Final answer:
The four squawk codes for special circumstances in aviation are 7500 for hijacking, 7600 for radio failure, 7700 for general emergencies, and 7777 for military interception operations.
Step-by-step explanation:
The four squawk codes for special circumstances in aviation are used as a means of communication between aircraft and air traffic control to convey specific situations. These transponder codes are:
- 7500 - Indicates a hijacking situation.
- 7600 - Indicates a radio communication failure.
- 7700 - Indicates a general emergency.
- 7777 - This code is typically reserved for military interception operations and should not be used by civilian aircraft.
When pilots set their aircraft's transponder to one of these codes, air traffic controllers are immediately alerted to the specific emergency, allowing them to take appropriate action and offer assistance as needed.