Cartoon: Orthopedic landings, from Chris Manno.
This airplane can make the performance numbers without a lot of fuss, just make sure you fly the 3° glide path on speed with the correct adjustments, cross the threshold at VREF, allow the auto-throttles to auto-retard, and fly the airplane onto the runway. Do not tolerate floating beyond the touchdown zone and do not applaud those grease jobs with four thousand feet of pavement behind you. Educate your fellow pilots and your passengers that the only good landing is one that comes off a controlled approach, touches down on speed and in the touchdown zone. Anyone who greases them on over and over again is doing something wrong.
Everything here is from the references shown below, with a few comments in blue.
The recommended approach speed is VREF plus an additive of half the steady state wind plus all of the gust increment, where the additive is no less than 5 and no greater than 20 knots. In a G450 if you are using just the 5 knots you can fly this in AUTO speeds and the airplane will do just fine for approach and missed approach. In a G550 the missed approach segment can end up being too slow so Gulfstream recommends you bug the appropriate approach speed and select MAN speeds to ensure you don't get too slow on missed approach.
[G450 Airplane Flight Manual §5.11-1] and [G450 Aircraft Operating Manual §13-03-10] Threshold speeds, VREF, for landing distance are shown for all flap settings, with final approach speeds computed as the landing threshold speed plus appropriate speed margins. The final approach speed margin must not be greater than that which can be bled off before the point of crossing the runway threshold. For the G450, a final approach speed margin of 5 KCAS is recommended but not mandatory
[G450 Aircraft Operating Manual §06-05-10] Cross runway threshold at VREF. Retard power levers as necessary for airspeed control, leaving power levers at idle after touchdown. Glide path should allow for a smooth flare into the touchdown zone. At touchdown, the PF will gently lower the nosewheels to the runway and, as necessary, deploy the thrust reversers and apply brakes to slow the aircraft.
You are planning on crossing the threshold at VREF and holding this speed until touchdown unless the runway is contaminated. But aren't you really crossing the threshold at VREF+5 with the auto-throttles engaged? Yes. I've noticed, however, that a normal flare results in a touchdown speed right at VREF. If you fly a proper glide path and VREF + 5, the autothrottles will serve you well and you will touchdown at VREF, see Normal Procedures & Techniques / Autothrottle Landing for the proof.
[G450 Operational Information Supplement OIS-02 pg. 25] and [G450 Performance Handbook pg. PA-5] Establish VREF + VΔ by 50 feet above the runway. The air phase is based on a glide slope of 3 degrees or less at 50 feet and an 8 to 9 knot speed reduction by touchdown. (This air phase performance is substantially different than the AFM Section 5 air phase data for dry and wet runways.) Immediately after touchdown, the nose is lowered and brakes are applied. Ground spoiler deployment is initiated at main gear touchdown by wheel spin-up. If auto ground spoilers are not available, the speed brakes are manually deployed immediately upon touchdown. A second after touchdown, the power levers are moved to the maximum reverse thrust position or the reverse idle position. Maximum reverse thrust is maintained to 80 KCAS. At 80 KCAS, reduce power levers so reverse idle thrust is established by 60 KCAS (reverser doors still extended). Thereafter, reverse idle thrust is maintained on both engines to a complete stop. Computed landing distances on contaminated runways have been increased by 15 percent. Contaminated landing distances determined in this fashion have then been compared to wet factored (dry x 1.92) landing distances presented in AFM Section 5 to ensure that they are never shorter. Finally, contaminated landing distance performance assumes both engines and thrust reversers are operational.
These are contaminated runway procedures, you don't normally plan on touching down at VREF minus 8 to 9 knots!
I can't think of any reasons to land flaps 20° unless the book tells you to. I can think of a few reasons why you shouldn't:
If you find yourself landing with less than full flaps and for some reason the display controller isn't giving you a flap-corrected VREF, you can come up with your own:
[G450 Aircraft Operating Manual §13-03-20] Landing distances based on 3.0° glide path at 50 feet and 6 FPS sink rate at touchdown.
That is more than a firm landing, that is a controlled crash! 6 FPS comes to a touchdown at 360 feet per minute, only half of your rate on ILS glide path. It will be hard to land that hard and not bounce, but that is what the performance numbers are based on.
From experience we know we can outperform the factored landing distance numbers with no trouble and come close to the unfactored number without flying controlled crashes onto the pavement. My G450-specific techniques:
Be sure to visit the following two sections for more:
Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013
Gulfstream G450 Operational Information Supplement, G450-OIS-02, Contaminated Runway Performance, Revision 1, August 3, 2011
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.
Gulfstream G450 Performance Handbook, GAC-AC-G450-OPS-0003, Revision 20, November 30, 2011