onsdag 30. mai 2012

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Racing the Storm: The 1999 Crash of American 1420

By Dan DePodwin, Meteorologist
May 30, 2012; 8:50 AM ET 
National Transportation Safety Board investigator Michael Kelly looks at the crash site of American Airlines Flight 1420 at Little Rock National Airport in this June 4, 1999 photo in Little Rock, Ark. A flight attendant on the plane told jurors Tuesday, May 17, 2005 at a federal trial in Little Rock that she never felt her life was in danger while Capt. Richard Buschmann flew American Airlines Flight 1420 from Dallas to Little Rock on June 1, 1999. (AP Photo/Danny Johnston)
The data for the following story was gathered from the official accident report issued by the National Transportation Safety Board.
As the sun set on the first day of June in 1999, passengers of American Airlines Flight 1420 boarded an MD-82 aircraft in Dallas, Texas, destined for Little Rock, Ark. It was warm, the air humid and the stage set for disaster.
A "Bowling Alley" Approach
In springtime, cool, dry Canadian air races southward while sticky, sultry, warm air resides across the Deep South. When these two air masses clash, the stage is set for violent thunderstorms. These ingredients came together on June 1, 1999 across Arkansas as Flight 1420 flew towards Little Rock.
Already delayed by poor weather in the Dallas area, Captain Richard Buschmann and First Officer Michael Origel were behind schedule and in danger of going beyond their allowed duty times. Prior to leaving Dallas, the crew was briefed on the developing thunderstorms in Arkansas, but believed they would be able to make it to Little Rock.
While in the air, an American Airlines flight dispatcher informed the flight crew that storms were closing in on Little Rock, but a "bowling alley" of clear air still existed and recommended expediting their approach to avoid the weather.
Just before 11:30 p.m. as Flight 1420 was about 30 minutes away from Little Rock, the airport weather observing station began reporting a thunderstorm. At this point, winds were still light, just 10 mph.
In the cockpit, Buschmann and Origel began to feel the effects of the increasingly bad weather with turbulence and frequent lightning. The increased workload of landing in poor weather would take its toll.

The "Bowling Alley" Closes-In
As Flight 1420 was on final approach, the weather rapidly deteriorated and the "bowling alley" closed in. Visibility on the runway dropped below the minimum required for landing and winds increased above the acceptable limit. Yet the pilots, tired from a long day of work, did not decide to abandon the approach and go to their alternate airport.
With lightning engulfing the plane, turbulence rocking it from side to side, and rain pelting the windows, the MD-82 touched down on the runway. Immediately, the plane began sliding, not losing speed. Despite applying the brakes, the plane continued through the end of the runway and careened into a steel walkway, coming to rest on the bank of the Arkansas River.
Captain Buschmann was killed instantly while 10 other passengers perished in the crash; 134 people survived.
The focus of the National Transportation Safety Board (NTSB) investigators quickly turned to the lack of braking and the weather. What they found would reveal a startling pattern in the aviation community.
An American Airlines MD-82 aircraft like the one involved in the accident. Courtesy of Flickr user Deanster1983

"Get There-Itis" and a Culture of Flying Through Storms
After months of investigation, witness interviews and studies of pilot behavior in thunderstorms, the NTSB found that two out of three pilots would land in a thunderstorm. They were more likely to do so if it was nighttime, they were behind schedule, or if other planes had landed in front of them.
This unsafe practice shocked many in the aviation community. It was also found that American Airlines had a vague policy about flight through thunderstorms. In response, more specific guidelines were adopted.
The storm that hit Little Rock late in the evening on June 1 was a severe thunderstorm. Just after the fatal crash, a wind gust to 88 mph was reported at the airport-clearly unsafe weather to attempt a landing. However, the flight crew decided to land anyway. Lead NTSB investigator Greg Feith described the insistence of landing despite weather "get there-itis."
But despite the poor weather, Flight 1420 had successfully landed. Why had the plane skidded off the runway without stopping? The key to unlocking this mystery was found on what was NOT heard on the cockpit voice recorder. There was no mechanical click signifying that the spoilers were armed.
The spoilers aid in braking by disrupting flow of air over the wing. In addition, they reduce lift which allows the plane to put its full weight on the wheels. In the case of Flight 1420, the flight crew forgot to arm the spoilers to deploy upon landing.
As a result, the pilots had extremely limited braking ability and could not slow the plane in time.
In the aftermath of this tragic accident, the NTSB recommended numerous improvements in cockpit procedures, communication of weather forecasts and flight crew training.
Despite the changes and lessons learned from June 1, 1999, weather continues to be a leading cause of aviation disasters. Incidentally, exactly 10 years later, Air France Flight 447 would vanish over the Atlantic Ocean, killing all 228 people on board--more on that fatal night coming soon.

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