Guest

Question: Flight Duration

Sat Aug 31, 2002 6:44 pm

I fly AMS-JFK-AMS about 12 times a year on a Delta B763. It always amazes me how much the flight duration varies.

A flight AMS-JFK can last as long as 7 hours and 40 minutes, or as short as 6 hours and 55 minutes.

A flight JFK-AMS can last as long as 6 hours and 40 minutes, or as short as 5 hours and 55 minutes.

So either way, there is a 45 minutes difference possible. Is this caused by weather only? Or are there other reasons as well? And is there a seasonable pattern??
 
tsentsan
Posts: 1921
Joined: Mon Jan 28, 2002 10:48 pm

RE: Question: Flight Duration

Sat Aug 31, 2002 7:07 pm

I'm guessing a tailwind of 60 kts and a headwind of 60 kts makes alots of difference...

If I'm not mistaken, there are seasonal winds across the atlantic.. in certain periods of the year, it goes east, otherwise it goes west usually...

apologies for not having more specific info...

also your flight plan would be different, covering less ground miles...
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backfire
Posts: 3467
Joined: Fri Oct 06, 2006 8:01 am

RE: Question: Flight Duration

Sat Aug 31, 2002 7:10 pm

It's almost certainly to do with the head/tailwinds. You can easily knock as much as an hour off a transatlantic flight if the winds are with you -- especially if the course optimisation to maximise a wind advantage also happens to minimise the distances involved. Don't forget that aircraft will usually fly offset to the great-circle distance because the wind advantage more than compensates for the additional flight distance.
 
airsicknessbag
Posts: 4626
Joined: Thu Aug 17, 2000 2:45 am

RE: Question: Flight Duration

Sat Aug 31, 2002 7:58 pm

There are basically three extreme tracks a flight can take:

- minimum time track
- minimum cost track
- minimum distance track

So, if the plane has to catch up a delay, the MTT might be the most sensible option - the direct cost is higher, but it might save some people´s connecting flights. If the flight is on time, the MTT would be pointless, so you choose the MCT, which gives you longer flying times etc.

It´s not only weather.

Daniel Smile
 
backfire
Posts: 3467
Joined: Fri Oct 06, 2006 8:01 am

RE: Question: Flight Duration

Sat Aug 31, 2002 11:02 pm

Could you please clarify that statement Daniel, just so people know:

(a) Why minimum cost does not equate to minimum flying time.

(b) Why an airline would choose to keep an aircraft flying longer than necessary in order to save money, especially when burning fuel is expensive.

Thanks.
 
Guest

RE: Question: Flight Duration

Sat Aug 31, 2002 11:09 pm

Backfire,

I am pretty sure it has to do with that when flying at maximum speed you burn more fuel than when flying at a lower speed.

So e.g. cruising at Mach 0.82 gives you a longer flying time, than cruising at Mach 0.86 but therefore burns less fuel. Same as in your car. When travelling at maximum speed you naturally get to your destination faster but you also need more fuel.
 
airsicknessbag
Posts: 4626
Joined: Thu Aug 17, 2000 2:45 am

RE: Question: Flight Duration

Sat Aug 31, 2002 11:18 pm

Yup, B737-700 summed it up pretty neat.

Another factor that comes into the equation are fees you have to pay to a country for overflying it. If you have a country which asks for high fees (e.g. Iran if I remember correctly), you might have the option to circumvent it - hence you leave the MTT in order to save money, the MCT might lead around that particular country.

Daniel Smile
 
backfire
Posts: 3467
Joined: Fri Oct 06, 2006 8:01 am

RE: Question: Flight Duration

Sat Aug 31, 2002 11:38 pm

My question was simply whether the cost in fuel burned outweighed the cost of fuel saved. Incidentally a car is more fuel-efficient at higher speeds.

I'd also assumed we were still talking about transatlantic flights, where you're not overflying Iran (or anyone else come to that).
 
ragousis
Posts: 29
Joined: Thu Dec 07, 2000 7:16 am

RE: Question: Flight Duration

Sun Sep 01, 2002 2:01 am

backfire, because all planes, trains, boats, cars etc have a speed called max range, if you go above this speed your fuel burn per mile traveled go up. For example a plane burns 500 gal per hour at 500 knots (max range speed), at 550 knots the plane burns 600 gal per hour. If you do the math a 1000 mile trip takes 2 hours at 500 knots and 1.8 hours at 550 knots. We know the burn rate per hour, so we get 1000 gal used in the first case (500 knots) and 1080 gal used in the second case (550 knots). All because cruise speed does not vary proportionate with fuel burn per mile traveled. And who told you cars travel more efficient at higher speeds? If by high speed you mean 45 mph then you are correct. Because for most cars if you are above that speed your fuel burn per mile traveled will go up. I do have a degree in Aerospace Engineering so I have done the research on this. If you want more evidence I can get out my 727 manual that has all the performance figures.
 
backfire
Posts: 3467
Joined: Fri Oct 06, 2006 8:01 am

RE: Question: Flight Duration

Sun Sep 01, 2002 3:56 am

I just wanted to see a few numbers...which you've provided Ragousis - thank you.

And yes, by "high" speed for cars I meant "non-urban" speeds as opposed to crawling about the town at 25mph.

Cheers anyway. Reminds be about the old joke about going faster in order to get there before the fuel runs out.
 
j-bird
Posts: 106
Joined: Sat Feb 17, 2001 6:47 am

RE: Question: Flight Duration

Sun Sep 01, 2002 5:16 am

There was actually a pretty good Discovery Channel Europe program called "The Flight" about two months ago that covered this. The program followed an Air Canada flight from Toronto to Frankfurt, and investigated the entire flight planning, execution and completion process.

A significant portion of the pre-flight preparation was dedicated to choosing which Atlantic track to request from Atlantic Control. Among the many variables considered were flight time, fuel burn and congestion on each track. Thus, it seems that while the time versus cost argument is carefully considered by the airline, the congestion factor plays into it quite extensively in that a particular route track request from an airline may not be approved by Atlantic Control. I would suspect the same is true for other busy airspace around the world too.

Also interesting to note that it is often cheaper for an airline to fly the maximum speed track, despite the extra fuel burn, in order to avoid having to accomodate passengers who missed connections. In the program I mentioned above, this was the case with the AC flight, which needed to get 15 passengers with close connections on the ground to avoid the cost of putting them up or otherwise dealing with them.

Cheers.
 
SafetyDude
Posts: 3654
Joined: Fri Sep 07, 2001 10:02 am

RE: Question: Flight Duration

Sun Sep 01, 2002 5:35 am

What makes the difference is:
-cost effective (fuel burning/speed)
-weather (winds)
-and also how much the pilot likes you  Wink/being sarcastic
Everyone who answered above did a great job of answering your question  Big thumbs up
-Will
"She Flew For What We Stand For"

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