Rotor Craft

AEROSPATIALE AS 350BA - Main Rotor Mast, Bearing Lock Broken

Main rotor gearbox was removed for metal contamination and sent for overhaul. Upon disassembly, the bearing lock (P/N 350A37-1183-22), located between the lower bearing inner race and the epicyclic carrier shoulder, was found broken into multiple fragments. This caused extensive damage to the epicyclic and contaminated the reduction gearbox assembly.

A service history review of past failures of the subject lock indicates that cracks may be a result of inadequate torque pre-load on the mast bearing lock. When replacing any one of the two mast bearings, the thickness of the shims must be adequate to obtain specified pre-load. If not, looseness and unwanted vibrations may result causing damage.

Transport Canada reminds maintainers to verify the bearing shim stack-up and to carefully check the subject lock for wear whenever mast seals require replacement.

BELL 212 - Bellcrank Shear Rivet Sheared

While on approach, the droop compensator system of a Bell 212 failed to respond and engine rpm increased as the collective lever was lowered. The pilot adjusted engine rpm using the electrical trim system (beep switch).

Subsequent inspection found that the engine governor control bellcrank shear rivet (P/N MS20470B3) had sheared. No binding could be found in the governor control system linkages. Failure of the shear rivet is likely the result of fatigue.

EUROCOPTER EC 120 B - Cabin Smoke

During cruise flight, smoke was noticed in the cabin. Shortly after an immediate and uneventful landing, all electrical power was lost (including battery power). Follow-up investigation revealed that the wire harness leading directly to the anti-collision light on the upper vertical fin had chafed through causing a direct electrical short to the Light Ancilliary Control Unit (LACU). The wiring was repaired and the rotorcraft returned to service. This particular rotorcraft has been in service for over 1000 hours time since new (TSN). A similar occurrence had previously occurred on a foreign registered EC 120 B rotorcraft. There are numerous inputs into the LACU such as landing/strobe/position lights, master battery "on", generator switch, fuel pump, pitot heat, rotor RPM, fire test, etc.

Transport Canada recommends that all EC 120 operators inspect this area for similar wire chafing pending further action from the manufacturer.

SCHWEIZER 300C - Main Rotor Drive, Lower Pulley Shaft Bearing Slipped

Drive Assembly and Main Rotor Transmission

While carrying out a detailed inspection of the belt drive (300-hour inspection), the engineer noted that the inner race of bearing, P/N 269A5050-85, had slipped on the shaft, P/N 269A5497-9, as indicated by the slippage marks. Upon disassembly of the "H" frame, it was noted that the bearing could be hand rotated on the shaft. The assembly was removed from service because the shaft and bearing are press fitted.

Investigation revealed that some shafts might have been manufactured incorrectly by the OEM with a very slight taper, which later resulted in the bearing becoming loose enough to rotate on the shaft. The OEM has a repair for tapered shafts, which is to grind and then nickel-plate the shaft.

Close attention to the slippage marks on the shaft should adequately detect any unwanted movement of the bearing.