If an engine fire handle in a 737-400 is pulled (but not turned), can it be reset in flight to attempt a restart, or is it strictly a one-way system?
Thanks,
Aircraft systems wise the simple answer to your question is "YES" the handle can be re-set in flight, and assuming there is no damage to the engine it can be re-started. Once the engine has started the tripped generator can also be brought back on line. (I have personally demonstrated this in flight)
As to why, and if you would do it is an operational decision and would depend entirely on the circumstances at the time. 