Originally Posted by
island_airphoto
Mode A/C only sends the numbers you set.
Mode S (and ADS-B) also has the airplane ID and
AFAIK that is not readily changed in flight.
EDIT: maybe not. Apparently some CAN change the airplane ID from the cockpit.
Anyone know if the 777 can do this?
Of course you can change your aircraft ID (call sign) in the cockpit. The call sign is your flight number as in "MH 370". This changes for each flight and is not specific to any one aircraft.
I think this only applies to ADS B or CPDLC where the crew enters the flight number for the particular flight in the Flight Management Computer.
Non ADS B flights would have the Call Sign entered by ATC when they assign the transponder code for the flight.
(please correct me if this information is not correct)