Im sure most of you have seen the shuttle landings on TV before. And a few lucky ones in person. The time between gear extension and mains touchdown is a mere 17 seconds. I know the chances of a gear extension failure on the space shuttle are slim to none. But obviously the shuttle is not invincible to failures. I.E. Challenger and Columbia. As well as many other failures im sure, though not leading to such disasters. 17 seconds is a pretty short amount of time to execute any (memorized im sure) checklist for such an event. I wonder what the plan of action is and how many different senarios they run in the simulators for this. Could be interesting having only 2 down with a touchdown speed of about 200 kts. It could happen...