AFAIK, you are correct, the thrust reversers are not an essential component. I am guessing they worried about an uncommanded reverser deployment like happened to the Lauda 767 In a message dated 2/20/2006 3:21:37 PM Central Standard Time, gfoley@xxxxxxxxxxxxxxx writes: Little strange to try a thrust reverser while in flight? Better check it before takeoff, if at all. I didn't think thrust reverser operability was required anyway.