AD 98-21-23
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| engine | CFM International, S.A. | CFM56-7B20 | Airworthiness Directives; CFM International, S.A. CFM56-7B Series Turbofan Engines |
| engine | CFM International, S.A. | CFM56-7B20/2 | Airworthiness Directives; CFM International, S.A. CFM56-7B Series Turbofan Engines |
| engine | CFM International, S.A. | CFM56-7B22 | Airworthiness Directives; CFM International, S.A. CFM56-7B Series Turbofan Engines |
| engine | CFM International, S.A. | CFM56-7B22/2 | Airworthiness Directives; CFM International, S.A. CFM56-7B Series Turbofan Engines |
| engine | CFM International, S.A. | CFM56-7B24 | Airworthiness Directives; CFM International, S.A. CFM56-7B Series Turbofan Engines |
| engine | CFM International, S.A. | CFM56-7B24/2 | Airworthiness Directives; CFM International, S.A. CFM56-7B Series Turbofan Engines |
| engine | CFM International, S.A. | CFM56-7B26 | Airworthiness Directives; CFM International, S.A. CFM56-7B Series Turbofan Engines |
| engine | CFM International, S.A. | CFM56-7B26/2 | Airworthiness Directives; CFM International, S.A. CFM56-7B Series Turbofan Engines |
| engine | CFM International, S.A. | CFM56-7B26/B1 | Airworthiness Directives; CFM International, S.A. CFM56-7B Series Turbofan Engines |
| engine | CFM International, S.A. | CFM56-7B27 | Airworthiness Directives; CFM International, S.A. CFM56-7B Series Turbofan Engines |
Unsafe Condition
Faults in channel B of the hydromechanical unit (HMU) fuel metering valve (FMV) resolver could result in an uncommanded engine acceleration event or inflight engine shutdown.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Install improved electronic engine control (EEC) software (per Alert Service Bulletin 73-A024) within 75 cycles in service (CIS) after the effective date of this AD or by November 9, 1998, whichever occurs first. This software reclassifies HMU FMV signal faults to engine control light level/no dispatch, obviating repetitive fault inspections.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
within 75 cycles in service (CIS) after the effective date of this AD or by November 9, 1998, whichever occurs first
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
CFM International, S.A. CFM56-7B series turbofan engines with EEC software part numbers 1853M78P07, 1853M78P08, 1853M78P10, or 1853M78P11 installed, including those on Boeing 737-600, 737-700, and 737-800 series aircraft.
AI-generated summary from the source AD text. Verify against the official source before acting.
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
This site is not affiliated with or endorsed by the FAA. Always verify with official sources.