Flight data recovery under adverse conditions

Methods for overcoming data loss, including bit dump, bit shift, forward and reverse readout, time displacement compensation (TDC), wideband TDC, and supersynchronization are discussed. Supersynchronization systems recognize acquisition of any one sync word as an in-sync condition and process accordingly. They open a window prior to the end of the subframe which enables the circuit to look for the next sync work up to 8 bits early. A feedback loop enables one shot timing methods to track the average bit rate automatically. A time duration equal to 70.7% of the average bit period is recommended. A digital bit averaging technique, in which the bit decision time is determined by the average of the two previous bits, gives excellent results. With forward and reverse processing, data are processed in the usual way through the engineering conversion process. Valid data, prior to the out of sync area, look normal. The computer then goes to the end of the subframe and processes data from this point backwards toward the sync loss area.