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Report: Brakes, pilots failed
Review of 2010 overrun points to 2 mechanical failures, captain not following protocol.
By Angus M. Thuermer Jr., Jackson Hole, Wyo.
Date: June 6, 2012
Pilots didn’t react properly after two sets of landing brakes failed.
That’s the short version of a report by the National Transportation Safety Board on an American Airlines jet that ran off the end of the Jackson Hole Airport runway in December 2010. The federal agency released an investigation summary Tuesday.
The agency outlined its findings in six pages, offering three recommendations to the Federal Aviation Administration to prevent similar incidents. It also listed the probable causes, including “a manufacturing defect” in one braking system.
The Boeing 757-200 from Chicago touched down at Jackson Hole just before noon Dec. 29 with 179 passengers and six crew members. It ran off the south end of the runway into deep snow, stopping 730 feet beyond the airstrip’s end.
Nobody was injured. The excursion damaged the jet slightly.
“Through this investigation, all of us — the investigator, manufacturer, operator, and pilots, alike — all learned important safety lessons,” NTSB chairwoman Deborah Hersman said in a statement. “The recommendations we issue today will make valuable contributions to improving aviation safety.”
The incident, along with others, prompted the Jackson Hole Airport board to pave an additional 700-foot safety apron beyond the south end of the airstrip. The work was done with the concurrence of Grand Teton National Park, in which the airport is located.
The following account comes from the report issued Tuesday.
The incident happened despite the plane being flown by seasoned American pilots, both of whom had flown into the short, 6,400-foot-high runway “on numerous occasions.” The two were familiar with winter conditions on the airstrip and “thoroughly assessed the pertinent weather, airport and airplane performance” before landing, a summary of the report said.
The jet touched down from the north 600 feet beyond the beginning of the 6,300-foot-long runway in what the investigation called a normal approach. It was good enough to stop the jet within 4,500 feet, had all systems worked correctly, the report said.
But they didn’t. First thing to go wrong was with the automatic deployment of speedbrakes, the safety board said.
Speedbrakes, also known as spoilers, are panels that rise up from the tops of jet wings just after touchdown. They “disrupt the airflow over the wings and greatly increase the wheel braking effectiveness,” the agency explained.
But they didn’t deploy automatically, the safety board said. The investigation blamed “a manufacturing defect in a clutch mechanism.”
Airlines and pilots have back-up procedures for such cases. A pilot can engage speedbrakes manually. To do that, however, the pilot must know that the auto deployment has failed. The “monitoring pilot” who is assigned to review systems as the operating pilot lands the aircraft, is responsible for determining whether speedbrakes have deployed.
In the 2010 incident, the captain was acting as the monitoring pilot, according to the report summary and accompanying news release. As such, a key responsibility of his was to monitor the speedbrakes.
The cockpit voice recorder revealed the captain saying “deployed,” in reference to the speedbrakes. In fact he was wrong, the safety board said.
“The captain’s erroneous speedbrakes ‘deployed’ callout was likely made in anticipation (not in confirmation) of speedbrake deployment after he observed the speedbrake handle’s initial movement,” the summary said. “If either pilot had observed that the speedbrakes had not automatically deployed and subsequently corrected the situation by manually deploying them, the airplane’s stopping distance would have been greatly decreased.”
A contributing factor in the overrun was “the captain’s failure to confirm speedbrake extension before announcing their deployment,” the investigation summary said. “Inadequate pilot training” for such situations is a “safety issue” identified in the investigation summary.
“The report cites three other events in which the pilots were distracted and did not ensure deployment of the speedbrakes,” the summary said. “Prompt speedbrake deployment after touchdown and monitoring of the speedbrake system during the landing roll is especially critical for increased braking effectiveness when landing on short and/or contaminated [wet or icy] runways,” the summary said.
Investigators said an alarm to warn pilots when the speedbrakes do not automatically deploy would be beneficial and recommended such to the FAA.
In addition to an “intelligible alert,” the investigation also recommended training for commercial passenger pilots to recognize speedbrake failures.
The captain didn’t recognize the failure of the auto speedbrake system for a few reasons, the report summary said. One was that the jet’s thrust reversers also did not deploy, and he turned his attention to them.
Thrust reversers redirect the engines’ push to help slow the plane on landing. Passengers can see them as cowlings around engines that unfold to redirect the jets’ force.
During the incident, the pilot who was landing the plane tried to deploy the reverse thrusters, but he was stymied by another safety system.
The summary does not completely explain that safety system, and a copy of the complete investigation hasn’t been released, the safety board said. It is expected in coming weeks.
Agency officials were unavailable for comment Tuesday evening after the News&Guide obtained the report.
Nevertheless, the context of events in the summary outlines the following:
A system in the jet lets other systems know when the craft is in the air or on the ground. The “air/ground” system gives out a “ground” signal after touchdown.
Such a system would prevent potentially disastrous deployment of reverse thrusters during flight. Conversely it would allow reverse thrusters to be deployed when a jet touches down.
During the landing in 2010, however, there was a “momentary interruption” in the “ground signal,” the summary stated. That prevented the reverse thrusters from deploying.
The interruption was caused by “an unloading event,” the agency release stated. While the statement and summary do not specifically state the plane bounced, at some point the plane “unloaded” to the point the air/ground system momentarily reckoned the jet was still in the air.
Such momentary interruptions would not normally affect deployment of the reverse thrusters, the report said. But in this incident, the interruption “coincided almost precisely with the initial deployment of the thrust reversers,” the safety board said. That “resulted in the thrust reversers locking in transit instead of continuing to deploy.”
In other words, reverse thrusters got stuck part way. Aviation officials knew shortly after the incident that the reverse thrusters didn’t immediately deploy because of a video posted on YouTube.
A passenger made a cellphone video through a window of the reverse thrusters beginning to move, then stopping. Eventually they deployed and acted as brakes — in a cloud of powder snow.
The video is easily found using the key words “Jackson,” “airport,” “crash” and “Wyoming.”
Investigators went on to tie the two failures together.
The captain, acting as the “monitoring pilot,” was supposed to be watching the speedbrakes. When the thrust reversers failed to deploy, that attracted his attention.
“The captain deviated from normal company procedures” and took over the thrust reverser operation from the landing pilot, the investigation said. He should have continued with his monitoring pilot tasks and confirmed speedbrake failure, the agency said.
“Although the pilots could have manually deployed the speedbrakes at any time during the landing roll, neither pilot recognized that the speedbrakes had not automatically deployed because they were both trying to resolve the thrust reverser issue,” the safety board statement said.
“The first officer, who was the pilot flying, tried to deploy the thrust reversers; when they did not initially deploy, the captain took over the thrust reverser controls, and they deployed about 18 seconds after touchdown.”
To make matters worse, the pilots didn’t know how to get the thrust reversers working again quickly, the investigation said. When jammed, levers need to be returned to their stowed position before trying again.
“Postincident interviews with American Airlines pilots indicated that company pilots were not aware of this technique,” which is counter-intuitive, the safety board said. If they had been aware, “the deployment of the thrust reversers could have occurred much earlier in the landing roll,” the safety board said.
In addition to speedbrake training and a speedbrake failure alarm, the safety board recommended Boeing establish guidance for pilots for procedures to follow when thrust reversers are locked closed.
2. The jet should have stopped within 4,500 feet, given conditions and its load.
3. Auto speedbrakes, also known as spoilers, failed to deploy due to a mechanical defect.
4. The captain, acting as the monitoring pilot and assigned to watch the speedbrakes, wrongly reported they were deployed.
5. The landing pilot tried to engage the thrust reversers, another braking mechanism.
6. An air/ground system message that the plane was on the ground was momentarily disrupted during landing by a “unloading,” apparently a bump in the plane’s landing trajectory.
7. Disruption of the system’s “ground” signal occurred at almost the exact instant the landing pilot tried to engage the reverse thrusters.
8. Disruption of the “ground” signal prevented the reverse thrusters from deploying.
9. The captain turned his attention from the monitoring of the speedbrakes to operation of the reverse thrusters, contrary to protocol.
10. Consequently the speedbrakes were not deployed manually, as they could have been.
11. Had the speedbrakes been deployed, they would have “greatly decreased” the landing distance.
12. Pilots didn’t know that when reverse thrusters do not immediately deploy, levers must be returned to the stowed position before attempting to deploy them again.
Contributing causes: Captain’s failure to confirm speedbrake extension, distraction due to thrust reverser failure.