Originally Posted by
JimL
Engines should meet a reliability figure of 1 x 10**-5; in ICAO parlance, this qualifies them as very reliable (the reason for the low standard is that a failure, at worst, should only result in an outcome of 'Major' - i.e. 'physical distress including injuries).
Tail-rotors should meet a reliability figure of 1 x 10**-9 because a failure could result in an outcome of 'Hazardous' or 'Catastrophic' - i.e. a fatality or multiple fatalities.
Reliability targets for tail-rotors are therefore 4 orders of magnitude better than engines - i.e. 10,000.
(A probability does not mean that a failure will occur after the reliability number has been reached, it can occur at any time but it should only occur once in the period.)
....
JimL
The actual figures for tail rotors according to the UK CAA make your representation of the maths
WRONG by a factor of about 50,000. And that's just the tailrotors!
Does that change your other maths? (why not?)
How many people died while using in upwards and backwards and PC type takeoffs?
There's the Norway 135 backing up into the real world wires maybe 4 or 5 other major accidents? (S76, 2x135, 139, 169, 902 others?)
10^-9 targets? really?
Catestrophic is having your rotorhead fall off,
major is having to glide to a street/park/tennis court/carpark/sea/hillside etc