8900.1 CHG 233



Section 2    Operational Emphasis Item—Uncommanded High Thrust

3-280    PURPOSE. This section supports the overall Thrust Control Malfunction Airworthiness Program implemented to support the safety recommendation issued by the National Transportation Safety Board (NTSB). This section also requests aviation safety inspectors (ASI) assigned to any operator of turbine-powered aircraft to share this information.

3-281    BACKGROUND. As a result of the Saudi Arabian Airlines Boeing 737-200 accident and associated NTSB recommendation A98-70, a joint Aerospace Industries Association (AIA)/European Association of Aerospace Industries (AECMA) committee, with support from the U.S., European, and Canadian airworthiness authorities, studied the risk associated with uncommanded high thrust failure on turbofan-powered transport category aircraft.

A.    Inability to Reduce Excess Engine Thrust/Power. These uncommanded high thrust failure conditions result in the flightcrew being unable to reduce excess engine thrust/power through normal means (e.g., throttle lever stuck or disconnected, fuel metering valve malfunctioning, engine control in “failed fixed” mode, etc.). Compliance with applicable airworthiness regulations has traditionally been based in part on accepting an assertion that the flightcrew can recognize and safely accommodate uncommanded high thrust conditions, including shutting down the affected engine via an independent fuel shutoff, as required.

B.    Uncommanded High Thrust Failure Conditions. Most traditional transport category turbine‑powered airplane type designs have some anticipated uncommanded high thrust failure conditions. Some trends, both in design and operation, are tending to increase the risks associated with uncommanded high thrust failures.

C.    Fuel Control Unit (FCU) and Full-Authority Digital Engine Control (FADEC). For transport category airplanes, the flightcrew normally controls engine thrust/power, either directly by means of a thrust/power/throttle lever through direct connection to the FCU or by a fly-by-wire FADEC system, or indirectly by means of an auto-throttle.

D.    The Effect of Traffic and Congestion. Increased traffic and congestion, as well as the increased use of parallel taxiways and runways, have increased the potential for an airplane experiencing uncontrollable thrust asymmetry to impact another airplane, ground support equipment, or terminal. The Federal Aviation Administration (FAA) is concerned that such a failure on one airplane could potentially affect the occupants of multiple airplanes, terminal spaces, and/or ground support personnel.

3-282    APPLICABILITY. This section applies to all ASIs.

3-283    ACTION. All principal maintenance inspectors (PMI) associated with air carriers operating under Title 14 of the Code of Federal Regulations (14 CFR) parts 121, 125, and 135 with aircraft certificated under 14 CFR part 25, and PMIs with responsibility for repair stations under 14 CFR part 145 that repair or overhaul FCUs, will do the following:

A.    Service Difficulty Report (SDR) Requirements. Encourage operators to report instances of uncommanded high thrust in accordance with the SDR requirements of part 121, § 121.703(a)(16) and (c);
part 125, § 125.409; and part 135, § 135.415(a)(16) and (c). The operator should file the report with the FAA no later than 5 working-days after the occurrence. The repair station management should forward reports that are in accordance with part 145, § 145.221 to the air carrier/air operators certificate-holding district office (CHDO) for further processing in accordance with the Service Difficulty Reporting System (SDRS).

B.    Reporting Airplane Failure Modes. Report all related information in the Program Tracking and Reporting Subsystem (PTRS), as detailed in the reporting paragraph.

1)    Operators must report information concerning the airplane failure modes identified that could lead to uncommanded high thrust.
2)    If reporting information on FCUs or FADEC components, include:

·    Part number of the component,

·    Part number of the item that failed,

·    Original discrepancy that led to repair,

·    Final corrective action,

·    Total time and cycle of the component (if known),

·    Time since last shop visit, and

·    Please provide the last teardown summary report, if available.


A.    Documentation. PMIs should document that they have read and conveyed this information to the appropriate operator and/or repair station accountable manager.

1)    Use PTRS activity code 3045 (special projects).
2)    Enter “8900UHT” (without quotes) into the “National Use” field.

B.    Information for Identifying Uncommanded High Thrust. Please report all failure modes and other information needed to identify uncommanded high thrust.

Indicates new/changed information.
1)    Use PTRS activity code 3460 in the “Numeric Misc” block.
2)    Enter “8900UHT” (without quotes) into the “National Use” field.
3)    The reported information will be available to the Aircraft Certification Service (AIR) for analysis.

3-285    REPORTING FOR THE AIR CARRIER OR AIR OPERATOR. The air carrier or air operator should document each incident in accordance with §§ 121.703, 125.409, 135.415, and SDRSs, and use
§ 121.703(a)(16) as a reporting vehicle.

RESERVED. Paragraphs 3-286 through 3-290.