400 feet is not mentioned in the AFM of any type flown by my company. I'm not at all sure that it is best practice - I think its tribal knowledge and promulgated by training organisations on types for which its not appropriate. Its a bad place for to use as a trigger for retracting the flaps precisely because its a common place for things to start happening - turning on a SID for instance, or getting told on the radio to contact another frequency. A height check is just not logical for moving flaps - the wing configuration is only dependent on speed so what is the logic? Its utter rubbish to say "you might move the wrong lever" otherwise it would be mandated that you leave the gear down and you can't go around under 400 feet. You degrade the climb performance of the aircraft in both the all engines operating and one engine inoperative conditions if you fail to retract the flaps once you are through the retraction speed (otherwise what is the logic in retracting them at all?).
The chap with the Hawker has the data - compare a typical take off with flap and without. Look at the OEI net take off climb chart for the same conditions. Which has the better gradient? If its clean, take off clean. If you cant take off clean because of runway limitations, why don't you raise the flap at V2+10 and benefit from the improved climb gradient at that point? What is the logic of climbing against drag? As soon as the flaps start to travel the aircraft is trending from the net gradient flapped to the net gradient clean so what stops you doing it? I'm getting a Hawker manual from a colleague today so I can see if its true that Hawker mandate that you can't do this in the AFM.
The argument about needing "maneuvering margin" when clean is also bogus. The minimum clean wing speed on a Challenger is 1.25Vs. At low weights this is V2+4, at high weights its V2+7. However, the manufacturer says flaps up at V2+20 - the margin is already there which is why they set that speed.
So far nobody has posted a regulation and nobody has posted an AFM reference which states this (I take Cough's comments on the Boeing and the Airbus because I have seen 400 feet and 1000 feet referred to in training notes but I very much doubt any operator of an airliner would exceed the minimum flap retraction speeds by 20 to 50 knots in the way that business jets routinely do).
Please, somebody, post the rule which prevents the flap retraction before 400 feet and, failing that, the section of the AFM which prevents the flap retraction during an all engines operating take off when passing V2+X. If that bit is hard to find, please explain why we bother to take the flaps up at 1500 feet if the climb is better with flap?
ta