And how is the acars still transmitting in a flat spin?
Good question. The Antenna used for the ACARS transmission is a low profile electronically steerable array.
On system power up, the antenna sweeps through 360o looking for a syncronisation signal and locks to this at the acquisition bearing. The system is then able to track this sycronisation signal on ground and in-flight and If looses lock,which can inevitably happens for a number of reasons, it then enters the re-acquisition mode and re-starts the sweep. This however would not be fast enough, or designed to be able to obtain and re-acquire lock if the aircraft was in a flat spin - therefore would loose the sycronisation path with the Satellite and loss of ACARS transmission.