Thanks Uli. My Turkish 'bible' has this as one of the three THK-10's built, differing from the earler THK-5 by having square, larger windows. The MKEK-5 was a project to further modernise the THK-5, but according to the book, the project was abandoned.
(Türk Uçak Üretimi by Tuncay Deniz)
Here's another twin - Walter posted it over ten years ago, and I hope he will forgive me for 'borrowing' it again. There seems to be very little information about it, so maybe Uli, Robert or Chris could enlarge ?