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An Airliner flies from LA to JFK in 5 hours. In the first 30 minutes the plane climbs to about 30,000ft. For the next 4 hours the plane flies at about 30,000ft. For the next 30 minutes the plane descends to JFK.

What % of the total fuel used for the flight is consumed in each of the 3 phases of the flight, i.e, the climb out, the cruise, the descent?

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    $\begingroup$ You forgot the 4th phase, at JFK: waiting 1 (or 2) hours to get a gate... Needs some fuel too, to keep passengers warm. $\endgroup$
    – kebs
    Jan 6, 2018 at 19:11

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  • From this site by Boeing for the B737-800: fuel used for TO and climb = 2,300 kg.
  • From this site: fuel burn in cruise for B737-800 is 2,500 kg/hr
  • From this site: fuel burn at idle of a CFM56 engine = 300 kg/hr, so for the half hour descent two engines burn through 300 kg.

Total fuel for a 4 hour cruise flight is therefore 2,300 + 4 * 2,500 + 300 = 12,600 kg. Percentages:

  • TO & Climb = 19%
  • 4-hour cruise = 79%
  • 30-minute descent at idle: 2%
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  • $\begingroup$ Interesting how close my estimations were to those values. $\endgroup$
    – Romeo_4808N
    Jan 6, 2018 at 6:39
  • $\begingroup$ I know pretty nearly nothing about airplanes, but I do fly a lot. Surely the "landing" phase has to take significantly more than that 2%—flaps come out about 10 minutes before landing, and engine revs go up significantly. Once the plane actually lands, engines go on full power for braking. And then there's the obligatory circling at low altitude over Heathrow... $\endgroup$
    – Auspex
    Jan 2, 2020 at 14:12
  • $\begingroup$ @Auspex Yes, you do not land with engines at idle. You want some engine power to control descent rate and increase safety if you cannot land. $\endgroup$
    – Ville Niemi
    Mar 22, 2020 at 18:37
  • $\begingroup$ Fuel savings due to higher TAS at cruise altitude does contribute to fuel economy, adding validity to the sourced data. $\endgroup$
    – Robert DiGiovanni
    Aug 6, 2021 at 17:27
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    $\begingroup$ @Auspex - for jets like B737, just prior to touchdown (varies, but 10-20 ft in the air) the throttles are pulled back to idle. After touchdown, when reverse thrust is deployed, the engine power is increased to an amount less than full power. Could be 50% - 80% (sometimes less) of full power depending on circumstances (remaining runway length, rain, ATC runway exit instructions, etc.) $\endgroup$
    – user22445
    Aug 6, 2021 at 20:28
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This one varies based upon selected power settings during climb, atmospheric conditions, aircraft loadout, winds aloft, etc. you would have to consult the performance tables in the operators handbook in question for this one. A good estimate would be about 85% of the total fuel consumed would be done during cruise flight, with around 10% used during taxi, takeoff and climb and about 5% consumed during descent.

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  • $\begingroup$ And of the 10% fuel used until cruise altitude is reached, roughly half (5 %) is used for altitude gain, no? (rest contributes to horizontal progress towards destination). $\endgroup$
    – Robert DiGiovanni
    Aug 6, 2021 at 17:18

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