American Airlines 2253
Does what we expect to happen influence our awareness?
Why is constant monitoring essential?
AA 757-200 Over-run
(AP)
Snowy Day
2253 was a Chicago to Jackson Hole, Wyoming (JAC), flight with experienced pilots flying in challenging but typical winter conditions. (The Captain had extensive experience flying into JAC.) JAC is located at an altitude of 6,400 feet and the active runway was 6,300 feet long.
Weather conditions were better than forecast with light snow and winds though the aircraft would be close to maximum landing weight. The flight crew conducted a very thorough en-route briefing evaluating runway conditions, weather and aircraft capabilities.
Runway conditions deteriorated during the final third of the length so the plan was to touchdown in the first 1,000 feet and come to a stop quickly. The aircraft slows and stops using a combination of main gear hydraulic brakes, engine thrust reversers and “speed brakes” or “spoilers.” These speed brakes cancel wing lift and allow the weight of the aircraft to settle on the main gear so the hydraulic brakes will be fully effective.
Deployed Thrust Reverser
Approach
Engine thrust reversers are manually deployed by the flying pilot after touchdown and the speed brakes can be “armed” for automatic deployment or manually activated at any time. In addition, the aircraft has a system that automatically confirms that it is on the ground so that deployment is appropriate.
The aircraft was configured for landing, the first officer was the flying pilot and the captain was tasked with monitoring pertinent systems. He would confirm and call out successful deployment of reversers and speed brakes, a common procedure.
Looking Aft
“Two in Reverse”
The aircraft touched down exactly as planned and the Captain called out “deployed” and “two in reverse” suggesting that the speed brakes and thrust reversers were operating. In the split second after touchdown the “on the ground” sensing system cycled from ground to air to ground again at the exact moment that the flying pilot was manually deploying the thrust reversers. They froze in mid-deploy position. In addition, because of an undetected fault in the speed brake system, they also failed to activate. The aircraft was barreling down the runway, unable to stop and heading for a sketchy runway surface.
Two things were wrong but the pilots noticed and focused only on one–the thrust reversers. The National transportation Safety Board (NTSB) referred to this as “tunnelled attention” since the pilot responsible for monitoring the “big picture” allowed his focus to be drawn to one area. The problem with the speed brakes could have been instantly resolved by manually moving the lever to the deployed position. Activating speed brakes even with late deployment of the thrust reversers would have stopped 2253 on the runway.
“Big Picture”
The NTSB discussed the inability for either pilot to pull back to focus on the “big picture” even though both commented that they were not slowing down. One of the aspects touched upon is our tendency to expect automated and highly reliable systems to always function correctly. (The Captain saw the speed brake handle start to move and assumed the rest.) Our analogous examples could include SCBA, fire pumps or patient monitoring systems.)
Luckily, 2253 rolled to a stop in heavy snow about 500 feet past the end of the runway. Their ski trip started early. We can profit by training ourselves to keep the big picture and by not falling into the trap of expecting systems to always function flawlessly.