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« on: February 04, 2008, 10:18:55 AM »
Not really good news, but I thought I would post it.
Tom
Use of Non-Aircraft Parts in Critical Systems in Amateur-Built Aircraft
An aviation safety information letter from the Transportation Safety Board of Canada (TSB).
On July 20, 2005, an amateur-built VariEze departed Runway 12 at the Lethbridge, Alta., airport on a visual flight rules (VFR) flight to Airdrie, Alta. The aircraft was observed to be trailing smoke as it departed on the downwind leg for Runway 12, and one minute and twenty seconds after takeoff, the pilot advised the Lethbridge flight service station (FSS) that the aircraft was on fire. The pilot subsequently attempted to force-land in a grain field approximately five-eights of a mile to the northwest of the airport. After touchdown the aircraft nosed over, struck the shoulder of a secondary road, and came to rest inverted on the road. An intense post-impact fire ensued and the pilot, the sole occupant, sustained fatal injuries. (TSB Class 5 occurrence A05W0148.)
The aircraft had been modified shortly before the accident, with the installation of a turbocharged, liquid cooled Rotax 914 UL-2 pusher engine (serial number: V9144874), which replaced the original Lycoming O-235 engine. This was reportedly the only VariEze flying at the time with this engine configuration. Post-impact examination of the airframe and engine indicated the aircraft had sustained an intense, in-flight engine fire. This was consistent with witness observations. The short duration of the flight and degree of in-flight fire damage to the engine and cowlings indicated the fire was fuel-fed from within the engine compartment.
In addition to the engine installation being unique to this model of aircraft, the engine itself was also highly modified, with the addition of an intercooler on the induction system and higher compression cylinders and pistons. A major repair or alteration to an amateur-built aircraft requires re-licensing and issuance of a new airworthiness certificate and operating limitations. Although the original Special Airworthiness Certificate that was issued to the aircraft specified that no changes could be made without notifying the Federal Aviation Administration (FAA), the recent modifications had not been reported to the FAA.
A piece of detached, heat-damaged tubing, complete with clamp and remnants of a burned rubber hose, was recovered from an unburned area of the wreckage trail. The tubing was submitted to the TSB Engineering Branch to determine if it was a fuel system component (see Figure 1) and the mode of failure. Examination of the fracture surface of the fitting did not identify any signs of a progressive failure; however, the fracture surface displayed fire damage. As the tubing, clamp, and hose were recovered from an area of the wreckage trail that was not exposed to the post-impact fire, the fire damage likely occurred prior to impact (see Figure 2).
Figure 1: Heat-damaged tubing, hose and clamp recovered from the wreckage trail
Visual and dimensional comparison of the tube fragment indicated it was the inlet post of a NAVMAN fuel flow transducer. Information provided by NAVMAN revealed the fuel flow transducer was designed for marine applications, and not for use in aircraft. At present, there is no FAA or Transport Canada (TC) regulation that precludes the installation of non-aviation parts in critical systems in amateur-built aircraft.
The major portion of the fuel flow transducer was not recovered. Due to the extent of fire and impact damage, the precise location of the transducer was not determined. The engine fuel system utilized a fuel pressure regulator that bypassed surplus fuel back to the fuel tanks; therefore, the transducer would most likely have been mounted between the fuel pressure regulator and the carburetors within the engine compartment so as to accurately record the amount of fuel actually being consumed. The transducer was designed to be mounted on the suction side of a fuel pump, rather than on the pressure side. It was manufactured from a composite glass FORTRON material. It had a published maximum operating temperature of 50°C and a component failure temperature of 509°C. Fuel flow transducers used in aircraft applications are normally mounted within the engine compartment, and transducer housings are usually made of stainless steel. The engine compartment would see temperatures of several hundred degrees Celsius during normal operation, particularly near the turbocharger, and if the transducer was mounted in the engine compartment, it could have been exposed to temperatures that exceeded its maximum designed environmental temperature range.
Figure 2: Close-up of heat-damaged fracture
The airframe and engine were fire damaged to the extent that no component testing or leak checks could be accomplished. While the occurrence is consistent with the aircraft having sustained a fuel-fed in-flight engine fire, the exact reason for the fire could not be determined.
There is a potential risk related to the use of non-aviation components in critical systems in amateur-built aircraft. Failure of a critical fuel system component, such as a non-aviation fuel flow transducer within an aircraft engine compartment, could result in a pressure-fed fuel leak which, if ignited, would generate an intense in-flight engine fire. Builders must consider the application, environmental exposure, and consequence of component failure when installing components that are not produced under a production certificate, a technical standard order (TSO) or a parts manufacturer approval on an amateur-built aircraft. While investigators were unable to directly link the origin of the in-flight fire to the marine fuel flow transducer in this case, there may be other situations where the use of non-aviation parts in critical systems present an on-going risk in the amateur-built aviation community.
Procedures in the event of in-flight engine fire in single-engine aircraft
The TSB issued a second safety information letter as a result of this occurrence. As noted above, the aircraft sustained an intense, in-flight engine fire. While the exact cause of the fire was not determined, the short duration of the flight and degree of in-flight fire damage to the engine and cowlings indicated the fire was fuel-fed from within the engine compartment.
Fuel was supplied to the engine through two electric boost pumps (one main pump and one auxiliary pump) and a fuel selector. The electric fuel pumps were capable of pumping fuel at rates in excess of 30 U.S. gallons per hour. Wreckage examination determined that the fuel selector handle was in the vertical position, which indicated it was selected to the auxiliary fuselage tank, and the fuel boost pump switches and magneto switches were in the ON positions at impact.
The standard emergency procedures in the event of an in-flight engine fire in a single-engine aircraft include placing the fuel selector and boost pump switches in the OFF positions, placing the magneto switches in the OFF positions, and performing an engine-out landing in the most suitable available area. If the fire does not extinguish quickly, a pilot may dive the aircraft in an effort to find an airspeed that will provide an incombustible fuel/air mixture. The VariEze Owner’s Manual states that in the event of an in-flight fire one should: determine the cause—if electrical, all electrical power off; if fuel, fuel off and electrical power off—and execute a precautionary landing as soon as possible.
The accident occurred within approximately three minutes of takeoff. The fire appeared to have burned with increasing intensity from the time the aircraft was first observed to be trailing smoke to the time of impact. While the pilot was able to maintain control of the aircraft up to the point of touchdown in the grain field, there was no evidence that he had taken the immediate actions necessary to stem the flow of fuel to the engine. Allowing fuel to continue to pressure-feed into the engine bay significantly increased the intensity of the fire and likely precluded any possibility of self-extinguishment.
Although generally rare events, in-flight engine fires are serious and time-critical emergencies. In this occurrence, non-actioning of the emergency procedures necessary to stem the flow of pressure-fed fuel to the engine may have contributed to the severity of the accident. Vital immediate actions—including selecting the fuel boost pumps, fuel selector and magneto switches to the OFF positions—are necessary to reduce the intensity of, or extinguish, an in-flight engine fire as soon as possible. Pilots must be familiar with the procedures to handle uncommon but critical in-flight emergencies, such as engine fires, and must respond accordingly in order to reduce the risk of structural failure, post-impact fire damage, or loss of control and destruction of an aircraft with related occupant injuries or fatalities.
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