Caldwell, ID, USA
N86PB
PRIDMORE LANCAIR IV
Several minutes after starting the engine, the pilot noticed an odor in the cockpit, which he thought was similar to that of burning plastic. He could hear the hydraulic pump cycle once, which he thought was unusual. He pulled the hydraulic circuit breaker out and within 30 seconds he observed smoke emanating from the engine area. He shut down the airplane and noticed flames at the bottom of the engine cowl. According to the pilot, the last conditional inspection was completed 6 days prior to the accident, and the airplane accumulated 2 flight hours since that inspection. An examination of the firewall revealed that its right side had a white coloration, which turned to a black soot color on the left side, consistent with the fire originating on the right side of the engine. On the right side of the belly area, near the nose landing gear compartment, a red/pink hydraulic fluid stain started and continued down toward the tail. The stain became small beads of pooling liquid at the low point of the belly, indicating a hydraulic leak. Above the stain, on the right side of the engine firewall, were two hydraulic fittings where hoses connected to either side of the nose landing gear actuator. Based on this evidence, it is likely that the fitting on the lower hydraulic line was not properly tightened, which allowed it to back off due to normal engine vibration, resulting in the line loosening during engine start. Pressurized hydraulic fluid then sprayed onto the right exhaust shroud and ignited.
HISTORY OF FLIGHT On June 27, 2010, about 1800 mountain daylight time, a Pridmore Lancair IV, N86PB, experienced an on-ground fire several minutes after the pilot started the engine at the Caldwell Industrial Airport, Caldwell, Idaho. The pilot, who was additionally the owner and builder, was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The airline transport pilot (ATP) was not injured; the airplane sustained substantial damage. The cross-country business flight was to originate from Caldwell with a planned destination of La Grande, Oregon. Visual meteorological conditions prevailed, and no flight plan was filed. In both a written statement and a telephone interview with a Safety Board investigator, the pilot reported that the airplane had flown three times earlier in the day. After parking the airplane for about 5 hours on the ramp, the pilot boarded the airplane with the intent of flying back to the airplane's home base in Oregon. The engine started normally and the cockpit gauge indications were normal. Several minutes after start, the pilot noticed an odor in the cockpit, which he thought was similar to that of burning plastic. He taxied the airplane about 50 feet ahead while making a 90-degree turn in an effort to determine if the odor was emitting from his airplane or elsewhere on the airport. The pilot further stated that he could hear the hydraulic pump cycle once, which he thought was unusual. He pulled the hydraulic circuit breaker out and moved toward the parking area. Within 30 seconds of the hydraulic pump cycling, the pilot observed smoke emanating from the engine area. He shut down the airplane and after egressing, he noticed flames at the bottom of the engine cowl in the vicinity of the nose landing gear wheel well. Fire suppression units were dispatched to the site to extinguish the fire. AIRCRAFT INFORMATION The experimental Lancair IV single-engine airplane, serial number LIV-154, was built in 1998. The airplane was equipped with a Teledyne Continental Motors TSIO-550-E-1B. The pilot reported that the airframe and engine had accumulated 560 hours total time. The last conditional inspection was completed on June 21, 2010, or 6 days prior to the accident; the airplane had accrued approximately 2 hours since that inspection. Hydraulic System Design The airplane was equipped with an electrically powered hydraulic system used to operate the landing gear and wing flaps. With the landing gear in the "up" position, the hydraulic pump is activated to provide 1,000 psi to the up side of an actuator. The electric pump is disabled by a limit pressure switch, although the pressure is maintained and holds the gear in its retracted position. Upon selecting the “down” position, 1,000 psi is provided to the down side of the cylinder and the gear is extended and driven to the overcenter (locked) position for the nose gear and to down and locked for the main landing gear. The kit manufacturer recommends that only MIL-H-5606 “red” hydraulic fluid be used in the system. TESTS AND RESEARCH Following recovery, a Safety Board investigator examined the airplane in a private hangar at the Caldwell Industrial Airport on July 01, 2010. The airplane was intact and the only damage observed was to that incurred as a result of an on-ground fire. The engine had been washed of fire retardant the day prior to the examination in an effort to reduce the corrosive effects. The upper and lower engine cowling had been removed and the battery was disconnected. Airframe The center section near the pilot's right rudder petal had sustained thermal damage, which continued over to the passenger side left rudder petal. In these areas the carpet fragments partially burned and the composite material appeared to have melted in areas. The fuel selector was in the "off" position, and both the hydraulic and ground-power circuit breakers were out, which the pilot reported he had pulled after the fire transpired. The hydraulic reservoir, located just aft of the baggage compartment, was about 3/4 full. Engine The engine had sustained thermal damage, most of which occurred near the firewall area. The upper engine cowl was charred in the area near the firewall, with evidence of bubbled paint. A hole was present in the far left area, where the oil breather was positioned. The bottom side of the lower cowl burn concentration was on the right side, with the most damaged region near the firewall and the nose gear wheel well. The inside of the lower cowl displayed white coloration in the same area of concentrated damage. The left side of the engine showed a black soot color around the area of the firewall. The right side of the engine revealed a predominantly white area near the firewall with black soot surrounding. In looking down the nose wheel compartment to the firewall there was evidence that the landing gear structure, doors, and hoses on the right side where lighter in appearance (white) and had sustained more intensive thermal damage. On the right side of the belly area, near the nose landing gear compartment, a red/pink stain started and continued down toward the tail. The stain became small beads of pooling liquid at the low point of the belly and was thinly covering the leading edge of the bottom blade antenna. The liquid and stain coloration was consistent with that of MIL-L-5606 hydraulic fluid. Above the stain, on the right side of the engine firewall, were two hydraulic fittings where hoses connected to either side of the nose landing gear actuator. The upper fitting and hose were charred to a white coloration, with the steel braiding observed underneath. The lower fitting was surrounded in a black residue that was sticky to the touch; the firewall area around the fitting was additionally sticky, with a rubber consistency. The lower hose was charred black around its black rubber surface, but had suffered considerably less damage than the surrounding hoses. The distance from the exhaust shroud to the hydraulic fittings was about 9 inches. Removal of the hoses surrounding the hydraulic fittings and the gascolator shroud revealed that the gascolator body was white on the side closest to the fittings. The firewall around the fittings was additionally white.
The failure of maintenance personnel to ensure that a hydraulic line fitting was adequately secured during a conditional inspection, which resulted in a leak and subsequent on-ground fire.
Source: NTSB Aviation Accident Database
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