In case of a multi-engine failure, what must the aircraft maintain on the route to be flown?

The correct answer is that the aircraft must maintain the Minimum Obstacle Clearance Altitude (MOCA) of the route. MOCA is crucial in ensuring that an aircraft has adequate clearance from obstacles in the area when operating under instrument flight rules (IFR). It considers the highest terrain and obstacles along the route, thus providing a safety margin in case of an engine failure.

When flying with multiple engines, any failure can compromise the aircraft's ability to maintain altitude or control, making it essential for pilots to adhere to the published MOCA. This altitude guarantees that the aircraft is at a safe height, avoiding any potential obstructions.

While maintaining a Minimum Safe Altitude or Altitude Above Ground Level is also important for safety, the MOCA specifically accounts for both the route's required navigation performance and obstacle clearance, making it the most relevant consideration in the event of a critical failure like a multi-engine failure. The Emergency Landing Area, while a good practice for emergency considerations, does not provide the consistent required altitude information necessary along the entire route.