What condition may disqualify an airport from alternate use?

The correct answer is based on the critical importance of having reliable navigational aids (NAVAIDs) for an airport to be considered suitable for alternate use. When NAVAIDs used for the final approach are unmonitored, it means that there is no active oversight or reliability verification of these navigation aids. This raises significant safety concerns since any issues or failures with unmonitored NAVAIDs may go undetected, compromising the ability of aircraft to safely navigate and land at the airport under low visibility or adverse weather conditions.

Utilizing unmonitored NAVAIDs increases the risk for pilots, especially during the critical phase of approach and landing. Therefore, an airport with such NAVAIDs would not meet the safety requirements needed for it to serve as an alternate airport during a flight, thereby disqualifying it from use in such scenarios.

While other conditions, such as the runway length, weather conditions, and the publication status of approach procedures, can affect operational decisions, the unmonitored status of NAVAIDs directly impacts the navigational safety and reliability necessary for alternate airport considerations.