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A350 & B787 cruising altitude question

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A350 & B787 cruising altitude question

Old 16th Jan 2021, 10:40
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Ant
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A350 & B787 cruising altitude question

Just watching on FlightRadar24 a Tui 787 just overhead us here in Kent at FL430, Stuttgart to Manchester.
It seems the 787 along with the 350 have somewhat higher cruise altitudes than say 777 or 330 flights.
Don't think I've ever seen a B777 at FL430, or am I wrong?

Last edited by Ant; 16th Jan 2021 at 18:09. Reason: oops, edit to put a "0" after FL43, but you knew what I meant!!
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Old 16th Jan 2021, 10:52
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A brief Google showed me that of the three aircraft you mention, the 777 has the highest max service ceiling.
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Old 16th Jan 2021, 11:09
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Back in the late 1970s I heard a Europe-bound C-141 call London "with ya at 410" - I was quite astonished that the old banger was as high as that and can't recall ever hearing anybody else above 39000 when having an airband radio on as much as possible was my thing (usually 134.9). Subsequently flew over to Miami on an AA 767 which was mostly at 41000 according to the Captain's announcement...
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Old 16th Jan 2021, 11:14
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For a 767 to be at FL 410 it must have been pretty light. Max level was 430, but achievable only at low weights. With the 200 series, 410 was achievable on shorthaul sectors with a full load, but with a full 300 series going longhaul the initial cruise level would be around FL330, maybe reaching 370 towards the end of cruise.
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Old 16th Jan 2021, 11:26
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It was a 200 and I don't recall it being particularly crowded - I had a window seat with no neighbours which suited me very well!
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Old 16th Jan 2021, 12:01
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787 and 350 in a class of their own regarding high altitude cruising FLís at standard weighs. Both with latest wing designs. Traditionally A330ís will fly at higher FLís than 777ís at comparable weights matching the historical mantra of Airbus having more wing than thrust and vise versa for Boeing. A mate on the 777-300ER used to say his machine had thrust to take them up to FLís the wing just didnít want to go to.
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Old 16th Jan 2021, 13:19
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B747-400 with RR engines could make FL451, although I only did it once, just to see what it was like. Very high, quiet (due to low IAS) and dark blue, as it turned out. Quite regularly achieved FL410 at the end of the flight, but FL390/400 was more normal.

B787-8 and-9 could make FL430 and we achieved that reasonably often. One remarkable memory I have at lower levels is taking off my headset and hearing the whoosh of opposite direction traffic as they passed 1000ft above or below. Even at M0.85, the flight deck was very quiet.
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Old 16th Jan 2021, 14:11
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Most modern airliners are not altitude limited by performance. The Max allowed altitudes are based on the time it takes to reach 10,000 feet in a decompression. Many pilots also assume the Max altitude is simply that number. Depending on the aircraft type it may be a pressure altitude so requesting FL 410 might be above the max allowed altitude.
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Old 16th Jan 2021, 15:57
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Originally Posted by Sailvi767 View Post
Most modern airliners are not altitude limited by performance. The Max allowed altitudes are based on the time it takes to reach 10,000 feet in a decompression. Many pilots also assume the Max altitude is simply that number. Depending on the aircraft type it may be a pressure altitude so requesting FL 410 might be above the max allowed altitude.
A large part of its limit is a function of engine thrust to maintain speed. The 787 runs out of thrust before it does ďwingĒ in a high level climb compared to older types
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Old 16th Jan 2021, 16:47
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Reminds me of a flight deck visit in 2000 of a VS A343 inbound JNB. Capt speaking about descent and approach, "This wing is so good at flying, it takes time to slow it down and you have to allow for that."

As I understand it, almost from the start, Airbus prioritised economy per seat mile as their USP.
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Old 16th Jan 2021, 17:00
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Originally Posted by MachBrum View Post
A large part of its limit is a function of engine thrust to maintain speed. The 787 runs out of thrust before it does ďwingĒ in a high level climb compared to older types
Depends on the model and outside temp.

787-8 generally tends to be thrust limited, whereas the 787-9 tends to be buffet (wing) limited until ISA+10 and thrust limited at higher temperatures. It may very depending on engine type and thrust rating.

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Old 16th Jan 2021, 23:04
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350 and 787 definitely fly higher. The 777 had a max altitude of 43100 but at max takeoff weight you are lucky to get to 30000... every couple hours you do a step climb but she was performed well at lower altitudes compared to others
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Old 16th Jan 2021, 23:43
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I don't know the details, but there was a change to the regulations regarding depressurization after the 747-400 was certified that basically limits newly certified aircraft to 43k (43,100 ft. if you want to get anal about it).
Regarding the 767, it depends on the engines. I went on a flight test on the 767 AOA ( https://www.globalsecurity.org/space/systems/aoa.htm ) many moons ago where we cruised around for hours at 43k - but it had JT9D-7R4 engines (~50k rating) and to get to those altitudes they had to strip out most of the interior to save weight (what I really remember is that they'd stripped out much of the insulation and it was really, really cold in the cabin).
The later versions of the 767-200 with CF6-80C2 or PW4000 engines could be rated as high as 60k and could easily make it to 43k if they weren't too heavy.
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Old 17th Jan 2021, 11:37
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Originally Posted by Ant View Post
Just watching on FlightRadar24 a Tui 787 just overhead us here in Kent at FL430, Stuttgart to Manchester.
It seems the 787 along with the 350 have somewhat higher cruise altitudes than say 777 or 330 flights.
Don't think I've ever seen a B777 at FL430, or am I wrong?
From the 777 & 787 FCOMs, Maximum altitudes are as follows:-

777-200. 43,100ft
777-300 43,100ft

787-8 43,100ft
787-9. 43,100ft
787-10, 41,100ft

Aircraft generally fly higher the lighter they are so, on the same route at any given point, a 777-200 would be higher than a -300 and a 787-8 would be higher than a -9 which would be higher than a -10. Obviously at the moment passenger aircraft aren't carrying huge payloads so they are flying higher than would be normal in better times.
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Old 17th Jan 2021, 17:10
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Originally Posted by Ant View Post
Don't think I've ever seen a B777 at FL430, or am I wrong?
I have....(777-200)...

From memory I think the published ceiling for both the -200 and -300 was 431 but I agree with the previous comments about the -300..it wasn't really a "high flyer" in comparison with the original "light twin".

As eckhard says the 744 was FL 451 but I was only ever in the position on that machine once where weight etc made it possible to go up here but because of time remaining to destination it didn't make sense to do so.
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Old 17th Jan 2021, 18:39
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Originally Posted by tdracer View Post
I don't know the details, but there was a change to the regulations regarding depressurization after the 747-400 was certified that basically limits newly certified aircraft to 43k (43,100 ft. if you want to get anal about it).
...
.
It was a change to 14 CFR 25.841 in 1996, amendment 25-87.
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Old 17th Jan 2021, 21:42
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wiggy
As eckhard says the 744 was FL 451 but I was only ever in the position on that machine once where weight etc made it possible to go up here but because of time remaining to destination it didn't make sense to do so.
Yes, only once for me too. Lagos-LHR with about 80 passengers. We were over northern Algeria at the time (so about 2.30 to TOD) and thought if we don't do it now, we never will.
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Old 19th Jan 2021, 14:52
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Many thanks for all replies, really interesting subject.

Just one purely hypothetical question on the subject of cruising altitudes if I may...
Assuming just for a moment that neither engines nor wings are a limiting factor in determining max cruising altitude, does there come a point where the limiting factor is the increasing differential air pressure with increasing altitude between the interior and exterior of the fuselage pressure vessel?

To put it crudely, "don't taker her any higher or she'll burst"!
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Old 19th Jan 2021, 17:56
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A good question and it would be a factor if one tried to hold a particular constant cabin altitude as one climbed. In practice, the pressure relief valves would crack open at a pre-determined “delta-P” (differential pressure) and so catastrophe would be avoided. The cabin altitude would then increase as aircraft altitude increased, so oxygen and pressure-breathing would become necessary eventually.
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Old 20th Jan 2021, 10:16
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As the aircraft climbs the cabin climbs to maintain the differential pressure so the cabin will never burst.
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