Airworthiness Directive · Amendment 39-15920 · Eurocopter Deutschland GmbH Model EC135 Helicopters
Eurocopter Deutschland GmbH Model EC135 Helicopters
This AD applies to Eurocopter Deutschland GmbH (Eurocopter) Model EC135 helicopters with a main transmission with a serial number of 0001 through 1420 and 1500 through 1749 installed, certificated in any category.
We are adopting a new airworthiness directive (AD) for Eurocopter Deutschland GmbH (Eurocopter) Model EC135 helicopters. This AD results from a report of abnormal main rotor blade vibrations on a Eurocopter Model EC135 helicopter. This AD also results from mandatory continuing airworthiness information (MCAI) issued by the European Aviation Safety Agency (EASA), which is the Technical Agent for the Member States of the European Community. The MCAI states that an operator reported unusual vibrations during the start phase of the main rotor blade on one helicopter. The vibrations stopped after the application of torque. Subsequent maintenance personnel found that six of the eight attachment screws of the lower hub-shaft bearing support were loose. This condition was discovered in two additional helicopters. Loose screws in the bearing support, if not detected and corrected, could result in abnormal main rotor blade vibrations and subsequent damage to the main transmission.
Within 3 hours time-in-service (TIS) if unusual vibrations are detected during the start phase or the shutdown phase when the main rotors are not at full operation RPM, or within 50 hours TIS after the effective date of this AD, whichever occurs first, do the following:
(1) Remove the lower transmission cover.
Note 1: You may drain the oil into a clean container so that it can be reused.
(2) Measure the clearance between the outer race and the transmission housing at four positions offset by 90° using a feeler gauge as depicted in Figure 1 of Eurocopter Alert Service Bulletin EC135-63A-013, Revision 02, dated September 12, 2008 (ASB). If the measured maximum clearance is:
(i) Less than or equal to 0.1 mm—install locking washers, tighten all screws, and re-measure the clearance by following paragraphs 3.B.(3) through 3.B.(7) of the ASB.
(ii) More than 0.1 mm—determine the difference between the smallest and the largest clearance and:
(A) If the difference is less than 0.4 mm—install locking washers, tighten all screws, and re-measure the clearance by following paragraphs 3.B.(2) through 3.B.(7) of the ASB.
(B) If the difference is equal to or more than 0.4 mm—replace the transmission before further flight with an airworthy transmission that has been modified in accordance with paragraph 3.B. of the ASB.
(iii) If the re-measured clearances obtained in accordance with paragraphs (e)(2)(i) or (e)(2)(ii)(A) of this AD are not less than or equal to 0.05 mm, replace the transmission with an airworthy transmission that has been modified in accordance with paragraph 3.B. of the ASB.
(3) Reinstall the lower transmission cover and replenish the transmission oil.
Note 2: If the transmission oil was drained into a clean container, it can be reused. Also, if the O-ring on the lower transmission cover is not damaged, it can be reused once.
(f) After the effective date of this AD, install only main transmissions that have been modified in accordance with paragraph 3.B.(3) of the ASB.
This AD does not require sending the main transmission to the manufacturer and does not refer to the transmission part numbers. Also, this AD uses the term “hours time-in-service”, the MCAI AD uses the term “flight cycles”.
The Manager, Safety Management Group, FAA, ATTN: Chinh Vuong, Aviation Safety Engineer, FAA, Rotorcraft Directorate, Safety Management Group, Fort Worth, Texas 76193-0111, telephone (817) 222-5116, fax (817) 222-5961 has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19.
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.
