No, what he said was he would have more headroom "under the Class A
airspace." Since the Class A would start when his altimeter reads
18'000ft (when set to 2992) regardless of what his GPS says, he would
not have any more room. He could very well be higher than 18,000ft
above MSL, which is a different thing altogether, and is really what
we care about for final glides, etc.

It's been a long time since I've done any IFR aviating, guess I need
to get back into the AIM again!

Kirk

"Marc Ramsey" wrote in message news:LcEPa.231 What he is saying that when the pressure altitude is reading lower than the GPS
altitude (which it does on typical summer soaring days), you get some extra
headroom on things like final glide, as you are that much higher above the
terrain. I've seen quite a few days when the altimeter, set to a nearby
reporting station, reads just under 18,000 feet, while the GPS altitude is
closer to 19,000 feet.

BTW, the floor of Class A airspace is 18,000 feet MSL, not FL180...

Marc