Well you could either make a macro called 'airbrake = SHF c' and then map that to the T9 button or just map the buttons directly to the button ie 'BTN 9 {SHF C}'
I think that should do it, curly brackets make the button carry out both buttons presses or macros together, for instance my HAT1 up position goes a little somethign liek this:
BTN H1U /I /H {Look_Forward Look_Up}
/O /H Look_Forward
With just HAT 1 pressed up you look forward, if you press the S3 button with HAT 1 pressed up it carries out the look forward and look up command (keys KP5 and KP8) which gives you a view just over hte top rim of the cockpit. The macro's for these commands are:
Look_Up = KP5
Look_Forward = KP8