AD 2021-15-05 Prompted By An In-Service Occurrence Of Loss Of Engine Thrust Control

The FAA is adopting a new airworthiness directive (AD) for all General Electric Company (GE) GE90-110B1 and GE90-115B model turbofan engines.

This AD was prompted by an in-service occurrence of loss of engine thrust control resulting in uncommanded high thrust. This AD requires initial and repetitive replacement of the full authority digital engine control (FADEC) integrated circuit (MN4) microprocessor. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective September 13, 2021.

Supplementary Information: The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to all GE GE90-110B1 and GE90-115B model turbofan engines. The NPRM published in the Federal Register on May 7, 2021 (86 FR 24554). The NPRM was prompted by an in-service occurrence of loss of engine thrust control resulting in uncommanded high thrust. The FAA received a report from the manufacturer of an in-service loss of engine thrust control that occurred on October 27, 2019, resulting in uncommanded high thrust.

Analysis by the manufacturer found accumulated thermal cycles of the MN4 integrated circuit in the FADEC, through normal operation, causes the solder ball joints to wear out and eventually fail over time. The FAA published AD 2020-20-17 (85 FR 63443, dated October 8, 2020) to prohibit dispatch of an airplane if certain status messages are displayed on the engine indicating and crew alerting system and if certain conditions are present per the manufacturer's service information. As a terminating action, AD 2020-20-17 also requires revision of the existing FAA-approved minimum equipment list (MEL) by incorporating into the MEL the dispatch restrictions listed in AD 2020-20-17. Since the effective date of AD 2020-20-17, the manufacturer published GE GE90-100 Service Bulletin (SB) 73-0118 R00, dated November 6, 2020, and Revision 01, dated April 27, 2021, to replace the FADEC MN4 microprocessor and solder. In the NPRM, the FAA proposed to require initial and repetitive replacement of the FADEC MN4 microprocessor using an approved overhaul procedure. The FAA is issuing this AD to address the unsafe condition on these products.

FMI: www.regulations.gov