What happened
During the takeoff roll, the flight crew heard a loud bang. Despite the noise, the pilot continued the takeoff and transitioned into a climb. Following the event, the crew found they were unable to pressurize the passenger cabin. The crew elected to divert the flight to another airport, where the aircraft landed without further incident.
The investigation
Post-flight inspections of the aircraft revealed a gash approximately 3 feet long and 1 foot wide on the underside of the fuselage, located aft of the passenger entry door. Damage was also found on the right nose gear tire.
An inspection of the departure runway identified an in-ground light cover, weighing approximately 100 pounds, which had separated from its mount and broken into two pieces on the runway. Black marks, matching the color and texture of rubber and resembling a tire tread, were found on the underside of the light fixture and within the optical lighting well.
The light cover was part of an in-ground, semi-flush mounted approach lighting fixture installed at the runway's approach end in 1997. At the time of the accident, the lighting system had not been commissioned due to a lack of FAA certification.
Examination of the fixture showed that the six bolts used to attach the lighting assembly to the base had sheared. The fracture surfaces on these bolts were smeared, which is consistent with low cycle fatigue fractures occurring over time. Because the bolts were located on the underside of the fixture, inspecting them required the removal of the fixture cover. While runway inspections for debris were conducted daily or during Duty Manager shift changes per 14 CFR Part 139, these specific uncommissioned fixtures were only subject to visual inspections.