What is the difference in regulations for commercial and military aircraft parts?

Answer 1

The biggest difference comes down to the prevention of failures in combat and high-performance situations. Commercial planes are required to use parts that are certified for use in mass transportation only. Military aircraft use parts that are Mil-Spec (Military Specification) since they can potentially see a lot more stress in combat and in multiple environments, and for fighters, they're exceeding g-forces and speeds that commercial planes never see during normal operation.

Military parts are also designed for longevity and environmental abuse, using tightly controlled design specs. Corrosion resistant coatings, high grade fasteners, strong alloy metals, and extreme testing, are all part of military designs.

As an example of what can happen when commercial grade hardware gets into a military vehicle, about 16 years ago there was a huge problem in the military when it was discovered that a contractor here in Maryland, Mil-Spec Fasteners, had been supplying commercial grade fasteners as Mil-Spec grade parts. Fasteners are used in everything from Helo's, Tanks, Submarines, you name it. There were multiple instances of helo rotors coming apart because of bad fasteners. One of the guys in my own group (I was working as a DoD QA Rep then) found out what they were doing and the FBI did a controlled buy. But finding them and replacing then was nightmare.