A320: Questions for the Pros

As I am digging deeper and deeper into the workings of A320, I have two questions that I would like to have answered:

1) Why are the PACKs turned off just prior to take-off? Is it a thrust issue? That would seem unlikely as the engines should produce more than enough thrust -- or in other words, the PACKs should not take such a toll on thrust that it would become an issue

2) When setting up the FMGC for both departures and approaches, how do you determine what NAVAIDs to specify in the FMGC? From what I can gather, sometimes you will put the ILS in both channels, sometimes not. Any clarifiaction on that would be greatly appreciated.

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Originally Posted by PittsburghLever

1) Why are the PACKs turned off just prior to take-off? Is it a thrust issue? That would seem unlikely as the engines should produce more than enough thrust -- or in other words, the PACKs should not take such a toll on thrust that it would become an issue

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I can answer this one based on experience but not of the A320.
2 reasons
1. To have all available air for combustion to avoid a compressor stall on takeoff.
2. Prevent engine odors in the cockpit & cabin until stabilization at higher RPM's.

1) You have a payload penalty for taking off with Packs on... Remember you are drawing power from the Engines to run the packs... Also it is better with take with FUll power in small contaminated runways...

2) The Ils is automatically tuned when you set on the MCDU the type of arrival you are setting up... So the Ils automatically gets tuned on both radios I have never seen it different.

Regards,
Roberto

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Originally Posted by dodiano

2) The Ils is automatically tuned when you set on the MCDU the type of arrival you are setting up... So the Ils automatically gets tuned on both radios I have never seen it different.

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I could have sworn I saw a cockpit video where an approach (to EHAM) where the radios were tuned to SPL as opposed to the ILS frequency (obviously, I cannot tell if the video cut out the segment where the radios were retuned.

Also, I seem to remember seeing that the radios are also tuned via the FMGS on departure. If that is the case, how do you know what to tune to, and when does the manual tuning revert to automatic tuning? Is that when there is a phase change in the flight plan?

The ILS and VOR's are independant... Ils is automatically tuned while Radio Navs as VOR's can be tuned manually by inserting them in the RAD NAV page of the MCDU... So your ILS where tuned but your radios where tuned to the VOR... You set them depending on how you are going to fly your departure to X-check Radial information in case of a Failure of your ND or MCDU you still have a Radio aid to guide you out, like a conventional plane.
When you cross 10,000 we clear the RAD NAVS and it goes back to automatic tuning.

Regards,

Roberto