For a player type? Use this
datablock PlayerData(PlayerNoJet : PlayerStandardArmor)
{
minJetEnergy = 0;
jetEnergyDrain = 0;
[b]canJet = 0;[/b]
uiName = "No-Jet Player";
showEnergyBar = false;
};
The part in the bold is the thing that makes jets not work.