EC135
Flight Crew Commercial
Training / Qualification; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action; General Release Refused / Aircraft Not Accepted
Aircraft; Human Factors; Procedure
While on final to the hospital helipad; triple tachometer failure of Engine Number 2 N1 was observed; crosscheck of the VEMD confirmed engine was indeed operational and landing was uneventful. Upon shut down triple tachometer recycled and when a test; by the pilot; was done by energizing the systems the triple tachometer failed in the self test procedure. A phone call was made to the base Mechanic advising of the failed instrument. The pilot on the phone with the base Mechanic attempted to recycle the tachometer by sequencing a self test. The gauge was failing 50% to 75% to complete the self test mode. After cycling the system and having the triple tachometer complete a successful self test. The aircraft was started; the gauge was monitored and cross checked against values displayed by the VEMD for several minutes. The aircraft was then re-positioned to home base from the hospital pad to base without any further incident of the gauge. When base Mechanic inspected the tachometer with the pilot; self test fail was noted by engine needle. A replacement triple tachometer was then ordered; the aircraft was taken out of service pending the arrival of the replacement tachometer. (It should be noted that the tachometer was indicating NR function at all times and was intermittent with Engine Number 1 & Number 2 RPM needle function)If such were to occur again in the future I would either MEL the gauge (if MEL is allowed for such gauge) if not a MEL allowed item I would ground the aircraft have maintenance out to inspect.
An EC-135 triple tachometer failed on approach with the engine functioning normally. After several successful self tests the aircraft was flown to its home base where the tachometer failed during testing; so the aircraft was removed from service.