In the dark of the night on 16th January 1942, TWA flight 3 ploughed into a vertical mountain cliff 50 km out from Las Vegas. Everyone on board including celeb film-actor Carole Lombard died immediately. This was long before black-box flight recorders and it was in the middle of WWII but the US Civil Aeronautics Board CAB met to determine how the accident had happened - nobody wanted such a thing to happen again.
It's interesting to reflect on how things were back then by noting that the flight from New York to Los Angeles had necessary intermediate stops in Indianapolis, St. Louis, and Albuquerque and Las Vegas. Carole Lombard's party boarded at Indianapolis and were about to be bumped in Albuquerque so that 15 Army Air Corps effectives could make it to California. But Lombard pulled celeb-rank - she had been raising money selling War Bonds for the gumment - and insisted on travelling onwards in that plane . . . now. I bet she wished she hadn't when she heard the pilot cry "Oh !@%$!&" seconds before he drove the bus into the moonlit cliff.
Before leaving Las Vegas, the flight crew had to fill in a flight plan which was left there when they took off (normal practice). The CAB noted that the intended course was 218o, which was indeed pointing directly at the fatal cliff but not really at their destination in Burbank CA. They formed a hypothesis that the pilots had, after a long day in the air, put in the coordinates for a flight from Boulder CO - Burbank by mistake. Both pilots had done that trip several times. Good idea, likely explanation. Amazingly, however, the CAB trawled through their bin of flight plans (data! - love it) and found another sheet with exactly the same mistake. the favored hypothesis became therefore much more likely.