What happened
While operating in precipitation within 10 miles of a level 5 thunderstorm associated with a squall line, the airplane was struck by lightning. The strike caused arching damage to the No. 1 elevator pressure and No. 2 elevator return hydraulic lines, which resulted in the depletion of hydraulic fluid from the No. 1 and No. 2 hydraulic system reservoirs.
The crew landed the aircraft on a wet runway. Following touchdown, two of the four main landing gear tires ruptured. The aircraft subsequently traveled off the left side of the runway, across a grass area, and came to rest after the nose landing gear separated from the airframe.
The investigation
Investigators discovered a loose cannon plug at the parking brake shutoff valve, which had prevented the operation of the alternate antiskid system; this specific area had been inspected two days prior to the accident.
The investigation also revealed that the aircraft was only equipped by design with one bonding strap, located on the left side of the airplane for the horizontal and vertical stabilizer, which failed during the strike. While an Advisory Circular recommends that such an area be designated for carrying substantial amounts of electrical current, the aircraft was not designed for those requirements.
Findings
Several contributing factors were identified regarding weather information and training:
- The flight crew was not provided with convective SIGMETs for the central U.S., which had indicated severe thunderstorms over Birmingham.
- The destination airport was located near the boundary of the east and central regions for convective SIGMETs.
- The airline does not include weather radar training in its recurrent, upgrade, or requalification training programs.
- The dispatcher failed to provide the flight crew with weather watches that were available 15 minutes before and 15 minutes after the flight's departure.