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TWA902fly
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Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 5:36 pm

I was clicking on random flights today on FlightRadar24, and I came across Qatar #777 DOH-MIA, an A350-900, cruising at 43,000 feet. Out of curiosity, I checked the service ceiling, which is listed as 43,100 feet. However, for the A350-1000, the service ceiling is 41,450 feet. I was wondering what accounts for this difference? I would assume the structure of the A350-900 and -1000 can withstand the same pressure differential, but this difference in service ceiling makes me question that. Does anyone have an answer?

Service ceilings taken from EASA Type Certificate Data Sheet: https://www.easa.europa.eu/sites/default/files/dfu/TCDS_EASA%20_A_151_Airbus350_Iss22-2019-11-27.pdf

Upon further investigation, I see that the Boeing 787-8 and 787-9 have the same service ceiling (43,100 feet), while the 787-10 has a lower one (41,100 feet). My initial thought had me thinking that maybe it has something to do with the volume of air held due to fuselage length differences, but then I would assume there would be a difference between the 787-8 and 787-9, which there is not.

Again, data taken from EASA TCDS: https://www.easa.europa.eu/sites/default/files/dfu/TCDS%20EASA%20IM%20A%20115%20B787%20Iss%2024%20-%2028%20Oct%2019.pdf

Thanks for any explanation!

'902
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ElroyJetson
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 6:00 pm

TWA902fly wrote:
I was clicking on random flights today on FlightRadar24, and I came across Qatar #777 DOH-MIA, an A350-900, cruising at 43,000 feet. Out of curiosity, I checked the service ceiling, which is listed as 43,100 feet. However, for the A350-1000, the service ceiling is 41,450 feet. I was wondering what accounts for this difference? I would assume the structure of the A350-900 and -1000 can withstand the same pressure differential, but this difference in service ceiling makes me question that. Does anyone have an answer?

Service ceilings taken from EASA Type Certificate Data Sheet: https://www.easa.europa.eu/sites/default/files/dfu/TCDS_EASA%20_A_151_Airbus350_Iss22-2019-11-27.pdf

Upon further investigation, I see that the Boeing 787-8 and 787-9 have the same service ceiling (43,100 feet), while the 787-10 has a lower one (41,100 feet). My initial thought had me thinking that maybe it has something to do with the volume of air held due to fuselage length differences, but then I would assume there would be a difference between the 787-8 and 787-9, which there is not.

Again, data taken from EASA TCDS: https://www.easa.europa.eu/sites/default/files/dfu/TCDS%20EASA%20IM%20A%20115%20B787%20Iss%2024%20-%2028%20Oct%2019.pdf

Thanks for any explanation!

'902


This issue came up once before. PInkmachine, a 787 driver, said due to the wing of the 789 and 788 it struggles to reach its service ceiling unless it is very light. He said he has taken both up to 43,000 feet, but rarely. He speculated this might be why the 787-10 has a service ceiling 2,000 feet lower (it is obviously a bigger aircraft with a heavier OEW). The wing simply will not allow it to fly higher.

As for the A350, I have no idea, but it may be the same issue. Maybe some A350 drivers can comment.
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 6:08 pm

I can only speculate. There is a requirement to drop the altitude quickly in an emergency. Is is possible cabin pressure cannot be controlled with the same climate control system from the higher altitude.

The other option is the estimated increased cabin pressure leakage increased enough to not have the required pressurization margin, with allowed equipment failures, to maintain the higher altitude.

Recall, the certification testing must demonstrate in a failure, such as loss of an engine or cabin pressurization compressor.

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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 6:17 pm

Passenger aircraft have a certification requirement to be able to descend from maximum operating altitude to 10,000 ft within a certain number of minutes in case of a rapid decompression. The larger variants of these aircraft are heavier, which means there is more potential energy that needs to be shed during the emergency descent (potential energy = mass * altitude). However, because the primary drag producing control surface, the speed brakes, are the same size, it means that the larger variant takes longer to descend the same amount of altitude. This limits the maximum operating altitude.
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dakota558
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 6:19 pm

There is a difference between service ceiling and maximum operating altitude. Service ceiling is the maximum altitude an aircraft can sustain a climb rate of 100 fpm. This can vary with weight and atmospheric conditions. Maximum operating altitude is the maximum certified altitude an aircraft can operate at. Without going into to much detail, it will depend upon pressurisation, the time it will take to descend to a safe altitude in case of a depressurisation, the margin between low speed buffet and high speed buffet (stall due too going to slow and stall due to flying too fast), and a few other factors.
And then you also have absolute ceiling, which is the maximum altitude the airplane will go to, which will be higher than the service ceiling and might be higher than the max certified ceiling.

As for the different certified altitudes for those aircraft, I do not know the reason for it. Could be due to time it will take to descend to a safe altitude in case of an emergency, or other factors.
 
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 6:57 pm

ElroyJetson wrote:
TWA902fly wrote:
I was clicking on random flights today on FlightRadar24, and I came across Qatar #777 DOH-MIA, an A350-900, cruising at 43,000 feet. Out of curiosity, I checked the service ceiling, which is listed as 43,100 feet. However, for the A350-1000, the service ceiling is 41,450 feet. I was wondering what accounts for this difference? I would assume the structure of the A350-900 and -1000 can withstand the same pressure differential, but this difference in service ceiling makes me question that. Does anyone have an answer?

Service ceilings taken from EASA Type Certificate Data Sheet: https://www.easa.europa.eu/sites/default/files/dfu/TCDS_EASA%20_A_151_Airbus350_Iss22-2019-11-27.pdf

Upon further investigation, I see that the Boeing 787-8 and 787-9 have the same service ceiling (43,100 feet), while the 787-10 has a lower one (41,100 feet). My initial thought had me thinking that maybe it has something to do with the volume of air held due to fuselage length differences, but then I would assume there would be a difference between the 787-8 and 787-9, which there is not.

Again, data taken from EASA TCDS: https://www.easa.europa.eu/sites/default/files/dfu/TCDS%20EASA%20IM%20A%20115%20B787%20Iss%2024%20-%2028%20Oct%2019.pdf

Thanks for any explanation!

'902


This issue came up once before. PInkmachine, a 787 driver, said due to the wing of the 789 and 788 it struggles to reach its service ceiling unless it is very light. He said he has taken both up to 43,000 feet, but rarely. He speculated this might be why the 787-10 has a service ceiling 2,000 feet lower (it is obviously a bigger aircraft with a heavier OEW). The wing simply will not allow it to fly higher.

As for the A350, I have no idea, but it may be the same issue. Maybe some A350 drivers can comment.

Keep in mind the 787-9 and -10 have the same MTOW. The wing, when lifting, doesn’t care how much of the weight is from the airframe and how much from payload onboard. That said your typical -10 will be operating at higher weights than a -9 on the same route.
 
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 7:39 pm

Polot wrote:
ElroyJetson wrote:
TWA902fly wrote:
I was clicking on random flights today on FlightRadar24, and I came across Qatar #777 DOH-MIA, an A350-900, cruising at 43,000 feet. Out of curiosity, I checked the service ceiling, which is listed as 43,100 feet. However, for the A350-1000, the service ceiling is 41,450 feet. I was wondering what accounts for this difference? I would assume the structure of the A350-900 and -1000 can withstand the same pressure differential, but this difference in service ceiling makes me question that. Does anyone have an answer?

Service ceilings taken from EASA Type Certificate Data Sheet: https://www.easa.europa.eu/sites/default/files/dfu/TCDS_EASA%20_A_151_Airbus350_Iss22-2019-11-27.pdf

Upon further investigation, I see that the Boeing 787-8 and 787-9 have the same service ceiling (43,100 feet), while the 787-10 has a lower one (41,100 feet). My initial thought had me thinking that maybe it has something to do with the volume of air held due to fuselage length differences, but then I would assume there would be a difference between the 787-8 and 787-9, which there is not.

Again, data taken from EASA TCDS: https://www.easa.europa.eu/sites/default/files/dfu/TCDS%20EASA%20IM%20A%20115%20B787%20Iss%2024%20-%2028%20Oct%2019.pdf

Thanks for any explanation!

'902


This issue came up once before. PInkmachine, a 787 driver, said due to the wing of the 789 and 788 it struggles to reach its service ceiling unless it is very light. He said he has taken both up to 43,000 feet, but rarely. He speculated this might be why the 787-10 has a service ceiling 2,000 feet lower (it is obviously a bigger aircraft with a heavier OEW). The wing simply will not allow it to fly higher.

As for the A350, I have no idea, but it may be the same issue. Maybe some A350 drivers can comment.

Keep in mind the 787-9 and -10 have the same MTOW. The wing, when lifting, doesn’t care how much of the weight is from the airframe and how much from payload onboard. That said your typical -10 will be operating at higher weights than a -9 on the same route.



You are correct which is exactly why I referenced OEW versus MTOW.
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 7:55 pm

It seems the 777-300 flies lower as well. Usually in the 29,000 - 34,000 range, while the smaller 200's fly higher. Does the larger 300's struggle to reach altitudes closer to 40,000?
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TWA902fly
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 9:52 pm

flybynight wrote:
It seems the 777-300 flies lower as well. Usually in the 29,000 - 34,000 range, while the smaller 200's fly higher. Does the larger 300's struggle to reach altitudes closer to 40,000?


According to the FAA TCDS, all 777 models (not including 777X) have a service ceiling of 43,100 feet. I am also wondering what the explanation is here? I assume the 29,000-34,000 range you state is you'll see some 777s flying lower in the early parts of their long-haul flights due to the weight of the fuel they're carrying.

FAA TCDS: https://rgl.faa.gov/Regulatory_and_Guid ... _Rev40.pdf

'902
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 10:37 pm

flybynight wrote:
It seems the 777-300 flies lower as well. Usually in the 29,000 - 34,000 range, while the smaller 200's fly higher. Does the larger 300's struggle to reach altitudes closer to 40,000?


The 773 and 77W both have smallish wings compared to the weight they're carrying. You will rarely a 77W past 360 unless it's either 1) extremely light and operating a short sector or 2) it's at almost of the end of a ULH flight and has been step climbing its way up there. It still has the original wing for the 772 with a little extension that includes raked wingtips, but it's the same wing for a plane that has a MTOW of over 100 tons more than the plane the wing was originally designed for.
 
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 10:42 pm

flybynight wrote:
It seems the 777-300 flies lower as well. Usually in the 29,000 - 34,000 range, while the smaller 200's fly higher. Does the larger 300's struggle to reach altitudes closer to 40,000?


All current B777s produced have a service ceiling of 43,100 feet. I remember flying last year on an Emirates B777-300ER from OJAI to OMDB, we were cruising at an altitude of FL390. So it can go higher than what you mentioned.
 
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 10:55 pm

Well, the 773ER has very high wing loading, (compared to A359/A3510) so it doesn't surprise me that unless it is very light its not going anywhere near FL400. The 777X rectifies that issue with its significantly larger wing area.

Actually, the issue of Boeing going the high wing loading route vs Airbus going the low wing loading route has been discussed in a previous post.
 
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Tue Mar 31, 2020 10:58 pm

xwb777 wrote:
flybynight wrote:
It seems the 777-300 flies lower as well. Usually in the 29,000 - 34,000 range, while the smaller 200's fly higher. Does the larger 300's struggle to reach altitudes closer to 40,000?


All current B777s produced have a service ceiling of 43,100 feet. I remember flying last year on an Emirates B777-300ER from OJAI to OMDB, we were cruising at an altitude of FL390. So it can go higher than what you mentioned.


Of course, on a short leg like that one it can fly at 390 or 400.
 
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Wed Apr 01, 2020 11:10 am

Two points. First I thought that the 43100ft ceiling was to do with flight deck oxygen masks. To fly higher you need a different type which is not worth fitting??

Second from my youth, The HS Trident 2 did not have a passenger oxygen system. It could descend fast with thrust reverse deployed and get down in the time limit to 10000ft!
 
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Wed Apr 01, 2020 3:31 pm

Well, I have about 4,000 hours in planes cert’d for F510 and the masks are the same as those below F430, so not sure about that one. Civil masks for pressure breathing are rare, in my understanding.
 
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Wed Apr 01, 2020 7:21 pm

ElroyJetson wrote:
TWA902fly wrote:
I was clicking on random flights today on FlightRadar24, and I came across Qatar #777 DOH-MIA, an A350-900, cruising at 43,000 feet. Out of curiosity, I checked the service ceiling, which is listed as 43,100 feet. However, for the A350-1000, the service ceiling is 41,450 feet. I was wondering what accounts for this difference? I would assume the structure of the A350-900 and -1000 can withstand the same pressure differential, but this difference in service ceiling makes me question that. Does anyone have an answer?

Service ceilings taken from EASA Type Certificate Data Sheet: https://www.easa.europa.eu/sites/default/files/dfu/TCDS_EASA%20_A_151_Airbus350_Iss22-2019-11-27.pdf

Upon further investigation, I see that the Boeing 787-8 and 787-9 have the same service ceiling (43,100 feet), while the 787-10 has a lower one (41,100 feet). My initial thought had me thinking that maybe it has something to do with the volume of air held due to fuselage length differences, but then I would assume there would be a difference between the 787-8 and 787-9, which there is not.

Again, data taken from EASA TCDS: https://www.easa.europa.eu/sites/default/files/dfu/TCDS%20EASA%20IM%20A%20115%20B787%20Iss%2024%20-%2028%20Oct%2019.pdf

Thanks for any explanation!

'902


This issue came up once before. PInkmachine, a 787 driver, said due to the wing of the 789 and 788 it struggles to reach its service ceiling unless it is very light. He said he has taken both up to 43,000 feet, but rarely. He speculated this might be why the 787-10 has a service ceiling 2,000 feet lower (it is obviously a bigger aircraft with a heavier OEW). The wing simply will not allow it to fly higher.

As for the A350, I have no idea, but it may be the same issue. Maybe some A350 drivers can comment.


We recently took a flight from DOH-CPT on a 787. Easily reached FL430 with 5+ hours left in the 10 hour flight.
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Wed Apr 01, 2020 8:41 pm

FriscoHeavy wrote:
ElroyJetson wrote:
TWA902fly wrote:
I was clicking on random flights today on FlightRadar24, and I came across Qatar #777 DOH-MIA, an A350-900, cruising at 43,000 feet. Out of curiosity, I checked the service ceiling, which is listed as 43,100 feet. However, for the A350-1000, the service ceiling is 41,450 feet. I was wondering what accounts for this difference? I would assume the structure of the A350-900 and -1000 can withstand the same pressure differential, but this difference in service ceiling makes me question that. Does anyone have an answer?

Service ceilings taken from EASA Type Certificate Data Sheet: https://www.easa.europa.eu/sites/default/files/dfu/TCDS_EASA%20_A_151_Airbus350_Iss22-2019-11-27.pdf

Upon further investigation, I see that the Boeing 787-8 and 787-9 have the same service ceiling (43,100 feet), while the 787-10 has a lower one (41,100 feet). My initial thought had me thinking that maybe it has something to do with the volume of air held due to fuselage length differences, but then I would assume there would be a difference between the 787-8 and 787-9, which there is not.

Again, data taken from EASA TCDS: https://www.easa.europa.eu/sites/default/files/dfu/TCDS%20EASA%20IM%20A%20115%20B787%20Iss%2024%20-%2028%20Oct%2019.pdf

Thanks for any explanation!

'902


This issue came up once before. PInkmachine, a 787 driver, said due to the wing of the 789 and 788 it struggles to reach its service ceiling unless it is very light. He said he has taken both up to 43,000 feet, but rarely. He speculated this might be why the 787-10 has a service ceiling 2,000 feet lower (it is obviously a bigger aircraft with a heavier OEW). The wing simply will not allow it to fly higher.

As for the A350, I have no idea, but it may be the same issue. Maybe some A350 drivers can comment.


We recently took a flight from DOH-CPT on a 787. Easily reached FL430 with 5+ hours left in the 10 hour flight.



You would have to ask pinkmachine. In the scenario you mentioned (maybe 6-7 hours of fuel left) that would indicate the 787 fuel tanks would be at least half empty. Obviously light enough to reach FL 43,000. The highest i have seen in flight radar is FL 39,000.

Again, I am not a 787 pilot, so they would probably be your best source.
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Wed Apr 01, 2020 11:57 pm

TWA902fly wrote:
Out of curiosity, I checked the service ceiling, which is listed as 43,100 feet. However, for the A350-1000, the service ceiling is 41,450 feet. I was wondering what accounts for this difference? I would assume the structure of the A350-900 and -1000 can withstand the same pressure differential, but this difference in service ceiling makes me question that. Does anyone have an answer?


Firstly we need to understand what this limit represents from FAR Sec. 25.1527 — Ambient air temperature and operating altitude the limit is "The extremes of the ambient air temperature and operating altitude for which operation is allowed, as limited by flight, structural, powerplant, functional, or equipment characteristics, must be established."

Now we need to understand a little about cruising levels. Between FL290 and FL410 are known as RVSM levels, where there is 1000 ft separation between levels in opposite directions. Above FL410 the next level is non RVSM, The next eastbound level above FL410 is not FL430, it is FL450, then FL490 (FL410, FL450. FL490). Westbound the highest RVSM level is FL400, next is FL430, FL470, then FL510. (FL400, FL430, FL470, FL510)

Then to confuse things a little more is Chinese RVSM which is metric, the highest metric flight level is 12500 meters (FL411). Above 12500 meters eastbound is 13100 (FL430), 14300 (FL469), 15500 (FL509) meters. Westbound is 13700 (FL449), then 14900 (FL489).

This is why we normally see maximum ceiling in civil airliners either at FL411 or FL430, it is the highest published cruising level the aircraft can attain meeting the minimum performance requirements.

There are a few more definitions
Absolute Ceiling the absolute ceiling is the altitude at which the (maximum) rate of climb goes to zero.
Service Ceiling the service ceiling is the altitude at which the maximum rate of climb is 500 ft/min (2.5 m/s) for jet powered aircraft.
Cruise Ceiling the cruise ceiling is the altitude at which the maximum climb rate is 300 ft/min

So by saying the ceiling is FL411 (12500 m) on the A350-1000 it is saying it cannot get to a higher cruising level (FL430) with a minimum of 300 ft/min at cruise speed, the the A350-900 could not get to FL450 with a minimum climb rate of 300 ft/min at cruise speed. The A350s best rate of climb is at M0.85 at those levels.

The reason why the performance drops off with altitude is air density decreases. This impacts the thrust and drag. However the rate that the thrust drops off is higher than the rate drag drops as altitude decreases. Where the amount of drag cross the amount of thrust is known as the absolute ceiling. This has been illustrated by this diagram from page 230 of "Aircraft Performance: An Engineering Approach" By Mohammad H. Sadraey

Image

The A350-1000 has more thrust than the A350-900, however it also has more surface area, that surface area means more skin friction drag, to overcome the skin friction drag it takes more thrust, as I just posted however the thrust drops off at altitude quicker than drag drops off.
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Fri Apr 03, 2020 8:51 am

This difference goes for B747-400 an B747-8 as well.
744: 45,000 feet
748: 43,000 feet
 
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Fri Apr 03, 2020 9:04 am

andrej wrote:
This difference goes for B747-400 an B747-8 as well.
744: 45,000 feet
748: 43,000 feet


If my feeble memory is correct you need to add 100 feet to each limit. It has to do with the autopilot in VNAV. It maintains a "soft" altitude rather than a "hard" altitude. The 100' is a buffer for the soft mode.
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Fri Apr 03, 2020 9:36 am

mmo wrote:
andrej wrote:
This difference goes for B747-400 an B747-8 as well.
744: 45,000 feet
748: 43,000 feet


If my feeble memory is correct you need to add 100 feet to each limit. It has to do with the autopilot in VNAV. It maintains a "soft" altitude rather than a "hard" altitude. The 100' is a buffer for the soft mode.


Yes, for B744 I know that it is FL451, but I was not sure if 100 feet is applicable to B748 as well.
Thank you for confirmation!

So corrected limits are:
744: 45,100 feet
748: 43,100 feet

Cheers,
Andrej
 
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Fri Apr 03, 2020 11:10 am

andrej wrote:
mmo wrote:
andrej wrote:
This difference goes for B747-400 an B747-8 as well.
744: 45,000 feet
748: 43,000 feet


If my feeble memory is correct you need to add 100 feet to each limit. It has to do with the autopilot in VNAV. It maintains a "soft" altitude rather than a "hard" altitude. The 100' is a buffer for the soft mode.


Yes, for B744 I know that it is FL451, but I was not sure if 100 feet is applicable to B748 as well.
Thank you for confirmation!

So corrected limits are:
744: 45,100 feet
748: 43,100 feet

Cheers,
Andrej


To be fully correct :

All 747 series up to and included the 744 : 45.100 feet.

747-8I : 43.100 ft
747-8F : 42.100 ft. (the 747-8F was original certified up to 42.100 ft, this is still stated in the TCDS)
After modification of some flight spoilers to permit a larger deflection (speedbrakes used in an emergy descend), the later certified 747-8I was certified up to 43.100 feet.

After completion of a Boeing SB during Heavy Maintenance, the 747-8F max altitude can also be raised to 43.100 feet.
Later built 747-8F aircraft have this SB already included during assembly.
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Sun Apr 05, 2020 2:13 am

747classic wrote:
andrej wrote:
mmo wrote:

If my feeble memory is correct you need to add 100 feet to each limit. It has to do with the autopilot in VNAV. It maintains a "soft" altitude rather than a "hard" altitude. The 100' is a buffer for the soft mode.


Yes, for B744 I know that it is FL451, but I was not sure if 100 feet is applicable to B748 as well.
Thank you for confirmation!

So corrected limits are:
744: 45,100 feet
748: 43,100 feet

Cheers,
Andrej


To be fully correct :

All 747 series up to and included the 744 : 45.100 feet.

747-8I : 43.100 ft
747-8F : 42.100 ft. (the 747-8F was original certified up to 42.100 ft, this is still stated in the TCDS)
After modification of some flight spoilers to permit a larger deflection (speedbrakes used in an emergy descend), the later certified 747-8I was certified up to 43.100 feet.

After completion of a Boeing SB during Heavy Maintenance, the 747-8F max altitude can also be raised to 43.100 feet.
Later built 747-8F aircraft have this SB already included during assembly.


At what gross weight can the 744 reach FL450?
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744SPX
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Sun Apr 05, 2020 3:55 am

Pellegrine wrote:
747classic wrote:
andrej wrote:

Yes, for B744 I know that it is FL451, but I was not sure if 100 feet is applicable to B748 as well.
Thank you for confirmation!

So corrected limits are:
744: 45,100 feet
748: 43,100 feet

Cheers,
Andrej


To be fully correct :

All 747 series up to and included the 744 : 45.100 feet.

747-8I : 43.100 ft
747-8F : 42.100 ft. (the 747-8F was original certified up to 42.100 ft, this is still stated in the TCDS)
After modification of some flight spoilers to permit a larger deflection (speedbrakes used in an emergy descend), the later certified 747-8I was certified up to 43.100 feet.

After completion of a Boeing SB during Heavy Maintenance, the 747-8F max altitude can also be raised to 43.100 feet.
Later built 747-8F aircraft have this SB already included during assembly.


At what gross weight can the 744 reach FL450?


I'm guessing that number has partially to do with the engines a particular 744 is equipped with (differences in cruise thrust)?

On a side note, The first 747SP in 1975 (prior to certification) reached and cruised at FL460 for a portion of its flight with 200 passengers on a flight from JFK to Haneda and landed with 30,000 lbs of fuel still remaining...
 
mmo
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Sun Apr 05, 2020 6:27 am

Pellegrine wrote:

At what gross weight can the 744 reach FL450?


It depends on many factors. Normally, 410 will be the max as there isn't much savings going to 450 and the fuel used in the climb is more than you would save for the cruise at 450. But IIRC, you'd need to be down to around 200,000KGS to get up that high. Have been at 450 a few times, to avoid CBs or traffic issues, and there was no appreciable reduction in fuel burn and we had a slower ground speed.

Also, the engine type really doesn't make much difference.






744SPX wrote:

On a side note, The first 747SP in 1975 (prior to certification) reached and cruised at FL460 for a portion of its flight with 200 passengers on a flight from JFK to Haneda and landed with 30,000 lbs of fuel still remaining...


Interesting since the max alt on the SP is also 451. Care to provide a reference???
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Pellegrine
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Sun Apr 05, 2020 7:50 am

mmo wrote:
Pellegrine wrote:

At what gross weight can the 744 reach FL450?


It depends on many factors. Normally, 410 will be the max as there isn't much savings going to 450 and the fuel used in the climb is more than you would save for the cruise at 450. But IIRC, you'd need to be down to around 200,000KGS to get up that high. Have been at 450 a few times, to avoid CBs or traffic issues, and there was no appreciable reduction in fuel burn and we had a slower ground speed.

Also, the engine type really doesn't make much difference.



Is this because of the tropopause or the altitude range of the jet stream? I'm asking about the fuel burn and the GS.
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Starlionblue
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Sun Apr 05, 2020 8:23 am

Pellegrine wrote:
mmo wrote:
Pellegrine wrote:

At what gross weight can the 744 reach FL450?


It depends on many factors. Normally, 410 will be the max as there isn't much savings going to 450 and the fuel used in the climb is more than you would save for the cruise at 450. But IIRC, you'd need to be down to around 200,000KGS to get up that high. Have been at 450 a few times, to avoid CBs or traffic issues, and there was no appreciable reduction in fuel burn and we had a slower ground speed.

Also, the engine type really doesn't make much difference.



Is this because of the tropopause or the altitude range of the jet stream? I'm asking about the fuel burn and the GS.


"The" jet stream is not really a thing, as in it is not a fixed phenomenon. There are several jetstreams around the world, with seasonal variations. Plus they move around even within a season.

The tropopause is also variable depending on location and season.

Jetstreams and the local tropopause do affect day-to-day operations. They do not affect the service ceiling.
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Pellegrine
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Sun Apr 05, 2020 8:56 am

Starlionblue wrote:
Pellegrine wrote:
mmo wrote:

It depends on many factors. Normally, 410 will be the max as there isn't much savings going to 450 and the fuel used in the climb is more than you would save for the cruise at 450. But IIRC, you'd need to be down to around 200,000KGS to get up that high. Have been at 450 a few times, to avoid CBs or traffic issues, and there was no appreciable reduction in fuel burn and we had a slower ground speed.

Also, the engine type really doesn't make much difference.



Is this because of the tropopause or the altitude range of the jet stream? I'm asking about the fuel burn and the GS.


"The" jet stream is not really a thing, as in it is not a fixed phenomenon. There are several jetstreams around the world, with seasonal variations. Plus they move around even within a season.

The tropopause is also variable depending on location and season.

Jetstreams and the local tropopause do affect day-to-day operations. They do not affect the service ceiling.


Ok yeah, but both of them vary in height, location, and for the jet stream speed and direction. I was asking about cruise altitude versus fuel burn and ground speed.
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Starlionblue
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Sun Apr 05, 2020 9:45 am

Pellegrine wrote:
Starlionblue wrote:
Pellegrine wrote:

Is this because of the tropopause or the altitude range of the jet stream? I'm asking about the fuel burn and the GS.


"The" jet stream is not really a thing, as in it is not a fixed phenomenon. There are several jetstreams around the world, with seasonal variations. Plus they move around even within a season.

The tropopause is also variable depending on location and season.

Jetstreams and the local tropopause do affect day-to-day operations. They do not affect the service ceiling.


Ok yeah, but both of them vary in height, location, and for the jet stream speed and direction. I was asking about cruise altitude versus fuel burn and ground speed.


I see. Yes. they vary. But that's a day-by-day decision, reflected first in the flight plan and later in tactical decisions in flight.
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mmo
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Sun Apr 05, 2020 12:54 pm

In one case I can remember, it was AMS-SIN, so we had a tailwind and we climbed to 450 and we were actually picking up about 30 knots less tailwind and our fuel burn was essentially the same at 410. So, in this case, it was a combination of both the Trop and the decreasing effect of the Jet Stream. Had be been going Westbound, it would have helped a little as it would have been a decrease in headwinds. Our flight plan had forecast similar winds at 410/450. So much for that.
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Pellegrine
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Mon Apr 06, 2020 4:35 am

mmo wrote:
In one case I can remember, it was AMS-SIN, so we had a tailwind and we climbed to 450 and we were actually picking up about 30 knots less tailwind and our fuel burn was essentially the same at 410. So, in this case, it was a combination of both the Trop and the decreasing effect of the Jet Stream. Had be been going Westbound, it would have helped a little as it would have been a decrease in headwinds. Our flight plan had forecast similar winds at 410/450. So much for that.


Interesting thanks.
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planewasted
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Mon Apr 06, 2020 11:06 am

The A350-1000 has a lower aspect ratio wing than the 900 (9.03 vs. 9.49 according do Wikipedia). I guess that could affect max altitude?
 
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Starlionblue
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Re: Service Ceiling Difference between A350-900 and -1000 (and 787-8/9 and -10)

Mon Apr 06, 2020 11:36 am

planewasted wrote:
The A350-1000 has a lower aspect ratio wing than the 900 (9.03 vs. 9.49 according do Wikipedia). I guess that could affect max altitude?


The reason for the lower aspect ratio is slightly higher chord to increase wing area by 4%. All else being equal, I think that would increase max altitude capability.
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