Wedge you can download a zip file with an example mission and everything you need from
hereJust unzip it into you're my Documents/ArmA/MPMissions directory.
I've written it so that the harrier spawns low on fuel and without bombs. Just pull up alongside the tent in front of you and after 5 seconds your plane should refuel and reload with an accompanying message.
Try parking the Hummer next to the tent but you'll find that the reload trigger is only activated by the harrier.
You'll also find when the aircraft respawns that its low on fuel and has no bombs so just park it next to the tent again and it will reload.
I've deliberately set the respawn time for both players and aircraft low so that you don't have to wait long for testing. You could also lengthen the time it takes to reload and refuel by making the "timeout" longer in the trigger.
It also seems to take a few seconds for the option to board the respawned harrier to appear, don't worry though just keep trying and after 20 sec or so it'll let you get in as the pilot.