They make an horrific noise when deployed, the blade tips are highly supersonic. I've heard one once as a groud observer and I can only imagine the racket they

They make an horrific noise when deployed, the blade tips are highly supersonic. I've heard one once as a groud observer and I can only imagine the racket they make in the cabin. For that reason they're not tested in routine service but there are ground-testing rigs that spin them up to a fraction of their maximum rotation speed. The A320 series have RATs but the 737s ( all series ) don't since they remain manually-flyable without electrical power.