The Weekly Reflektion 05/2022

Even the most advanced technology with sophisticated computer programs to control its use still has the human element.

The burnt our wreck of a B2 stealth bomber

How do you incorporate informal procedures into your management system?

The B-2 stealth bomber ‘Spirit of Kansas’ crashed on take-off at the Andersen Air Force base on Guam on 23rd February 2008. Up until today the crash was the only loss of a B-2 bomber and with an estimated cost of USD 1.4 billion this was the most expensive air crash in history.

The aircraft was on a routine mission returning to the Whiteman Air Force base in Missouri. Just before take-off the crew noticed an alarm indicating a problem with the calibration of sensors that provide input to the flight computer for the calculation of flight parameters including speed. A maintenance technician was called, and he ran a calibration routine and the alarm cleared. As the aircraft taxied down the runway a new alarm activated, this was a ‘yellow’ alarm and did not require an immediate abort of the take-off. The alarm cleared after a few seconds. When the aircraft took off the nose suddenly pitched up. The crew gave full power however the aircraft went into a stall and the left wing touched the ground. The crew ejected and the aircraft crashed and was soon engulfed in flames.

The investigation identified the cause of the accident as faults on three sensors that are installed in an array of 24 on the front of the wing. The B-2 bomber is inherently unstable and requires the onboard computer to continually trim the aircraft as well as respond to the crews’ actions. The incorrect readings from the three sensors caused the inflight computer to calculate an airspeed that was 22 km/hr less than the actual speed, and a negative pitch angle (nose pointing down). As the aircraft lifted off the runway the computer immediately commanded a 30 degree pitch up and this combined with the low speed resulted in the stall.

The day before the flight there was a tropical rainstorm that delayed the flight mission. The B-2 was left outside instead of returning it to the hanger. Water entered the three sensors and affected their function. When the computer detected deviation in the measurements before take-off it initiated an alarm. The technician recalibrated the sensors which effectively reset their values to correspond with the other 21 sensors. During the take-off preparations a heater is switched on that warms the sensors and this dried out the three sensors. These then returned to their normal state however in this state measured incorrectly. The alarm during take-off was the computer registering the discrepancy.

Recalibration of the sensors at the Guam airbase was carried out more frequently than at the other B-2 bases due to the tropical conditions. One of the technicians had spoken to engineers about the problem and was told to use the heater to dry out the sensors before running the recalibration. Not all the technicians and crew were aware of this, including the ones involved in the incident. The routine had not been incorporated into the maintenance procedures. Had this informal procedure been followed the crash would have been prevented.

Do you have informal procedures that are crucial to the safety of your operation? Does everyone know about them?

Reflekt AS