Human error stubborn snag in airline safety

As the jet roared toward takeoff, it seemed "sluggish" and struggled to lift off, the captain said later. It climbed only 100 feet before the control column started shaking violently, a warning that the jet was on the verge of plummeting to the ground.

Only then did the crew of the Boeing 737-800 head off tragedy. The co-pilot pulled a lever to extend flaps and slats, critical devices that add lift to the wings and must be used on takeoff. The pilots had forgotten to set them, the captain said.

This incident in May 2005 at Reagan Washington National Airport, recounted in a NASA database of pilot reports, is eerily similar to a crash in August in Madrid that killed 154 people.

The pilots of a Spanair Boeing MD-80 filled with holiday travelers also did not extend the flaps, according to a preliminary report by Spanish investigators. The jet lifted off briefly before striking the ground tail-first and bursting into flames.

Just as in the Washington flight, the warning horn designed to prevent such accidents did not sound, according to the report. The captain on the Washington flight said a circuit breaker on the warning horn had tripped, preventing it from working.

Despite a string of fatal crashes because of failure to set flaps, including two in the USA in the late 1980s, such incidents continue, according to the NASA Aviation Safety Reporting System.

From 2000 to the present, pilots reported 55 cases in which they attempted to take off without properly extending the flaps, according to the data. In nearly all cases, the warning horn functioned normally and prevented tragedy. But pilots — many surprised that they made such a critical error — say that stress, fatigue or interruptions to their routines caused them to make big mistakes.

"The cause of this potentially dangerous situation was a breakdown in checklist discipline attributable to cockpit disruptions," said the captain in the Washington incident. Pilots and airlines are not identified in the reports.

Pilots thrown off track

Safety has improved dramatically in the airline industry in recent decades. But the human mind remains a stubborn impediment to wiping out crashes altogether.

"You'll do the same thing correctly 1 million times and then not do it correctly one time," says Ben Berman, a former National Transportation Safety Board (NTSB) investigator who has studied human behavior for NASA. "Things like a moment of stress, a spike in workload, a change in routine — all these things can throw humans off track."

Distractions played a role in fatal accidents in Detroit and Dallas blamed on flaps and slats, the NTSB ruled. They were often cited in the NASA reports.

"It's a good reminder for crews to understand that you've got to be following your procedures," says Terry McVenes, an accident investigator, safety expert and airline pilot. "And if there are interruptions while you are doing your checklists, you've got to stop and be vigilant to make sure you don't miss anything."

Some specific cases

Distractions similar to those documented in previous accidents — including a handful of cases in which pilots also may have sidestepped procedures intentionally — dominated the cases in the NASA data:

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