Many people are pretty much there with these guesses. It's a GAPCI, designed and built in Bahrain in 1971 to satisfy the CAA's requirement that Gulf Aviation's new Skyvans should have some way to communicate information and instructions from the single pilot to the passengers, there being no cabin staff or PA system. The system worked well; the pilot used a pad (GA Form GAPCI 1046.A.Eng) to write down the message, and would then rap on the door behind him. A passenger would then open the door, the pilot would poke the GAPCI at him, he would take the message and pass it round.
All sorts of useful messages were sent; "We are halfway, landing in 30 minutes", "I know 1 engine has stopped, but the other one should hold out", "Both engines have stopped. Don your lifejackets", "Please stop making curry on the primus, the smell is bad", and so on. Many pilots learned Arabic to ensure full comprehension among their passengers.
Its use was discontinued in 1974, either because a steward began to be carried on most flights, or a PA was fitted. My records don't show which.
PS
Parabellum: It could never have been a hook earthing device...it hasn't got the long piece of wire that you gave the newest recruit (or any officer) to hold while you stood on the load and touched the hook with the other end; it was a kind of rite of passage really, usually not fatal.
I'm wondering if you remember the GAPCI, though. (GA Pilot - Cabin Interface, in case you had forgotten.)
Last edited by old,not bold; 13th Dec 2008 at 16:03.