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fuel savings

Old 29th Jul 2004, 06:41
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fuel savings

Last winter in Phoenix our A320 did all the taxi with one engine only. I was astonished to hear the packs going off for the second engine start sequence exactly 45 seconds before TOGA comand.
I heard that one minute time is legal before applying max trust on the CFM however how sad was that little bird taxing assymetrical, how sad we would have be if the second started engine was unprepared for max trust? Is this an efficient fuel safing in USA?
is this approuved elsewhere in the world?
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Old 29th Jul 2004, 07:14
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We never do one engine taxi prior TOGA.

Only sometimes when all codition fits, we shut No1 eng after landing 3 min cool down if reverser has been deployed.

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Old 29th Jul 2004, 09:21
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Many moons ago, the British Midland Viscounts (at LBA) frequently used to start the two inboard engines on stand, taxi off and then crank up the two outboard engines whilst approaching the holding point, something I never recall the BA machines doing in the 70s.

Not that a Viscount is an A320 (although they sound uncannily similar when flying overhead) but there's probably a common reason behind it all.

Any ex-Viscount jockeys care to comment

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Old 29th Jul 2004, 09:53
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Perhaps the packs went off for a packs off takeoff?

A CFM takes about a minute to start and stabilise, so if TOGA was pressed 45 secs after the start sequence had been initiated there would have been a fair bit of thrust asymmetry during the initial acceleration - as well as a thermally 'shocked' engine!
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Old 29th Jul 2004, 11:44
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Caution at all times!

There was the DC 10, operated by a large American company that recommended starting the tail engine just before take off. It seemed to be very sluggish on the climb out.

Fortunately the Manual covered in-flight starting!.

And with Viscounts: I believe it was the old British European that used to shut down two engines on landing to save fuel taxying in.
Unfortunately they changed from the 700 series to the 800 series and one crew still shut down the same engines.

One difference on the two types was the engines that supplied the brake system. Fortunately an RAF building in Malta acted as a standby system.

Personally, I have always been keen on saving fuel but not if it has required War Readiness power to be needed on the remaining engines to make a turn!
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Old 29th Jul 2004, 13:28
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Pack Flow Control Valve
General Information (ref A320 AMM)

Each air conditioning pack has a flow control valve which gives variable flow and shut off control. These valves are electro-pneumatically operated.
They will open when the PACK 1 (2) pushbutton switches are pushed in (the OFF legends go off) if the conditions which follow exist:

the engines are not in a starting sequence,
an ENGINE FIRE pushbutton switch is in the normal position (the light in the pushbutton switch is off),
the DITCHING pushbutton switch 13HL is released (the ON legend is off),
the bleed air pressure is more than the minimum pressure needed to open the flow control valves.

Also from A320 AMM (Engine Auto start)

2. Instructions on performing auto start & starting
3. When the engine idle speed is stable, on the ENG panel 115VU:
Set the ENG/MODE/CRANK/NORM/IGN/START selector switch to NORM.

NOTE: It is recommended that the engine operates at or near idle for a minimum of 2 minutes before you increase to high power. You must move the throttle control lever, slowly, carefully and smoothly when possible.
NOTE: You can use taxi time at or near idle as part of the 2 minute warm-up time

Hope this provides some insight stefanoperer
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Old 29th Jul 2004, 22:01
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Haste makes waste...

Some years ago an airline that I was working for decided to delay starting a wing engine until just before takeoff...fuel savings of course.
This proved to be rather unfortunate one day when a crew decided to attempt takeoff, while the engine was just spooling up...the hot end got very much hotter.

The chief pilot was not amused, and the late starting practice was discontinued, pronto.
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Old 29th Jul 2004, 22:14
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Our Ops specify that T/O will not be attempted until the last engine started has run at least 5 minutes.
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Old 31st Jul 2004, 12:29
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Once, in JFK, B767, after being given start and taxi, we then discovered we were No. 50 in the takeoff. queue. With some landings on the same Rwy we calculated we had at least 80mins taxi to do. We had to shut down an engine otherwise we would have departed with less than minimum fuel. It was the first and last time JFK caught me out, thus. Fuel saving, yes, but out of dire need rather than SOP.

I wonder if such an inefficient ATC procedure/system still exists there? If it does it is a real gas-guzzler. And if it does, Why? Can not some sequencing be done with start clearances, or is to vacate the gate for inbounds?
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