What specific regulations cover multi-engine aircraft operations?

The regulation that covers multi-engine aircraft operations primarily includes Federal Aviation Regulations Part 91 and Part 135. Part 91 applies to general aviation operations, including the rules governing the operation of aircraft, the responsibilities of pilots, and safety regulations that all civil aircraft must comply with, irrespective of their classification. It addresses both single and multi-engine aircraft comprehensively, detailing flight rules, maintenance requirements, and operational conduct.

Part 135 focuses on commuter and on-demand operations, which often involve multi-engine aircraft used in commercial capacities. This part establishes the operational criteria for air carriers operating under this service, including maintenance, crew requirements, and more stringent operational standards that also apply to multi-engine aircraft.

The other regulation sets listed in the other options do not specifically pertain to the operations of multi-engine aircraft in the same direct manner. For instance, Parts 61 and 141 deal with pilot certifications and flight training, while Parts 121 and 145 address scheduled air carrier operations and repair stations, respectively. Parts 151 and 155 refer to specific airport and landing area regulations which are not directly about aircraft operations. Therefore, the first choice effectively captures the pertinent regulations governing multi-engine aircraft operations.