WPR10LA319 · 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.

Verbatim NTSB analysis and probable cause from the NTSB dataset