Federal investigators say they believe adventurer Steve Fossett encountered a downdraft over California that was too much for his small plane to handle.

In its final report on the fatal 2007 crash, the National Transportation Safety Board said Thursday that Fossett most likely ran into a downdraft that he could not climb out of and slammed into the mountains near Mammoth Lakes.

The NTSB said in its report that the downdrafts in the area at the time likely had a speed of 400 feet per minute. Fossett's Bellanca 8KCAB-180 aircraft would have been unable to climb out of anything over 300 feet per minute.

The wreckage of the Bellanca was discovered more than a year later at an elevation of around 10,000 feet. An inspection indicated it had turned 180 degrees from its original course and hit the ground at high speed, exploding on impact.

The veteran aviator, who set numerous speed and distance records, had been unable to send a distress call. The NTSB said the his plane's emergency locator transmitter was destroyed in the crash.