Incident
During a night approach in visual conditions, the flight crew was being vectored for a final approach when they lost radio contact with the control tower and detected smoke odor inside the airplane. Despite the issues, they continued the approach and landed without further incident. After taxiing to their parking position, ground personnel observed flames penetrating the top of the aft fuselage between the engines. Airport firefighting personnel quickly extinguished the fire.
Investigation
Postaccident examination revealed that a hydraulic return line in the aft equipment bay had evidence of electrical arcing and a small hole, which could allow hydraulic fluid to escape. Additionally, a 115-volt electrical line used for heating the horizontal stabilizer showed signs of rubbing on its surface. The fire also damaged a pressurized fuel line to the auxiliary power unit (APU), resulting in fuel leakage.
Tests and Findings
Investigators conducted tests simulating an electrical line arcing in the presence of a leaking hydraulic line. In each of three tests, a fire resulted, confirming that such a scenario could ignite a fire. The findings indicated that the proximity of electrical lines to flammable fluid lines was a key factor.
Regulatory Context
Cessna’s production standards did not specify a minimum separation distance between electrical lines and flammable fluid lines. The Federal Aviation Administration (FAA) had certified the airplane without requiring Cessna to define such spacing.