Step Climb Mid-Cruise

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📍 Route: EGLL → KJFK⏱ ~5 minutes📊 5 steps🎓 Enroute Operations

Westbound over the Atlantic at FL340 and getting lighter. Read OPT and MAX on the CRZ page, then step to FL360.

What this scenario covers

As fuel burns off, the altitude at which the aircraft is most efficient rises. The CRZ page shows optimum and maximum altitudes for the current weight; a step climb takes the aircraft up to collect the saving once the numbers allow it.

The sequence is check then act. Requesting and accepting a level the aircraft cannot comfortably hold is how a cruise ends up at maximum continuous thrust with the speed slowly decaying.

How it applies in flight ops

Oceanic operations plan step climbs into the flight plan and request them at defined points, because on a track system you cannot simply climb when you feel like it. The fuel saving is real enough that dispatch plans for it.

MAX on the CRZ page is a buffet-margin limited figure, not a thrust limit. Treating it as the ceiling is the professional habit; recomputing margins by hand mid-ocean is not.

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Step-by-step: Step Climb Mid-Cruise

  1. Open the RTE page and enter ORIGIN airport EGLL. Type EGLL and press 1L.

    Westbound and eastbound transatlantic flights typically step climb 1-2 times during cruise. As fuel burns off, the aircraft's optimum altitude rises — flying at OPT saves fuel directly. The OFP usually pre-plans these step climbs, but you have to execute them by updating CRZ ALT when ATC clears the new level.

  2. Enter DEST airport KJFK. Type KJFK and press 1R.
  3. Set initial cruise level FL340 on PERF INIT. Type 340 and press 1R.

    Westbound (track 180-359° magnetic) uses even levels; eastbound uses odd. Heavy aircraft can't reach OPT immediately — at takeoff weight, FL340 may be the highest practical level for a 737-800 on a long Atlantic crossing. As fuel burns the OPT rises by ~1000–2000 ft per hour.

  4. Two hours into the cruise, fuel has burned off enough to step up. Open the CRZ page to see OPT and MAX.

    The CRZ page shows live cruise data — ECON SPD, current CRZ ALT, and on the right at row 5 the OPT/MAX altitudes. MAX is the absolute ceiling for current weight; OPT is the most fuel-efficient level (usually 2000-4000 ft below MAX). Step up to a level below MAX to leave margin for turbulence and weight uncertainty.

  5. Step up to FL360. Type 360 on the CRZ page and press 1R to update CRZ ALT.

    After updating CRZ ALT the FMC recalculates the remaining cruise at the higher level — fuel burn drops, ETA shifts slightly. Real 737 pilots cross-check the new fuel prediction against the OFP step-climb plan before accepting. If predicted arrival fuel falls below reserves, you don't step up even when ATC offers it.

What to take away

  • Optimum altitude climbs as weight falls — the step collects the efficiency.
  • CRZ shows OPT and MAX; check them before requesting.
  • MAX is buffet-limited, and it is the practical ceiling.
  • On track systems the step is planned and requested, not taken.

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