You should never taxi, takeoff, or land the airplane without the brakes system page up someplace where both pilots can see it, preferably as near to the center of the airplane as possible to minimize head movement. And you should have the following procedure down flawlessly, by memory, without hesitation
If brake failure is suspected:
If brake pedals still not effective:
Step 1 overcomes a failed left hydraulic system and failed automatic switching of the PTU and Aux hydraulic pumps. If that doesn't do it, step 2 disables the anti-skid and removes the digital anti-skid control unit as a possible problem. If that doesn't do it, it also changes the scale on your brakes system page so you can move on to the final step.
A word about that parking/emergency brake handle. You can use your thumb as a leverage point to smoothly pull the handle. Just pull it slowly until you see a reaction on the brake pressure scale. Once you achieve either a noticeable feel in the deceleration of the aircraft or 400 psi, keep the handle where it is. As the brakes heat up that amount of pressure will become more and more effective. You may not need anything else.
The brake pedals don't work.
You may have arrived at this point after several hydraulic failure checklists and have prepared yourself for the task at hand. Or you may have found out after a noneventful landing with your right hand full of reverse levers and most of the runway behind you. Either way the response is the same.
[G450 AFM 4-18-40]
CAUTION: ANTI-SKID PROTECTION IS NOT AVAILABLE WHEN USING THE PARK / EMERG BRAKE SYSTEM. USE OF THE PARK / EMERG BRAKE SYSTEM WHILE THE AIRPLANE IS MOVING IS STRICTLY AN EMERGENCY PROCEDURE. CAUTION SHOULD BE USED NOT TO EXTEND THE HANDLE BEYOND THE POSITION WHERE BRAKING IS FIRST FELT (1/4 TO 1/2 INCH). AS AIRPLANE DECELERATES, REDUCING EMERGENCY BRAKE PRESSURE MAY BE NECESSARY TO PREVENT SKIDDING, ABRUPT STOPPING OR BLOWN TIRES.
NOTE: When the ANTI-SKID switch is selected to OFF, the pressure scales depicted on the Brakes system page change to provide improved monitoring of brake application pressures.
CAUTION: DO NOT EXCEED 400 PSI INDICATED BRAKE PRESSURE WHEN APPLYING PARK / EMERG BRAKE.