At a slowing speed and typically at near-idle thrust. The aircraft exchanges gravitational potential energy for velocity through most of the descent.
The only high-trust portions are when reverse thrusters are engaged, typically for a few seconds following landing, or if TOGO power is invoked for an aborted approach.
Which is effectively level flight / continued cruise, a low-power flight segment, not a high-powered one. That last would only apply if the aircraft had aborted an approach, which typically gives priority.
Again: the original claim was that both take-off and landing were high-fuel-consumption flight segments. That's untrue. Under normal conditions only take-off is, and even most deviations from a nominal approach have a fairly minor impact.
You're going to extreme lengths to avoid admitting this, and are making the issue personal to boot. Any particular reason for that?
> 1.1.4.6 With the need to ensure that CDO does not compromise safety and capacity, it may not always be possible to fly fully optimized CDO. As well, it may be necessary to stop a descent and maintain level flight for separation or
sequencing purposes. The aim should be, though, to maximize CDO to the extent possible, whilst not adversely affecting safety and/or capacity.
Obviously level flight near sea level is less fuel efficient than at cruising altitude.
Likewise, descending into a significant headwind, or avoiding adverse weather will require more fuel than the optimal.
I'm not saying that a continuous descent is actually guzzling gas like crazy. There's very many smart people that have been optimising fuel usage in planes for decades.
I just want to emphasise that while the ideal descent is very fuel efficient, not every descent is ideal.
And of course, it varies significantly based on the plane.
This paper shows that interestingly, some A330 models used equivalent, or even more, fuel on approach than takeoff. Although I speculate that's more due to very efficient takeoffs rather than inefficient approaches.
I'm trying to correct the implied claim repeated in this thread that the ideal descent can be used to model every descent.
Oddly enough, nobody asked that question.
I'm not saying that a continuous descent is actually guzzling gas like crazy.
Well, at least you're admitting as much.
For a trip segment, takeoff and climbout are the initial high-fuel-flow phase. Note that LTO (landing and take-off) data are based on flight segments at and below 3,000 ft. AGL, which is 1/10 or less of cruise height of FL30 -- FL40. See Fig. 1 of your reference. The LTO data (limiting climbout / descent phases to <= 3000ft) are relevant to local emissions concerns near airports, the focus of the paper, but not to total fuel / emissions of an entire aircraft flight profile as we're discussing here, and omit 90%+ of the relevant climb/descent characteristics. As discussed in the paper.
Figure 2. also provides a strong clue as to why the LTO data show lower total fuel use in the approach vs. climbout phases, again, <=3000 ft: the aircraft monitored are spending 2-5x longer in the approach phase. That is, they're climbing out steeply, with very high fuel-flow rates, whilst they're descending slowly (and hence, spending more total time <=3000 ft) at a much lower fuel-flow rate.
Again: you're wrong, given your own cited reference.
The slowing isn't using gas - its not like they put the plane in reverse to slow it down. They're descending and trading potential energy for energy to maneuver at low altitudes. The thrust is near idle.
True, but not every approach to an airport is a nice constant vector.
Continuous descent operations are the optimal, but there's plenty of suboptimal airport approaches that require level flight at a height where fuel efficiency is far less than at cruising altitude.
Do you have any statistics to say it happens so often that airplane landings are so suboptimal that they use anywhere near climbing fuel rates and times that it matters to the overall discussion? It seems unlikely to me.
