MUNDAY, TX, USA
N3298Y
Ayres S2R-G10
During the initial takeoff climb, the agricultural airplane's engine lost power, and the pilot executed a forced landing in a plowed field. The airplane nosed down in the soft ground. Examination of the airplane by the operator revealed that the right wing fuel tank was empty, and the left tank contained approximately 80 gallons of fuel. Both fuel lines leading from the left wing tank to the fuselage header tank were blocked by pellets of what appeared to be silicone rubber. Chemical analysis confirmed that the pellets were composed of silicone rubber. The 1995 model airplane had accumulated 612 hours total time. The operator expressed the opinion that the silicone rubber might have been applied to the gaskets of the wing fuel tank access panels during manufacture of the airplane; however, a representative of the manufacturer stated that the company did not use silicone rubber to seal fuel tanks. An inspection of the manufacturer's production line by FAA personnel revealed no evidence that silicone rubber was being used to seal fuel tanks. The source of the silicone rubber contamination could not be determined.
On May 8, 1997, approximately 1310 central daylight time, an Ayres S2R-G10 agricultural airplane, N3298Y, registered to and operated by Bridwell Spraying Service, Inc., of Haskell, Texas, sustained minor damage during a forced landing following a loss of engine power on takeoff near Munday, Texas. The commercial pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed and no flight plan was filed for the Title 14 CFR Part 91 positioning flight which was departing the Munday Municipal Airport with an intended destination of Haskell when the incident occurred. In a written statement provided to the NTSB, the pilot reported that the engine lost power when the airplane was on initial takeoff climb approximately 2 miles from the airport. During the ensuing forced landing in a soft plowed field, the airplane nosed down, and the propeller struck the ground. Damage was limited to the propeller blades which were bent. During a telephone interview conducted by the NTSB investigator-in-charge (IIC), the operator reported that an inspection of the Garrett TPE331-10 engine, performed at the facilities of Allied Signal in Phoenix, Arizona, revealed no evidence of any mechanical discrepancies that would have resulted in the power loss. He further reported that during examination of the airplane, the left wing tank was found to contain approximately 80 gallons of fuel and the right wing tank was found to be empty. Further examination by the operator revealed that several "pellets" of what appeared to be silicone rubber had "completely blocked" the two fuel lines leading from the left wing tank to the fuselage header tank. The operator provided one of the pellets to the NTSB. Visual examination of the pellet by the IIC revealed that it was a cylindrically shaped object, measuring approximately 1/4 inch in diameter by 3/8 inch in length, composed of clear rubber-like material. The pellet was forwarded by the IIC to Chemier/Polytech Laboratories, Inc., of Maryland Heights, Missouri, for chemical analysis. In their report dated October 28, 1997, Chemier/Polytech stated that the pellet "appears to be composed primarily of a poly(dimethylsiloxane) elastomer. This class of material is commonly known as a silicone rubber." According to the operator, at the time of the incident, the airplane had accumulated a total of 612 hours since he took delivery of it new in December 1995 from the Ayres Corporation in Albany, Georgia. The operator reported that the airplane was flown from the factory in Albany to a maintenance facility in Vernon, Texas, where a single-point refueling system was installed. He further reported that no other modifications or repairs to the airplane's fuel system had been made since that time. The operator expressed the opinion that the silicone rubber had been applied to the gaskets of the wing fuel tank access panels during manufacture of the airplane. A representative of the Ayres Corporation stated that the company did not use silicone rubber to seal fuel tanks. The Safety Board has investigated one other mishap in which silicone rubber was found blocking fuel lines of an Ayres S2R-G10. For details of this accident, refer to NTSB Factual Report FTW97LA219, Biggers, Arkansas, June 13, 1997, Ayres S2R-G10, N6133X. In October 1997, in response to the findings of this incident investigation and the investigation into the June 13, 1997, accident, personnel from the FAA's Aircraft Certification Office in Atlanta, Georgia, and the Manufacturing Inspection Satellite Office in Mobile, Alabama, inspected the production line at the Ayres Corporation's factory in Albany, Georgia. No evidence was found that the company was using silicone rubber to seal fuel tanks. On October 30, 1997, the Ayres Corporation issued Service Bulletin No. SB-AG-40, entitled "Fuel Tank Inspection," applicable to "all turbine powered S2R aircraft including conversions." The bulletin stated that "as a result of contamination, several aircraft have experienced fuel flow problems between the wing fuel tanks and the header tanks." It provided instructions for a one-time inspection of the wing fuel tanks, the header tank, and the fuel lines from the wing tanks to the header tank for contamination and obstruction. On December 16, 1997, the FAA issued Special Airworthiness Information Bulletin (SAIB) No. ACE-98-17 to advise owners/operators of turbine powered Ayres S2R aircraft of the safety information contained in Ayres Service Bulletin No. SB-AG-40. The SAIB stated, in part: Issuance of SB No. SB-AG-40 was prompted by reports of silicone rubber compound clogging fuel lines. There were two reports of accidents involving model S2R-G10 airplanes; one resulted in the destruction of the airplane while the other resulted in only minor damage to the airplane. ... An investigation revealed that it is highly unlikely for the contamination to have been introduced into the fuel system at the factory. It is therefore concluded that these silicone rubber compounds were introduced into the system after manufacture. Silicone rubber is not compatible with jet fuel; it enlarges several times the original size when placed in contact with or immersed in jet fuel. ... The source of the contamination has not been determined. The airplanes noted above were located in different parts of the country and do not share a common history. A possible scenario is that silicone rubber is being used to seal refueling hoses/nozzles, tank fittings, etc. and excess material at joints could break loose and either fall or be swept into the airplane fuel tank.
blockage of both fuel lines from the left wing tank to the header tank by silicone rubber contaminants (foreign material), which resulted in fuel starvation. A related factor was the lack of suitable terrain for the forced landing.
Source: NTSB Aviation Accident Database
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