Actually, the guy that originally invented the Navaid a/p did come up with an altitude hold. Unfortunately, he didn't document well, and when he died, the info was lost. A couple of people had it, but that was all. Last I asked the new Navaid guys, they were "working on it." Of course that was at least a year ago. -- Bob Ginsberg - Velocity N173BG - Big Ape Gyms