To: Dave Jackson
What you say is true however the requirements that govern Reliability at least as far as aircraft are concerned deal with the probability of failure per million hours of operation of the total number of items under analysis. This is expressed as failures per 10 6 hours. In the case of a weapon it might be expressed as shots per million hours of operation per that specific weapon. In some cases it is expressed as cycles per million hours of operation.
When it comes to systems safety especially on commercial aircraft the probability of a catastrophic system failure that can down the aircraft or cause death to the occupants is specified as 1 10 9. Although different certification agencies use different terminology the basic mathematical figures expressing failure are basically the same 1 10 9.
In reliability the probability of failure for one hour of flight is expressed as 1 10-6 and for safety the probability of system failure is expressed as 1 10-9 per hour of flight.
