RT_INS_Lon_Dist_To_Start_Mark: INS Longitudinal Time and Distance to Start Marker Impact
RT_INS_Lon_Dist_To_Start_Mark: 142, 27 (0x8E2120 + unit id) (0x3A1)
Bytes 0-3: Longitudinal time to impact (s)
Bytes 4-7: Longitudinal distance to impact (m)
Time to impact resolution is s/1000.
Distance to impact resolution is m/1000.
Validity and impact flags are provided by RT_INS_Lat_Dist_To_Start_Mark.