Would it be more accurate to say "...without any signs of wear being detected by the Aircraft systems or Engineering surveillance procedures..."?
Originally Posted by
Colibri49
I haven't looked at this topic for a few weeks, so hopefully I'm not about to repeat something which might already have been raised by others. As someone with thousands of hours flying the EC225, I know that there is a chip detector spring-loaded toggle switch above the pilots' heads. Moving it one way tests all chip detectors, both for the engines and gearbox. While holding the switch against its spring you see in sequence "Chip1" for engine 1, "Chip2" for engine 2 and "Chip" for the gearbox, all showing on the VMS display panel. This test gets done before every flight. Moving it the other way in flight would put a high voltage electric pulse through the very smallest (hair fine) metal particles on the detectors and burn them off.
Two such "fuzz burns" are allowed in flight, after which if it's a gearbox "Chip" warning a landing must be made as soon as possible e.g. on the nearest available helideck offshore. I've only ever had a "Chip 1" in flight and I brought engine 1 back to idle in the cruise, to minimise further possible damage. The particle was found to be negligible and the engine was returned to service.
With the removal of the magnets from the gearbox after the REDL disaster, I would hope that the slightest particles from wear or spalling in the epicyclic gears at the top of the gearbox would be detected long before any risk could arise. But this doesn't seem to have been the case in Norway. Yet photographic evidence and some opinions suggest that there was wear. In which case why weren't particles being detected during several hours of flight before the rotor head came off? As for missing roller bearings in one of the planet gears, is the metal of the gear-wheels elastic enough to allow rollers to escape during violent deformation of all components?
I still feel on balance that the cause was detachment of one of the gearbox suspension rods, for as yet unknown reasons. Sudden shattering of gearbox internal components without any prior signs of wear seems beyond belief.