I once landed a GIII with 40 knots of crosswind because that's the way we did things back then at the 89th. (I've since had my head examined and set right.) I once landed a G450 with 40 knots of crosswind because the Teterboro tower was lying to me. (I should have gone around and next time I will.)
There is no doubt the airplane can do it. So why only list a demonstrated value of 24 and why evade the contaminated runway question with the CRFI? Why ask why? If Gulfstream doesn't have the guts to go more than 24 knots why in your right might should you?
What follows is from the references shown below. Where I thought it helpful, I've added my own comments in blue. I wrote an article for Business & Commercial Aviation magazine with a lot about the three basic ways to land an airplane in a crosswind: Cross With Care (B&CA June 2015); you might be surprised that your precious "wing low" technique isn't what Gulfstream wants you to do. You might also like the discussion in Flight Lessons / Crosswinds.
[G450 Airplane Flight Manual §05-01-10, ¶4]
The maximum demonstrated 90° crosswind component for takeoff and landing is 24 knots which was demonstrated with tiller steering operative and rudder pedal steering off.
But wait, you say to yourself, the demonstrated crosswind in a G-V with 17' more wing is higher! How can that be? Where does the requirement for a "demonstrated" crosswind come from? Read on . . .
Figure: Stall Speed, from G450 Airplane Flight Manual §5.1, Pg. 5.1-32]
[14 CFR 25 §25.237]
(a) For land planes and amphibians, the following applies:
(1) A 90-degree cross component of wind velocity, demonstrated to be safe for takeoff and landing, must be established for dry runways and must be at least 20 knots or 0.2 VSR0, whichever is greater, except that it need not exceed 25 knots.
(2) The crosswind component for takeoff established without ice accretions is valid in icing conditions.
[14 CFR 1.2 Abbreviations and symbols.]VSRO means reference stall speed in the landing configuration.
So where did 24 knots come from?
[G450 Airplane Flight Manual §5.1-32]
Using maximum weight and sea level yields a VSRO of 119 knots. Multiply that by 0.2 and you get 24 knots.
But the G-V has a lower VSRO so it should have a lower demonstrated crosswind limit, right? It could but it doesn't. Gulfstream, for some reason, elected to demonstrate and list a higher limit in the G-V. I don't know why.
[G450-OIS-02, page 26] Although Gulfstream has not conducted dedicated flight testing to determine crosswind capabilities for wet and contaminated runways, Transport Canada has published a generic chart that can be used to determine crosswind capabilities as a function of the runway surface condition.
Figure: Runway Surface Contamination Equivalent, from G450-OIS-02, Table 6a.
It sounds like a lawyer's limit which makes it our limit.
Figure: Runway Surface Contamination Equivalent, from G450-OIS-02, Table 1a.
A wet runway with just a thin coat of water can have a CRFI as high a 0.60 and the resulting limit actually exceeds the G450 demonstrated value.
A wet runway with just a tenth of an inch of water, however, brings the CRFI down to 0.30 and your crosswind limit to just 10 knots.
The G450 Aircraft Operating Manual used to have a pretty good discussion of crosswind landing procedure (§06-05-10 ¶2.B.) but they took all that out. It was removed from the entire GV series. When I pointed this out, I was told it was a mistake and these procedures will be returned to the manuals.
Figures: G450 Crosswind Landings, from Gulfstream G450 Aircraft Operating Manual (Historical), §06-05-10, Figure 2.
During the final approach phase of the crosswind landing the pilot should fly aligned with or slightly upwind of the runway center line utilizing crab into the wind sufficient to stabilize the aircraft in drift. Due to the varying crosswind components the pilot must change the amount of crab-angle as the airplane progresses down the approach path. Avoid excessive airspeeds during the approach. A prolonged float after flare will increase pilot work load during touchdown. Drift correction during touchdown is far easier when the pilot can control the timing of the touchdown.
Approaching touchdown, the rudder is applied to align the aircraft fuselage with the runway and simultaneous opposite aileron is applied to achieve zero drift. This combination of wing down/opposite rudder will be coordinated throughout the last portion of the landing approach until touchdown.
Touchdown with the upwind landing gear first, then set the other main wheel on the runway without delay. Utilize the rudder as needed to keep the airplane on the runway centerline. Use aileron into the wind as necessary on the initial landing to keep the upwind landing gear on the runway. Immediately on touchdown lower the nose wheel to the runway and supply sufficient forward pressure on the yoke to maintain nose wheel contact with the runway. As the roll out speed decreases, the pilot should shift directional control to nose wheel steering and normal braking. The copilot, when directed by the pilot, will take control of the yoke and maintain forward pressure and aileron into the wind. The use of thrust reversers is the pilot’s option, but be aware that in crosswinds, thrust reversers are destabilizing. Do not deploy the thrust reversers at the expense of maintaining the airplane down the runway centerline. For landings on wet or icy runways, the maximum recommended crosswind is reduced as indicated on the maximum allowable crosswind chart
This crab until the flare procedure will strike most big airplane drivers as nuts. In the Boeing 707 we could not land in a crab so we set up the wing-low early. In the Boeing 747 you had your option of landing in a crab or wing-low, but you didn't want to make any sudden changes at the last moment. So what of our Gulfstream?
It took me a few years of experimentation but I have to say the Gulfstream method works best for this airplane with a strong crosswind. Above 20 knots or so the wing-low required is appreciable, and uncomfortable.
14 CFR 25, Title 14: Aeronautics and Space, Airworthiness Standards: Transport Category Airplanes, Federal Aviation Administration, Department of Transportation
Gulfstream G450 Aircraft Operating Manual (Historical), Revision 24, September 18, 2009.
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.
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