In REDL's accident report you will also find reference to this:
1.18.4 Accident to Aerospatiale SA330J, 9M-SSC, 16 December1980
On 16 December 1980, an Aerospatiale SA330J Puma helicopter, 9M-SSC, crashed in a swamp forest near Kuala Belait in the State of Brunei. The crew of two and all 10 passengers were fatally injured in the accident, which resulted from an MGB failure similar to that which occurred on G‑REDL. The MGB of the SA330J is fundamentally similar in layout to those of the AS332 series of helicopters, although the components are not interchangeable and the gear material specifications are different. The gearbox in the 9M-SSC accident had a recent history of quantities of metallic debris being found on the magnetic chip detector in the main module. The epicyclic module was not equipped with a detector.
The synopsis of the report on this accident contained the following:
‘The accident occurred following the loss of the main rotor assembly, together with the attached bell housing containing the second stage gears of the epicyclic gearbox. Almost simultaneously, the entire tail boom section parted from the aircraft.
It is concluded that the most likely cause of the accident was a planetary gear failure in the second stage of the two stage epicyclic main gearbox reduction gear; the associated metal debris caused jamming within the rotating assemblies, generating forces which fractured the common epicyclic ring gear and the main gearbox casing. This resulted in the gross instability in the rotor system, which caused blades to strike the fuselage.
The initial cause of the accident was due to the mistaken health monitoring of the gearbox, leading to a deterioration of the mechanical condition of the gearbox components.’
The first of two causes stated in the report was as follows:
‘The accident was caused by the disintegration of a secondary stage planet pinion [gear] within the gearbox following a seizure of its associated roller bearing.’
The break-up of the second stage planet gear in this accident was precipitated by a maintenance error which allowed a severely deteriorated gear to fail. No part of the failed gear was recovered and the entire first planetary stage was missing. However, the break-up of the gear resulted in circumferential failures of the ring gear casing, above and below the epicyclic stages, together with a vertical rupture.