To: T'aint
When you compare the fatalities associated with different helicopter types you should zone in on a specific type of accident. It is suggested that you read the NTSB report contained in Dave Jackson’s’ post above as it deals with loss of rotor control, mast bumping and/or rotor incursion.
Bell has suffered many mast bumping incidents and most of them occurred prior to the US Army discovering the cause. Bells have suffered probably no more than 60 rotor loss incidents since the introduction of the two-blade rotor system. I may be off a bit regarding the total incidents covered in the NTSB reports but I believe it is around 18 or more. Since the report was written and the introduction of AD 95-26-04 at least five more incidents have occurred and several of those were in the UK and Ireland.
Now compare the number of flight hours for both helicopters and divide those hours by the number of rotor loss incidents. The Robinson still comes off with the higher ratio.
Now for something that you may not have been aware of is what is acceptable.
When the Apache was designed the Army indicated that it was acceptable to have a single point failure or some defective procedure among other things that would result in the loss of an aircraft every 34,000 hours of collective flight hours.
If an aircraft is designed in accordance with FAA AC-25-1309-1A the frequency of suffering a catastrophic loss of an aircraft and crew is based on system or component reliability. The acceptable rate of system failure due to a single point failure or induced system failure is 1 10 9 or one time in a billion hours of collective fleet operation. There is no aircraft design at present that has ever met that design requirement and that includes 747s and R-22s.
