What action should be taken if radar contact and radio communication are lost unexpectedly?

When radar contact and radio communication are lost unexpectedly, declaring an emergency is the appropriate action to take. This response is essential because the aircraft's safety may be at risk due to the loss of situational awareness and communication with Air Traffic Control. Declaring an emergency allows for prioritization of handling the situation, ensuring that resources can be allocated quickly to aid the aircraft and facilitate its safe return to communication or radar contact.

Aircraft operating under these circumstances are presumed to be in a potentially hazardous situation, hence the significance of declaring an emergency. This designation prompts expedited assistance, ensures coordination with all aircraft in the vicinity, and allows for necessary procedural adjustments by air traffic controller personnel.

By contrast, other actions such as waiting for the situation to resolve itself or considering it may be an error can lead to delayed response and increased risk, while checking for known malfunctions, while important, does not replace the urgency of declaring an emergency when communication and contact are lost. Thus, the priority remains on ensuring flight safety by effectively communicating the emergency to relevant authorities.