Inconsistencies in tire pressure checks were found in the FAA’s Feb. 26, 2009, response to Bombardier Learjet regarding its Model 60. In the letter, the FAA stated that checking the tires on that model is preventive maintenance, and as such pilots would not be permitted to do it as part of a preflight check.

However, the NTSB noted that, according to the FAA’s interpretation, a pilot working for an FAR Part 135 charter operator would be allowed to check tire pressures on a Learjet 60 in preparation for an FAR Part 91 ferry or maintenance flight. And yet, that same pilot would be prohibited from performing the check on the very same airplane for a charter flight carrying revenue passengers or cargo. Go figure.

Because of the nature of charter operations, it is not unusual for a flight crew to remain with an airplane away from home base for several days while flying both revenue and positioning flights. The safety board acknowledged that the different rules that apply to Part 135 flights generally represent a higher level of safety than those contained in Part 91. In this case, however, it noted that the FAA’s interpretation could have an unintended negative effect on safety.

Probable Cause

The safety board 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.

Contributing to the accident were (1) deficiencies in Learjet’s design of and the 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; (2) 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; (3) inadequate industry training standards for flight crews in tire failure scenarios; and (4) the flight crew’s poor crew resource management.

SAFO

On Jan. 6, 2011, the FAA issued a Safety Alert for Operators (SAFO), The Importance of Properly Inflated Aircraft Tires, to help ensure that tires are properly inflated and detailing the potential consequences that improper pressure can have during taxi, takeoff and landing.

The SAFO, which discusses the 2008 Learjet 60 accident in Columbia, South Carolina, also describes the 1991 crash of a McDonnell Douglas DC-8 shortly after takeoff from Jeddah, Saudi Arabia. The probable cause of the crash was underinflated tires, which in turn caused an overheated tire to explode during taxi, which then caused other tires to catch fire during the takeoff roll. The fire continued as the wheels were retracted into the wheel wells, eventually causing a loss of hydraulic control and finally an inflight breakup that destroyed the aircraft. All 261 crewmembers and passengers on board were killed as a result.

The SAFO goes on to suggest that any individual associated with aircraft maintenance make certain their procedures ensure tires remain inflated to within their appropriate maintenance-manual-specified inflation range.