[Mayhemxpc]

As stated below, Skymaster models from straight 337 to 337D increased every year with no (or very slight) changes to the airplane. As it was explained to me at RTC, every year, Cessna was able to demonstrate to the FAA, through the proof of time and testing, that the airplane COULD handle more weight. The manuals were changed each year because the increase in gross weight led to decreased performance at that weight.

The O-2. The O-2B was a stock 337A in USAF Gray. MGW=4200. The O-2A was a very modified 337B, with FAA certification at 4300 lbs. BUT these modifications included heavier wing spars, attach points, landing gear and brakes. ALSO the USAF purchase went from 67 to 69. For model year 68, Cessna gave the civilian C337C a 4400 lbs MGW without any changes in airframe or powerplant. (Am I confusing you yet?) SO...although the basic certified weight for the O-2A was 4300 lb, for military use it was 4400 lbs. WAIT! There is more. Up to 4850 could be carried as long as anything over 4400 was jettisonable stores on the wing. If you weren't carrying anything on the pylons, you could take off at 4600 lbs, but you were limited in G-loading and could not land in excess of 4400. Clear? Too bad, there is one more thing. The performance data for the O-2A includes gross take off weights up to 5000 lbs! (Single engine climb is less than 100 fpm, even at sea level.)

Bottom line: FAA says 4300. The Air Force wasn't bound by that and established limits based on their own testing. Real world: I wouldn't worry if I were a little over 4300. The O-2A can handle it.