A B-2 bomber costs $1.4 billion — moisture in the sensors brought it down

The B-2 Spirit is the world's most expensive bomber, built by Northrop Grumman at a unit cost of $1.4 billion. Its stealth design requires a sophisticated flight control system that relies on flush-mounted air-data sensors rather than external pitot tubes that would compromise radar evasion. Only 21 B-2s were ever built; each is considered a strategic national asset.

On 23 February 2008, B-2 AV-12 'Spirit of Kansas' was departing Andersen Air Force Base in Guam when heavy rain caused moisture to enter the aircraft's flush-mounted air-data sensors. The water condensed inside three pressure transducers, causing them to fail. The flight control computers received inaccurate airspeed and angle-of-attack data — calculating a negative angle of attack and a lift-off speed that was 12 knots too slow.

As the aircraft lifted off, the computers detected a falsely negative angle of attack and injected an uncommanded 30-degree pitch-up maneuver at 1.6 Gs. The combination of the slow lift-off speed and the extreme pitch caused the aircraft to stall, yaw, and crash back onto the runway. Both crew members ejected safely, but the B-2 was destroyed — the first loss of a B-2 in its 20-year service history.

The entire B-2 fleet was grounded for 53 days while the Air Force investigated the failure and implemented corrective actions. The loss was valued at $1.4 billion, making it the most expensive aviation accident in history at the time. The incident revealed a critical vulnerability in the B-2's unique air-data system that had not been considered during design.