AAIB investigation to Boeing 737-8AS, EI-GJT
IRS fault and associated system malfunctions, en route from Porto Airport, Portugal to Edinburgh Airport, 9 October 2018.
Summary:
Shortly after reaching cruise at FL360 the commander’s attitude indicator malfunctioned affecting numerous aircraft systems, and the aircraft climbed 600 ft. After a significant time delay an irs caution was displayed. The Quick Reference Handbook (QRH) was followed by the crew and the left Air Data Inertial Reference Unit (ADIRU) was put into ATT mode. The left Primary Flight Display (PFD) continued to display erroneous attitude information to the pilot, and other systems were also affected. The aircraft was flown manually to Edinburgh where it landed safely.
The left Inertial Reference System (IRS) suffered a transient fault in one of its accelerometers which led to an erroneous calculation of position. False position information led to the incorrect attitude information on the commander’s PFD, and the autopilot (AP) responded by initiating a slow climb.
One Safety Recommendation is made concerning the Boeing 737 QRH.
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Safety Recommendation Document: