Airworthiness Directive · Amendment 39-17624 · Main rotor head
Bell Helicopter Textron, Inc. (Bell) Helicopters
This AD applies to Model 412 and 412EP helicopters with a main rotor yoke assembly (yoke), part number (P/N) 412-010-101-123, -127, -129, or -133, installed; and Model 412CF helicopters with a yoke, P/N 412-010-101-127 or -129, installed; certificated in any category.
We are superseding Airworthiness Directive (AD) 2009-05-09 for Bell Model 412, 412CF, and 412EP helicopters. AD 2009-05-09 required reidentifying each affected part-numbered main rotor yoke (yoke) on its data plate, reducing the retirement life of the reidentified yoke, and revising the Airworthiness Limitations section of the maintenance manual or the Instructions for Continued Airworthiness (ICAs) accordingly. This new AD retains the requirements of AD 2009-05-09 with the exception of the P/N marking location. This AD was prompted by fatigue analysis that shows the retirement life should be reduced on certain yokes. We are issuing this AD to correct the unsafe condition on these helicopters.
You are responsible for performing each action required by this AD within the specified compliance time, unless it has been accomplished previously.
Within 10 hours time-in-service (TIS):
(1) Review the helicopter records to determine all of the helicopter models on which an affected yoke has been installed since its production and the hours TIS of each affected yoke.
(2) If an affected part-numbered yoke has ever been installed on a Model 412CF helicopter or on a Model 412 or 412EP helicopter with a slope landing kit, P/N 412-704-012-101, installed, do the following:
(i) Reidentify the P/N on the side of the yoke by using a vibrating stylus and etching two lines through the last three digits of the existing P/N and etching “137FM” adjacent to where you etched through the last three digits of the original P/N. This converts each affected yoke P/N to a new yoke P/N 412-010-101-137FM. The serial number remains the same.
Note 1 to paragraph (f)(2)(i) of this AD: The “FM” P/N suffix denotes a field-modified part.
(ii) Treat the etched surface with chemical film, and apply primer and paint.
(iii) Record the reidentified P/N on the applicable component history card or equivalent record.
(3) If you cannot determine all the model helicopters on which an affected yoke has been installed since its production or whether it has ever been installed on a Model 412 or 412EP helicopter with a slope landing kit, P/N 412-704-012-101, installed, perform the actions required by paragraphs (f)(2)(i) through (f)(2)(iii) of this AD.
(4) For each reidentified yoke, P/N 412-010-101-137FM, reduce the retirement life from 5,000 hours TIS to 4,500 hours TIS. Record the revised life limit on the applicable component history card or equivalent record.
(5) Revise the Airworthiness Limitations section of the applicable maintenance manual or the Instructions for Continued Airworthiness by reducing the retirement life from 5,000 hours TIS to 4,500 hours TIS for each reidentified yoke, P/N 412-010-101-137FM.
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.
