What altitude should you fly at during lost communications?

During a loss of communication situation, the appropriate altitude to maintain is the last altitude assigned by Air Traffic Control (ATC). This course of action is crucial for several reasons. Maintaining the last assigned altitude helps ensure your flight remains within the traffic environment anticipated by ATC, reducing the risk of conflict with other aircraft. ATC has provided that altitude based on traffic patterns, airspace structure, and safety considerations, so it serves as a reliable reference point.

Flying at the last assigned altitude allows you to remain predictable to ATC and any other nearby aircraft that may still be communicating. It is important to remain vigilant and prepared to follow any relevant procedures, such as squawking an emergency code if appropriate, or proceeding to the flight plan's destination if the situation permits.

Other factors, such as lowest safe altitude and standard cruise altitude, are not appropriate in this situation because they may not align with established ATC expectations or the specific traffic environment. Additionally, flying at sea level altitude is generally impractical and can be unsafe depending on terrain, obstructions, or airspace classification. Hence, using the last altitude assigned is the best practice in a lost communications scenario.