Originally Posted by Machinbird
A stick pusher is a requirement for T-tail aircraft that can become locked into a stall if stalled too deeply. I recall reading that the DC-9 and MD-80 aircraft were apparently tweaked and demonstrated to not enter that regime, so no stick pusher was required.
To my knowledge that is not entirely correct. The regulation calls for stall warning preceding the stall to enable the pilot to avoid stalling, and it calls for acceptable 'stall identification' and stalling characteristics during recovery, but always assumes that the pilot initiates recovery "as soon as the airplane is stalled". The regulation recognizes three acceptable indications of a stall. One of these is "a nose-down pitch that cannot be readily arrested". This is where the 'tweaking' comes in, and where interpretations may differ. I suspect that the nose-down pitch that the FAA found acceptable was too weak for the CAA.
You are correct in that lack of nose-down pitch often goes together with a tendency to develop a 'locked in' stall if recovery action is not taken promptly.
FAA AC 25-7 Flight Test Guide refers to a stick-pusher as a "stall identification device".