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Subsonic Fuel Consumption


Kyprianos Biris

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Kyprianos Biris

For the sake of the discussions regarding subsonic fuel and range I just submit my data for the longest subsonic flight I did so far.

ENGM - UBBB flight executed with Concorde-X 1.34 in P3D 3.2

MASEV Z183 LEGPO L199 RASEL Y130 SOPUN L199 MILTA Y130 RUDNI N623 LOVIK M996 GUKOL A225 LATRI G118 OGURA B450 KZ B122 MKL B494 BUMAR N67 NOBVA

1899 nm (1930 track miles flown with departure & approach)

VATSIM flight log http://www.vataware.com/flight/57668f7b5352334ec3000003

Barbados pax load (89 tons), 90 tons fuel at ramp before start up.

Flight at FL310, IAS 360 / Mach 0.95 T/ AS 550 Kts

Fuel consumption at cruise started from 20,5 tn/hr and before top of descent was 17.2 tn/hr

Fuel at Take Off : 88.5 tons

Fuel at landing : 16 tons

Flight time : 3:42 

Average flight fuel consumption : 72.500 / 3.7 = 19,6 tn/hr

So roughly the range of Concorde-X for full subsonic flight is 2,000nm + reserve

 

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Fraser Gale

I have a graph that shows a subsonic range of up to 2500NM, but you need a tail wind of 90 knots to make it work. 

Flight time of 5:35 if the above conditions exist and fuel usage of around 90000kgs. 

I wouldn't like to test this though...

Frazz

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Konstantin

I see that you flew at a constant cruise altitude of 31000 feet. I am sure that you could have reduced your fuel burn (and increased your range) if you had performed step climbs while you became lighter. It is said that the most efficient cruise altitude at heavy weights (after takeoff) is circa 28000 feet, and I am sure that you could have easily reached 39000 feet or more before the descent. Flying Concorde at a constant altitude during the entire cruise regime means to relinquish fuel efficiency.

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Kyprianos Biris

@afterburner I agree but I have no way of calculating the Concorde step climb points for subsonic. After all this aircraft was not made for this kind of flying and my flight was an exception to the usual ones.

Also for the Delta Wing Concorde I am not sure if at higher levels where IAS would decrease to still maintain Mach 0,95 the increased drag due to higher angle of attack would make sense in fuel per mile ratio.

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Konstantin

Yes, the IAS would decrease at higher levels, but because you would be lighter, the angle of attack would stay more or less constant. 

One hint at optimal subsonic flight levels is provided in the official flight plans supplied by FS Labs in the folder "Flight Plan Routes". On the flight London-Bahrain, which has a substantial subsonic section, you can see that the target cruise altitude is FL270 for the segment from London to the Mediterranean see. However, for the return flight from Bahrain to London, you can see that the flight plan instructs you to descend to a subsonic cruise altitude of FL380 once you have reached the Italian coast. I assume that this is the most fuel-efficient subsonic flight level at light weights.

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7 hours ago, petakas said:

I have no way of calculating the Concorde step climb points for subsonic.

Here you are.

Now you have a way of doing it :)

Do keep .95

If you need more, I have the tables, but the graph is quite good I think.

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Kyprianos Biris

Some help in DISTANCE SPECIFIQUE please.

I guess its the range in nm. How do I read this to find the range ?

The rest about FL's and and where the mass curve meet, I understand

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Konstantin

I think that "DISTANCE SPECIFIQUE" gives information about how many nautical miles you can fly per 1000 kg of consumed fuel at a given altitude.

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Confirmed. The optium level ("Niveau Optimal") is the one for which you have the higher distance covered with 1 T except for mass > 170 T where the optimum altitude would make M0.95 > VMO

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Jip van Kuijk
On 20/06/2016 at 3:30 PM, Cyril said:

Here you are.

Now you have a way of doing it :)

Do keep .95

If you need more, I have the tables, but the graph is quite good I think.

Shit you have the real deal!! ME WANT! ;)

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Hi.

Try to Google "air france concorde manuel" ;)

The volume II's URL isn't very difficult to guess.

I lost my digital BA's files (only have the printed document) but they are available on Avialog's site. One month's subscription isn't very expensive.

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Brian Furlong

I still use the updated FDE pack in the unsupported mods section of this site because, although I love her, concorde X seems to use unrealistic levels of fuel whilst subsonic.  At least when I flew it did.  Maybe I just had a corrupted fuelflow.ini file but without the mod, I would consistently get higher fuel flow per engine while subsonic than when I was supersonic.  It was something like a FF of 5,600 kgs per engine per hour while subsonic at FL370 after decelerating from a supersonic transatlantic crossing.  With that amount of fuel burn a lot of the JFK to Nice, or the entirely subsonic JFK to California flights air france did occasionally in the 80s would've never been possible.

According to a concorde pilot:

Quote

Concorde, whilst more fuel efficient at M2.00, had a much higher fuel flow at M2.00 than at M0.95. 

If we take a Concorde, at 140,000 kgs, in ISA conditions, in still air, flying at the optimum altitude for her weight and speed we find: 

• 4e...FL520...M2.00...1,147 kts...5,783 kg/eng/hr...23,132 kg/hr
• 4e...FL290...M0.95......562 kts...3,576 kg/eng/hr...14,304 kg/hr
• 3e...FL270...M0.95......567 kts...5,560 kg/eng/hr...16,680 kg/hr
So, from these figures, we can see that Concorde’s fuel flow, at M2.00, was, very roughly: 

• 60% higher than her 4-engined cruise at M0.95
• 40% higher than her 3-engined cruise at M0.95.

 

We can see, from the above table that Concorde used around: 

• 20kg of fuel to travel each supersonic mile, at M2.00
• 25kg of fuel to travel each subsonic mile, at M0.95 (four engines)
• 30kg of fuel to travel each subsonic mile, at M0.95 (three engines)
Factor in the decel, descent, approach and landing (all of which had obviously been originally flight planned at subsonic speed anyway) and the actual decrease in range, following a speed reduction, was roughly: 
• M2.00 to M0.95 (four engines) a range reduction of 20%
• M2.00 to M0.95 (three engines) a range reduction of 30%

 

As for how far she can actually go subsonically, I took a look at some flight logs recorded by air france crews.  I'm looking at flight AFR4798 which flew from new york to oakland as part of a world tour in november of 1986 with 100 passengers and a recorded distance of 2231nm.  The amount of fuel they took at the gate is listed as 84200kg.  Another is AFR4801 which flew from JFK to sacramento in june of 1988 with 80 passengers and a recorded distance of 2205nm.  The amount of fuel this flight took at the gate was just 80,000kg and it says she landed with 12,000kg remaining.  So I guess that gives you a rough estimate of max range while subsonic.   I'm not sure I'd even be able to replicate these flights with the fuel flow I was getting before the mod.  Well maybe I'd have made an unexpected landing somewhere in the Nevada desert  :D

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Kyprianos Biris
12 hours ago, SanxDiegoxSand said:

I still use the updated FDE pack in the unsupported mods section

Which file do you mean ? and are you flying FSX or P3D ?

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Brian Furlong
3 hours ago, petakas said:

Which file do you mean ? and are you flying FSX or P3D ?

 

I fly on FSX acceleration, the boxed version.  The file was posted here back in 2010 and includes an updated concorde.air file, a fuelburn.ini file, and an aircraft.cfg file.  it's located here:  

What I did after the latest 1.3 update is, I kept the aircraft.cfg file the same, no changing it at all.  I replaced the concorde.air file in the FSLabs_BAe-Concorde folder with the one included in the updated FDE mod, and I merged the two fuelburn.ini files together, taking some information from the latest update and some from the "updated FDE" pack.  Now my fuelburn is exactly according to what I've read.  The only issue is my supersonic accelerations take a minute or two longer, but it's effect seems to be negligible on fuel consumption overall..

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  • 2 weeks later...
Konstantin

After investigating a little bit, I have found that it is not the fuelburn.ini file that is responsible for a higher-than-supposed subsonic fuel consumption, but the .air-file.

I have compared the original air-file with the one from the modified FDE package (as mentioned above) using the program "AAM 2.2", and it looks like the original air file has a higher wave drag at M0.95 in the section that plots the wave drag vs. mach number. I remember having used that modified air-file for a flight from KIAD to EGLL two years ago, and after having reached FL260 at M0.95, the fuel flow was around 4700 kg/h/e, which is quite consistent with the data on specific range outlined in the document linked by Cyril. On my recently posted flight from EGLL - KCHS, I had a fuel burn of 5500 kg/h/e during that stage, which is higher than it should be. If you fly longer subsonic legs, it can make a substantial difference to the achievable range or fuel left on arrival.

The observation that it takes longer for supersonic acceleration is also attributed to the air file. I have noticed that the wave drag in the M1.0 - 1.6 range is slightly higher in the modified air file than in the original one.

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Fraser Gale
On 26 June 2016 at 8:27 AM, SanxDiegoxSand said:

As for how far she can actually go subsonically, I took a look at some flight logs recorded by air france crews.  I'm looking at flight AFR4798 which flew from new york to oakland as part of a world tour in november of 1986 with 100 passengers and a recorded distance of 2231nm.  The amount of fuel they took at the gate is listed as 84200kg.  

Are you sure they did this subsonic? I think BA did this same route on a round the world but they flew north from Kennedy, accelerating and flying supersonic over northern Canada. This would be consistent with the figures you have quoted. 

I don't know the Sacramento route but if there was sparsely populated areas or a way they could avoid populated areas they probably would have gone supersonic.

Frazz

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Brian Furlong
16 hours ago, Frazz said:

Are you sure they did this subsonic? I think BA did this same route on a round the world but they flew north from Kennedy, accelerating and flying supersonic over northern Canada. This would be consistent with the figures you have quoted. 

I don't know the Sacramento route but if there was sparsely populated areas or a way they could avoid populated areas they probably would have gone supersonic.

Frazz

yep they did it subsonically.   BA did it too:

BA9001C.jpg

 

I remember reading that the US banned supersonic flight over all of it's territory in the early 70s, probably had something to do with our own SST not coming to fruition, but either way I'm almost positive there were no exceptions made to this rule ever, even over sparsely populated areas.   And I've gotta add, there's a site you can visit to check out some flight logs and other info on Air France concorde flights, it's called :  http://www.lesvolsdeconcorde.com/

it's a bit buggy but a great source of info, I get a lot of information and ideas for flights from there.  Hope you find some great stuff, I've only gotten through maybe half of the flight logs.

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Brian Furlong
On 7/10/2016 at 2:31 PM, afterburner said:

After investigating a little bit, I have found that it is not the fuelburn.ini file that is responsible for a higher-than-supposed subsonic fuel consumption, but the .air-file.

I have compared the original air-file with the one from the modified FDE package (as mentioned above) using the program "AAM 2.2", and it looks like the original air file has a higher wave drag at M0.95 in the section that plots the wave drag vs. mach number. I remember having used that modified air-file for a flight from KIAD to EGLL two years ago, and after having reached FL260 at M0.95, the fuel flow was around 4700 kg/h/e, which is quite consistent with the data on specific range outlined in the document linked by Cyril. On my recently posted flight from EGLL - KCHS, I had a fuel burn of 5500 kg/h/e during that stage, which is higher than it should be. If you fly longer subsonic legs, it can make a substantial difference to the achievable range or fuel left on arrival.

The observation that it takes longer for supersonic acceleration is also attributed to the air file. I have noticed that the wave drag in the M1.0 - 1.6 range is slightly higher in the modified air file than in the original one.

I fly subsonically about half the time during my flights so I use the modified files.  But do you know if the higher wave drag in modified .air file is realistic?  If the acceleration times I'm getting are a bit too unrealistically high I'd maybe look into going back to the original files.  Is there any way I could modify the "modified" .air file myself, or is it too difficult for a novice like me?   Thanks for the info man, it really helps

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Fraser Gale

I had a look at my flight logs and I was getting mixed up. BA went to Oakland from Acapulco supersonic (unless it was a different Oakland!) so you are quite right. 

USA were a little jealous about it all. I tend to stick with BA routes but I'll have a look at it.

Frazz

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Konstantin

Hello SanxDiegoxSand,

I have modified the original .air-file by slightly reducing the wave drag at M0.95, which should give you a more realistic fuel burn at that speed. The drag for supersonic speeds (as well as other parameters) is unaffected (the same as in the original) and does not impact the acceleration time to Mach 2.

This is the file that I am using personally for my flights. Let me know how it "behaves" on your Concorde.

 

[EDIT April-10-2017:  The files have been updated. Please refer to the following thread to download the files and learn more how they affect the subsonic fuel consumption. If you have downloaded the files previously, please redownload them.]

 

 

 

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Konstantin
10 hours ago, Beardyman said:

Hi Afterburner,

Would like to ask how your air file modification stands against real numbers ?

Yes, here is some data that I have measured (Temp ISA +-0):

 

What the fuel flow should be roughly according to the chart provided by Cyril and the Concorde pilot:

FL260  M0.95  170T    ->    4400 kg/h/e

FL290  M0.95  140T    ->    3600 kg/h/e

FL330  M0.95  120T    ->    3100 kg/h/e

 

How much fuel is consumed by ConcordeX v1.32 (original .air-file)

FL260  M0.95  170T    ->    5600 kg/h/e

FL290  M0.95  140T    ->    5000 kg/h/e

FL330  M0.95  120T    ->    4200 kg/h/e

 

How much fuel is consumed with my modified .air-file

FL260  M0.95  170T    ->    4500 kg/h/e

FL290  M0.95  140T    ->    3850 kg/h/e

FL330  M0.95  120T    ->    3350 kg/h/e

 

I hope that information is helpful. (By the way, I did one correction on the .air-file after offering it for download, so please redownload it if you have done so and don't forget to back up your original file - just in case).

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Beardyman

Interesting...

Quite significant discrepancy between 'original' and real values.

Would be interesting to hear some comment from FSL.

I think i will give a try to ur air file.

One more question - does ur modification affect fuel burn in supersonic flight ?

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Konstantin

No, supersonic fuel burn should not be affected by the modification (since I didn't alter the wave drag in the supersonic region; I did only do so for speeds in the M0.95 vicinity).

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Beardyman

Hi Afterburner,

For the purpose of creating Concorde subsonic profile in PFPX, i try to find charts and specific fuel consumption data.

Do you know any source of real world data ? 

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Konstantin

I have simply used the chart linked by Cyril in this thread:

On 6/20/2016 at 3:30 PM, Cyril said:

Here you are.

Now you have a way of doing it :)

Do keep .95

If you need more, I have the tables, but the graph is quite good I think.

 

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Andrew Wilson

I believe it may be possible to extend the fuel burn logic implemented for V1.3 (supersonic only) to subsonic cruise as well - but it will require a lot of data to be inputted by hand into tables. 

With the imminent release of our A320-X - that's not something we have time for right now. However, if someone is up to the task - send me a private message and I can send you details on what's required. We can then extend the code base for subsonic flight and you'll then have realistic fuel burn values for subsonic and supersonic cruise. 

Note this method of setting the fuel burn is independent of the air file. 

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Konstantin

Beardyman, what information do you need to create a subsonic profile?

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Beardyman

As Andrew wrote "I can send you details on what's required. We can then extend the code base for subsonic flight and you'll then have realistic fuel burn values for subsonic and supersonic cruise."

 

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  • 6 months later...
Steve Prowse

Just a quick question; did the fuel issue for sub sonic flight get resolved?   I've just had tea and biscuits with the Chief Pilot:wacko:.  I have just finished my New York-Fort Worth leg all flown sub sonic, First time ever I landed with well below the planned fuel level not even enough to pump forward......all very embarrassing :(.......so any comments much appreciated guys.

 

all the best 

Steve.

 

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  • 2 weeks later...
Kyprianos Biris
On 2/13/2017 at 3:07 PM, Steve Prowse said:

First time ever I landed with well below the planned fuel level

What method did you use to plan that fuel ?

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Steve Prowse

Hi Kyprianos,

I always use CPS...which I think gives the correct fuel required for that subsonic flight.  I guess that Afterburner's,  .air file mod,  was never included in any update...what do you think?

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Konstantin

There have not been any official updates on subsonic fuel consumption yet. I am not sure if one is still planned for the future (maybe the developers have more information), but until then, the best thing you can do is to download and use my modified .air-file.

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Konstantin

Updating the fuel burn tables was postponed into the future, because the developers were focusing all their resources on the FSL Airbus A-320. I don't know whether the workload has relaxed a little bit in the meantime.

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Kyprianos Biris
On 2/26/2017 at 7:55 AM, Steve Prowse said:

I guess that Afterburner's,  .air file mod,  was never included in any update...what do you think?

I would not assume that CPS takes in to account a modified file unless the developer stated so somewhere.

As far as I know Concorde-X flight model has received quite some changes from FSL in 2016 since the "past" and the variables used are not only the ones in the .air file but others as well embedded in the aircraft.cfg like the drag tables etc.

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  • 3 years later...
Ramón Cutanda
On 7/12/2016 at 5:55 AM, Brian Furlong said:

And I've gotta add, there's a site you can visit to check out some flight logs and other info on Air France concorde flights, it's called :  http://www.lesvolsdeconcorde.com/

I know I arrive very, very late to this post, but man... THIS IS PURE GOLD! WOW! WHAT AN AMAZING WEBSITE. I am "suffering" the problems of fuel calculation for long subsonic routes. In particular, I am trying to make the KJFK-KOAK route of one of Concorde's world tour. For 80 PAX and a ZFW of 87,367, CPS-X calculates just 56,382 of fuel at FL320. As much as I have tried to keep the optimal FL for weight along the route using step climbs and a CG of 55%, it does not take long before it is pretty obvious that it is not possible to complete the flight with those figures. Now, thanks to the flight plans stored at lesvolsdeconcorde.com/ I have been able to learn that F-BVFF flew that route (2,231nm) with 90,00T of fuel... for ONLY 9 PAX!!! (05:39 block time) No wonder I could not make it with CPS-X calculations!!!

http://www.lesvolsdeconcorde.com/Concorde/VOLSYN/QA0AAE~mOBZ5cGxiZHNpYlNJAgA

Another flight for that route by F-BVFF used 84,20T of fuel and 05:34 of block time. There is no info about PAX for this flight but it must have been another "light" flight.

http://www.lesvolsdeconcorde.com/Concorde/VOLSYN/QA0AAN7tSRZ5cGxiZHNpYlNJAgA

I still have A LOT to learn about subsonic flights, but, again,  lesvolsdeconcorde.com, is an invaluable source of information.

THANKS SO MUCH!!!

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Fraser Gale
52 minutes ago, Ramón Cutanda said:

I know I arrive very, very late to this post, but man... THIS IS PURE GOLD! WOW! WHAT AN AMAZING WEBSITE. I am "suffering" the problems of fuel calculation for long subsonic routes. In particular, I am trying to make the KJFK-KOAK route of one of Concorde's world tour. For 80 PAX and a ZFW of 87,367, CPS-X calculates just 56,382 of fuel at FL320. As much as I have tried to keep the optimal FL for weight along the route using step climbs and a CG of 55%, it does not take long before it is pretty obvious that it is not possible to complete the flight with those figures. Now, thanks to the flight plans stored at lesvolsdeconcorde.com/ I have been able to learn that F-BVFF flew that route (2,231nm) with 90,00T of fuel... for ONLY 9 PAX!!! (05:39 block time) No wonder I could not make it with CPS-X calculations!!!

http://www.lesvolsdeconcorde.com/Concorde/VOLSYN/QA0AAE~mOBZ5cGxiZHNpYlNJAgA

Another flight for that route by F-BVFF used 84,20T of fuel and 05:34 of block time. There is no info about PAX for this flight but it must have been another "light" flight.

http://www.lesvolsdeconcorde.com/Concorde/VOLSYN/QA0AAN7tSRZ5cGxiZHNpYlNJAgA

I still have A LOT to learn about subsonic flights, but, again,  lesvolsdeconcorde.com, is an invaluable source of information.

THANKS SO MUCH!!!

@Ramón Cutanda is this not what was being discussed on the other thread when I did a rough fuel calculation for the route?  Someone had given the CPS figure for the subsonic route which I felt was a bit low but @Ray Proudfoot felt that CPS had been programmed to cope with subsonic only flights.  I can't comment on that as I don't use it, but from the planning programs I've written and from using the manual planning figures, I know that planning subsonic only flights is quite a different ball game, so I would understand if CPS didn't quite cover it. 

I think I calculated a minimum trip fuel of 60+ tonnes but that was with zero wind.  Chances are head winds would bring that up to the figures you are getting from that website.  Figures are on the other thread - I'm getting confused now with all these old threads coming up!

Frazz

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Ramón Cutanda

As I just said, I still have A LOT to learn about subsonic flights, fuel management and GG...  and I am not in any hurry at all to do so. Less than two weeks ago I renewed my BA documentation, getting updated documents (most recent dated 5th May 2003). Because these are scanned versions, I am manually bookmarking all sections to be able to quickly find whatever I need in the future. This takes a while, of course... Should I learn anything not already said about this topic, obviously I will share it.

Bests,

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Ray Proudfoot
38 minutes ago, Fraser Gale said:

@Ramón Cutanda is this not what was being discussed on the other thread when I did a rough fuel calculation for the route?  Someone had given the CPS figure for the subsonic route which I felt was a bit low but @Ray Proudfoot felt that CPS had been programmed to cope with subsonic only flights.  I can't comment on that as I don't use it,

Frazz

Yes, CPS-X has an option for subsonic as well as supersonic (obviously). Even if you don’t want to use it I would have thought it would be useful to have for comparison with your own procedures. Available here. https://library.avsim.net/search.php?SearchTerm=CPS-X&CatID=root&Go=Search

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