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Continental TurboProp crash inbound for Buffalo

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Continental TurboProp crash inbound for Buffalo

Old 21st Feb 2009, 12:50
  #781 (permalink)  
 
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wilyflier, khorton, and microcruzer, I agree, if the AP was holding pitch up to maintain altitude at a slowing airspeed, then AP release should result in a nose down moment, not nose up. The stick pusher should also add to the nose down moment. Tail stall (if it happened) would also result in a nose down moment.

So where did the nose UP moment come from?
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Old 21st Feb 2009, 13:26
  #782 (permalink)  
 
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"Anyone more recent on the Q400 has an idea of what rotational forces there are when applying max power from a trimmed idle position?"

After doing many real missed approaches in the Q400 I can say it does pitch up considerably and takes a fair bit of stick forward pressure to maintain the GA attitude.

"One more question related to this article: "All Q400 take-offs have to be brakes-off, rolling start." No explanation is given as to why, do any Q400 drivers know why this is the case?"

Engine limitations.


"I had assumed that the stick is totally free after a normal and uninterrupted push, but I don't know. So therefore it was specifically the time that the pusher took to release the force, that I was referring to, based on my assumption. On some jet transports it was released as soon as the push completed and the vertical flow on the veins returned to an acceptable figure."

There is no time limit, as long as the Stall Protection Modules detect the stall (• Angle of attack
• Flap position
• Mach number
• Power lever angle
• Condition lever angle
• Icing status) the stick pusher will activate.

In trying circumstances; bad weather, icing, low time, intercepting LLZ, both heads down looking at the FMS to confirm all is OK, it is very possible that the pilot did not immediately recognise that a Stick Push was occuring and his first reaction may have been to increase power to increase the airspeed and commence a missed approach.

An interesting point to consider; with INC REF ON (as you select in icing conditions), the speed that the Stick Pusher activates is increased by 20 knots, regardless of whether or not the increase is needed. In other words, if you forget to turn INC REF ON to OFF when you are out of icing conditions, the Stick Pusher will still activate at the higher speed, even though the extra 20 knots is not required.

I would hate to think that the upset caused by the Stick Pusher possibly activating 20 knots too early may have set off this disaster.
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Old 21st Feb 2009, 14:39
  #783 (permalink)  
 
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An interesting point to consider; with INC REF ON (as you select in icing conditions), the speed that the Stick Pusher activates is increased by 20 knots, regardless of whether or not the increase is needed. In other words, if you forget to turn INC REF ON to OFF when you are out of icing conditions, the Stick Pusher will still activate at the higher speed, even though the extra 20 knots is not required.
Intuitively, it seems logical to me that the AOA for the shaker is changed and not the pusher. This would give stall warning some 20 kts early but not push 20 kts early. Can anyone verify this? If this is the case, it weakens quite a few speculative scenarios because the pilots would have had plenty of stall warning.

With that in mind I would still like to know the answer to what I asked in post 783 if any of you would be kind enough to find out.
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Old 21st Feb 2009, 14:47
  #784 (permalink)  
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"One more question related to this article: "All Q400 take-offs have to be brakes-off, rolling start." No explanation is given as to why, do any Q400 drivers know why this is the case?"

Engine limitations.
What limitations are they then? I have been on board when the engineers are doing ground runs, they sit there with full power on for over five minutes.

It was explained to us that it was to prevent pitting of the props and fuselage due to fod damage.
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Old 21st Feb 2009, 14:50
  #785 (permalink)  
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Because they are Resin? What does the Bandit do? Rolling T/Os are preferred in all normal (not limited) T/O, No?
 
Old 21st Feb 2009, 15:08
  #786 (permalink)  
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Just because the props are so big as far as I know. We never used reverse unless it was absolutely necessary. SAS used reverse for every landing and the forward part of their fuselage were severely fodded.

We didn't do standing starts even if it was limiting as the perf is all predicated on rolling starts.
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Old 21st Feb 2009, 16:23
  #787 (permalink)  
 
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My guess is that the pitch up is from pilot control input. I would like to share some perspective I have on type training. In all courses I have attended stall training is performed in one of the early simulator sessions and typically performed as something out of context that needs to be done. I respect this since it is very hard to surprise the crew by creating a stall situation. In all my courses however windshear training has been inserted in different phases of the training and can be inserted by surprise to the crew.

Coming from a type rating training you would be likely to have performed quite a lot of go-arounds and possibly a few surprising windshear escapes in the simulator.

Once again I would like to point out that the windshear escape in the Q400 manual promotes pitch before speed. This does not mean that I believe there was any windshear present in this accident and not even that the crew believed there was. However if they were surprised by sudden low speed and stall warning the reaction could have been a manouver more similar to go-around and even windshear escape than a stall recovery.


Btw, to my knowledge SAS did not use reverse unless very exceptional cases.
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Old 21st Feb 2009, 16:45
  #788 (permalink)  
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Southernboy;
And so does the ring of kicking tin.
No it doesn't. A far less familiar sensation. Decry it all you like but there are sections of the industry where the problem is endemic. I've seen it & ex colleagues still report it.
I think there's a bit of a disconnect in our exchange. I suspect we're in strong agreement.

Both minimal training and fatigue issues have that "familiar ring" and, as you stated, nothing has been done regarding fatigue regulation, especially here in Canada where a three-pilot crew (captain, F/O, Relief Pilot - there are no requirements for a 4th pilot - that's negotiated at contract time) can legally remain on duty for 20hrs, (23 in "unforeseen circumstances). I've watched training on the 320/340 series for a very long time and while generally very good in places, it is spotty and there is very little focus on manual flight including manual thrust levers. The specific consequence is, there is a great reluctance to disconnect and actually fly an airplane like a 172, which the Airbus does, beautifully.

My "kicking tin" comment, perhaps clumsy, was an expression of "sad regret" that "here we are, still picking up pieces when it may possibly have been avoided", (we don't know that yet - it was a comment on accidents, not this accident). We've all seen the pattern but neither legislation nor corporate executive awareness of the importance of training, fatigue risk management and knowing what the organization's airplanes are doing on a daily basis through FOQA just to name three outstanding issues among a host of others, has changed.

We're fighting for the same cause.
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Old 21st Feb 2009, 17:14
  #789 (permalink)  
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microCruzer I defer to your geographical advantage. I only know that the few SAS Q400's I've seen in the hangar have had the fuselage forward of the props, well, knackered really.
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Old 21st Feb 2009, 17:18
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DFDR Snapshots

In his NTSB briefing held Feb.16, Chealander said:

"The first motion of the airplane when the upset started, was a pitch up of 31 degrees. I'm giving you the maximum numbers now, not giving you each of the snapshots - we have snapshots of the flight data recorder every 5 seconds - and what I'm giving you are the maximums that it attained."
Surely he wasn't implying the DFDR was recording attitude parameters on a 5 second sampling rate.

Did he mean that the pitch & roll numbers he stated (up 31-degrees, down 45-degrees, left 46-degrees, right 105-degrees) occurred 5 seconds apart?

36 minute video of the NTSB briefing held by Chealander Feb.16 can be viewed here.
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Old 21st Feb 2009, 18:59
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Surely he wasn't implying the DFDR was recording attitude parameters on a 5 second sampling rate.

Did he mean that the pitch & roll numbers he stated (up 31-degrees, down 45-degrees, left 46-degrees, right 105-degrees) occurred 5 seconds apart?
There are all kinds of interpretations on this but I dare say that like many board members he debriefs the DFDR chairperson and jots notes down on pieces of paper just like a reported does before calling in to the office. BTDT

I suspect that the order is correct and that the max excursions are correct and that the rough time interval of the snapshots was 5 secs. In between his spoken points there could be other cycles not as significant.

Now I'm hoping that the sampling rate is much more often but that the time base records a time stamp only at 5 sec intervals.

Hopefully somebody who has recently worked with a recorder type like that on the Q400 will chime in.
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Old 21st Feb 2009, 19:44
  #792 (permalink)  
 
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All Q400 take-offs have to be brakes-off, rolling start." No explanation is given as to why, do any Q400 drivers know why this is the case?
Not sure if this is the same reason for the Q4, but take a look at this quote re the Learjet 60XR:

Rolling take offs are standard in the Lear 60XR. It never makes a standing start take off, applying power with the brakes set as you might do in a lesser jet, because it has so much thrust the wheels would simply be dragged, locked, along the surface, flatting, and possibly bursting the tyres.
KING LEAR - Flying the The LearJet 60XR
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Old 21st Feb 2009, 20:08
  #793 (permalink)  
 
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FOD

As mentioned before, the rolling takeoff is to prevent foreign object damage (FOD) to the props and fuselage.

This was standard practice on the DC-3, 4, 6, and 7. and the Connies.

Helicopter pilots like to get out of ground effect as soon as possible for the same reason.

All you're doing is beating up dirty air.
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Old 21st Feb 2009, 20:08
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For what it΄s worth, this is a quote from an AAIB investigation report concerning flight data recorder sample rates:

Figure 1 shows a time history of selected parameters recovered from the DFDR fitted to G-RJXC recorded during the incident landing. Pitch Attitude and Lateral Acceleration are sampled at 0.25 second intervals, Normal Acceleration at 0.125 second interval, Roll Attitude at 0.5 second interval and Altitude, CAS, Groundspeed and Heading at 1 second intervals
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Old 21st Feb 2009, 21:24
  #795 (permalink)  
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Finn47;

Those sample rates are reasonable and for the circumstances referred to by the AAIB would be of course accurate but these sample rates would not necessarily apply to all DFDRs. Sample rates depend upon the software installed, the size of the data frame and the design of the LFL, or Logical Frame Layout. FOQA QAR's are typically far richer in both the number of parameters recorded and the sample rates achieved. The data is typically on the ARINC 429/717 data busses (plus a few others) and being digital can be picked off at any rate - the data sampled and the rates achieved are a matter of equipment installed, storage medium and programming. In some military MFOQA applications, (thinking specifically of the C-17), approximately 40,000 parameters may be available. On our 320's, just under 2000 parameters are available whereas typical DFDRs will capture around 600 parameters. As usual, cost drives that is captured by each type of recorder.
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Old 22nd Feb 2009, 00:24
  #796 (permalink)  
 
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Runaway Trim?

So where did the nose UP moment come from?
Any chance of runaway nose-up trim? If the autopilot went to its limit to compensate for runaway nose-up trim, would it disconnect itself and allow a huge pitch up?
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Old 22nd Feb 2009, 02:09
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Ok, if anyone wants to correct me on specific technical aspects of the Q400 feel free....otherwise I still think that the pitch-up can be easily explained without resorting to pilot-inputs or malfunctions. I proposed what I think is a very possible scenerio in post #741,

Here is my take on the accident:
It seems to me that icing was not as much an aerodynamical problem as it was a distraction for the crew. The pilot flying allowed the airspeed to decay and when the stick shaker activated one or both of the pilots recognized the low-speed situation and called for go-around power. With the significant nose-up trim that the aircraft would have been holding, the addition of power (with the autopilot now kicked off) would have initially pitched the nose up. I think the nose would have pitched up even without the pilot's input. As the pitch increased and the plane stalled the pusher would activate and lead to a rapid pitch decrease. The amount of ice present MAY (and I emphasize MAY) have decreased aircraft controllability during the upset. Once the upset began at this relatively low altitude the crew didn't have the time or altitude to properly recognize what was happening and recover.
As I understand, the autopilot is automatically disengaged at stickshaker activation and there are another couple of degrees of AoA before stickpusher activation. If anyone can verify this specifically it would be appreciated.

Again, if the pilot(s) applied max/firewall power at the stickshaker I believe the trim setting (normal for the speed the A/P disconnected at) and the excess power would lead to a rapidly increasing pitch situation that could realistically achieve ~30 degrees before stickpusher activation.
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Old 22nd Feb 2009, 02:14
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Perhaps this explanation from post #771 is clearer

I think the pitch up prior to the stick pusher could have happened even without the PF over-riding it. If the crew called for max/firewall power at the stick shaker when they became aware of the low speed situation, the plane would pitch up quite quickly with no manual inputs. This is because the aircraft would have had significant nose up trim to maintain the slow speed and now the autopilot is kicked off. With the combination of increased prop wash over the elevator and the aircraft literally "powering" it's way to the nose-up attitude, I can easily see the aircraft attaining a 31 degree nose-up attitude prior to stick-pusher activation....and all this without any input from the pilot.
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Old 22nd Feb 2009, 03:04
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I had to laugh...then cry.

when I read the bit about the Lear 60 being so powerful, the brakes wouldn't hold

it sounds to me like that plane has weak brakes, not strong engines.

I've held the brakes on JT8d powered jets and ran up to full blast and then released prior to takeoff...brakes and engines matched just right.

picking up FOD with those big props is probably a good enough reason not to hold brakes.


AS to the NOSE UP moment. Sadly, I think the pilots, plural, both pulled back thinking they were in a TAILPLANE STALL due to ICING. It will come down to training, experience, certification of training program and pilots. AND anyone who can contact Bombardier should make it clear to all pilots that the plane is unlikely to tailplane stall. Maybe make a video to show alongside the Otter video?

I guess the Saab 340 does have a tailplane stall problem...Ready to fight the wrong war.

Sad.
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Old 22nd Feb 2009, 06:45
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The FDR model used on Q400 aircraft seems to be a Honeywell/Allied Signal 980-4700-027, also found on some jets, so at least that should not be a limiting factor. With all the Thales glass avionics and FADEC engine controls, it would seem digital data gathering would be easier than in older turboprop models?

Looking at this Japanese DHC-8-402 incident report and specifically the attached FDR data graphs (from Figure 4.1 onwards) there seem to be quite significant changes in parameter values inside a time frame of 1 second, which again indicates a high sampling rate:

http://www.mlit.go.jp/jtsb/eng-air_report/JA841A.pdf

so I would be rather surprised if the "sampling rate" would be only a "snapshot every 5 seconds".
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