Airworthiness Directive · Amendment 39-21508 · Auto flight
The Boeing Company Airplanes
This AD applies to all The Boeing Company Model 737-300, -400, and -500 series airplanes, certificated in any category.
The FAA is adopting a new airworthiness directive (AD) for all The Boeing Company Model 737-300, -400, and -500 series airplanes. This AD was prompted by a flap synchro wire failure that may go undetected by the autothrottle (A/T) computer. This AD requires repetitive BITE (built-in test equipment) tests of the A/T computer to detect a flap synchro wire failure, and corrective action if necessary. The FAA is issuing this AD to address the unsafe condition on these products.
Within 250 flight hours or 2 months after the effective date of this AD, whichever occurs first: Perform the applicable A/T computer BITE (built-in test equipment) test, “A/T BITE TEST LRU INTERFACE,” and before further flight do all applicable corrective actions, in accordance with paragraphs 1. through 5. of Boeing Multi-Operator Message MOM-MOM-21-0145-01B(R2), dated March 30, 2021, except as provided in paragraph (h) of this AD. Repeat the test thereafter at intervals not to exceed 2,000 flight hours.
Although paragraph 1. of Boeing Multi-Operator Message MOM-MOM-21-0145-01B(R2), dated March 30, 2021, specifies to prepare the airplane for BITE testing “using the reference/A/, AMM 22-04-00 or 22-04-10, paragraph 3 and 4 as necessary,” this AD does not require using that service information to accomplish those steps, but operators may refer to that information for guidance on the procedures.
Although Boeing Multi-Operator Message MOM-MOM-21-0145-01B(R2), dated March 30, 2021, specifies to report test results, this AD does not require any report.
