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Old 01-08-2008, 03:00 PM   #1 (permalink)
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Do airline pilots hypermile?

Do airline pilots hypermile?

Or would saving fuel cost too much money overall through lower passenger throughput (due to going slower)?

I would think that an obvious opportunity to save fuel (aside from flying slower) is in the approach to land.

I don't fly often, but have wondered:does a pilot typically make the most of the opportunity to literally glide in toward landing, or do they do the equivalent of what most drivers do: hard on the gas, late on the brakes?

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Old 01-08-2008, 03:11 PM   #2 (permalink)
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I would think their training is centered solely on safety. This would mean doing everything gradually.
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Old 01-08-2008, 03:13 PM   #3 (permalink)
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No "death turns" then? :P

I know we have a couple of pilots here. It'll be interesting to hear about it from them.
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Old 01-08-2008, 03:25 PM   #4 (permalink)
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On comercial jets they don't usually go full speed...that's how they "make up time in the air" if they depart late...I read something recently about some airport opening up new air space to allow planes to approach directly, which reduced the need to circle and therefore fuel use...so I think they try as much as safety allows.
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Old 01-08-2008, 03:46 PM   #5 (permalink)
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Generally the descent is done at idle power (basically gliding) as the situation allows.

Turbine engines are most efficient (thrust per pound of fuel) at high power settings.





Disclaimer: I am a pilot.
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Old 01-08-2008, 03:50 PM   #6 (permalink)
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Larger aircraft are very unstable gliders (they're always under power - even while landing... just throttled back) :/ Going slower in flight could be an option.... That would change the cycle life of the engine (more hours = more service - luckily, turbines don't require too much in the way of service compared to other engines ). I wonder if there's unforeseen consequences of that though - like needing more aircraft in the air to meet cargo demands...

I found an estimation of a Boeing 777-300's parasitic drag to be .0106 (just thought I'd throw that out there - seems low, but not unreasonable).

----
Here's an interesting chart (date is 2007)... I came across a fuel consumption by industry chart awhile back - and can't seem to find it again...


Another interesting point (not directly related to FE) is the cooling effect from aircraft contrails... The airline grounding due to 9/11 allowed scientists to get empirical evidence that ice clouds from aircraft actually deflect some heat off the planet....
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Old 01-08-2008, 03:53 PM   #7 (permalink)
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What's the difference between a personal truck and an automobile?
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Old 01-08-2008, 03:58 PM   #8 (permalink)
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Only a private pilot, but I think that only Albatrosses and glider pilots are the only real hypermilerpilots... the rest have a bit less than a 100% focus on energy conservation.

All planes have clear specifications that are quite specific on what ranges/FE they have at what airspeeds - unlike cars where it is some weird avg done on a dyno. You don't typically take any more fuel that what you'd need for a 45 minute reserve so when doing your flight plan you are extremely aware of wind speeds and directions and various altitudes and plan exactly and accordingly. The jetstream is used when favorable and avoided when unfavorable. The exchange between saved fuel and extra time would be an operational decision.

ATC controllers tend to be the bane of good mileage for airliners. They'll give them a set speed on a set vector and want the pilots traveling that speed without too much delay. Planes glide down from the cruising altitudes where thinner air helps range... few non-military planes have speed brakes, so descents are economical and well executed. Once in the pattern, planes typically fly at very inefficient speeds (flaps down)... so that planes of differing speeds are overrunning each other. In fact most commercial planes even need to use power when descending -- but it does help control and you can't control the wind when you are aiming to touchdown at a particular spot.

Planes often get straight in approaches when traffic allows. The tough part I have found is that typically all of your pre-landing checks are down on the downwind leg in slow level flight and you get used to doing it that way. When trying to do the same while maintaining a glide scope, it's change and can get a bit more intense. You are often very close before you realize you need to even start them.
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Old 01-08-2008, 04:03 PM   #9 (permalink)
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Quote:
Originally Posted by SVOboy View Post
What's the difference between a personal truck and an automobile?
My Jetta versus the F150 I'm parked next to

That doesn't take into consideration semi trucks or delivery trucks (although, I've been wondering if it includes fleet trucks)... I don't know if it includes SUV's - but I'm inclined to think so given the farm equipment loophole...
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Old 01-08-2008, 04:21 PM   #10 (permalink)
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I don't fly for an airline( I have lots of friends that do) but I did stay at a Holiday Inn express last night.
All in all with the major carriers it is all about fuel. They plan altitude for best fuel and route with the winds aloft and aircraft weight(if there is not a lot of turbulence at the desired altitude). They will taxi out on one engine, shutdown on the end of the taxiway if excessive delays. Ask for straight in approaches, ask to keep the speed above the 250 kt limit below 10,000 ft. Of course if the airspace is saturated it's all for not but they figure that all into the planning because they are going into the same places. I know some of the overnight freight companies will give bonus to the crew if they beat the predicted fuel burn and I'm sure that is for the regular carrier too.

Here's some data on fuel. It dated (3 years old) but it will give you the general idea.

Quote:
What does a one-cent increase per gallon in jet fuel mean for a carrier like American, the
largest in the nation? Last year, American consumed 2.956 billion gallons of jet fuel. A
penny increase will jack up fuel costs by $2.5 million per month. So far, prices are 12
cents higher per gallon compared with last year. Talk about sticker shock.
As far as gliding into landing. Most turbojet engine have a lag time of about 5-13 seconds from idle to full power, depending on the engine, So if you flight idle it you would be committed from about 800 feet above the ground. It takes a while to arrest the sink rate of a 100,000 pound airplane once the engine hit max power. So they have procedures that they will have the approach stabilized at 1000 feet with power setting appropriate for the aircraft landing configuration.

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Last edited by Lazarus; 01-08-2008 at 04:26 PM.. Reason: landing
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