A method of verifying trustworthiness of position information transmitted from an aircraft , the method comprising: an off board aircraft tracking system receiving a message from a satellite communications system comprising a communications satellite and ground facilities , the message comprising: an onboard tracking system message generated by an onboard tracking system on the aircraft , the onboard tracking system message comprising onboard tracking system position information indicating a first position of the aircraft determined by the onboard tracking system ; and a header added to the onboard tracking system message by the satellite communications system , the header comprising transmitter position information identifying a second position of transmission from the aircraft of the onboard tracking system message received by the communications satellite in the satellite communications system , wherein the ground facilities of the satellite communications system determine the second position ; the off board aircraft tracking system comparing the first position from the onboard tracking system message to the second position from the header to determine whether the onboard tracking system position information is trustworthy , thereby enabling taking an action using the onboard tracking system position information with a reduced concern that the onboard tracking system position information is not trustworthy ; and taking the action using the onboard tracking system position information from the onboard tracking system message in response to a determination that the onboard tracking system position information is trustworthy . an off board aircraft tracking system receiving a message from a satellite communications system comprising a communications satellite and ground facilities , the message comprising: an onboard tracking system message generated by an onboard tracking system on the aircraft , the onboard tracking system message comprising onboard tracking system position information indicating a first position of the aircraft determined by the onboard tracking system ; and a header added to the onboard tracking system message by the satellite communications system , the header comprising transmitter position information identifying a second position of transmission from the aircraft of the onboard tracking system message received by the communications satellite in the satellite communications system , wherein the ground facilities of the satellite communications system determine the second position ; an onboard tracking system message generated by an onboard tracking system on the aircraft , the onboard tracking system message comprising onboard tracking system position information indicating a first position of the aircraft determined by the onboard tracking system ; and a header added to the onboard tracking system message by the satellite communications system , the header comprising transmitter position information identifying a second position of transmission from the aircraft of the onboard tracking system message received by the communications satellite in the satellite communications system , wherein the ground facilities of the satellite communications system determine the second position ; the off board aircraft tracking system comparing the first position from the onboard tracking system message to the second position from the header to determine whether the onboard tracking system position information is trustworthy , thereby enabling taking an action using the onboard tracking system position information with a reduced concern that the onboard tracking system position information is not trustworthy ; and taking the action using the onboard tracking system position information from the onboard tracking system message in response to a determination that the onboard tracking system position information is trustworthy . <EOS>