Accident Overview
On July 9, 2019, at approximately 0813 mountain daylight time, a Beech 65 airplane, registration N62069, experienced a left wing explosion during takeoff roll from Sidney Municipal Airport (SNY), Sidney, Nebraska. The airline transport pilot was not injured, and the airplane sustained substantial damage to the left wing. The airplane was registered to and operated by Bemidji Aviation Services, Inc., operating as a Title 14 Code of Federal Regulations Part 91 positioning flight. Day instrument meteorological conditions prevailed, and an instrument flight rules flight plan was filed. The flight was originating from SNY and destined for Denver, Colorado.
Pre-Takeoff Events
According to the operator, the pilot had topped off the outboard fuel tanks prior to departure, and the airplane contained about 230 gallons of fuel. While taxiing and advancing the engine throttles, the stall warning horn sounded. The pilot pulled the circuit breaker as a corrective action, which stopped the stall warning horn. The pilot believed the stall warning horn was in error and took no further action before the takeoff.
Takeoff and Explosion
During the takeoff roll, the pilot heard a loud bang and observed significant damage to the outboard left wing. Initially, the pilot thought the airplane might have struck an animal or impacted a pothole on the runway. While taxiing back to the ramp, the pilot noted a small amount of smoke coming from the top of the left wing. The pilot taxied the airplane to the corner of the ramp, performed an abbreviated shutdown, grabbed a fire extinguisher, and evacuated. The pilot did not observe any additional smoke or fire and did not discharge the fire extinguisher.
Postaccident Examination
Postaccident examination of the airplane by a Federal Aviation Administration inspector and personnel from the operator revealed fire and thermal damage near the wing root area, including melted and burned wiring. As a precaution, the airplane was defueled by the operator. To determine if a fuel leak was present, fuel was added to the outboard left wing during the examination. After fueling with 15 to 25 gallons of fuel, fuel began leaking from the top of the left wing fuel sending unit. Safety wire on the fuel sending unit screws was removed, and the screws were found loose. The screws were tightened, and the fuel leak stopped. A hole was cut in the wing skin to examine the melted and burned wiring. A wiring harness was found pinched between a metal clamp and a wing rib. The clamp was removed, and metal-to-metal contact was noted between exposed wiring and the wing rib. Due to the thermal damage, the wiring harness could not be separated to determine if the stall warning system could be functionally tested.
Relevant Maintenance History
On February 22, 2019, the airplane was involved in an accident that required the replacement of the outboard left wing. According to the operator's director of maintenance, the electrical wiring in the wing was not inspected during the wing replacement. Additionally, during recent maintenance at an unknown time, the inboard left fuel sending unit was replaced. The most recent continuous airworthiness inspection was completed on June 26, 2019.