Description

On September 19 2008, a Learjet 60 being operated on a non scheduled passenger flight by Global Exec Aviation overran the departure runway after initiating a rejected take off in normal night visibility conditions at Columbia Metropolitan Airport. After the aircraft left the runway at speed, it passed through the 1,000-foot Runway End Safety Area, struck airport lighting and navigation antennas and descended down a steep slope before striking various obstructions, exiting the airport perimeter and crossing a five-lane road before hitting an embankment on the far side of the road at which point it was seen to explode into a fireball. The Captain, First Officer and two of the four passengers were killed and the other two other passengers were seriously injured. The aircraft was destroyed.

Investigation

An investigation into the accident was carried out by the National Transportation Safety Board (USA) (NTSB). It was established that the aircraft had attempted take off with severely underinflated main landing gear tyres, which led to the sudden failure of at least one becoming apparent to the fight crew during the take off roll shortly after V₁. Whilst the First Officer indicated that the take off should be continued, the Captain decided to reject the take off and deployed the thrust reversers. The investigation found that the tyre failure had damaged a sensor, which had the effect of causing the thrust reversers to return to their stowed position after deployment. This meant that whilst Captain was trying to stop the airplane by commanding reverse thrust, forward thrust was being provided at near-takeoff power because the thrust reversers were stowed. The Investigation determined that the unintended forward thrust contributed to the severity of the accident outcome.

The Investigation also noted a similar uncommanded forward thrust accident that had occurred during landing in 2001 and that whilst the modifications introduced after that accident had provided additional protection against uncommanded forward thrust upon landing, no similar protection had been provided for the rejected takeoff case.

The Findings of the Investigation included the following:

• In the absence of evidence that the airplane was uncontrollable, the captain’s execution of a rejected takeoff for an unknown anomaly after the airplane’s speed had passed V₁ was inconsistent with her training and standard operating procedures.
• The accident airplane’s uncommanded forward thrust, which accelerated the airplane at a time when the flight crew commanded full reverse thrust to decelerate the airplane, increased the severity of the accident because the uncommanded forward thrust substantially increased the airplane’s runway excursion speed.
• All four main landing gear tyres on the airplane were operating while severely underinflated during the takeoff roll, which resulted in the tire failures.
• The accident airplane’s insufficient tyre air pressure was due to Global Exec Aviation’s inadequate maintenance.
• Learjet’s system safety analysis for and the Federal Aviation Administration’s review of the Learjet 60’s thrust reverser system modification and revised crew procedure were inadequate because they failed to effectively address an unsafe condition for all phases of flight, specifically, uncommanded forward thrust during a rejected takeoff.
• The Federal Aviation Administration’s 1993 certification of the Learjet 60 as a changed aeronautical product, which allowed the airplane’s equipment, systems, and installations to conform to some regulations applicable to the original 1966 certification, did not ensure the highest level of safety and allowed for deficiencies that would not likely have been present if the current regulations had applied.
• The accident pilots would have been better prepared to recognize the tyre failure and to continue the takeoff if they had received realistic training in a flight simulator on the recognition of and proper response to tire failures occurring during takeoff.
• The captain’s indecision in responding to the anomaly and her failure to follow standard operating procedures was the result of a combination of poor crew resource management skills, limited experience as a pilot-in-command in the Learjet 60, and, during the accident sequence in particular, her less than confident and assertive leadership in the cockpit.

Probable Cause

The NTSB determined that “the probable cause of this accident was the operator’s inadequate maintenance of the airplane’s tires, which resulted in multiple tire failures during takeoff roll due to severe underinflation, and the captain’s execution of a rejected takeoff after V₁, which was inconsistent with her training and standard operating procedures.“

The Board also noted that “Contributing to the accident were

• deficiencies in Learjet’s design of and the Federal Aviation Administration’s (FAA) certification of the Learjet Model 60’s thrust reverser system, which permitted the failure of critical systems in the wheel well area to result in uncommanded forward thrust that increased the severity of the accident
• the inadequacy of Learjet’s safety analysis and the FAA’s review of it, which failed to detect and correct the thrust reverser and wheel well design deficiencies after a 2001 uncommanded forward thrust accident
• inadequate industry training standards for flight crews in tire failure scenarios
• the flight crew’s poor crew resource management.“

Safety Recommendations

As a result of the Investigation, the NTSB made the following 14 Recommendations to the FAA that they should:

• Provide pilots and maintenance personnel with information that
  1. transport-category aircraft tires can lose up to 5-percent pressure per day,
  2. it may take only a few days for such tires to reach an underinflation level below what the aircraft maintenance manual specifies for tire replacement, and
  3. the underinflation level that would require tire replacement is not visually detectable. (A-10-46)
• Require that all 14 Code of Federal Regulations Part 121, 135, and 91 subpart K operators perform tire pressure checks at a frequency that will ensure that the tires remain inflated to within aircraft maintenance manual-specified inflation pressures. (A-10-47)
• Require that aircraft maintenance manuals specify, in a readily identifiable and standardized location, required maintenance intervals for tire pressure checks (as applicable to each aircraft). (A-10-48)
• Allow pilots to perform tire pressure checks on aircraft, regardless of whether the aircraft is operating under 14 Code of Federal Regulations Part 91, Part 91 subpart K, or Part 135. (A-10-49)
• Require tire pressure monitoring systems for all transport-category airplanes. (A-10-50)
• Identify the deficiencies in Learjet’s system safety analyses, both for the original Learjet 60 design and for the modifications after the 2001 accident, that failed to properly address the thrust reverser system design flaws related to this accident, and require Learjet to perform a system safety assessment in accordance with 14 Code of Federal Regulations 25.1309 for all other systems that also rely on air-ground signal integrity and ensure that hazards resulting from a loss of signal integrity are appropriately mitigated to fully comply with this regulation. (A-10-51)
• Revise available safety assessment guidance (such as Advisory Circular 25.1309-1A) for manufacturers to adequately address the deficiencies identified in Safety Recommendation A-10-51,
• Require that designated engineering representatives and their Federal Aviation Administration (FAA) mentors are trained on this methodology, and modify FAA design oversight procedures to ensure that manufacturers are performing system safety analyses for all new or modified designs that effectively identify and properly mitigate hazards for all phases of flight, including foreseeable events during those phases (such as a rejected takeoff). (A-10-52)
• Revise Federal Aviation Administration Order 8110.48 to require that the most current airworthiness regulations related to equipment, systems, and installations (14 Code of Federal Regulations 25.1309) are applied to all derivative design aircraft certificated as changed aeronautical products. (A-10-53)
• Review the designs of existing derivative design aircraft that were certificated as changed aeronautical products against the requirements of the current revision of 14 Code of Federal Regulations 25.1309 and require modification of the equipment, systems, and installations to fully comply with this regulation. (A-10-54)
• Define and codify minimum simulator model fidelity requirements for tire failure scenarios. These requirements should include tire failure scenarios during takeoff that present the need for rapid evaluation and execution of procedures and provide realistic sound and motion cueing. (A-10-55)
• Once the simulator model fidelity requirements requested in Safety Recommendation A-10-55 are implemented, require that simulator training for pilots who conduct turbojet operations include opportunities to practice responding to events other than engine failures occurring both near V1 and after V1, including, but not limited to, tire failures. (A-10-56)
• Require that pilots who fly in 14 Code of Federal Regulations (CFR) Part 135 operations in aircraft that require a type rating gain a minimum level of initial operating experience, similar to that specified in 14 CFR 121.434, taking into consideration the unique characteristics of Part 135 operations. (A-10-57)
• Require that pilots who fly in 14 'Code of Federal Regulations (CFR) Part 135 operations in an aircraft that requires a type rating gain a minimum level of flight time in that aircraft type, similar to that described in 14 CFR 121.434, taking into consideration the unique characteristics of Part 135 operations, to obtain consolidation of knowledge and skills. (A-10-58)
• Require that tire testing criteria reflect the actual static and dynamic loads that may be imposed on tires both during normal operating conditions and after the loss of one tire and consider less-than-optimal allowable tire conditions, including, but not limited to, the full range of allowable operating pressures and acceptable tread wear. (A-10-59)

The Final Report of the Investigation was adopted on 6 April 2010 and may be seen in full at SKYbrary bookshelf: Accident Report NTSB/AAR-10/02 PB2010-910402 Runway Overrun During Rejected Takeoff, Global Exec Aviation Bombardier Learjet 60, N999LJ, Columbia, South Carolina, September 19, 2008 

Further Reading

• Runway Excursion
• Engineered Materials Arresting System
• Rejected Take Off
• Beyond the Runway End Safety Area
• Maintenance Error
• Pilot judgment and expertise (OGHFA BN)
• Crew Resource Management (OGHFA BN)
• Rejected Takeoff (OGHFA SE)