Which of the following is NOT an exception for the ELT requirement?

The determination that all aircraft must have a working Emergency Locator Transmitter (ELT) is the correct answer because it represents a regulatory requirement for certain aircraft operations. The ELT requirement is part of the safety measures that ensure an aircraft is equipped with a device that can help locate it in the event of a crash or emergency.

In this context, the other options are considered exceptions to the general rule that most aircraft need to be equipped with functioning ELTs. For instance, flights within 50 nautical miles of the departure airport may not require an ELT, as the risk of being far from search and rescue abilities is mitigated by proximity. Similarly, certain agricultural flights, which often have unique operational parameters and may not operate over unpopulated areas, might not be subject to the same ELT requirement. Single-seater flights can sometimes fall under different regulations regarding equipment, depending on the aircraft's design and operational intent.

Therefore, asserting that all aircraft must have a working ELT recognizes a baseline safety requirement, while the other scenarios highlight specific conditions under which the regulations can be relaxed.