Stealth Bomber Crash
In 2008 the B-2 stealth bomber, a highly-sophisticated Air Force plane that cost $1.4 billion, took off. It was one of 21 bombers made at the time. Unfortunately, the plane had a faulty sensor which caused it to stall immediately after taking off during a test flight in Guam.
Fortunately, the two pilots aboard were able to eject to safety before impact. But the plane itself crashed and an investigation into what happened showed that water got into the sensor because a technique to deal with that type of moisture in the engines wasn’t properly handled.