Expert: Malcolm Dickinson - 11/24/2009

Question
Are pilots of commercial aircraft such as American, Continental, Delta, Northwest, United, US Airways, and TWA required to monitor 121.5 MHz at all times in the United States?  

Is it difficult for a boat (watercraft) of able to establish contact in case of a mayday with a commercial aircraft (example Delta) and or air traffic control, if they transit a mayday on 121.5 MHz, yes or no?  

Are they allowed to do this, yes or no?  The boat is unable to reach any body on Marine VHF radio Channel 16, (156.8 MHz).  

Is this correct, yes or no?  

The aircraft emergency frequency (also known as guard) is a frequency used on the aircraft radio band reserved for emergency communications for aircraft in distress. The frequencies are 121.5 MHz for civilian, also known as International Air Distress (IAD) and 243.0 MHz for military use, also known as Military Air Distress (MAD). Both are in use at the international level.  In the United States, 121.5 MHz is monitored by most air traffic control towers, FSS services.  

If an aircraft violates or is on a trajectory that will violate Restricted or Prohibited airspace, it will be warned of military interception on 121.5 MHz. The frequency may also be used by ATC to establish contact with an aircraft that has inadvertently switched to an incorrect frequency.  Pilots are strongly recommended to monitor 121.5 MHz at all times.  

Answer
I believe pilots of commercial aircraft are encouraged to monitor 121.5 but are not required to do so.

A boat or aircraft in distress could transmit on 121.5 and could be fairly sure of reaching an airplane - though this would depend on how many aircraft are overhead that particular place at that time.

I don't see any problem with a boat transmitting on 121.5 if they are unable to reach anyone on their marine band radio.  It's true that boats are not allowed to transmit on 121.5 but these sort of rules do not apply in an emergency.

best,
Malcolm