FAR 91.3 makes the pilot in command of an aircraft "directly responsible for" and "the final authority as to" the operation of the aircraft. That's very broad, encompassing language. When it comes to handling emergencies, the regulations spell out this authority a little more specifically by providing that "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." With one limited exception, this language has been consistently interpreted to mean that pilots are excused from violating any operating or flight rule so long as the violation was necessary to deal with an in-flight emergency. That means the FAA should not be permitted to pursue any enforcement action against a pilot who may have committed a violation as long as it was in response to an emergency situation and did not extend beyond coping with that emergency condition.
The one exception to this emergency authority is not specifically contained in the language of the regulation. Rather, it is an exception that has evolved over the years as different individuals have been called on to interpret the scope of the pilot in command's deviation authority. This exception says that the pilot may not be excused for violating a regulation if the pilot must exercise this authority when the emergency was of the pilot's own making. For example, if a pilot on a VFR flight encounters instrument weather conditions, warranting immediate action to bring the aircraft safely out of those conditions, the pilot may be excused from any resulting violations as long as the pilot carefully prepared for and carried out the flight, including properly checking all available current weather reports and forecasts. Certainly, we all know that weather can be unpredictable and can close in on a pilot despite his or her best preparations. In that circumstance, the pilot will be afforded the full benefits of his emergency authority, including being ex-cused from punishment for any regulations he may have violated in the process of bringing the aircraft to safety. However, if the pilot inadequately prepared for the flight or didn't exercise vigilance during the flight, the emergency may be considered to be one of the pilot's own making, and any resulting violations will not be excused.
FAR 91.123 contains two sections pertaining to a pilot in command's emergency authority. FAR 91.123(a) says, "when an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory." And FAR 91.123(b) says, "except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised."
These FAR 91.123 provisions give the pilot in command authority to deviate from a clearance or an instruction to the extent required to meet an emergency. Of course, no one should take deviating lightly, but neither should a pilot focus on trying to comply when an in-flight emergency requires the pilot's attention. Air traffic controllers understand a pilot's emergency authority. Pilots must also understand that authority and be trained under FAR 91.113(c) to give another aircraft experiencing an emergency the leeway needed to respond to that emergency. That is, "an aircraft in distress has the right-of-way over all other air traffic."
So, what is an emergency? That's not an easy question to answer - but one that we will tackle in the future.