Airworthiness Directive · Amendment 39-17876 · Tail rotor drive
Airbus Helicopters Deutschland GmbH (Airbus Helicopters) (Type Certificate Previously Held by Eurocopter Deutschland GmbH) Helicopters
This AD applies to Airbus Helicopters Model MBB-BK 117 A-3, MBB-BK 117 A-4, MBB-BK 117 B-1, and MBB-BK 117 C-2 helicopters with a Metro Aviation, Inc., vapor-cycle air conditioning kit pulley (pulley) part number (P/N) 30001 installed in accordance with Supplemental Type Certificate (STC) No. SH3880SW.
We are publishing a new airworthiness directive (AD) for Airbus Helicopters Model MBB-BK 117 A-3, MBB-BK 117 A-4, MBB-BK 117 B- 1, and MBB-BK 117 C-2 helicopters with a certain Metro Aviation, Inc. (Metro), vapor-cycle air conditioning kit pulley (pulley) installed, which was sent previously to all known U.S. owners and operators of these helicopters. This AD supersedes AD 2013-12-06, which required inspecting the pulley for looseness and properly installed lockwire and re-installing the pulley. Since we issued AD 2013-12-06, we received a report of a possible design and manufacturing deficiency in some pulleys wherein they did not have sufficient thread depth, allowing the pulley to detach from the rotor brake disc. This AD requires inspecting each pulley attaching bolt hole to determine if there is sufficient depth of the threads and either removing the pulley if the depth is insufficient or installing dual locking tabs under each pulley attaching bolt if the depth is sufficient. These actions are intended to prevent the pulley from detaching, resulting in damage to the tail rotor (T/R) driveshaft, and subsequent loss of control of the helicopter.
You are responsible for performing each action required by this AD within the specified compliance time unless it has already been accomplished prior to that time.
Within 5 hours time-in-service, inspect each pulley attaching bolt hole to determine the depth:
(1) Relieve tension from the compressor drive belt and remove each bolt that attaches the pulley to the rotor brake disc. Do not remove all three bolts at the same time.
(2) Remove AN960-416 washer or MAI-145-DUAL LOCK TAB washer.
(3) Using a bolt or screw with 1/4 -28 threads with 0.5 inch of threads and a minimum of 0.8 inch grip length, coat the shank with blue dye or permanent marker and thread into hole until threads have lightly bottomed (finger tight). Scribe the shank flush with the face of the rotor brake disk. Measure distance from end to scribe mark (length protruding into assembly). This dimension represents total depth of threads and stack-up of the brake disk.
(4) If the depth measures less than 0.61 inch, remove the pulley.
(5) If the depth measures 0.61 inch or more, install dual locking tabs as described in the Accomplishment Instructions, paragraphs 3.E. through 3.G., of Metro Aviation, Inc., Alert Service Bulletin No. MA145-21B-003, Revision B, dated December 20, 2013.
Within 10 days after inspecting the pulley as required by paragraph (f)(3) of this AD, submit a report with the helicopter model, helicopter serial number, hole number 1 thread depth, hole number 2 thread depth (if measured), and hole number 3 thread depth (if measured) to the person identified in paragraph (h)(1) of this AD.
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.
