Originally Posted by AerisArmis

Many years ago, I remember a cockpit jumpseating mechanic (on duty) fooling around with VHF-3 (changing freqs as he was trying to listen in on the radio) after our MD-11 took the runway at SIN enroute to PEN. Next thing we knew, a SIA 747 was going around over our head and we were getting yelled at on guard to clear the runway. Upon our return from PEN, the Capt got to go up in the SIN tower for an a$$ chewing from the tower supervisor. So yes, to answer your question, having a mechanic riding jumpseat could be detrimental to the safe operation of the aircraft. I would expect this to be an isolated incident, much like your example of when you were a hero and prevented disaster. However, whether the mech could be a detriment or could be helpful is irrelevant when it comes to PIC authority and personal jumpseating in the cockpit.