Gravel Kit's and soft ground Ops
Early in the 70's the Essendon based Reg 203 Op in those days was "BizJets" and they started with a Falcon 20 which was modified for Gravel Ops, different tyres, larger diameter, not sure now, long time ago
It's my understanding and I stand corrected; the Hawker 700/800/900's are all gravel approved ex the factory, all you require is the AFM supplement. Antennae protection strips etc
For the Citation 500/550 Citation I and Citation II, a gravel certification was possible with a nose wheel 'spin up' kit, these were also approved for 'soft ground' Ops, ie:Grass etc. It's all to do with the MLG undercarriage oleo leg fairing not striking the ground.
The Citation 560 Encore has Gravel kit available, but soft ground Ops not permitted due oleo leg fairing clearance. It's all in the AFM supplement.
I don't know of any gravel kit that is approved for wet runways
There is a kit available for the C525 series of CJ jets, there is one in PNG with a kit fitted, dry runway and gravel only, no grass.
T/O and landing charts are factored for gravel use. Some models have a reduced T/O mass.
Thrust reversers not to be used for gravel Ops.
Again, I stand corrected on what I have said, times change, memory becomes blurred over 40 years
I hope the RFDS enjoy their PC-24's, good luck to them. IMHO not the smartest choice but time will tell.
Costly for them to operate. Williams engines on the TAP Elite/Gold 'power by the hour' programmes require compressor rinse after every days flight in Coastal environments. Pilot's can di it, but it does tie up a lot of staff.