Tommoutrie
Yes, the modern Hawker 125 series is descended from the Dominie albeit with more powerful fan engines as opposed to the original constant thrust, variable noise Viper turbojets.
There seems to be confusion between second segment and noise abatement climb profiles and what they are trying to achieve. 1500' agl is the end of the second segment climb and is the point at which you will accelerate, retract flap if used, and accelerate to en-route climb speed, having had an engine fail at V1. The calculation allows for the aircraft in this condition, if flown straight ahead at V2 to 1500', to clear all obstacles to that point. If this is not possible then an emergency turn procedure is devised. At least, that is how our performance programme works, and it will give profiles for both flap 15 and flap 0.
Noise abatement profiles assume both engines operating and are designed to leave as much noise in the vicinity of the airport as possible with as much height gained over distance travelled as possible (vx) prior to cleaning up and reducing power to a level sufficient to give an acceptable rate of climb or height in time (vy) with minimum noise nuisance.The goal of a noise abatement climb is to reduce noise whereas the goal of second segment climb is to clear obstacles.
Now consider a standard departure where both engines function correctly. If the performance calculation shows that you could clear all obstacles to1500'agl if the aircraft is flown correctly with an engine out at V1 with flap 0 or flap 15, then all that is required to stay safe with two engines operating is a sufficient rate of climb to satisfy the requirements of the SID. This is generally less than a 5% gradient which is the same as a standard ILS, or 750'pm at 150kts. The best two engine performance for our aircraft is achieved by initially pitching to 12degrees and retracting flap and reducing power at the calculated flap retract speed, which is usually reached by 400'agl. Leaving flap extended beyond that speed will result in unnecessary drag and a performance penalty. I generally accelerate after flap retraction to 180-200kts for the initial turn on the SID and control rate of climb with power to avoid exceeding 1000'pm in the final 1000' to level-off (our SOP). This profile exceeds the obstacle clearance requirements of a standard SID four-fold on an ISA day at sea level with climb power set!
Clearly, all departures are briefed and profiles adjusted to suit conditions, terrain and airport requirements. I can't think of any scenario, however, when it is advantageous to leave flap at take-off setting past calculated flap retract speed on our aircraft with both engines operating.
Sorry for the ramble, I really haven't been drinking!
AP