Points for low fuel consumption?

[abev107]

With commercial jets/props - do you have a choice how fast you can fly? Can you "floor-it"? (Within operation limits, of course)

Does anyone in the airline say "You had a 100kt tailwind, you didnt need to use that much fuel." Or if you have a strong tailwind are you encouraged to take it easy?

 

[Hubie]

From what I understand once a crew pushes they own every last bit of fuel in the tanks, which they could have haggled with dispatch over more, before they pushed and they can use any or all of it to complete the trip.

 

[Hubie]

But…

A good crew is going to find that 100 kt tailwind and exploit it anyway…

 

[CesnaCaptn]

It Depends

At my airline, dispatch provides the crew with a planned cruise speed and altitude. The speed will either be .74 or .77 mach. Of course the altitude varies. If we flew the company way all the time we would most likely fly as high as we can at the given speed. Some people will use "go home power" on the last leg which means push the thrust up to either max N1 or keep it out of red line. Also, the most efficient cruise altitude might be FL350 for a flight. If you really want to get home quick a pilot might choose FL280 as a final. Of couse flying low and fast burns a lot of fuel. I don't know anyone who does that, but I've heard of people doing it.

 

[banned username 2]

We have total control in our choice of Altitudes, Speed and Routings...

Typically when we are flying domestically we fly at FL 410 or FL430 and cruise at Mach 0.82 - Mach 0.85

Flying longer trips (7 to 9 hours) we will typically fly FL 410 or FL 430 and do Mach 0.80...

For very long legs (over 9 hours) we will fly at FL 410, FL430, FL450 and do Mach 0.77

Sometimes guys will say on a short trip, say 3 hours... "I wanna go low and fast, so you might see a guy going M0.85 at FL350 instead of M0.83 at FL430 but you will find in our case that trip will burn about 8,600 lbs of fuel instead of burning 6,700 lbs of fuel at FL 430 and will only save maybe 6-9 minute.. but burned 285 gallons more fuel (about $750 more fuel to save a whopping 6-9 minutes).... not smart...

 

[Jeff Helgeson]

Depends, consider all the factors...

Let's say your A/C burns around 6000lbs an hour, that is 100lbs per minute. If you can shave 10 minutes off the flight plan, you will burn 1000lbs. less for the flight time. The extra thrust will increase the fuel flow or burn rate, but it is possible to actually beat the flight plan and arrive early at the gate with more fuel in the tanks. This tend to work best for flight around 1-2 hours.

The engineers will tell you no, but line experience often says yes. There are other factors as well. Let's say a number of A/Cs are in bound at about the same time. If you bump it up and beat the crowd, again less air time = less fuel burned.

Many planes can be flown by fuel flow settings. If asked to slow by ATC to a certain speed, the fuel flow is often the same at the slower speed as it was at the higher speed, but now it will take longer to complete the flight. That means you will burn more fuel.

A quick check to see if the time vs. fuel burn will pay off is to increase the speed and then check the fuel flow to maintain that speed. Compare the extra fuel burn for 1 hour to the anticipated time savings. If you shave 10 minutes off the flight plan at an extra burn of 500 lbs. for that hour, then you saved 500 lbs. of fuel and you deserve a full can or two of soda with plenty of ice..........dammit!

There are other techniques as wells, stay at altitude as long as possible , descend at a faster IAS, stay clean longer, etc.

It is not an exact science. Every airplane has it's own bias. Some tend to burn more than others. It could be due to trim, a slightly bent plane. Just like some cars that are the same model get different MPG, so do planes. Many airlines track each airplane and figure in the bias as a percentage on the flight plan and adjust the fuel load accordingly. It's not real tangible, but it is there.

Last leg of a trip, trying to catch a commuter flight home, let it burn.

 

[fokkerjet]

Fuel is just one factor to take into account, how about aircraft operating costs or crew duty times? I've flown out to the west coast at FL280 in order to get out of the wind, which saved about an hour of flight time. Of course I burned several thousand pounds more fuel in doing so, but when you factor in maintenance costs, keeping on schedule, and reducing our duty day, the extra fuel burned didn't cost us much.

 

[Jeff Helgeson]

Big Motor Foker?

Was that in the big moter fokker or the little motor fokker?

 

[Captain X]

A good crew is going to find that 100 kt tailwind and exploit it anyway…

....as long as their employer gives them Profit Sharing.

 

[Hugh Jorgan]

Re: Depends, consider all the factors...

If asked to slow by ATC to a certain speed, the fuel flow is often the same at the slower speed as it was at the higher speed,

Now THAT's a neat trick!

 

[Sphincter Boy]

Re: Re: Depends, consider all the factors...

Now THAT's a neat trick!

Thats what I was thinking.

 

[FracPilot]

Now THAT's a neat trick!

Not really. He's just forgetting to stow the airbrakes after slowing to the requested speed.

 

[350DRIVER]

It usually depends on numerous circumstances, the biggest is whether or not we are running on time or late. The 100, 300, and 350 can be somewhat costly at low altitudes so if we are empty, early, on time, the leg is a short one, and final altitude is low then we will usually pull the power back and target a set fuel burn to conserve. Although "we" are not paying for the fuel so there are some days when we will push it and go fast down low just to get there "quicker"-0

After a long duty day sometimes "conserving" isn't as important as getting home if we have an early next day to look forward to.

3 5 0

 

[abev107]

thanks everyone for the info, and thanks 350driver for getting us back on topic

 

[Mickey]

Jeff wrote:



"Let's say your A/C burns around 6000lbs an hour, that is 100lbs per minute. If you can shave 10 minutes off the flight plan, you will burn 1000lbs. less for the flight time. The extra thrust will increase the fuel flow or burn rate, but it is possible to actually beat the flight plan and arrive early at the gate with more fuel in the tanks. This tend to work best for flight around 1-2 hours."


Jeff, you are missing a basic principal here. Like drag. Let's look at basic math. If we were traveling at 405kts we could cover 405nm in 60 minutes. To save 10 minutes we would have to do 486kts. I don't know what kind of engines you have but, most will change their fuel burn quite a bit to make a 20% increase in airspeed. When I look at any specific range chart they always show an inrease in range as airspeed drops until a certain point.

I've tested this in flight and the graphs and the engineers are correct.

Take care.

 

[pilotyip]

Depends upon the design of the wing

You have to look at the tables and find out FF/TAS or Mach and get the SFC (specific fuel comsumption) that optimizes the range. Then again you have cost factor engine reserves vs fuel savings. We teach this to our DA-20 crews and they are routinely flying non-stop from Mexican boarder to Canada, saving us a fuel stop. It the P-3 the rule of thumb in dealing with winds before the days of computers and computerized flight plans, was IAS plus 5% of the headwind, and minus 10% of a tail wind.