Hello all,

            Working in the computer field I was wondering  why so much time in the aircraft industry is concerned with minimizing the mean time between failure (MTBF) on a single component. For example in the computer field we have moved extensively to a concept called RAID (Redundant Array of Inexpensive Disks), in the “old” days a mainframe disk drive with an average of a one MTBF every million hours cost tens of thousands, versus a PC drive had an MTBF of a thousand hours and sold for a few hundred. With RAID you would mirror the data between two PC drives, and the chance then of a both failing at the same time was back up to a million hours. Two PC drives would cost significantly less than the equivalent mainframe, the result is that the cost of disk drives for servers has gone down significantly. In addition, computer staff has become used to a failure mode for disk drives  resulting in reduced data loss and better recovery procedures. In the aircraft industry we have continued to engineer for the MTBF of a million hours, with two consequences. One, everything is very expensive, two pilots are not used to any failures; so when a failure occurs the pilot does not know how to effectively deal with it. Therefore, why do we not accept a lower MTBF and have two complete avionics systems, fly by wire controls, engines…. The point could continue to everything except core structural elements.

Tim