Many jets have thrust reversers to help slow the aircraft on landing. Famously, a thrust reverser deployed accidentally on a Lauda Air 767 over Thailand back in the early '90s, resulting in the (at the time) first hull loss of a '67. I remember this because a couple of months after the Lauda Air accident, I was aboard a BA 767 which aborted a takeoff owing to what the crew said was a thrust reverser warning light, and I was only too happy to have them delay the flight and fix it.