Fuel Savings
Hello everyone,
I am writing about fuel savings, and wanted to ask the wider airline pilot population about their own operators' procedures and, what they have found, to work best in the following:
It might be safe to assume that on Boeing or Airbus most of us arrive at the CDU/MCDU respectively, and input an OFP and company derived cost-index for the mission that will take into account cost of fuel and cost of time and accordingly adjust parameters for cruise climb, cruise, and descent.
Recent economical considerations got me thinking again...
Whatever is takeoff configuration we use (flap, derate, assumed/flex, derate plus assumed/flex, EAI/Packs and so on) and however we are prescribed the initial climb, NADP1 NADP2 and so on, that all takeoffs until 10,000AGL/FL100 roughly follow the same 250 kias speed regime unless otherwise required by performance (WAT) or ATC.
I am more interested in the bit from FL100, or greater than 250 kias, until ToC.
Most of use tend to fly this in VNAV or Managed Speed at an FMC/FMGC derived high-speed climb, until crossover to Mach is achieved somewhere near to or around FL300 (type specific).
It has been rumoured that a number of airlines use this technique, and I have trialled on A320,A330 and B777 types, the benefit of climbing from FL100 to ToC at "best rate of climb" speed (Vy). Airbus=Managed speed with cost index '0' set in either OPEN CLB or CLB, Boeing = Vref30+140 in either of VNAV or FLCH.
In many cases, the results have been quite pleasing. In others, the results decidedly inconclusive. Speaking to a mate of mine, this procedure of Vy climb from FL100 to ToC, will actually burn more fuel on the four-engined B747 or A340/380. This I do not understand (confused?)
Naturally we might consider some the following:
- less time spent with THR CLB, CLB power
- less time spent in the lower, more dense air
- an increase in deck/body angle
- an increase in time spent at CRZ thrust
- an increase in total flight time
Does anyone out there have any empirical data on using 'Vy' as a climb strategy on narrow -vs- wide body, and two-engined -vs- 3 or 4 engined wide body aircraft? Similarly, does anybody know of a library where this kind of data is available? Or would anyone be willing to share their own experiences?
Of course this may seem very academic, especially when up at MTOW/PLTOW and Vy and CI=x climb are nearly coincidental, and when one considers the minimal fuel savings that (may) result. However, if this works, then very real savings might be realised on a fleet-wide application.
Anyone with similar interest, it would be great to get engaged on this topic.
Last edited by voice_of_peace; 29th Oct 2017 at 16:25.