Quote:
Originally Posted by =c=
It would be great if you could enter the pressure and have the GPS do a conversion to give you pressure alt using the lapse rate or via a built in static port like my watch.
Is there a reason why folks wouldnt want pressure alt?
|
There are a bunch of issues here:
1) Static in a cockpit is generally hundreds of feet off from the right altitude, due to the airflow around the aircraft. It can be high or low depending on the plane, and changes with airspeed. This is why planes have external static ports.
2) Static in the cockpit doesn't work in pressurized planes
3) GPS altitude isn't wrong. In fact, on a perfectly standard day, pressure altitude and GPS altitude are the same. Personally, I've never seen a standard day though.
If we had GPS when we started flying, we would all just fly GPS altitude. We use pressure altitude because it's what we have, and when everyone uses the same baro setting, if you are in the same place, you are using the same altitude reference. But that works because the altimeter doesn't know or care if the day is standard or not, it just knows the pressure where you are right now. So there's no way to model this in GPS, since the deviation from the ground station is totally unknown without a pressure sensor.
There is a great thread here on VAF on GPS vs Pressure altitude.
http://www.vansairforce.com/communit...ad.php?t=89446
So to sum it up, yes, people would want pressure altitude, but there is no way to do that in a certified plane without hooking to the static system, which would require the D2 to be certified.