If "the dice are loaded against" someone, they do not have the right conditions to achieve success. e.g. In the horse race, John's horse was blind and had three legs. John wanted to win but the dice were loaded against him. It's a silly example but I hope you get the point.

The image of a loaded dice comes from gambling. A way of cheating at a game involving dice is to use a die/dice that has been weighted so that it will fall on particular number. Using a loaded dice gives one player an unfair advantage, and therefore disadvantages the other player or players. If the dice is loaded against you, it means that you are unlikely to win the game. It goes without saying that 'the dice are loaded against the green crews', or in other words, that it is more than likely that they will not survive. Green crews already have a higher than average chance of being shot down and killed, and - addition to this - they are given old worn-out aircraft to fly. This makes their chance of survival even lower.