Southwest Pilots Reported Buffalo ILS can cause Planes to go Nose Up

[RamboLiberal]

A problem with the instrument landing system at the Buffalo airport can cause airplanes to move suddenly to a nose-up position, a pilots’ union warned on Thursday, but the flaw seems unlikely to have played a role in the crash of a plane during its approach there on Feb. 12.

The union, the Southwest Airlines Pilots’ Association, said it had described the problem to the crash investigators. The runway at Buffalo Niagara International Airport is the same one that Continental Connection Flight 3407 was approaching before it crashed, but the problem occurs when making a right turn to line up with Runway 23; the Continental plane was turning left.

The phenomenon is drawing attention partly because the Continental plane’s nose pointed up 31 degrees just before it crashed. But that pitch-up, investigators say, appeared to have been caused by pilot action, after the autopilot disengaged. The problem described by the Southwest pilots occurs when a plane is on autopilot.

It has happened to Southwest planes twice within the past three months, the pilots’ association said. The union called it a “potentially significant hazard,” and said that “if conditions present themselves in a certain manner,” they could put a plane near a condition called stall, when airflow over the wings, given their angle and the plane’s speed, is insufficient to sustain flight. The plane that crashed was in such an aerodynamic stall.

A spokeswoman for the Federal Aviation Administration, Laura J. Brown, said the problem had been noted for years on aeronautical charts and resulted from uneven terrain near the Buffalo airport. Planes flying over a small valley were prone to receiving “anomalous altitude readings” that caused the problem, she said.

http://www.nytimes.com/2009/02/20/nyregion/20beacon.html?ref=nyregion