Airworthiness Directive · Amendment 39-17337 · Tail rotor blades
MD Helicopters, Inc., Helicopters
MDHI Model 500N and 600N helicopters, with a NOTAR fan blade tension-torsion strap (T-T strap), part number (P/N) 500N5311-5; and MDHI Model MD900 helicopters, with a T-T strap, P/N 500N5311-5, P/N 900R3442009-101, P/N 900R3442009-103, or P/N 900R6442009-103; certificated in any category.
We are adopting a new airworthiness directive (AD) for MD Helicopters, Inc. (MDHI) Model 500N, 600N and MD900 helicopters to require determining the cure date for each NOTAR fan blade tension- torsion strap (T-T strap), establishing a calendar-time retirement life for certain T-T straps, reducing the retirement life of certain T-T straps, marking each T-T strap with the expiration date, creating a component record card for each T-T strap, and revising the airworthiness limitations section of the maintenance manual to reflect the changes to the retirement life. This AD was prompted by a report from the T-T strap manufacturer that, over a period of time, moisture may reduce the strength of a T-T strap. The actions are intended to prevent failure of a T-T strap, loss of directional control 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.
(1) Within six months, determine the manufacturer's cure date of each of the 13 T-T straps.
(i) For a T-T strap with five or more calendar years from the manufacturer's cure date, before further flight, replace the T-T strap with an airworthy T-T strap.
(ii) For a T-T strap with less than five calendar years from the manufacturer's cure date, mark the expiration date on the T-T strap face in permanent ink.
(2) Thereafter, before installing a T-T strap, mark the expiration date on the T-T strap using permanent ink. The expiration date is five years from the date the T-T strap package was opened, or if that date was not recorded, five years from the manufacturer's cure date.
(3) On or before the date you comply with paragraph (e)(1) or (e)(2) of this AD, create a component record card for each T-T strap and record on the card the manufacturer's cure date or the date that the T-T strap package was opened, if that date was recorded previously, and the T-T strap expiration date.
(4) Revise the Airworthiness Limitations section of the maintenance manual by establishing:
(i) A calendar life limit for the T-T straps, P/N 500N5311-5, 900R3442009-101, 900R3442009-103, and 900R6442009-103 of five years from the date the T-T strap package was opened, or if that date was not recorded, five years from the manufacturer's cure date.
(ii) A 2,500 hour time-in-service (TIS) life limit for any T-T straps, P/N 500N5311-5, installed on a Model 500N or Model 600N helicopter that was previously installed on a Model MD900 helicopter.
Note to paragraph (e) of this AD: For the MDHI Model MD900 helicopters, AD 2006-18-01 (71 FR 51095, August 29, 2006) contains additional TIS life limits for T-T straps, P/N 900R3442009-103 and P/N 900R6442009-103 and additional inspection requirements for all four affected T-T straps, P/N 500N5311-5, P/N 900R3442009-101, P/N 900R3442009-103, and P/N 900R6442009-103.
