Saturday, May 16, 2009

Flight 3407 crew failed to heed loss of speed

Flight 3407 crew failed to heed loss of speed
Slowdown preceded air crash in Clarence
By Jerry Zremski and Michael Beebe

WASHINGTON — The crew of Continental Connection Flight 3407 wasn’t paying enough attention to notice that the plane was losing speed to the point where its stall warning sounded, the head of the National Transportation Safety Board said Friday.

“There was a bleed-off of speed with no attention paid to it,” said Mark V. Rosenker, who presided over three days of hearings in the Feb. 12 crash that claimed 50 lives in Clarence.

“This should have been a normal approach” to landing at Buffalo Niagara International Airport, Rosenker added in an interview with The Buffalo News.

Rosenker’s comments address one of the abiding mysteries of the crash: why the plane’s speed got so slow that the stall warning system activated.

Much has been made of the pilot’s inappropriate reactions in response to the stall warning system, but Rosenker’s comments, along with testimony in the hearings, make it clear that the crew’s errors had begun earlier.

The crew slowed the speed of the Bombardier Dash 8 Q400 in preparation for landing — as it was supposed to do.

Data released by the safety board this week shows the plane’s speed slowing from 185 knots to 139 knots in 24 seconds.

“That’s not necessarily a rapid slow-down,” Rosenker said.

The problem is, the plane was then allowed to slow to below 138 knots—the correct “target speed” for the aircraft on approach to landing in icing conditions, a report from the Safety Board’s Operations Group said. Other sources familiar with the Q400 said they would not recommend flying the plane slower than 140 knots.

In fact, 3.9 seconds after Flight 3407 was flying at 139 knots, its speed fell to 131 — and the “stick shaker,” part of the stall warning system, activated.

While investigators initially thought ice on the wings may have slowed the plane down, the safety board later found that the moderate level of ice on the wings had a “minimal impact” on its stall speed.

But the plane’s pilot, Capt. Marvin Renslow, apparently had a major impact.

An animated re-creation of the flight’s last seconds shows that at 10:16 p.m. — less than a minute before the crash — the plane’s throttle was moved back to near the “flight idle” position, which is intended to slow the aircraft.

The animation shows the plane slowing quickly after that, and slowing down even more as the crew lowers the landing gear and the flaps, which also slow the plane down.

The trouble is, the plane just got too slow and entered what’s called an aerodynamic stall — in which it, in essence, was moving so slowly that its wings no longer could keep the aircraft flying.

Renslow apparently did not notice that the speed had dropped too far — and neither did First Officer Rebecca L. Shaw, who was supposed to be monitoring the instruments at that point.

Complete Buffalo News coverage of the Flight 3407 crash investigation, including documents, video and profiles of the victims.

Other testimony at this week’s hearings revealed that Renslow and Shaw responded incorrectly to the ensuing stall.

Renslow pulled back on the plane’s yoke when he should have done just the opposite, and Shaw put the plane’s flaps up even though doing so was the wrong response, witnesses testified.

Several officials at the hearing questioned whether a National Aeronautics and Space Administration video that Colgan pilots had been shown — which shows how to recover from a stall caused by icing on the plane’s tail—might have influenced Renslow’s decision to pull back on the yoke.

Renslow’s response would have been correct if the plane had experienced a tail stall, said Tom Ratvasky, a NASA test pilot and icing expert. But it was precisely the wrong response to a wing stall, which is what the plane experienced.

Several questioners said they wondered why that video would be shown to pilots, given that the Federal Aviation Administration will not certify planes that are susceptible to tail stalls.

Ratvasky said showing pilots that video was valuable, but acknowledged it could create confusion for pilots who get a stall warning.

“Remember,” he said in his final comments, “you have very little time to correctly diagnose the problem and take the proper corrective action.”

No comments:

The Rams Horn

The Rams Horn on Facebook