What frequency would you attempt to contact on if you lost communication with ATC?

In the event of a loss of communication with Air Traffic Control (ATC), the appropriate frequency to attempt contact is 121.5 MHz. This frequency is designated as the international emergency frequency. It is monitored by various air traffic services and is used for distress and emergency communications. Pilots and aircraft can utilize this frequency to alert others of their situation, and it is the primary frequency for emergency situations globally.

Choosing 121.5 MHz is based on established protocols in aviation safety. It is important for pilots to be aware of this frequency as it is universally recognized for emergency use. Other frequencies, while they may be used for various forms of communication in aviation, do not hold the same critical importance in emergency situations.