LAKEWOOD, NJ, USA
N25AN
Aerospatiale AS-332L
After three flights, the helicopter was landed and the engines were shut down. When a passenger was boarded, the engines were restarted, and the pilot taxied the helicopter for takeoff. While waiting to takeoff, about 5 to 10 minutes after the engines were started, the pilot noticed a stiffness in the flight controls. This was followed immediately by illumination of electrical warning lights, loss of power from both alternators, and an odor of smoke in the cabin. Both engines were shut down, fire bottles were discharged, and the crew and passenger exited the helicopter. Examination of the fuselage revealed a fire had been centered around the right lateral hydraulic servo. The number two hydraulic lower cylinder distribution module of the right lateral servo had melted, and the high pressure lines were found 'free' of the module. The helicopter's alternators, located aft of the main transmission, contained internal cooling fans that drew air through the alternators. The alternators and their respective wiring bundles were extensively damaged by fire. The ignition source of the fire was not determined. The fire detection system (with visual and aural signals) did not activate prior to the electrical warning lights.
On July 5, 1996, at 1630 eastern daylight time, an Aerospatiale AS-332L, a helicopter, N25AN, was substantially damaged by a hydraulic oil fire, while waiting for takeoff at the Lakewood Airport, Lakewood, New Jersey. The certificated airline transport pilot-in-command, co-pilot, and one passenger were not injured. Visual meteorological conditions prevailed for the corporate flight that was destined for Morristown, New Jersey. No flight plan had been filed for the flight conducted under 14 CFR Part 91. According to the pilot-in-command (PIC), the helicopter was flown from the Teterboro Airport, New Jersey, to Atlantic City, New Jersey, to the Lakewood Airport (N12). The helicopter engines were shut down at N12, while the auxiliary power unit (APU) provided electrical power to the helicopter. After about 30 minutes, a passenger was boarded, the engines were restarted, the APU was shut down, and the PIC taxied the helicopter for takeoff. About 5 to 10 minutes after the engines were started, and while waiting to takeoff, the PIC noticed a stiffness in the flight controls. This was followed immediately by electrical warning lights illuminating, the loss of power from both alternators, and an odor of smoke in the cabin. The co-pilot looked out the left side of the helicopter and observed smoke coming from the vicinity of the number one engine. The flight crew shut down both engines and discharged the fire bottles into the number one and two engines, and the APU. When the crew and passenger exited the helicopter, smoke and flames were observed emitting from the right side of the main transmission. The co-pilot attempted unsuccessfully to extinguish the fire with the helicopter's hand extinguisher. The fire was extinguished about 10 minutes later by a local fire company. Examination of the fuselage revealed the fire was centered around and below, the right lateral hydraulic servo. The number two hydraulic lower cylinder distribution module of the right lateral servo was melted down, and the high pressure lines were free of the module. A hole was burned through the transmission deck into the cabin area, below the right lateral servo. The melting of aluminum and other fire damage was observed on the main rotor head, main rotor blades, flight controls, hydraulic servos, rotor brake, alternators, number two hydraulic reservoir and pump, and the engine/transmission cowlings. A main transmission oil supply line, located on the aft side of the transmission, was melted free of its connecting point. Maintenance personnel stated that the transmission oil level was 1 to 2 liters below the normal 19 liter capacity. According to the Aerospatiale maintenance manual, the operating temperature of the transmission oil was about 120 degrees C. The number two hydraulic reservoir was melted down on the forward side, facing the vicinity of the right lateral servo. The bottom of the reservoir contained a few inches of an oily water mix. About 2 feet aft of the main transmission, and directly aft of the melted transmission line, were the helicopter's 2 electrical alternators. Each alternator contained an internal cooling fan that drew air through the alternator. The alternators and their respective wiring bundles were extensively fire damaged. Abeam the alternators, the oil cooler fan intake was located on the starboard side (left side) of the helicopter, and was also fire damaged; however, the number one hydraulic oil reservoir, positioned just forward of the oil cooler fan intake was not melted down. The insulation on electrical wires attached to the reservoir were melted. The helicopter was equipped with a fire detection system with visual and aural signals. The system contained 13 detectors that monitored the areas around the engines and the main transmission. In addition to detection, the system also contained a failure indication mode which would activate with a failure of a detection line or a detector. According to the flightcrew, prior to the activation of the electrical warning lights, there was no fire detection warning. A report by a Federal Aviation Administration (FAA) Investigator, from the FAA Technical Center, Atlantic City, New Jersey, stated: "...Extensive fire damage was observed in the area of the main rotor gear box...The only sources of fuel observed in the area were hydraulic fluid from the number two system and transmission oil...It appears that the initial fuel source for the fire was hydraulic fluid from the number two system. A smaller quantity of transmission oil probably contributed additional fuel later in the fire. No ignition source could be identified. Hot surface ignition from the heat shield adjacent to the number two engine exhaust is a possibility along with a bleed air tube in the same general area. The flash point of the sample of hydraulic fluid from the number one system came out lower than the minimum of 205 degrees C..."
a number two system module hydraulic oil leak, which was ignited by an undetermined source and resulted in a hydraulic fluid fire.
Source: NTSB Aviation Accident Database
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