Intruder,
I don't know what or where you fly
I referenced the 737, that's what I fly. Where is irrelevant, we use near standard Boeing procedures.
but nobody I know tries to retract flaps in "an immediate turn after take-off." In fact, the general rule in airline operations is NO turn until above 400' AGL!
An immediate turn after takeoff is generally defined as normally a turn at 400'. Abnormally is another question. I presume we are talking about normal ops here.
Further, flap retraction after takeoff is done...DURING ACCELERATION.
As I wrote.
If the pilot adheres to the flap retraction schedule, adequate stall and gust margin is available to 40+ deg of bank
What type are you referring to? For the 737 it isn't a gust margin or a stall margin, it is a margin to stick shaker and "adequate" is not 40º+, it is 15º + 15º overshoot. "Full" is defined as 25º + 15º overshoot.
There is nothing unsafe about retracting flaps in a turn, as long as the design parameters are met.
For the 737, "full" manoeuvre capability is only "guaranteed" for takeoff flap and V2+15 or the flap setting and the associated flap manoeuvring speed. That means that between V2+15 (flap 5) and say 190kts (flap 1) it may be assumed to be less than "full" manoeuvring capability. The word "guaranteed" is only used in association with the "flap manoeuvre speed" and not the EFIS speed tape "minimum manoeuvre speed" amber band. The amber band is calculated differently. However, Boeing does say that the amber band and the flap manoeuvring speeds are independent means of assuring "full" manoeuvring capability. Which is a slight contradiction to what is written elsewhere. You decide what is safe. For me I will continue follow the Boeing recommended practice for an immediate turn which is unambiguous.