From a former airlines SDM.

2. Stick Pusher
The SPM’s, calculating an average angle of attack based on inputs from AOA 1 and AOA
2, activate a stick pusher mechanism during a stall condition to assist the crew in reducing the angle of attack. The stick pusher is an electric actuator which drives the elevator control quadrant connected to the left control column. The stick pusher actuator requires two independent signals from SPM 1 and SPM 2 to operate.
Stick pusher operation can be turned off (i.e. in response to a Stick pusher malfunction) by pressing either of the STICK PUSHER SHUTOFF switchlights located on the left and right sides of the glareshield.
Pressing either switchlight will result in the illumination of the PUSH OFF caption on both switchlights and the illumination of the PUSHER SYST FAIL caution light. The stick pusher system is rendered inoperative if either of the AOA transducers fails or if there is a substantial difference between the two AOA transducer inputs. The SPM’s are programmed to provide the push command for up to15 seconds if necessary,with a subsequent delay of 1 minute.
(It is also possible for the pilot to manually override stick pusher operation by applying approximately 80 lbs of back force on the control column).

 

More stuff on the system

VI. STALL PROTECTION SYSTEM
A. General Description
The Stall Protection System (SPS) provides indications when the aircraft is nearing a
stall condition, provides indications when the aircraft is actually in a stall condition,
and provides positive inputs to assist the crew in eliminating the stall condition. The
SPS has two primary functions, they are:
• Stick Shaker
• Stick Pusher
The SPS uses stick shakers to provide tactile and aural warnings to alert the crew of
an impending stall. Also it uses a stick pusher to assist the crew in eliminating a stall
by moving the elevators to reduce the angle of attack (i.e. pushing control columns
forward). Two Stall Protection Modules (SPM 1 and SPM 2) calculate when the
aircraft is approaching a stall condition and determine when to activate and cancel
both stick shaker and stick pusher operation.
B. Stall Protection Modules (SPM)
1. SPM1 and SPM2 use the following parameters to determine an approaching
stall condition and the need for stick shaker activation:
• Angle of attack data – the average of two Angle of Attack(AOA) inputs
• Flap position – input from Flap Position Indication Unit
• Mach number – input from ADU 1 & 2
• Engine torque
• Icing status – input from the REF SPEEDS switch
When the SPM’s detect an impending stall condition they activate their related
stick shaker and signal the Automatic Flight Control System (AFCS) to
disengage the autopilot.
2. SPM 1 and SPM 2 use the following parameters to determine when stick pusher
operation needs to be activated.
• Angle of attack – the average of two Angle of Attack(AOA 1/AOA2) inputs
• Flap position – input from Flap Position Indication Unit
• Mach number – input from ADU 1 & 2
• Power lever angle
• Condition lever angle
• Icing status – input from the REF SPEEDS switch
C. Stall Protection System Operation
The Stall Protection System operates when the conditions that follow are met:
• Calibrated airspeed (true) is less than 215 knots
• Altitude is more than 500 feet AGL
• The Stick pusher SHUT OFF switchlight is not pushed to the OFF position

 

Wasn't the shaker activated due to the slow airspeed causing the autopilot to trim to a higher AOA? Could still have been Tail Ice at that point could it not? Recovery is whats different.

 

According to what I have read the NTSB has said that ICE had a minimal impact if any on the crash

 

I think we all agree that in a full-fledged stall, NONE of us would EVER MAINTAIN pitch attitude and apply full power.. we would ALL do what we have been trained to do since pre-private... pitch DOWN to break the damn stall and add full power, THEN pitch back up to regain altitude

 

I would tend to agree with your assessment that the crew could possibly have misidentified the situation as a tailplane stall. A stick-shaker would not be an indication of a tailplane stall, but a stick-pusher could be misinterpreted as a "snatch" of the yoke common to tailplane icing, especially combined with a recent configuration change (lowering flaps), and the perception that you had sufficient flying speed.

The result in this case would still be "human error" if they misidentified a tailplane stall. Other indications such as angle of attack, aircraft speed and stick shaker activation would weigh against it being a tailplane stall. Having been in some split second situations (for example a stall warning horn immediately after takeoff) I recognize there is not always enough time to process what has happened, and therefore "instinct" and "proper training" takes over. As a result I intend to give the flight crew the benefit of the doubt until we have more information.

My curiosity as to whether tailplane icing was involved centers around whether we are being counterproductive in our training programs by emphasizing a less likely event at the expense of being able to respond to a more likely event. I am not sure enough information has been revealed to either establish the mis-identification of tailplane icing as a cause, nor do I think there is enough information regarding the true cause. I for one am interested to see the final results of the investigation.

WJI

 

"--they were in icing conditions
--had just configured flaps and gear
--the yoke suddenly moved forward very quickly"

When gear and flaps are lowered on the this plane, does the nose pitch up or down?

Could they have been reacting to this, in combination to maybe a slower than normal approach, and an out of trim condition with the AP, which caused an unintentional stall?

Just asking.

Nitro.

 

I have a feeling that if you asked that flight crew a week before the accident, they probably would have said the same thing as you.

The problem, as others have pointed out, is that in an emergency situation a person will revert to the training that they have received. A person who has been subjected to the normal imminent stall recovery procedure every 6 to 12 months, will tend to apply that technique rather than the full stall recovery which is both very different and typically not trained after one receives their Commercial Pilot license (a long time ago for some of us). Also something to consider, if a person has been subjected to regular simulator based tail stall recovery procedures, such as the ones that Colgan teaches or at least used to, they will likely be sensitive to tail stalls and may revert back to that recovery in an unexpected event such as the one that happened here. Train for the normal...Talk about the unlikely.

 

VTCharter, BIrwin, and shfo, I just wanted to say thanks for your replies.

Regards to all my flying compadres,

 

The 121 carriers I have been involved with (3 plus one 142 training) have taught to lose little to no altitude. You release back pressure enough to reduce the AOA, simultaneous adding TO, GA or MCT depending on the conditions. I don't recall having trained to recover from a tail stall in my turbo prop days. I have flown in the ice for many years (Pacific Northwest) and I don't recall any hanger flying dealing with the given situation. That begin said, if you break through the gate on the Q400 you have nearly 14000 SHP! I have only flown turboprops for one company and only know their training program. I am not pointing fingers, just pointing out what I have learned over the years which is different from others.