Feedback Issue 2/2009

Rotorcraft

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Tail Rotor Assembly - Inner Sleeve

SDR submitted:

The rotorcraft was undergoing a test flight for radar altimeter troubleshooting when five minutes into cruise flight; a sudden vibration was felt in the airframe and from the flight controls. The pilot immediately returned to base for an unscheduled landing without incident.

Inspection of the aircraft found that the tail rotor blade assembly mounting fork was binding when moving the blade to the feather position. It was noted that this blade had no available movement in the flapping axis. Removal of the tail rotor inner sleeve (1053172904) assembly revealed that an outer bushing was protruding beyond the inner sleeve by 1.80mm.

Further inspection of the mounting fork revealed abrasion marks on the inside, which were thought to be caused when the dislodged bushing contacted the fork assembly. It is suspected that the airframe and flight control vibrations resulted from tail rotor assembly imbalance, which was likely caused by the weight shift of the bushing and compounded by blade rigidity in the flapping axis.

The tail rotor assembly had logged only 65 TSN (time since new) and 253 CSN (cycles since new). The submitter added that the part is being returned to Eurocopter Canada for warranty exchange and inspection

Transport Canada Comments:
A search of the SDR database revealed nine reported worn inner sleeve bushings. As in this case, if vibrations are felt through the flight controls and/or airframe then an immediate inspection should be warranted.

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Inline Check Valve

SDR submitted:

After a fuel filter replacement, a two-minute engine ground run was required, with the boost pumps off to ensure there were no air leaks in the fuel system. During this two-minute ground run, the engine flamed out after approximately 90 seconds, indicating an air leak.

The fuel system was inspected and the inline fuel/check valve (P/N ZT2CV06A08B) was found stuck in the open position. When this valve is stuck open air can be sucked from the front fuel tanks if they are empty. The check valve was cleaned and an engine ground run was carried out and the fuel system was declared serviceable.

The submitter indicated that this defect was likely caused by fueling from drums for an extended period of time and a small quantity of dirt entered the fuel system.

Transport Canada Comments:
TC advises operators to be cautious when using fuel from fuel drums. Water and other solid contaminates can enter the fuel system causing problems.

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Collective Rigging

SDR submitted:

The aircraft was climbing at approximately 6 000 ft. ASL (OAT 1°C). The collective reached its upper stop plate during a power increase. At this point the torque reading was approximately 65%. T4 and NG were well within maximum continuous limitations.

Two-weeks prior to this event, Eurocopter SB 67.00.12, Revision 2 was carried out on this aircraft. This modification involved the installation and positioning of a new stop plate on the upper part of the collective quadrant. Positioning this stop plate (P/N 350A27-1343-20) in accordance with the instructions provided in SB 67.00.12, Revision 2, Paragraph 2.B.2 results in the upper collective travel being limited as well as limited travel of the servo input rods to approximately 6mm at full collective position.

Paragraph 2.B.3. of SB 67.00.12 requires that the rigging of the collective pitch control be checked. Although an independent control check was carried out after this installation, the rigging of the collective pitch control was not carried out as required.

The aircraft was returned to service.

Transport Canada Comments:
This occurrence underlines the importance of a full independent control check following the disturbance of any flight-critical item.

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Main Transmission Chip Light

SDR submitted:

While in cruise flight, returning from an oil rig, the pilot heard a loud bang and the aircraft yawed left and right accompanied by a loud rumbling sound. The cockpit indication showed a transmission chip and a chip sump caution light. The pilot descended the rotorcraft to approximately 400 feet and prepared for ditching. After approximately 1 1/2 to 2 minutes, the rumbling stopped and the aircraft noise level seemed normal. The pilot proceeded to land without event and shut down the helicopter.

After inspection, numerous chips and flakes of metal were found on the oil sump pump chip detector, the collector gear detector and the magnetic drain plug. There was also some metal found on the L/H input quill chip detector and in the oil filter.

As a result, the main transmission gearbox (P/N 430040003) was replaced.

Transport Canada Comments:
Metal particles in the lubrication system of an engine or gearbox, are the first indication of an impending failure. Chip detectors are an invaluable device.

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Tail Rotor Mounting Bracket Cracks

SDR submitted:

The Operator reported seven cases of the right hand tail rotor bellcrank mounting bracket cracking. The affected aircraft models are: Aerospatiale AS 350 B2 and AS 350 B3.

All of these aircraft have the Eurocopter Canada Limited (ECL) STC SH96-32 (FAA STC SR00429NY) left hand pilot modification installed.

Transport Canada Comments:
TC recommends that operators who have installed STC SH96-32 follow the inspection requirements in SB ECL-122 issued by ECL.