AC25.07D covers the background for 25.255, however the B737 is an aircraft with a powered trim system ergo "it must be possible from an overspeed condition at VDF/MDF to produce at least 1.5 g for recovery by applying not more than 125 pounds of longitudinal control force using either the primary longitudinal control alone or the primary longitudinal control and the longitudinal trim system". The 30lb load is applicable to an aircraft that did not have a powered trim system. This saga has highlighted that the aircraft can be placed in an condition that exceeds the 3 seconds out of trim motion of the trim system. In that respect it is similar to the awareness that grew out of AA587 of the limitations of the term Va in the protection of the structure. The industry learnt from that lack of comprehension and moved on without tails falling off around the circuit. Having an long forgotten technique that exceeds the criteria of 25.255 is hardly comforting, and suggests that remediation is needed, the simplest being by training.
1. Once again, FAR 25.255 is about pilot applied mis-trim, it is a stand alone regulation that has nothing to do with system runaways. Do you have any evidence that FAR 25.255 is not effective for the pilot applied mis-trim case for which it was developed?
If you can make a case which proves that pilot mis-trims actually result in a worse situation than addressed by FAR25.255 best of luck getting the regulators, manufacturers and airlines to show any interest.
33. Out-Of-Trim Characteristics -
§ 25.255. a. Explanation. Certain early, trimmable stabilizer equipped jet transports experienced “jet upsets” that resulted in high speed dives. When the airplane was MISTRIMMED in the nose-down direction and allowed to accelerate to a high airspeed, it was found that there was insufficient elevator power to recover.
2. The dive recovery requirements of FAR25.255 are agnostic as far as the type of trim system is concerned ergo - I don't understand why you choose a to make some point about powered trim systems.
3. This "saga" has not highlighted anything other than that powered systems can runaway and there are a number of FAR requirements to deal with probability, effect, crew action and time intervals for recognition and reaction. Taking a particular case, the certification recognition time could be 3 seconds and the reaction time a further 3 seconds. So the certification standard certainly recognises that runaways can continue for longer that 3 seconds.
These accidents appear to have been the result of an uninterrupted SAS system runaway - I have no idea on the chain of event which lead to these tradgedies.
4. The story of Va is that a misconception of what Va is was somehow generated in the operational section of the aviation industry. This misconception is still widely held despite attempts to explain the the reality. I see no similarity here. The structural design rules with respect to Va are unchanged.
5. Once again, your "long forgotten technique" has no relevence to FAR25.255 - it is not an issue for a compliant aircraft. I understood that it was a procedure developed for the trim runaway case.
6. Without having access to all the cerification committee meeting minutes, compliance plans, compliance reports this is really a pointless exercise.