Cough..
Its great that its in the commercial type you previously flew - which type was it?
An all engines flap retraction height is not in the Challenger manual, its not in the XLS manual, its not in the Lineage manual, its not in the Phenom manual, its not in the Citationjet manual, its not in the Hawker 125 series manual, and I don't understand what scares you. I've never seen an all engines flap retraction height in any flight manual ever. I've never seen a flap retraction height at all - only acceleration altitudes. If you don't need the level platform then no platform exists.
The obstacle clearance is irrelevent to the arguement because the take off performance calculation is exactly the same - the obstacle clearance and net take off flight path calculation is based on OEI at V1 so nothing has changed. What I think is misunderstood is the effect of retracting the flaps as per the manufacturers AFM and performance data. In fact, I'll go further. If you don't do it the way the manufacturer says, you are on unknown ground. What type do you fly and what departure profile do you use for a noise abatement and non noise departure? Lets see how compliant it is.
Explain exactly what scares you. I do the same perf calcs as anyone else - almost certainly a lot more as I cross check the FGP data. I then fly the aircraft as the flight manual states. Does it scare you that I don't simply copy what I learned on an airliner and apply it to a business jet? Does it scare you that I'm doing exactly what it says in the manual?
I've kind of had enough of tribal knowledge ruling this thread. Post the legislation that imposes a flap retraction height in the case of an all engines operating take off. Post the data which shows a flap retraction height as opposed to an acceleration altitude exists at all. Post any AFM procedure which states that exceeding V2 by 30, 40, 50 knots is acceptable practice and has no effect on aircraft performance. You need 1.25 V2 to have the flaps retracted on a challenger - thats what the speed to fly table gives you. Thats not even V2+20 so at V2+20 you have plenty of handling margin and thats probably why the speed was chosen. What you definitely dont have is any idea how much you have degraded the flight path by if you dont raise the flap.
bizarre that you all think this is sensible but don't have any data or any statements in the AFM that show it!
Last edited by tommoutrie; 27th Nov 2012 at 20:40.