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Old 29th November 2008, 01:43 PM
Will T Will T is offline
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Join Date: Mar 2008
Location: Sydney, Australia
Posts: 175
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Thanks guys!

And sorry, I should've explained the 'Packs Off' procedure. Basically, pressurisation and air conditioning (cooling and drying) of the cabin air is accomplished by three separate and independent 'Packs'.

Hot, high pressure bleed air extracted from the compressors of each engine is sent to the packs where it is cooled (via a heat exchanger fed from those ducts you see near the wing root) and dried (centrifugally) and then fed to the cabin air conditioning system. Outflow valves at the rear of the aeroplane allow a certain amount of this pack air to escape overboard at a controlled rate, so that the cabin doesn't end up over-pressurising. By controlling the rate at which the air is allowed to escape overboard, the pressurisation system can therefore control the cabin altitude.

Anyway, when the engines are rotating at their maximum speed (ie. at takeoff), a certain amount of air flowing through them is diverted to run the packs, rather than providing useful thrust for takeoff. So, a 'Packs Off' procedure involves turning all three packs off for the takeoff roll and initial climb, and so allowing all of the engine airflow to be used for thrust. The packs are then switched on by 3000ft AGL. On the 744, we only really use this procedure when our normal, 'Packs On' takeoff configuration doesn't provide enough thrust to lift the payload. Generally, this is the case at JNB where the high airport altitude (low density air) and high airport temperatures conspire to limit many of our takeoffs.

Mont, unfortunately I didn't keep our nav log (this has to go to the QF archival department ), but I was surprised at just how quickly we got down there. We also had a roaring tailwind (courtesy of a jetstream) all the way down there, in the range 100-130kt. Plugging a groundspeed of 610kts into Great Circle mapper gives an ETI of around 4 hours from YSSY to S63, and that seems about right.

Obviously hundreds and hundreds of photos were taken. I'll put up a few more ones from the flight deck this afternoon once I've gone through them.
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