An apparatus and method of verifying the trustworthiness of position information from an onboard tracking system on an aircraft. An onboard tracking system message comprising onboard tracking system position information indicating a first position of the aircraft is generated by the onboard tracking system and transmitted to an off board aircraft tracking system via a communications satellite in a satellite communications system. The satellite communications system adds a header comprising transmitter position information identifying a second position for transmission of the onboard tracking system message received by the communications satellite to the onboard tracking system message to form a message. The message is received from the satellite communications system by the off board aircraft tracking system and the first position from the onboard tracking system message is compared to the second position from the header to determine whether the onboard tracking system position information is trustworthy.