Above The Clouds Even though it seems that the ACARS had been disabled the FMC GPS's would probably still been sending and receiving signals to EGNOS or the MSAS satellite system, are these signals traceable ?
To my understanding SBAS is a one way augmentation system, the GEOs just transmit the GPS corrections and they do not receive anything from the aircraft. Therefore MSAS or GAGAN, the two SBAS systems possibly covering the flight profile would not have 'seen' the aircraft. Furthermore, to my understanding very few 'high end' aircraft are fitted with SBAS receivers.