Under what condition can an aircraft fly an instrument approach procedure (IAP) of a lower category?

An aircraft can fly an instrument approach procedure (IAP) of a lower category if it is certified and capable of performing that approach safely. This allowance is primarily based on the aircraft's performance characteristics and the pilot's qualifications.

When considering why this option is correct, it's essential to understand that IAPs are categorized based on the aircraft's approach speed and performance capability. While it is acceptable for a more capable aircraft to execute an approach designed for a lower category, it is crucial that the pilot has the necessary training and qualifications for that specific maneuver. This ensures not only compliance with regulations but also safety during the approach.

For example, if a higher category aircraft meets the requirements for an approach intended for a lower category, and the pilot is trained for instrument approaches generally, then flying that procedure is permissible. This flexibility allows for more adaptable and efficient use of the airspace and enhances operational safety, provided that the conditions of the IAP are met and understood by the pilot.