To: Heliport
The ultimate document that defines the safety and by association the reliability of an aircraft is the Fault Tree Hazard Analysis. The ultimate descriptor of safety is the probability of occurrence of a catastrophic failure that could cause loss of the aircraft and or, death to one or more crewmembers. If you are dealing with a helicopter that is in commercial service the frequency of this occurrence is stated as 1 10 9 operating hours for the fleet of helicopters. To get the frequency of occurrence and the definition of the effects of the failures on the aircraft the FMEA (Failure Modes Effects Analysis) must be prepared. The FMEA by definition must investigate any and all failures even if there is no effect at the system or aircraft level. This includes catastrophic failures as described above.
I do not know if a Safety Hazards Analysis was prepared for the Merlin and all other military derivatives but this analysis was most likely prepared for the commercial variant. However when I supervised the preparation of the FMEAs for the EH-101 I had the analysts include all catastrophic failures in the dynamics and powertrain systems. After several months of involvement in this effort the manager of the R&M group (an Agusta employee) overrode me and told the analysts to remove all references to catastrophic failures. In essence he was saying that the EH-101 was 100% reliable and would never fail catastrophically. This has been proven false on at least two occasions and if the Royal Navy is wrong then it is three occasions. The worst part is that if a Safety Hazard Analysis is performed for commercial certification then there will be no catastrophic failures included in this analysis as well.
The most catastrophic failure that was predicted was the lock-up of the main transmission. It was predicted that the rotorhead would self-destruct in the process of breaking through the lock-up using the kinetic energy of the blades.
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The Cat