Moisture In Transducers Led To Flight Control Errors

The US Air Force says distorted data introduced by a B-2 Spirit's air data system skewed information entering the bomber's flight control computers, ultimately causing the crash of the aircraft on takeoff at Andersen Air Force Base, Guam, February 23. That's the conclusion reached in an Air Combat Command accident investigation report released Thursday.

Moisture in the aircraft's Port Transducer Units during air data calibration distorted the information in the bomber's air data system, causing the flight control computers to calculate an inaccurate airspeed and a negative angle of attack upon takeoff.

According to the report, this caused an, "uncommanded 30 degree nose-high pitch-up on takeoff, causing the aircraft to stall and its subsequent crash."

Earlier reports stating a fire onboard may have contributed to the crash were apparently erroneous. Instead, the USAF says, moisture in the PTUs, inaccurate airspeed, a negative AOA calculation and low altitude/low airspeed were substantially contributing factors in the mishap.

Another substantially contributing factor was the ineffective communication of critical information regarding a suggested technique of turning on pitot heat in order to remove moisture from the PTUs prior to performing an air data calibration.

The pilot received minor injuries, and the co-pilot received a spinal compression fracture during ejection. He was treated at Tripler Army Medical Center, Hawaii, and released. The aircraft was assigned to the 509th Bomb Wing at Whiteman Air Force Base, MO.

The cost of the lost aircraft is about $1.4 billion.

FMI: www.langley.af.mil