There are many different reasons why airplanes crash. The two main ones are of course during take off and landing. For the most part take offs are relativity easy and safe. There are a number of...
There are a lot of factors that can cause the loss of lift in an aircraft, such as changing the shape of the airfoil, changing the speed, a change in air temperature which causes a change in air...
Your question can generate various responses of all sorts depending on the odor, but my best guess and from my own experience it was probably the passing of gas by a fellow passenger.