Fuel efficient descent

[Tandemrotor]

Could anybody please give me a FACTUAL answer to this question please:

How much fuel is likely to be saved in a descent from approx FL350, by adopting a 'thrust levers closed' descent, ie as per FMC (or FMGC), rather than a managed descent in V/S or FPA at approx 1000' per min, starting 10 to 20 miles earlier?

Interested really in A320 answers.

[quid]

I was waiting for a 320 pilot to step in, but you'll have to settle for an old Jurrasic pilot's opinion.

Anytime you are off your optimum altitude, it will cost you some fuel. If you keep that 1000 fpm to 10,000', it will take 25 minutes to get from FL350 to 10,000. That'll take a heck of a lot of fuel. But I think you are asking if a "gentle" push over 10-20 miles earlier will cost any. Sure, it will cost a little, but not enough to make a difference. I doubt if it will amount to 200-300 lbs.

Configuring early will cost more, or adding 5 miles or so for spacing at pattern altitude.

But why leave optimum before you have to?

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[Tandemrotor]

Thanks quid

That's pretty much as I thought.

Cheers

[jtr]

On the 330 some (myself included) will push for managed descent (thus giving v/s-1000 initially) 2 or 3 miles before calculated descent point. Giving smoother push over, and smaller power/pressurisation variations. Difference in fuel? So insignificant that anyone questioning it probably needs to get out a tad more. Have looked at the fuel estimate figures for the next WPT pre, and post maneouvre, never shows any variance, for what thats worth.