The US Air Force reported that the February crash on take-off of the $1.4 billion B-2 stealth bomber called the Spirit of Kansas was caused by moisture interfering with the operations of 3 of the aircraft's 24 air pressure sensors. The sensors were all on the port side of the aircraft. The moisture problem was found to skew the data being fed into the aircraft's flight control computers.
According to news reports, "The aircraft crew believed the bomber had reached the takeoff speed of 140 knots when in reality it was traveling ten knots slower and rotated for takeoff. The mis function also meant that the sensors showed the plane to be in a nose down position, causing it to command a high level of pitch, around 30 degrees. This, combined with the low takeoff speed, caused the aircraft to stall and veer to the left."
The pilot and co-pilot ejected successfully, although the co-pilot was hurt.
What the Air Force noted was that the crash could have prevented by more effective risk communications.
Again, according to the story, "The vulnerability of the sensors to moisture was first detected by air crews and maintenance staff in 2006, at which time it was discovered that turning on the 500 degree pitot heat prior to sensor calibration would evaporate the water and cause a return to normal readings. However, this was never formally noted and so the pilots of the aircraft were unaware of the potential problem or its solution."
In fact, another B-2 had to abort a takeoff at the same base because of the same problem apparently last year, but the pilots of the B-2 that crashed hadn't been briefed about it.
On a personal side, the B-2 belong to the 509th bomb wing, my old outfit. I was an avionics tech back in the early 1970s, and I find it strange that the problems with the sensors were not logged, nor that when an abort happened, the causes were not formally briefed. I also find it interesting that the information about heating the pitot at the very least wasn't informally spread among the very small B-2 pilot community. If memory serves me correctly, the problem back when I was in the Air Force was that pilots complained about everything - even if a system worked as designed but didn't work the way they wanted it to - on their aircraft during after-flight debriefs, which were all noted, filed, cataloged and analyzed. No issue was too small not to make note of.
Video of the crash can be found on the crash investigation website.