A350 & B787 cruising altitude question

[Ant]

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?

[TURIN]

A brief Google showed me that of the three aircraft you mention, the 777 has the highest max service ceiling.

[treadigraph]

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...

[kenparry]

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.

[treadigraph]

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!

[Weary traveller]

787 and 350 in a class of their own regarding high altitude cruising FL’s at standard weighs. Both with latest wing designs. Traditionally A330’s will fly at higher FL’s than 777’s 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 FL’s the wing just didn’t want to go to.

[eckhard]

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.

[Sailvi767]

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.

[MachBrum]

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 “wing” in a high level climb compared to older types

[PAXboy]

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.

[Sidestick_n_Rudder]

A large part of its limit is a function of engine thrust to maintain speed. The 787 runs out of thrust before it does “wing” 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.

[casablanca]

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

[tdracer]

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.

[Flying Fred]

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.

[wiggy]

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.

[Dave Therhino]

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.

[eckhard]

wiggyAs 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.

[Ant]

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"!

[eckhard]

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.

[Captain Capstan]

As the aircraft climbs the cabin climbs to maintain the differential pressure so the cabin will never burst.

[tdracer]

As the aircraft climbs the cabin climbs to maintain the differential pressure so the cabin will never burst.

Eventually you could get to an altitude where - at that constant differential pressure - the cabin altitude got too high (10k) and the masks drop - which would obviously be bad.
People tend to assume that the stated cabin altitude (8k for most airliners, 5 or 6k for some new ones such as the A350 and 787) is used all the time at cruise - in reality those numbers are maximums and if you do a low altitude cruise, the cabin altitude will generally be lower than that.

[FlightDetent]

The last piece of the puzzle, easy to fill in with others already in place:

The strength (good) and weight (bad) that invariably go hand in hand are both determined by the designer's decision which altitude will be the max. And then everything is optimized (thinned-down) for that. I would hazard a guess than unlike peak static overpressure on the hull, it is the blow/vent cycles in the long run that are the most demanding on the structure. But in a sense, you indeed cannot go any higher because the margins on lifetime accumulated strain would be reduced below what's allowed (sheldonspeak for "blow up"). Yet other things would immediately come out of the woodwork as well, it's built that way on purpose.

The cynic in me would also believe, that in no shape or form was the lower cruising cabin altitude a hard target in the design, toward which any strengthening of the fuselage took place. Weight increase destroys the economics of the product, even more so on a long haul craft.

The best speculation I could come up with would be that for other physical reasons, thanks to new materials and contemporary manufacturing processes, it turned out that with long-haul expected cycles the structure would take the higher peak pressure. Surely a lot of work may have been done to reach for such perhaps not-so-low hanging fruit, but only meaningless weight increase was sacrificed if any at all.

[Ant]

Here's a 767 at unusually high cruising altitude FL430, showing that it's not always the 787s and A350s up that high!

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/2000x1471/fl24_803d8781f231450b3c4269a621f5a6be71fbdcd8.png

[awair]

In the early 777-200 models (249t), not the’IGW’ or 200ER, we would get to 430 on HKG-MNL or HKG-BKK.

Short sectors, lighter weight.

On long or full flights typically the maximum would be 370/390.

With the -300, initial climb would typically only be to 330. And as previously stated, the 300ER could only make 280/290/300 initially on a 15-hour sector!

[Una Due Tfc]

From my own experience as an ATCO, general initial cruising altitude for wide body twins goes 767<777<330<787=350. Cruising speeds 767<330<777<787=350. I certainly see the 777 match the newer twins when the 777 isn't operating ULH but obviously she needs to burn more fuel to do so. Fastest I've had a commercial widebody so far was a B744 at M.090 with a medical EMG on board. I have had a B744F at FL450 once, asked them how they got up there, she was an empty positioning flight. The descended shortly after as their ground speed was higher and fuel burn lower at FL410 with a big tail wind.

I always assumed the reason the 330 gets up there so much earlier than similar vintage Boeings was that the wing needed to take all the extra weight of the 340, so when on a lighter 330 it was almost overkill. Seeing how shockingly slow the A343 in particular climbed backed up that assumption in my head

[FlightDetent]

Here's a 767 at unusually high cruising altitude FL430, showing that it's not always the 787s and A350s up that high! :} Slingshot?

[FlightDetent]

the 300ER could only make 280/290/300 initially on a 15-hour sector! Just wondering, what exactly do you mean by initially ... on a 15 hr sector?! :\

[awair]

Initial cruise altitude on a 15-hour sector at MTOW (350t) would give a Max altitude of around FL300, so depending on direction of flight, and temperature, optimum would be 280/290.

After an hour or so, 310 would be achievable. Step climbing as the aircraft burns fuel.

Maximum fuel on departure would be around 140t, landing with 6-8t.

We used to carry a table for maximum altitude vs weight. Now the only reference is on the FMC.

[FlightDetent]

Thanks, funny facts every day. When I started the cautious of the pool would swear by no less than 4 t on arrival. To FRA, on a -500.

[Mr Mac]

The highest I have flown on a commercial jet was on a lightly loaded EK A340-500 from Phuket up to DXB on a very clear moonlight night in Nov 2012, and we arrived in DXB about 70min early, and the place was deserted. We cruised at FL43-440 from the start as I recall, with quite a tailwind. I never did the Concorde thing, but have flown in exec jets at that height, and even a little higher, but that is my max for a commercial jet as far as I am aware.

Cheers
Mr Mac