SUBJECT:water contamination of fuel tank systems
Reference : SAIB CE 12-16
Cessna 52/Cessna 172/Piper
Water may enter the fuel tank system via any penetration in the wing fuel tank and from moisture condensation inside the tank. Water in the fuel may come out of solution, settle and make its way to a drain location in the form of a blob, pea, or BB-shaped translucent mass found at the bottom of the sampler cup.
Water suspended in the fuel may lead to a cloudy or hazy appearance in the sampler cup. Water may have dissolved in the fuel, but the conditions have not yet occurred to cause the water to come out of solution and perhaps adhere to the dry tank upper surface or walls (similar to condensation). Understanding this, all pilots, owners, operators, maintenance, and service personnel should assume some water exists in the fuel tank system on the airplane.
1. Become familiar with all drain locations on a specific model of airplane. From model to model in a series of airplanes, the number, type, and location of drains may not be the same. There is no single point of drainage that can be used to check for all fuel system contaminants simultaneously. Take the time to properly check all drain locations, before each flight.
2. With the airplane in the normal ground attitude and starting at the highest drain location, check all drain locations for contaminants before every flight, whether or not refueling has occurred. Have fuel sample disposal provisions and proper lighting at your disposal to properly check for fuel tank system contamination.
• Drain at least one cup of fuel (using a clear sampler cup) from each drain location.
• Drain the fuel strainer as required to completely flush its contents in each of the fuel selector positions.
• Check for water, clarity, cloudiness, haze, proper fuel type/grade (i.e.; 100LL is light blue in tint, jet fuel is clear or yellowish), odor, or other contaminants.
• Allow time between fueling and draining. It takes time for any contaminates to settle to sump area prior to draining tanks.
• If any contamination is detected in the fuel tank system, thoroughly drain all drain locations again.
• If contamination is observed, take further samples until the fuel appears clear, and gently rock the airplane in both the roll and pitch axis to move any additional contaminants to the drain points.
• Take repeated samples from all drain locations until all contamination has been removed.
• If contaminants are still present, do not fly the airplane. Have qualified maintenance personnel drain and purge the fuel tank system. Remove all evidence of contamination prior to further flight.
3. Take proper precautions to preclude water from entering into your fuel tank system from an external source (washing, rain, snow, sleet, etc.). Regularly check all external entry sites (caps, access panels, etc.) for evidence of water ingress into the fuel tank system. When possible store the airplane indoors. If stored outdoors or exposed to wet conditions (washing, rain, snow, sleet, etc.), examine the fuel tank system drains for contamination more frequently.
• Pay particular attention to airplanes that have been externally cleaned and/or refinished.
• Avoid using pressure washers near fuel system caps/filler areas, when washing the aircraft.
• It is a good idea to remove accumulated snow/ice from the fuel tank entry sites to prevent ingress of water during melting.
4. During annual or 100-hour inspections do the following:
(Note: compliance through extra off job sheet along with 100hr schedule)
• Check fuel caps, cap gaskets, cap adaptors, cap adaptor gaskets, fuel filler neck to adaptor sealer, fuel gage transmitter gaskets, gage transmitter access covers, and upper surface inspection covers for condition, proper sealing, security, alignment, etc. Ensure to service and clean these areas, replacing parts as necessary.
• Drain and flush the fuel strainer and carburetor bowl completely.
• Inspect the interior of metal fuel tanks for signs of corrosion, which may indicate water contamination.
• Inspect the interior of bladder tanks for wrinkles, broken or missing hangers, etc.
• If signs of contamination are found, alert the owner and fuel supplier of your findings for corrective action.
5. If aircraft has a fuel drain valve replaced with a cap or plug, you should suspect water contamination in the respective tank. Strongly consider having a qualified maintenance technician install the proper drain valve prior to flight
6. Take precautions to preclude water migration in the fuel tank system from an internal source (free water coming out of solution). Keep fuel tanks full when the airplane will not be operated regularly to minimize moisture condensation within the tanks. Keep fuel tanks full between flights, provided weight and balance limitations permit. Limit the fuel tanks exposure to large temperature fluctuations as much as possible. If the airplane has been exposed to sustained wing low or unusual attitudes or a fuel tank has been run dry, sump contaminants may have migrated throughout the fuel tank system.
7. Know your fuel supplier. Regularly check and verify quality controls are in place to ensure you receive only dry, uncontaminated fuel from a supplier. Have on-field checks and verify to ensure continued supply of dry uncontaminated fuel to an operator. Gain assurance that the fuel supply has been checked for contamination
and is properly filtered before allowing the airplane to be serviced. When ordering fuel, specifically state the exact fuel grade and quantity needed. Be present at each and every refueling and observe the fueling process.
8. Collect all sampled fuel in a safe container and dispose of properly.
9. Replace all safety items removed during contamination checks. Correct all unsatisfactory conditions found during or any examination prior to further flight.