Originally Posted by
Colibri49
The lack of further chips might be explained by the design of the gearbox, which up until that time had a series of powerful magnets mounted on a shallow conical tray just beneath the epicyclics. Almost immediately thereafter the factory ordered all such magnets removed and I saw with my own eyes when this was done.
What were those magnets for? Possibly to catch the bulk of metal particles thereby preventing damage to components lower down the gearbox. I guess the philosophy was that at least one or two particles would pass through the ring of magnets and reach a detector lower down, giving enough warning of an impending problem at the top of the gearbox. This actually happened and yet the factory somehow allowed REDL to continue flying.
The reason for the haste with which those magnets were removed (the original Mk1 Super Puma didn't have them) has never been explained well enough for my liking.
According the the REDL report the ring of magnets was put in to protect the lower part of the gearbox, as you though, from particles released in the epi and mast areas to try to make a modular MGB. The problem was that the epi chip detector is not very efficient, small size, big epicyclic case radius, so in the event that a chip was found on the epi plug you had to inspect the ring of magnets which probably hoovered up the majority of chips coming from high up in the MGB.
The reason they removed the ring of magnets is that they effectively masked the master chip detector. Removing them increased the probability of detecting chips as all of the oil goes into the sump and the MGB chip detector is in a low spot in the sump, near to the oil scavenge line. On the 332 it would also trigger the chip warning in the cockpit, which doesn't happen for an epicyclic chip detection, that only triggers on HUMS