Copyright Robert Hart
Flying Alice has led me to write a sequence of articles that originally I posted to some gliding mailing lists. However, I had interest in these from elsewhere and so I decided to create a web site for Alice, her photos and her experiences teaching me to fly cross country and in competitions.
(A number of these articles have been published in the gliding press.)
In Australian aviation, altitude is measured in feet. For those visitors from metric countries, 1000ft is about 300m
It is the standard in Australia to talk about altitude above mean sea level. This is known as QNH altitude (or just qnh). For glider pilots, however, it is also very important to know one's altitude above ground level (agl). The reason for this is that it is our height above ground that determines how far we can fly before we hit the ground. It is this altitude that determines when a glider pilot must stop flying cross country and find a paddock to land in. I use 2000 ft agl as my 'break off' height - but Alice is still some time away from having to land. We use that time to finalise our landing plans whilst searching for lift to take us back up to where we can resume our cross country flying.
So - in Alice's articles you will generally find altitude referred to as 7000ft or 7,000 ft qnh - which means the height above mean sea level. You will also find I refer to altitude above ground level - such as 3000ft agl.
Altitude is also important in one other respect. As you climb, the air pressure decreases and so the amount of oxygen avalable in a lungful of air decreases. Low levels of oxygen create all sorts of problems in terms of poor judgement (very dangerous when flying) and eventual loss of consciousness (very dangerous for a pilot).
In Australia, a glider pilot is not allowed above 10,000ft qnh without an approved oxygen system.
In Queensland, days when one can soar to over 10,000ft are rare. Despite this, we have fitted an oxygen system to Alice for a couple of reasons.
First of all, spending a long time above 5000 ft can be very fatiguing (as I experienced on my 750km flight in Dec 2003), using oxygen above 5000ft significantly reduces this fatigue.
Secondly, Alice goes away to fly in competitions in New South Wales and South Australia. During the summer, thermals there regularly go above 10,000ft - and to be competitive, one must be able to use them.
Last edited on 17 March 2006