Friday, June 06, 2008

Air Force: Moisture Caused B-2 Crash

The Air Force on Thursday said the first crash of a B-2 stealth bomber was caused by moisture in sensors and estimated the loss of the aircraft at $1.4 billion.

The crash probably could have been avoided if knowledge of a technique to evaporate the moisture had been disseminated throughout the B-2 program, said Maj. Gen. Floyd L. Carpenter, who headed an accident investigation board.

The "Spirit of Kansas" abruptly pitched up, rolled and yawed to the left Feb. 23 before plunging to the ground at Andersen Air Force Base on the island of Guam. Both pilots ejected safely just after the left wing made contact with the ground in the first crash since the maiden B-2 flights nearly 20 years ago.

"It was just by the grace of God that they were safe, and the good (ejection) system," Carpenter said.

Water distorted preflight readings in three of the plane's 24 sensors, making the aircraft's control computer force the B-2 to pitch up on takeoff, resulting in a stall and subsequent crash.

Carpenter said the pilots and crew followed procedures and "the aircraft actually performed as it was designed. In other words, all the systems were functioning normally."

However, a technique learned by some two years ago that had gone widely unknown and unadopted probably would have prevented the crash, Carpenter said. The technique essentially heats the sensors and evaporates any moisture before data calibrations.

"This technique was never formalized in a technical order change or captured in 'lessons learned' reports. Hence, only some pilots and some maintenance technicians knew of the suggestion," according to Carpenter's executive summary of the accident.

The report said, "The human factor of communicating critical information was a contributing factor to this mishap."

The general said his responsibility was solely for the investigation of the crash and added that the report was forwarded to commanding officers to determine if any disciplinary measures are required.

The sensors measure air pressure to help calculate everything from airspeed to altitude. Because of the bad data, flight computers had inaccurate airspeed and wrongly indicated a downward angle, which contributed to an early rotation and uncontrolled 30-degree pitch up.

Carpenter said the lack of altitude and airspeed prevented the pilots from correcting the aircraft.

Guam, 3,700 miles southwest of Hawaii, is known for its humidity. But the Air Force said water in the sensors never caused any problems.

The Spirit was delivered in February 1995 and expected to be in service for another 50 years.

The bomber had been returning to Whiteman Air Force Base in Missouri, where the 21-plane fleet is based. The Air Force grounded the B-2s and resumed flying them in late April.

Carpenter said procedures and policies are now in place to guard against similar crashes.

"It's fortunate the crew was able to safely eject. It's unfortunate, however, that we lost one of our nation's penetrating bombers," said Gen. Carrol H. Chandler, commander of Pacific Air Forces.