When writing an answer to this question regarding flight deck access during flight, I mentioned the authority of the PIC to deviate from regs as necessary for safety purposes, citing the usual FAR, 14 CFR 91.3(b), which says:
In an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule of this part to the extent required to meet that emergency.
However, the exact wording used here made me wonder exactly how far this reg has been interpreted to go. In particular, it grants the PIC emergency ability to deviate from
"Any rule of this part", which would be 14 CFR Part 91. So, does this authority extend only to Part 91 of the FARs or does it extend to all of the FARs? The exact wording seems to suggest it only applies to Part 91 and not, say, Part 121, which was the part under consideration in the other question.
So, the major things I'm wondering are:
- What is the extent of the authority granted by 14 CFR 91.3(b)? and
- If 14 CFR 91.3(b) indeed only applies to Part 91, is there a similar explicit emergency PIC authority exception to the other Parts of the FARs?
Obviously, the PIC is the one in charge and will deviate where necessary for safety regardless of regs and worry about the explaining later after he's ensured he'll be alive to explain, but I'm curious about the regulatory basis for deviation from FARs.