To: heedm
rjsquirrel, 5 in 55,000 equals 9 in 100,000. Don't bother insulting others unless you keep yourself perfect.
Actually it is 9 in 99,000 hours if you want to be correct in the use of numbers.
The point is that the EH-101 has suffered one catastrophic failure in 11,000 hours of operation.
When I worked on the program we accounted for every catastrophic failure point and tried to design them out. However the catastrophic failures were removed from the FMECA so that the official word was that the helicopter would never suffer a single point catastrophic failure. The rotor brake problems and the tail rotor problems were accounted for in the initial analyses but were later removed from the analyses.
The sad point is that the helicopter received a civil airworthiness ticket and the airworthiness authorities never even checked the FMECA and the subsequent safety hazards analyses.
The EH-101 transmission as originally designed had a shear point that would fracture if the transmission ever locked up in flight.
The necessary force to effect the fracture is the kinetic energy in the blades. When the transmission locked up the blades would sweep forward compressing the dampers and when the dampers locked up there was a solid mechanical linkage which would effect the fracture. The dampers had a normal operating load of 1,800 pounds of linear force with a safety factor of 1.5 to limit load. When the blades sweep forward the dampers would fracture resulting in damage to the elastomeric feathering bearings.
To my knowledge the EH-101 transmission and rotorhead were never tested to demonstrate the fracture capability.
On the Apache it was written into the design spec that the US Army would accept one catastrophic failure resulting in loss of the airframe and crew every 34,000 hours of operation. The Apache is a combat helicopter the EH-101 is not. If the EH-101 continues at the present rate for catastrophic failures it is totally unacceptable not only for military applications but especially for the Presidential flight.
