Tcas Fault
RE: ACARS msg "TCAS FAULT (2:10)" not yet fully explained?
The exchange in posts #3872, #3873 and #3874 made me go back to BEA's Interim report on AF447 to count how many of these 24 ACARS messages have been marked as "not yet fully explained". I counted 4, and while going to the list it occurred to me how the TCAS FAULT can possibly be linked to pitot failure.
Others in this thread have explained that TCAS uses altitude and does not use airspeed. However, altitude is based on the pressure measured at a static port, which must be corrected for the position error of that port. The position error correction (PEC) is usually expressed as a pressure coefficient cp, which must be multiplied by the dynamic pressure measured at the pitot, to obtain the pressure correction. Some system must have 'reasoned' that since airspeed was unreliable, altitude was also unreliable, and hence TCAS would not be able to perform its intended function.
The PEC occurred to me while reading The Air Caraibe story, where it notes a sudden drop in altitude at the time that CAS and Mach drop, and the altitude steps up by about the same amount when airspeeds come back.
regards,
HN39