Fuel Tank Sloshing Sealer Advisory
The following information is provided for owners, builders and operators of the BD-5 experimental aircraft- all models.
The purpose of this Advisory is to provide owners, builders and operators notification of potential compatibility problems when using particular sloshing sealers with particular fuels. This is not to be confused with MIL-S-8802F or "Proseal", a fuel tank/ pressure bulkhead sealant used in Boeing commercial aircraft, and in all phases of assembly for the BD-5 aircraft. TOP of PAGE
On Sunday, June 21, 1998 at approximately 3:30pm PST, N50TX was damaged during a forced landing in a field approximately 5 mi. NE of CVO. The incident occurred while formation flying during a photo/ video session. The pilot exited the aircraft, and sustained no injuries.
Pilot Robert Donatz reported a loss of power, and attempts to restart the engine were unsuccessful. This indicates a loss of fuel to the engine. A preliminary review of the aircraft revealed the possibility of fuel system blockage, and the fuel tank sloshing sealer is suspect. It appears that the sealer was partially dissolved by the jet fuel and settled in the lower areas of the fuel tank. TOP of PAGE
An examination of the wing fuel tanks revealed the sloshing sealer was being dissolved and flowing towards the inboard (lowest) portion of the wings, where heavy deposits of the sealer were found. In construction, the optical gauges, quick drain, and fuel pick up tube are installed after the wing tank area is sloshed, and should have been clear of any sloshing sealer. We found that the fuel quick drains and pick-up tubes were coated with the sloshing sealer, also indicating that the sealer was being dissolved and redeposited on these components. The Randolph 802 Sloshing Sealer used in this aircraft normally appears as a thin coating the color of yellow zinc chromate. In this instance, the sealer had taken on a caramel like color and appearance.
Close examination of the fuel system revealed blockage of the third stage paper fuel filter element [p/n AN6235-3A (10 micron)]. This was not readily apparent by visual inspection, however the blockage was clearly evident in flow testing the filter element.
The engine was visually examined and no damage was noted. It was placed on a test stand to be test run, following electrical control and fuel line connection. Upon energizing the start button, the engine lit off and ran without hesitation- with RPM and all temperatures normal and within specification. In early taxi tests, it was noted that the Quantum H-95 was not prone to flame out. Also at this time, the engines relight capability was verified by inducing flameout with fuel shutoff. In this series of tests, the engine performed flawlessly. As long as the engine receives fuel, it will run.
A procedure was established for testing the sloshing sealer. In co-operation with NTSB, test strips were coated with sloshing sealer. Following 4 weeks cure (in simulation of N50TX), one strip was held as a control, and four strips were placed into a container of Jet A fuel obtained from the fuel supplier. A strip was removed from the fuel at the end of 1, 2, 3, and 4 weeks, examined and allowed to dry. This test was performed with each of the following combinations:
Test 1 was performed by BD-Micro. Following the first week of test 1, there were definite signs of sloshing sealer breakdown, as it was visibly flowing down the strip with a slight build up at the bottom. Each successive strip had more and more sloshing compound accumulated on the test strip bottom. The 4th strip was almost devoid of sloshing compound and had dripped and puddled on the test can bottom. The NTSB inspector observed and photographed test results.
Test 2 was performed by the NTSB investigator. Results indicated no breakdown of sloshing sealant. No discoloration, softening or accumulation at bottom of test strips.
Test 3 was performed by BD-Micro. Results indicated no breakdown of sloshing sealant. No discoloration, softening or accumulation at bottom of test strips. TOP of PAGE
The turbine engine flameout was clearly the result of the fuel tank sealant having been dissolved, and carried in solution by the fuel, where it plugged the main fuel filter. Prist, a jet fuel additive, was found to have caused the sealant breakdown. Prist is an alcohol-ketone based additive put in jet fuel for anti-icing and anti-microbial agent. Normally, Prist is added to the aircraft fuel tanks at the pilots discretion.
Randolph Sloshing Sealer 802 was used in N50TX. Promotional literature from Cooper Aviation Supply Catalog 41 page 1470 states, "FUEL TANK SEALER 802 -Designed for aircraft metal fuel cells that have no structural defect yet have seepage’s leaks around rivets or seams. Material will not flake or chip, remains flexible. Ideal for automobile, motor bikes, boats, or other metal gasoline tanks. Easy to use, follow instructions on container label. MIL-L-6047." Randolph 802 was not recommended for fuels with alcohol additives. On receiving the can, the label indicates "Not recommended for use with aircraft fuel tanks." Recent promotional literature from Randolph offers the following contrast "These sloshing sealers are not approved for use in aviation fuel tanks. Use of these products could result in serious engine problems due to deteriation of the sealer." Nonetheless, these products are currently readily available through aviation supply companies.
It was also discovered that in some geographical areas, almost all of the Jet-A provided to FBO's comes from the distributor already containing an ethanol additive. This report can be referenced at the following internet address:
http://www.ntsb.gov/aviation/SEA/lnarr_98A109.htm
A Randolph company chemical engineer was anonymously contacted by BD-Micro Technologies, Inc., and the NTSB inspector on separate occasions. He indicated on both occasions that Randolph 802 is compatible with jet fuels. While this may be true in a strict sense, NTSB findings indicate that it is not compatible with jet fuels containing deicing additives as supplied by some distributors, and routinely added by fuel suppliers. Thus from a practical sense, Randolph 802 is NOT compatible with Jet A fuel.
To add complexity to this matter, research revealed a surprising number of other cases where problems resulted from fuel tank sealants. In one instance, a DC-3 aircraft crashed on takeoff as the result of fuel starvation. Examination of the inside of the fuel tanks revealed "sealing compound flakes, some as large as an adult’s hand, floating freely in the tanks. ..." Randolph Sloshing Compound 912 had previously been applied to the tanks. They noted that "A search of FAA records revealed 15 other accidents/incidents involving interrupted fuel flow caused by this and similar sealing compounds." This article was written by a former NTSB Air Safety Investigator and FAA Airworthiness Inspector, and can be referenced at the following internet address:
http://www.mac-experts.com/macnewsletters/fall96/sealants.htm
To slosh or not to slosh, that is the question. As reported in BD-Micro Newsletter #16 (Sept. 12, 1980) "Odds and Mods - BD-5 Wings, Twelfth commandment - All BD-5 wings shall leak unless sloshed. We experience with only eleven sets of wings, but all eleven leaked until sloshed. We were using Fuller compound but found that it is hard to get and will not tolerate oil. Are now using a 3M product called ScotchClad #776 "Fuel Resistant Coating". This dries to a pale tan color and is for all petroleum products, fuel, jet fuel and oil. This means the 2-stroke fuel/oil mix planes can now slosh."
Whether or not to slosh is not the real question, the real question is which sloshing compound to use. This will largely depend on fuel requirements for the engine installed in the particular aircraft. Randolph 912 Sloshing sealer is being used in several BD-5’s, and they report no fuel tank problems. We do suggest that whatever sloshing compound is selected, make sure it is compatible with the type of fuel, including any additives, to be used. Be sure to perform compatability testing if there are any doubts.
No matter what sloshing compound is used, proper preparation of the fuel tank area is of prime importance. Follow directions provided on the container label. Before applying to the fuel tanks test the compound by soaking test strips in the fuel to be used. We recommend notation of the sealant type used, and fuel compatibility information be prominently noted in the builders construction log, and airframe logbook for future reference. This information should be available to operators and future owners of the aircraft. Though some brands appear to be more sensitive to fuel tank preparation, builders can achieve better overall compatibility by using alcohol resistant types of fuel tank sloshing sealant.
Due to the excessive wing spar
deflection they experience, BD-5s flying without our SuperSpar
will be more prone to fuel tank seepage. This wing deflection
will work rivets and seams loose, allowing fuel to seep out.
Continual flexing of the wing skin under flight loads, will cause
fatigue and in extreme cases, the development of cracks in wing
skins. We have received reports from owners of BD-5’s in
service that confirm this occurance. TOP of PAGE
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