Honeywell T53 Series Engines - Service Difficulty Alert

AL 2004-05
28 September 2004

Engine Fuel Control Unit Drive Shaft and Spline Wear

Transport Canada has received several Service Difficulty Reports (SDRs) describing various failures of certain Goodrich Fuel Control Units (FCU) mounted on Honeywell T53 series engines.

Engine Fuel Control Unit Models TA-2, TA-7 and TA-10 are installed on Bell 204 series, Bell 205A-1, Bell 205B, Kaman K-1200, Bell UH-1, Bell AH-1, and Augusta AB-205 rotorcraft.

One of the SDRs (Bell 205A-1 with a T53-17B engine) had an in-flight engine pump failure warning. Follow-up investigation revealed that one element of the dual element pump failed due to worn out splines. The second driveshaft was estimated to have half an hour of operating time left before certain failure, which would have resulted in engine shutdown. This particular operator had previously experienced three FCU pump-main driveshaft failures. Some FCUs failed in the mid-life range of between 1,400 hours to 1,900 hours, respectively. Another FCU was found with extensive spline damage after only 434 hours since installation.


Another SDR (Bell 205A-1 with a T53-17A engine) had a sudden engine stoppage at 700 feet above ground level (AGL). Autorotation was successfully carried out with no injury to any of the crew or passengers. The pilot did not attempt to switch to FCU manual mode due to low altitude. Disassembly determined that the spline cluster common to the driveshaft assembly, P/N 91620, female splines, and the secondary driveshaft, P/N 85571, male splines, had stripped.

Another operator investigated two tip seal pumps and main driveshaft failures on FCUs fitted with tip seal pumps. Failure of these parts lead to loss of fuel to the FCU, both automatic and emergency supply, causing engine flame

Further to the above, Transport Canada has been in constant contact with the Federal Aviation Administration (FAA) and the Original Equipment Manufacturer (OEM) on this safety issue. The FAA has informed TC that a Notice of Proposed Rulemaking (NPRM) has been initiated with intended Airworthiness Directive (AD) action in the near future. The FAA AD would mandate initial and repetitive inspections for wear of pump splines.

In the interim, Transport Canada strongly recommends that operators comply with the following recent Service Bulletins (SBs):

  1. Honeywell SB T53-0138; and
  2. Goodrich Pump and Engine Control Systems, Inc. (GPECS) TA series 73-42.

Any defects or further occurrences should be reported by sending a Service Difficulty Report to Transport Canada, Continuing Airworthiness, Ottawa.

For further information, contact a Transport Canada Centre, or Mr. Barry Caldwell, Continuing Airworthiness, Ottawa, telephone (613) 952-4358, facsimile (613) 996-9178 or e-mail

For Director, Aircraft Certification

B. Goyaniuk
Chief, Continuing Airworthiness

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