Airworthiness Directive · Amendment 39-11647 · Eurocopter Deutschland GMBH Model MBB-BK 117 Helicopters
Eurocopter Deutschland GMBH Model MBB-BK 117 Helicopters
Model MBB-BK 117 helicopters, serial numbers 7001 through 7250 and 7500 through 7509, with tail rotor (output) drive bevel gear (bevel gear), part number (P/N) 117-12215-01, installed, certificated in any category.
Note 1: This AD applies to each helicopter identified in the preceding applicability provision, regardless of whether it has been otherwise modified, altered, or repaired in the area subject to the requirements of this AD. For helicopters that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (d) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.
This amendment adopts a new airworthiness directive (AD), applicable to Eurocopter Deutschland GMBH (ECD) Model MBB-BK 117 helicopters, that requires changing the retirement life for the tail rotor (output) drive bevel gear (bevel gear). This amendment is prompted by a fatigue analysis of the bevel gear conducted by the manufacturer due to installation of different tail rotor blades. The actions specified by this AD are intended to prevent fatigue failure of the bevel gear, loss of tail rotor drive, and subsequent loss of control of the helicopter.
To prevent fatigue failure of the bevel gear, loss of tail rotor drive, and subsequent loss of control of the helicopter, accomplish the following:
(a) Within 100 hours time-in-service (TIS):
(1) Record in the accessory replacement record and historical record “Main Transmission” section the retirement life of 18,500 hours TIS for the bevel gear.
(2) Determine the total hours TIS of the bevel gear. If the total hours TIS cannot be determined, use the operating time of the main transmission.
(b) If the bevel gear's total hours TIS is equal to or greater than 18,400 hours TIS, remove the bevel gear within the next 100 hours TIS and replace it with an airworthy bevel gear. If the bevel gear's total hours TIS is less than 18,400 hours TIS, remove the bevel gear on or before 18,500 hours TIS and replace it with an airworthy bevel gear.
(c) This AD revises the helicopter Airworthiness Limitations section of the maintenance manual by establishing a new retirement life for the bevel gear, P/N 117-12215-01, of 18,500 hours TIS.
The aircraft, engines and makers this AD names, by the model designations in its text. A model listed here may still be outside the AD's serial ranges.
