EASA AD US-2021-18-17
Auto Flight - Operational Program Software - Inspection
Summary
Airworthiness Directive 2021-18-17 is a final rule issued by the Federal Aviation Administration addressing certain Boeing 737-600, -700, -700C, -800, -900, and -900ER series airplanes. It requires inspection and potential updating of the operational program software (OPS) of the flight control computers (FCCs) to correct issues with autopilot coupled instrument landing system (ILS) approaches where the airplane may not capture or track the glideslope correctly.
What Changed
This directive supersedes AD 2012-21-08 by retaining the inspection requirement for FCC OPS part numbers and adding a new requirement to update the FCC OPS software version if necessary. It also expands the applicability to include Boeing 737-900ER series airplanes and updates references to the latest Boeing service bulletins for software installation.
Why It Matters
The directive addresses a critical unsafe condition where improper glideslope capture during autopilot coupled ILS approaches could lead to controlled flight into terrain. Compliance ensures flight safety by preventing descent below the glideslope beam due to outdated or incorrect FCC OPS software. Operators, maintenance, and compliance teams must ensure affected aircraft have the correct software versions installed to maintain airworthiness.
What To Do
Operators must inspect the FCC OPS part numbers on affected Boeing 737 models and install and test updated FCC OPS software if required. Compliance with this AD is mandatory by December 20, 2021. Service information from Boeing Alert Requirements Bulletin 737-22A1322 RB, Revision 1, dated January 28, 2021, should be used for software updates.
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