Cat Driver
The fact that an unlocked primer can cause rough running is good enough for me to make sure that it is locked when I have an engine failure. It may not be the primer that has caused the problem but the idea of the engine failure cx is to eliminate all the possible causes,or hopefully find the problem. As you say it is only a remote possibility but for all the time it takes its worth checking. Even if it had been locked, the locking pin could have broken!!! ok so that really is a remote possibility but we read strange things in accident reports all the time.