What is required under FAR Part 91 regarding pilot certification?

Under FAR Part 91, the requirement states that pilots must possess a valid pilot certificate that is appropriate for the type of flight operation they intend to conduct. This means a pilot must hold the specific certification that aligns with the category of aircraft and the operation they are flying, such as private pilot, commercial pilot, or airline transport pilot certificates. This regulation ensures that pilots are adequately trained and qualified to operate the specific type of aircraft safely.

In terms of other options, the requirement for a minimum of 500 flying hours is not specified under Part 91; rather, different types of certificates and operations may require varying amounts of flight time. Completing a written exam every year is not a general requirement under Part 91 either; while recurrent training and checks might be needed for certain operations, these are not mandated for all pilots. Lastly, holding an airline transport pilot certificate is only necessary for pilots who wish to act as captains of commercial air carriers, not for all pilots under Part 91. Each of these options reflects different standards applicable to various kinds of flying or qualifications not universally required under Part 91.