Related Clues:

• Active beginning?
• Communication medium
• Gun at a ball game
• Air-traffic aid
• "M*A*S*H" character with great hearing
• 'M*A*S*H*' palindrome
• Speed gauge
• Aircraft equipment
• Marconi's medium
• Dashboard feature
• Walkman, perhaps
• Gun in a dugout
• Air-traffic detector
• Defense mechanism?
• Sound medium