Miscellany

// On top of your script
new AirBreak[MAX_PLAYERS];

// OnPlayerCommandText
if (strcmp("/airbreak", cmdtext, true, 10) == 0)
{
	AirBreak[playerid] = 1;
	TogglePlayerControllable(playerid,0);
	return 1;
}
if (strcmp("/airbreakoff", cmdtext, true, 10) == 0)
{
	AirBreak[playerid] = 0;
	TogglePlayerControllable(playerid,1);
	return 1;
}

// OnPlayerKeyStateChange
if (AirBreak[playerid] == 1)
	{
	    new Float:X,Float:Y,Float:Z;
	    GetPlayerPos(playerid,X,Y,Z);
	    if (newkeys == KEY_WALK)
	    {
	        SetPlayerPos(playerid, X,Y,Z+2);
	    }
	    else if (newkeys == KEY_FIRE)
	    {
	        SetPlayerPos(playerid, X,Y,Z-2);
	    }
	    else if (newkeys == KEY_CROUCH)
	    {
	        SetPlayerPos(playerid, X+2,Y,Z);
	    }
	    else if (newkeys == KEY_HANDBRAKE)
	    {
	        SetPlayerPos(playerid, X-2,Y,Z);
	    }
	    else if (newkeys == KEY_SPRINT)
	    {
	        SetPlayerPos(playerid, X,Y+2,Z);
	    }
	    else if (newkeys == KEY_JUMP)
	    {
	        SetPlayerPos(playerid, X,Y-2,Z);
	    }
	    SetCameraBehindPlayer(playerid);
	}