Wednesday, February 18, 2009

Flight 3407: A Case for Tailplane Icing

As previously stated, I had talked to a pilot about the crash and he agreed on icing and said it was icing on the tail that caused the problem.

Here is a link to a study done by NASA on tailplane icing.

Testing at NASA Lewis found that the sharper edges of the horizontal stabilizer collects more ice than the rounded edges of the wings.

"This means if there's any ice on the wing, there may significantly more ice on the horizontal stabilizer," the narrator warns. If a pilot notices ice anywhere on the airplane, he should be aware that ice may already be accumulating on horizontal stabilizer. However, pilots can't see the horizontal stabilizer from the cockpit.

The ice can disturb the flow of air over the tail plane, the horizontal stabilizer. The horizontal stabilizer acts as an upside-down wing, pushing the tail down to counterbalance the lift provided by the wings, which are usually behind the aircraft's center of gravity. If the smooth flow of air is disturbed over the tail plane, the horizontal stabilizer isn't providing the necessary downforce and the nose of the aircraft may pitch downward, the video warns.

Says our narrator:

"Tail plane stall due to ice accretion is rarely a problem in cruise flight. During this part of the flight, the horizontal stabilizer is not working anywhere near its performance limits. Consequently, flight crews may not have any aerodynamic clues that ice may be building up on the tail plane until the aircraft configuration is changed.
"The effects of ice contamination on the horizontal stabilizer are typically noticed during an approach after flaps are extended and when the aircraft is near the ground. During this part of the flight, the horizontal stabilizer is working near its performance limits.

"If the tail stalls at this point, recovery is very difficult."

The NTSB has said the pilots had commented on a significant build-up of ice on the windshield and elsewhere on the airplane shortly before the airplane went out of control as it was approaching the Buffalo airport.

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