I had the same thing happen to me the other day... I had a 10X5 Master Airscrew on an O.S. 40 AL. The outside air temp was in the low 30's, I started it, adjust the needle valve to high RPM's and then backed off a quarter turn (like the manual says) ... yet the prop came loose on take-off (Mostly minor dammage but the wing will have to be replaced). This is the first Airscrew I've used, I usually fly APC or wooden props... and I've never had a probelm with a prop coming loose before yesterday.