Climb Speeds for Economy (from "A Few Notes from my Notebook - a series of 1000")
For the B777 here are some actual figures - the same principle applies to other Boeing (all ?) FMS equipped aircraft.
The Best Rate of Climb (ROC) Speed is extracted from the FMC by using Cost Index (CI) 0. The VNAV1 (Climb) page will then show climb speeds to achieve Minimum Fuel = Best ROC Speed for the climb. This is weight and ISA Temperature sensitive so is subject to change as the climb progresses. However the ISA change variation on speed required is small and setting a TOC ISA in the First Waypoint after TOC in LEGS will achieve virtually perfect results without having to leave the FMC in CI = 0 throughout the climb segment (see below).
Obviously if there is an ATC climb restriction then the nominal 250 to 10K will have to be observed, but if possible accelerate to optimum climb speed ASAP after the Forth Segment (Clean A/C). Removing the standard Climb Restraint in VNAV1 will achieve this automatically.
From a theory point of view all of the above posts are just about on the money so no repeat is required.
The other Climb / Fuel issue is regarding Derated Climb. Derated climbs save engine life and not Fuel. Cancelling the Derate (which washes out by 13K anyway) will achieve a small saving in Trip Fuel also. (Obviously by allowing cruise altitude to be aquired ASAP).
From a practical viewpoint and also to avoid clashing with SOPs, it is best to query the CI = 0 Climb Speed before departure (after a valid ZFW/Fuel/AUW is inserted + a TOC ISA) and manually inserting that in the VNAV1 (Climb) page. Remember to set the CI back to the Company Approved value.
In real life a saving of 300-400 kgs can be made on a B777 using a CI=0 climb profile and another 200Kgs by cancelling the Climb Derate. If you are going to be on a "tight" sector these are obviously useful savings that can be "banked" from the TOC fuel check.
These are proven numbers (for me) and do result in savings on fuel at the cost of a small (1-2 minutes) increase in flight time. Obviously there are a lot of variables and savings do vary depending upon AUW. All other influences being factored out on the CFP - try it for yourself. I have always wondered why it isn't SOP particularly on "redispatch fuel" type flights. Maybe it's just too hard to understand.
MG