Last January 30th, a U.S. C-17 transport landed at Bagram airport in Afghanistan without lowering its landing gear. At the time, it was reported that the aircraft was unable to lower its landing gear, and slid about 1,500 meters down a runway. There was no fire, and no injuries. The underside of the aircraft was badly damaged.
An investigation of the incident revealed that the landing gear was not lowered because the crew never got around to it. To make matters worse, the personnel in the airport tower, who are supposed to make a visual check to see that the landing gear is down, failed to do so. There was also supposed to be a Ground Proximity Warning System alarm going off in the cockpit, when the aircraft was too low, and the landing gear was not lowered. But that alarm had been accidentally turned off by one of the pilots. The two pilots also failed to monitor each other's actions while going through the landing check list. That check list was not used at all. The crew is in big trouble.
The 290 ton (max takeoff weight) C-17 can carry up to 100 tons (including one M-1 tank) anywhere in the world because of in-air refueling. C-17s cost up to $300 million each. Most aircraft accidents these days are the result of human error.