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Service Difficulty Advisory

No. AV-2008-03
2008 05 28

Fuel System Icing
(Suspended Water in Fuel)

An Aero Commander 500B was at a cruising altitude of 5500 feet AGL for approximately 45 minutes when the crew noted an abnormal fuel flow indication/RPM decay followed by a reduction to idle power on the right engine. Shortly thereafter, the identical problem occurred with the left engine. The crew was unable to maintain level flight and thus had to conduct a forced landing. The aircraft was damaged beyond economic repair; fortunately there were no fatalities.

Two months before this event; the aircraft had been fully fueled from a commercial fuel supplier and then stored in a heated hangar. Prior to flight, the aircraft fuel sumps were drained with no visible evidence of water. No fuel additive icing inhibitor was used, nor was the operator required to do so.

Investigation of the two installed Lycoming IO-540-B1A5 engines, by the Transportation Safety Board of Canada (TSB), determined that the fuel supply to both engines was blocked. It has been determined from previous tests, that the amount of ice derived from as little as two droplets of water may affect most fuel injection systems. This problem can be eliminated in part by the use of fuel additive icing inhibitors.

Previously, a major aircraft manufacturer conducted high altitude testing using pressurized aircraft powered by reciprocating engines and experienced numerous partial and isolated losses of engine power. The tests concluded that as aircraft climbed to colder altitudes, dissolved water in the fuel precipitated out of the fuel solution, due to agitation of the fuel as it passed through the fuel pump and/or vapor separator. A tendency for retention of water is inherent to all hydrocarbon fuels; thus aviation fuels still contain various amounts of dissolved water in spite of precautions adopted by refineries, transportation/distribution facilities and aircraft servicing stations. In-service experience reveals that numerous difficulties and accidents have been traced to blockage of airframe and engine fuel systems by frozen contaminations of water, precipitated from the fuel stream.

Transport Canada Civil Aviation (TCCA) would like to remind all operators of aircraft powered by reciprocating engines to be aware of the inherent dangers related to the freezing of dissolved water in fuel systems. TCCA strongly emphasize the importance of following the procedures and precautions contained within the respective aircraft and engine operating manuals for the prevention of fuel system icing in cold weather environments.

TCCA also advise piston aircraft operators to be familiar with TCCA Publication TP 14371E Aeronautical Information Manual, AIR - AIRMANSHIP GENERAL INFORMATION, paragraph 1.3.3 titled “Fuel Anti-icing Additives”, and FAA Advisory Circular AC 20-113, regarding the prevention of fuel system icing in reciprocating engines. Additionally, Lycoming Service Letter L172C and Teledyne Continental Motors Service Information Letter SIL99-2B provide guidance to operators regarding fuel anti-icing additives in their respective reciprocating engines.

Defects, malfunctions and failures occurring on any aeronautical product should be reported to Transport Canada, Continuing Airworthiness in accordance with the CAR 591 mandatory Service Difficulty Reporting requirements.

Display of fuel supply lines

For further information, contact a Transport Canada Centre, or Mr. Barry Caldwell, Continuing Airworthiness, Ottawa at 613-952-4358 or e-mail

For Director, National Aircraft Certification

Derek Ferguson
Acting Chief, Continuing Airworthiness

Note: For the electronic version of this document, please consult the following Web address:
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