Auto Flight - Flap Position Sensor - Testing

Published: May 26, 2021
Effective: Jun 2, 2021
Deadline: Jun 2, 2021
Replaces: 2000-23-34

Boeing 737 300 400 500

AI-generated summary of the official EASA document. Verify against the PDF before acting.

What to do

Operators of Boeing 737-300, -400, and -500 series airplanes must perform the initial BITE test on the autothrottle computer within 250 flight hours or 2 months from June 2, 2021, whichever comes first, and continue repetitive testing as specified. Any detected failures must be corrected promptly following Boeing's service instructions. Comments on this directive must be submitted by July 2, 2021.

Summary

Federal Register Volume 86, Number 94 (Tuesday, May 18, 2021) Final Rule titled 'Auto Flight - Flap Position Sensor - Testing' is an FAA Airworthiness Directive affecting all Boeing 737-300, -400, and -500 series airplanes. This directive addresses a flap synchro wire failure issue that may not be detected by the autothrottle computer, potentially compromising the asymmetric cruise thrust monitor function.

What changed

This new FAA Airworthiness Directive requires repetitive built-in test equipment (BITE) tests of the autothrottle computer to detect flap synchro wire failures and mandates corrective actions if failures are found. It introduces an initial compliance time of 250 flight hours or 2 months after the effective date, whichever occurs first, to ensure timely detection of latent failures.

Why it matters

This directive is critical for aviation professionals because undetected flap synchro wire failures can prevent the asymmetric cruise thrust monitor from engaging during thrust asymmetry events, increasing the risk of loss of airplane control. Operators and maintenance teams must implement regular testing to maintain safety and regulatory compliance, reducing the risk of accidents related to this failure mode.

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