727glasair
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The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 4:47 am

Representing the AOPA, and as a known flight efficiency expert, I have been named to a committee that will soon give suggestions for saving fuel as ATC goes through some changes. My primary interest and focus is arrival/approach descent altitude profiling. I believe it is safe to say that this is one area where great potential exists for substantial fuel savings....especially for shorter haul and commuter planes, as they make a relatively high number of landings!

Currently a typical scenario might be: about 110 miles out, ATC says descend to 24,000 at pilots discretion. They are directed, quite often, to a point maybe 20-30 miles downwind of the target airport.....depending on many factors. Sadly, it is only a slight exaggeration to say that the flight turns final about 22 miles out, at a low altitude, and drags it all the way in under substantial engine power.

I am operating on an assumption that the MOST fuel efficient approach (in a perfect world) would be to set up the airplane's most efficient rate and angle of descent and be able to hold this directly to the runway threshold....and if needed, make only ONE close-in turn to final. This is an example of allowing the wings to do the work and having the engines burn very little Jet-A.

Obviously things such as poor weather, instrument approaches, high traffic volume, etc, can necessitate longer and flatter approaches. Nevertheless, my main point is that a lot of fuel is being wasted in our current system of descent/sequencing. Any thoughts??
 
mmo
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 6:41 am

Are we talking GA or Commercial? Of my 23,000 hours I have about 80 hours of SEL recip time, so my GA experience is very limited. However, from what I remember about domestic flying in the US is ATC does a fairly good job of planning and the days of being 50NM from the field are long gone. Personally, I always check the FMS for descent planning and using the 3:1 rule and adjusting for head or tail wind is a good technique. LHR has a very good handle on continuous descent approaches and it works quite well. I'd suggest looking at them for a good start.
If we weren't all crazy we'd all go insane!
 
thepinkmachine
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 6:44 am

Hi! Very interesting topic. Low/draggy descents/long finals have always been a pet peeve of mine - both due to ATC constraints, as well as due to pilot techniques, which vary considerably from one, to another, even on VNAV equipped aircraft.

The only thing - so far I haven't found any quantification of actual descent profiles vs. ideal ones. I.e. how big potential fuel penalties we are talking about and if it's worth the effort. All I have seen is some vague data in Airbus publications, but would love to see something more in-depth...
 
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VirginFlyer
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 6:55 am

You may want to have a read of this: http://aucklandflightpathtrial.co.nz/ and specifically http://aucklandflightpathtrial.co.nz/wp ... report.pdf

I know Airservices Australia have done work on this too, though I'm struggling to find details.

Here's a brochure from Eurocontrol too: https://www.eurocontrol.int/sites/defau ... re-web.pdf

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zeke
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 7:50 am

727glasair wrote:
I believe it is safe to say that this is one area where great potential exists for substantial fuel savings....especially for shorter haul and commuter planes, as they make a relatively high number of landings!


I dont agree, the trip fuel for a 50 seat regional on a 200 nm hop would be less than the taxi fuel for a widebody. One simple way to make flying more efficient is to maximize the number of seats per movement. Frankly aviation would be a lot more efficient if a lot of the lower capacity aircraft the provide very high frequency services were taken out of the equation and the network was optimized on higher seat count per movement. That would overnight reduce ground and air congestion that is killing advances made in aircraft design. I believe the head of DL that said last year it takes as long today to fly between ATL to DCA as it did with a DC-6, the advances and efficiencies with new aircraft design are all being eaten up by ATC delays.
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B777LRF
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 8:38 am

The main reason for 'early' descends is traffic. This is particularly evident on the US eastern seaboard, London TMA and central Europe. NATS have gone to great lenghts designing constant descent approaches, proving it can indeed be done when arriving LHR. That is, as long as everything goes to plan and the weather cooperates. In my experience the 'problem' is most prevalent when approaching any of the metropolis areas on the US eastern seaboard; starting the descend inbound to JFK from around 200-250NM away is not uncommon. The descent will be in stages, e.g. FL380 to 340, stay for a while, continue down to 280, stay for a while etc. I possess neither the knowledge or skills to suggest a solution.

SAS did a test a few years ago, in cooperation with the DK and SE ATC providers. They sent an A320 on what was essentially a 'free flight' trajectory, involving a below FL100 accelleration to around 320 KIAS, a 'direct to' the FAP, a cruise climb and a constant descent approach. The saving was around 300kg of fuel, but the test also showed these trajectories are not workable day-to-day due to present day ATC restrictions.

'Free-flight' is the golden goose of flight ops, and may one day become possible. But it will require an entirely new approach to flight planning, and will probably involve individual aircraft being able to 'talk' to each other to, in coordination with ATC, ensure seperation.
From receips and radials over straight pipes to big fans - been there, done that, got the hearing defects to prove
 
leghorn
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 8:44 am

I remember I remember reading something about optimised flight paths and flight levels being investigated in Scandinavia but I can find no material online at the moment.
 
leghorn
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 8:50 am

It was SAS.
URL was http://www.aviationrecord.com/search-re ... icleId=340 but it has expired.

Green Landings is the keyword

viewtopic.php?t=751537
 
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Starlionblue
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 9:21 am

As B777LRF says, "free flight" is the holy grail. On an ideal profile, you would be at idle from TOD until around 2500 feet when the gear comes down. Dragging it in for a long, level final is frowned upon.

Just to give a framework, on the 330 and 350 the mental calculations for an "ideal" descent:
- From cruise to 15000 feet: 4 track miles to the threshold for every 1000 feet altitude.
- 15000 to the ILS (or other glidepath): 3 track miles to the threshold for every 1000 feet altitude, plus 1 mile for every ten knots above 150. (E.g. 10000 feet at 230 knots is 30+8=38 miles.)
- On the ILS or other glidepath: 3 track miles to the threshold for every 1000 feet altitude, or even more accurately 1 track mile for every 320 feet altitude. (This assumes a 3 degree glidepath.)

Again, this is the ideal. In real life you do what you can but then ATC gives you a 10 mile shortcut or a hold which throws your carefully managed profile out of the window. Or the STAR has a level segment at 2000 feet. Or there's a lot of wind.

The best way for ATC to make more descents "ideal" would be to slow or speed up aircraft WAY before start on the arrival. That way you'd reduce holding, extra track miles etc.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
flyby519
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 9:46 am

Speed reductions while in a descent are a pain, especially if you are already in an idle thrust/max angle descent. So to create some wiggle room most pilots descend at a shallower rate to account for possible speed reductions.

Also less is more. The less constraints on an RNAV arrival the better. With a bunch of speed changes/altitude constraints it creates more headache. I know this isn't always possible, but just a thought.
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Starlionblue
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 10:05 am

flyby519 wrote:
Speed reductions while in a descent are a pain, especially if you are already in an idle thrust/max angle descent. So to create some wiggle room most pilots descend at a shallower rate to account for possible speed reductions.

Also less is more. The less constraints on an RNAV arrival the better. With a bunch of speed changes/altitude constraints it creates more headache. I know this isn't always possible, but just a thought.


Word. "Descend 9000 feet level by SAMBA. Reduce speed 230 knots." ARGH!!!!! :banghead:
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Mattokun
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Jun 08, 2017 2:28 pm

Prof. John-Paul Clarke at the Georgia Tech Air Transportation Lab has been looking into this for quite a while now. It may be worth contacting him if you want to know the current status of research.
 
WPvsMW
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Re: The status quo in descent profiles: a killer of fuel economy

Sat Jun 10, 2017 8:07 am

@Mattokun, welcome to anut.
 
Mattokun
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Re: The status quo in descent profiles: a killer of fuel economy

Fri Jun 16, 2017 3:25 pm

@WPvsMW, thanks! Been lurking for a while, but felt that this one, I could actually provide some inputs for :)
 
744lover
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Re: The status quo in descent profiles: a killer of fuel economy

Fri Jun 16, 2017 8:14 pm

Starlionblue wrote:
flyby519 wrote:
Speed reductions while in a descent are a pain, especially if you are already in an idle thrust/max angle descent. So to create some wiggle room most pilots descend at a shallower rate to account for possible speed reductions.

Also less is more. The less constraints on an RNAV arrival the better. With a bunch of speed changes/altitude constraints it creates more headache. I know this isn't always possible, but just a thought.


Word. "Descend 9000 feet level by SAMBA. Reduce speed 230 knots." ARGH!!!!! :banghead:



Well, that's when I select VS mode on MCP, reduce speed selector to 230, extend the speed breaks and start to pray :pray:


BRGDS,
744lover
 
mcdu
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Re: The status quo in descent profiles: a killer of fuel economy

Sat Jun 17, 2017 1:57 am

727 you say you are an expert but your provided assumptions don't seem to reflect the real world whatsoever. I haven't been given a PD clearance to FL240. Almost all of the major airports in the USA have been transitioned to the profile descent with descend via clearances. These are designed to be flown clean and idle with altitude windows. Maybe the work you think you are doing has already been done....
 
gloom
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Re: The status quo in descent profiles: a killer of fuel economy

Sat Jun 17, 2017 4:05 pm

Starlionblue wrote:
Word. "Descend 9000 feet level by SAMBA. Reduce speed 230 knots." ARGH!!!!! :banghead:


ROFL. Anyone'd rather take "descend 3000, qnh 1017, direct WA534, 27 track miles". And you know what? It happens... sometimes :/

Cheers,
Adam
 
FlyHossD
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Re: The status quo in descent profiles: a killer of fuel economy

Sun Jun 18, 2017 4:30 pm

B777LRF wrote:
The main reason for 'early' descends is traffic. This is particularly evident on the US eastern seaboard, London TMA and central Europe...


New York is a great example of this with EWR, JFK, LGA, TEB and other airports essentially occupying the same airspace. So ATC has divided the airspace into blocks of "territories" that include blocks of altitude and must filter the traffic into those blocks. Thus, it was common to descend into EWR for an upwind, downwind and an extended base leg which forced each flight to burn several hundred pounds (narrow body airliners) of extra fuel and generally added 7-10 minutes of time. Then there's the environmental impact as well.

In my experience, the addition of the ATC TMUs (Traffic Management Units) did not make the situation better. In our current age of advanced computing, I often wondered if there wasn't a better way...
My statements do not represent my former employer or my current employer and are my opinions only.
 
c933103
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Re: The status quo in descent profiles: a killer of fuel economy

Thu Aug 10, 2017 1:57 am

I have just read a document that say the New Chitose airport in Japan (CTS) uses the continuous descent approach for noise reduction and also for fuel saving

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