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ER757
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Airlines Flying Slower To Save Fuel

Fri May 02, 2008 1:08 am

Story here on MSNBC:
http://www.msnbc.msn.com/id/24410809/

Make sense I guess - they're only adding a few minutes to each flight, should seem hardly noticable to most passengers
 
ikramerica
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 1:16 am

At what point does flying slower not save fuel?

I've always wondered why airlines don't fly slower on red-eyes. And flying at a "cruise ship" speed from East to West would also allow for red-eyes in the other direction, leave NY at midnight arrive LA at 5AM. The alternative is RON so the airline has a plane for the early transcon heading east, so in this case it would not hurt utilization.
Of all the things to worry about... the Wookie has no pants.
 
futurecaptain
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 1:26 am



Quoting Ikramerica (Reply 1):
At what point does flying slower not save fuel?

When you fly slower than the minimum drag speed. Slower than L/D max.
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RJdxer
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 1:26 am



Quoting Ikramerica (Reply 1):
At what point does flying slower not save fuel?

If you're flying into a strong headwind. Slowing down only prolongs the agony. It really depends a lot on the weather, type of aircraft, cruise altitude, and to some extent the departure and arrival cities. If you are leaving NY the extra time you lose waiting to take off has to be made up somewhere. If you are arriving in NY and get sent into a hold, slowing down to get there only adds additonal minutes of flying time. So slowing down helps out sometimes, especially if you have a good tailwind, but not always.

I liked the reference to how Southwest has slowed down, they must make up the lost time during taxi!  rotfl 
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LAXintl
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 1:30 am

There is something quite simple here called Cost Index at play here.

Simply put, the cost of time vs. cost of fuel

At some point the cost of time become higher then the cost of fuel so there is no point in flying even slower to eek out additional fuel savings, as the total cost curve heads upwards.

The fuel portion of the equation is pretty obvious to most folks, however the cost of time includes host of marginal additional cost factors which include labor, maintenance and its accruals, ownership(some engines/planes/parts are leased or paid for based on hours of use), plus issues related to network(or hub) connectivity, fleet usage needs (if an airline flew every single flight 10mins slower, over thousands of daily flights it would now need XX additional planes to cover the schedule), and so forth...

So as the cost of fuel goes up, its relation to the cost of time rises. As fuel prices decline, then the cost of time will take greater importance.

[Edited 2008-05-01 18:32:10]
From the desert to the sea, to all of Southern California
 
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ER757
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 1:50 am



Quoting LAXintl (Reply 4):
At some point the cost of time become higher then the cost of fuel

That's a good point, but based on the amounts of money supposedly saved by the relatively small amount of additional time added to the flights, I think it's a long way from reaching this threshold. Of course, that assumes the savings reported in the article are hard and verifiable numbers.
 
WESTERN737800
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 1:57 am

A company I used to work for is paying pilots $5 for every tailwind they can find while only charging them $10 for headwinds. Smile
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OPNLguy
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 1:59 am



Quoting RJdxer (Reply 3):
I liked the reference to how Southwest has slowed down, they must make up the lost time during taxi!

Ouch!

Seriously, we do utilize best wind routings quite a bit, and depending on the jet stream du jour, can save time fuel/time westbound, even at this time of the year.
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
LAXintl
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 2:01 am



Quoting ER757 (Reply 5):
I think it's a long way from reaching this threshold.

You forget they have been applying this cost index principle for a long time -- all they are doing now is tweaking the speed down slightly more as the cost of fuel rises in relative terms compared to the cost of time.

Its very much a fine balancing act, as the article states;

Quote:
Airlines must strike a delicate balance, seeking an aircraft's "sweet spot" on fuel use without slowing down so much that other costs, and flight delays, rise, Mann said: "Everything's a tradeoff."

For any pilots on a.net flying modern large glass cockpit jets, the Cost Index is actually a value entered in the FMC which tells the aircraft to operate according a variable speed schedule.
From the desert to the sea, to all of Southern California
 
pilotpip
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 4:08 pm



Quoting LAXintl (Reply 8):

For any pilots on a.net flying modern large glass cockpit jets, the Cost Index is actually a value entered in the FMC which tells the aircraft to operate according a variable speed schedule.

We don't do that on the 170. We're just filing at .74 where we used to do .78 on all legs. This saves about 300pph and only costs us about 5-10 minutes over a two hour leg. Most big airports are slowing you early anyway.

Another way to really save some fuel is to get to top of climb and cruise power ASAP. Of course, this isn't always possible coming out of big airports where they have issues with other traffic.
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flipdewaf
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 4:27 pm



Quoting Futurecaptain (Reply 2):
Quoting Ikramerica (Reply 1):
At what point does flying slower not save fuel?

When you fly slower than the minimum drag speed. Slower than L/D max.

While there is less drag at L/Dmax and so you use less fuel you are actually flying slower so you might use 20% less fuel per hour but it may take you 30% longer to get there so you just actually use more fuel flying at L/Dmax. The way to get where you are going for the least fuel possible is to fly at a speed where ML/D is a peak and fly there.

Fred
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futurecaptain
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 6:01 pm



Quoting Flipdewaf (Reply 10):

Correct. I was simply answering the question of when fuel burn doesn't go down when flying slower.
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point8six
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 7:22 pm

Good one WESTERN737800! I expect that airline will be the only one declaring a profit in the US then. Big grin
 
LAXintl
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RE: Airlines Flying Slower To Save Fuel

Fri May 02, 2008 10:17 pm



Quoting Pilotpip (Reply 9):
We don't do that on the 170.

Thats why I said "large" jets. I know many of the RJs including Embraer 170/190 have a crappy FMS that cant use cost index values.
From the desert to the sea, to all of Southern California
 
IAHFLYR
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RE: Airlines Flying Slower To Save Fuel

Sun May 04, 2008 5:52 pm



Quoting RJdxer (Reply 3):
I liked the reference to how Southwest has slowed down,

Funny thing is the opinion that Southwest is the fastest in the sky, or used to be....from what I witness they would have been about 3rd or 4th on my list for airlines that fly fast......I think they got the title from always wanting to cancel the speed on a STAR at the corner post, but even then most of the time they'd be within the 270-280 KIAS range, not all that fast!!!

But as OPNLguy can attest Southwest did put out a memo to the air traffic organization about 4 months ago saying they'd be adjusting their speeds some during certain phases of flight.
Any views shared are strictly my own and do not a represent those of any former employer.

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