A Hooker harness is a secondary harness which is just a lapstrap and which goes over the primary harness. It's a 'belt over the braces' as well as being a very strong negative g restraint. It has a ratchet system to tighten and there is no give in it at all. They tend to be fitted to aerobatic aircraft such as Extras. This must mean that on this Tuc, the seat has been deactivated and they have fitted extra straps.