WATER IN AVIATION FUELS
Some problems are ongoing. Reading Advisory Circular, AC No: 20-125, dated 12/10/85, is as current today as it was then. The problem is water in aviation fuel. Water in fuel continues to contribute to aircraft incidents and accidents. Water can enter fuel at any step in the fuel handling chain. Keeping fuel free of water is called keeping it dry. The responsibility for maintaining dry fuel is a joint responsibility of the aircraft manufacturer, maintenance personnel, each person who handles the fuel from the refinery to the aircraft, and the pilot who flies the aircraft. We want to be sure that only clean and dry fuel is received into storage and delivered into an aircraft.
What are we looking for? Water occurs in aviation fuels in two forms: dissolved and free. All aviation fuels dissolve water in varying amounts depending on fuel composition and temperature. Dissolved water is not a problem, but if the temperature cools enough, the dissolved water condenses into free water.
Free water can appear either as water slugs or as entrained water. A water slug may be a pint or less, or it may be gallons in a large fuel tank. Entrained water is suspended in tiny droplets in the fuel. Individual droplets may not be visible to the eye, but fuel will appear cloudy or hazy depending on their size and density. These droplets can join together to form large drops or slugs of free water.
There are a number of ways to detect water in fuel. Entrained water can be detected by testing with a clean and dry clear glass bottle. If the fuel is acceptably dry it will appear bright with a fluorescent appearance and will not be cloudy or hazy. This is known as the "clean and bright" test. The fuel is clean when it is clear and is bright when it is dry. The container should be large enough to provide a test sample of 10 ounces or more.
The white bucket test, or stainless steel bucket test is useful when checking for water in jet fuel. Obtain an unchipped, spotlessly clean, white porcelain, enameled, or a stainless steel bucket (approximately 10-quart size). Drain 4 or 5 inches of fuel into the bucket. With a clean mixing paddle, stir the fuel into a swirling "tornado-shaped" cone; remove the paddle. As the swirling stops, contaminants and water will gather under the vortex at the center of the bucket bottom. Add several drops of household red food dye. The dye will mix with any water in the bottom of the bucket. If no water is present, the dye will settle in the bottom of the bucket.
There are also water sensitive papers available that will change color in the presence of water. Water detectors are specially made for determining free or entrained water in jet fuels.
When a chemical test is requested by a customer or local authority, the Hydro and Aqua-Glo II detector kits are recommended. The Hydro Kit chemical powder is sensitive to water concentrations down to 30 ppm (parts per million). The Aqua-Glo II Kit can detect levels of water as low as one ppm. When you are maintaining fuel systems, you should consult the manufacturers' maintenance manuals and service information, as well as airworthiness directives, for the latest requirements and information .
Particular attention should be given to checks for water and to the removal of all water from fuel tank pump drains, fuel system line drains, gascolators, strainers, and filters where drain plugs/caps are provided to check and drain an aircraft system of water. Drain plugs/caps should be removed for checks and properly reinstalled. If quick drains are not installed in places required by an airworthiness directive, recommended by the manufacturer, or at points that can be checked frequently, such information should be brought to the attention of the owner/operator for corrective action.
For airplanes equipped with bladder type fuel cells, the general condition and security of each of the cells and the installation should be inspected to ensure that the bladder has not deteriorated or loosened from its mountings. These conditions will cause wrinkles, wells, or depressions to form where water can accumulate, avoid drainage, and, eventually, find its way to an engine in flight.
Fuel tank filler openings and attachments would be checked for security, general condition, and sealing. Fuel tank caps should be checked for their general condition, plus security and proper sealing when installed. Fuel tank filler opening scupper drains should be checked for free flow to prevent both the accumulation of water in the tank and the entrance of water into the fuel system.
We will take a look at what can be done to identify suspected unapproved parts as well as steps you can take to keep unapproved parts from entering the parts inventory.
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The update provides new references to various sections in Part 21, to coincide with the October 16, 2009 changes in Part 21.