Figure: Learjet 60 N999LJ, from Aviation-Safety

Eddie Sez:

Maintenance Malpractice

The cause of this mishap, that is the thing that started it all, were tires that were found to be 36 percent under-inflated. Learjet procedure called for checking the tires before the first flight of each day or every 10 days they are not in use, but they hadn't been checked for three weeks. The Learjet maintenance manual further stipulates that a tire should be replaced if it ever falls below 15 percent. The organization's director of maintenance was unaware of this requirement and it appears the tires on the accident airplane had not be checked in three weeks. An underinflated tire is prone to fail and that's what happened here.

So let's assume your tires are checked before the first flight of the day whenever you depart home plate. But what about on the road? The NTSB report brought up some interesting points on who can check tires, legally, and who cannot:

[NTSB Safety Recommendation, April 14, 2010, A-10-46 through -59, page 4] On February 26, 2009, the FAA’s assistant chief counsel for regulations responded that checking the tire pressure on a Learjet 606 airplane is preventive maintenance, which pilots would not be permitted to do as part of a preflight check. However, the FAA further explained that a pilot flying a Learjet 60 under Part 91 may perform tire pressure checks but that a pilot flying a Learjet 60 under Part 135 may not.

I think you should have a firm understanding of the tire pressure loss pattern of your aircraft and measure the pressure when on the road at appropriate intervals. If you are flying under 14 CFR 91, you should have your mechanic train you for the task and equip the aircraft with a properly calibrated gauge. If you are flying under 14 CFR 135, you need to make the appropriate arrangements to have a qualified mechanic perform the task. More about tire pressure here: G450 Systems / Landing Gear / Tire Pressure, which includes lessons for more than just G450 operators.

Maintenance teams do not always face the same scrutiny as pilots. The FAA performed 159 inspections of one sort or another on this 14 CFR 135 organization but never detected what had to have been a lax attitude towards regular tire pressure checks. Smaller operations, especially those with a single mechanic, are susceptible to the pressure to take short cuts, may lack a quality assurance structure, and can suffer from poor training. These, with the added factor of fatigue, make up what I call: Maintenance Malpractice

Pilot Malpractice

Now onto the second problem: takeoff abort procedures. This pilot initiated the abort above V1, thought better of it, and then decided to abort again. The initial abort began two seconds after the first officer called V1. I think had the captain remained committed to the abort, even though it was after V1, they could have survived the stop. But as the takeoff progressed the main landing gear weight on wheels switches were damaged and the thrust reversers stowed and her throttle inputs resulted in forward thrust. They departed the runway well over 100 knots. More about decision speed here: Technical / V1.

Why would a properly trained pilot have such a problem with an abort decision after V1? The NTSB report hypothesizes she may have been startled by the unexpected tire failure, which in the cockpit was a loud noise, the right wing dropping a few inches, and vibration. Back in the days when we expected a tire failure now and then you got used to it. These days we need to practice the scenario in a simulator. I think if you have experience with the world falling apart around you, this might not be an issue for you. But if your aviation experience has been nothing but blue skies from the day you started flying, you should make an effort to load yourself up in a simulator.

What follows comes from the references shown below and my comments shown in blue.


Accident Report


Narrative

Figure: Map of Columbia Metropolitan Airport, showing integrated sound spectrum data, CVR comments, and wreckage locations plotted, from NTSB AAR-10/02, figure 6.

[NTSB AAR-10/02, ¶1.1]

[NTSB AAR-10/02, ¶1.5]

[NTSB AAR-10/02, ¶1.6]


Analysis

The Captain

[NTSB AAR-10/02, ¶2.1] Interviews with other pilots, a Learjet 60 proficiency check evaluator, and flight and ground training instructors who were familiar with the captain’s flying and training in recent years revealed that none expressed any concerns about the captain’s competence.

[NTSB AAR-10/02, ¶2.4] The captain’s action to reject the takeoff and her lack of a callout, contrary to her training, may have been the result of the “startle factor,” which is often lacking in training scenarios. In most V1 training scenarios, pilots are in a simulator, are aware that they will be receiving an anomaly (usually an engine failure) on takeoff, and are prepared to respond. In the real world, the situation is more dynamic, the consequences are greater, and the pilot is not aware that a failure will occur or what type of failure it is. This “startle factor” can increase the stress level of the pilot, resulting in an incorrect decision being made.

Tires

[NTSB AAR-10/02, ¶1.16.3]

[NTSB AAR-10/02, ¶2.1] The relatively new set of tires on the accident airplane showed no evidence of failures in design, manufacturing flaws, or exterior damage, such as punctures or other damage from striking foreign objects. Therefore, the NTSB concludes that the following were not factors in this accident: tire design, tire manufacture, or damage to the exterior of any tire.

[NTSB AAR-10/02, ¶2.3.1]

Thrust Reversers

[NTSB AAR-10/02, ¶1.16.4]

Rejected Takeoff

[NTSB AAR-10/02, ¶2.2]


Probable Cause

[NTSB AAR-10/02, ¶3.2]


See Also:

Abnormal Procedures / Maintenance Malpractice

G450 Systems / Landing Gear / Tire Pressure

Technical / Fault Tolerance

Technical / V1


References

Aviation Safety Network

NTSB Aircraft Accident Report, AAR-10/02, Runway Overrun During Rejected Takeoff, Global Exec Aviation, Bombardier Learjet 60, N999LJ, Columbia, South Carolina, September 19, 2008

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