What is the designated emergency frequency for aircraft communications?

The designated emergency frequency for aircraft communications is 121.5 MHz. This frequency is used by aircraft in distress to communicate with air traffic control and other aircraft. It is a global frequency that allows pilots to call for help when they experience emergencies, including system failures, navigational issues, or other critical situations that require immediate assistance.

121.5 MHz is monitored by air traffic control facilities and many commercial airlines, ensuring that there is a higher likelihood that a distress signal will be heard. In addition, it is also utilized by various search and rescue organizations to coordinate responses to emergencies.

The other frequencies mentioned in the options have specific uses but are not intended solely for emergencies. For instance, 123.4 MHz is often used for general aviation communications and is not dedicated to emergency situations. Similarly, 119.9 MHz is commonly associated with en-route air traffic services, while 126.7 MHz is designated for UNICOM or non-towered airport communications. Therefore, 121.5 MHz is the universally recognized frequency for emergencies, making it the correct choice.