are extended, and a tailplane stall results, the
aircraft immediately pitches down. There is no stall warning or
stick shaker activation.

In the case of the Buffalo accident, the nose did not drop, but the
stick shaker activated shortly after the flap setting was made. The
stick shaker is fired by low air speed, and is only a warning of
impending wing stall, with some airspeed margin. It is not an
indication of tailplane stall, or of an actual wing stall.
Therefore, the correct action when the stick shaker fired should have
been to push the nose down to keep speed up and reduce AOA. No
question.

Further, the Q400 supposedly will never see a tailplane stall in
icing, but the crew may not have known that. The Saabs the captain
previously flew are subject to tailplane stall in icing, and he might
have reacted based on his previous training and apprehension about
such stalls.

Ah hah, that makes sense. Given that the stick shaker had activated,
they should have known it was a regular stall and performed a regular
recovery. A tail stall would have happened abruptly with no stick
shaker. Is that about right? Makes sense if so.

The FDR data shows the following happening in quick sequence:

- Ice warning showing up on display for first time
- Flap handle setting increased
- Stick shaker activated

The flaps had only extended about 1 or 2 degrees when the stick shaker
fired, but was the crew somehow influenced by the ice warning and the
fact that the flaps setting had just been changed? They certainly took
the wrong action in response to the stick shaker. Why?

In article ,
Sylvain wrote:

Mike Ash wrote:
Ah hah, that makes sense. Given that the stick shaker had activated,
they should have known it was a regular stall and performed a regular
recovery. A tail stall would have happened abruptly with no stick
shaker. Is that about right? Makes sense if so.

The thing though, at least according to the FAA video on tail stall thing
(it's on video.google.com, search for 'Tailplane Icing') it seems that
tail stall also manifests itself by odd pitch feedback on the yoke... I am
really wondering if there is any clear cut way to identify tailplane stall
from main wing stall as easily as you make it sound...

Well, I was just summarizing what I was replying to, to see if I had got
it correct.

In any case, it seems that, if there is not a clear-cut way to
distinguish between the two types of stalls, some way needs to be
created or else these aircraft are too dangerous. (Either that or it
needs to be made impossible to stall them at all.)

Maybe this is just my small aircraft experience misinforming me, and
stalls are rare enough that the potential for a screwup when they happen
is not something to be excessively worried about?

--
Mike Ash
Radio Free Earth
Broadcasting from our climate-controlled studios deep inside the Moon

"Jessica" wrote in message
...
xyzzy wrote:
On May 13, 2:14 pm, Ron Garret wrote:
In article
,



bod43 wrote:
On 13 May, 12:57, Robert Moore wrote:
James Robinson wrote
The drop in airspeed was unnoticed, and the stall seemed
to catch them completely by surprise.
I wonder what the stall warning was doing all of this time?
Bob Moore
It appears that it was the stall warning (stick shaker) that the
captain (pilot flying) reacted to.
The reaction was to immediately pull back pretty hard
quickly precipitating an actual stall. 80% power was also
selected immediately. The stick was held back pretty much
until impact.
This boggles my mind. I'm just a PP but throughout my training I've had
it drilled in to me to lower the nose on an impending stall. How can
any pilot not know that, let alone one who is getting paid to fly
passengers?

It may boggle the mind of a PP like you (or me for that matter) who
seldom or never flies in icing conditions. However in icing
conditions a tail stall is possible, and the recovery from that is
exactly what this flight crew did. Yes, I know the Q400 is alleged
not to be suspectible to this but the captain had just come from a
type that is, and the FO spent a good part of the five minutes before
the crash chatting about how she feared icing, had never experienced
it before, and how would she handle it, etc. So then after chatting
and worrying about icing, they got something that felt/looked like it
could be an ice-induced tail stall and since it was on their minds
they did the recovery from that. They acted on instinct and it was
the wrong instinct. IMO.

Perhaps that is exactly what happened. But their indication was the stick
shaker (aircraft stall warning system), which only indicates wing stalls,
not tail stalls. Regardless of type, the only correct response to the
stick shaker/stick pusher was to perform normal (wing) stall recovery.
Instinct should lower the nose immediately when the stick starts shaking.

Maybe. But, if the Q400 has a stick pusher, then it could really confuse
the issue--take a look at the FAA/NASA video on tailplane icing at
http://video.google.com/videoplay?do...23060735779946

Here is a link for considerable additional info, although it does appear to
include the FDR data which is linked elsewhere in this thread:
http://aircrewbuzz.com/2009/02/dash-...o-buffalo.html

We really don't know whether they actually had tailplane ice at the time,
not whether they did not, and we never will know because that sort of
evidence would not reasonably survive a crash.