Revealing mistake: When Dirk and Al are struggling through the desert, chained to the trailer, they slip and fall into the pit. They coast down the slope, thud into a drift and fly through the air and land. However, in the next scene, their tracks are shown behind them as if they had not flown through the air at all.
Other mistake: When the two heroes are wind riding the plane they more or less repaired (about 1 hour and 30 minutes from the beginning of the movie), the wind blows from the right side of the plane to the left, but the hero is counter balancing the plane on the left side as if the wind were coming from the left. He should be standing on the right side of the plane to really balance it.