ClarkeKent
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Boeing 747 Max Altitude Changes

Sat Aug 10, 2019 2:14 pm

Hi all,

Wondering why the 747-8 can’t fly as high as the 747-400.

If anyone in the know has any ideas; I’d love to hear them.
 
zionite
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Re: New queen v old queen max alt

Sat Aug 10, 2019 2:25 pm

After reading the topic, before opening the post, I rushed to BBC.com to check if the Queen retired and handed over the reins to Camilla.
 
LH707330
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Re: New queen v old queen max alt

Sat Aug 10, 2019 6:20 pm

The new wing has less drag, so the emergency decompression descent limited the 748 to F431 from F451, IIRC. It also has a lower MMO of .90 vs .92, but a higher opt mach of .855. Kinda funny how these things work.
 
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lightsaber
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Re: New queen v old queen max alt

Sat Aug 10, 2019 6:21 pm

LH707330 wrote:
The new wing has less drag, so the emergency decompression descent limited the 748 to F431 from F451, IIRC. It also has a lower MMO of .90 vs .92, but a higher opt mach of .855. Kinda funny how these things work.

So the required time down to low altitude could only be met by reducing the maximum cruise altitude. Interesting.

Lightsaber
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Varsity1
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Re: New queen v old queen max alt

Sat Aug 10, 2019 6:40 pm

lightsaber wrote:
LH707330 wrote:
The new wing has less drag, so the emergency decompression descent limited the 748 to F431 from F451, IIRC. It also has a lower MMO of .90 vs .92, but a higher opt mach of .855. Kinda funny how these things work.

So the required time down to low altitude could only be met by reducing the maximum cruise altitude. Interesting.

Lightsaber



LH707 is 100% correct.

L/D ratio on the new wing is better, getting down is more difficult.
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rrbsztk
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Re: New queen v old queen max alt

Sat Aug 10, 2019 6:40 pm

Does F451 offer any benefits over 431? I know in general higher=thinner air=less fuel, but not sure if it's a meaningful difference from 431 to 451. Just wondering if there's a downside to topping out at 431/reason a customer would want or need the extra 2000ft.
 
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747classic
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Re: New queen v old queen max alt

Sat Aug 10, 2019 6:42 pm

The limiting factor is the ability of the aircraft to do an emergency descent and get to FL140 (14,000') in 4 minutes or less.
AFAIK initialy the max certified altitude was 42100 ft (747-8F), later the deflection and sequence of the spoilers was modified and the max certified altitude was increased to FL431 (747-8I and later built 747-8F)
Earlier built 747-8F aircraft can be modified.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
Busyboy2
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Re: New queen v old queen max alt

Sat Aug 10, 2019 6:49 pm

Additionally, at least in the USA above FL410 at least one pilot has to stay on Oxygen the whole time above FL410. The 737 max is FL410 and most airliners rarely go above that.
 
SteelChair
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Re: New queen v old queen max alt

Sat Aug 10, 2019 7:31 pm

In reality, what percentage of the time did the 744 ever spend at FL450? IIRC, it had to be very very light on pax and cargo and very light on fuel with just the right atmospheric conditions to achieve FL450 at the end of a long flight for a very limited time. And one of the pilots had to go on oxygen above FL410, so really, not worth the effort.
 
SQ317
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Re: New queen v old queen max alt

Sat Aug 10, 2019 9:44 pm

A few months back, when BA flew one of their 744s LHR-DUB for painting into a retro livery, it went straight up to FL450 (for all of about 2 minutes) before descending into DUB..
 
skipness1E
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Re: New queen v old queen max alt

Sat Aug 10, 2019 9:48 pm

Are you sure about that?
 
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Starlionblue
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Re: New queen v old queen max alt

Sun Aug 11, 2019 2:40 am

Busyboy2 wrote:
Additionally, at least in the USA above FL410 at least one pilot has to stay on Oxygen the whole time above FL410. The 737 max is FL410 and most airliners rarely go above that.


Is that requirement not waived if quick donning masks are installed?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Zeke2517
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Re: New queen v old queen max alt

Sun Aug 11, 2019 3:42 am

LH707330 wrote:
The new wing has less drag, so the emergency decompression descent limited the 748 to F431 from F451, IIRC. It also has a lower MMO of .90 vs .92, but a higher opt mach of .855. Kinda funny how these things work.


Wow that’s actually really interesting when you think about it. A great new wing capable of much more than the previous version, a “better” wing, cannot realize all of its benefits. Too good, perhaps.

Man, airplanes are fascinating.
 
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747classic
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Re: Boeing 747 Max Altitude Changes

Sun Aug 11, 2019 8:13 am

Max certified 747 Speeds :

The original 747 wing platform as installed on the 747-100/100B/200B/300/SP series was was limited by VMO 375 kts and MMO 0.92.
The adapted wingplatform of the 747-400 series with the same wing profile plus 6 ft win tip extension and winglets : VMO 365kts and MMO 0.92
The new 747-8 series wing profile (but with the same strengthend -400 wingbox for grandfathering) plus raked wingtips : VMO 365kts and MMO 0,90

Economical speeds : CRZ econ

This a function of several inputs : wingplatform , fuselage wing interaction (area ruling), installed CRZ thrust, aircraft weight and altitude.
First noted with the introduction of the SP, the position of the upper deck hub influenced the economical speed.
On the 747-300 series the economical speed was raised 0.5 mach due the length of the upper deck structure (area ruling).
On all series the freighter (short upperdeck) has a approx 0,5 mach lower economical speed.

On the 747-8 series the wing L/D factor has so much improved, to the point that the aircraft was unable to reach 14.000ft in 4 minutes, in case of an emergency decent from FL451.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
GalaxyFlyer
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Re: Boeing 747 Max Altitude Changes

Sun Aug 11, 2019 5:05 pm

I would think the Econ cruise changed by M0.005. Hard to believe by .5
 
mmo
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Re: Boeing 747 Max Altitude Changes

Sun Aug 11, 2019 5:54 pm

Be aware the O2 requirement at Fl410 is only an FAA requirement. With the FMC when you are light enough, you can what if so it was interesting to see the effect of climbing from 410-430 or even 450. In reality, unless you are going to spend about 3 hours up there it's not worth the fuel used in climbing to go up.
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747classic
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Re: Boeing 747 Max Altitude Changes

Sun Aug 11, 2019 6:26 pm

GalaxyFlyer wrote:
I would think the Econ cruise changed by M0.005. Hard to believe by .5



M0.005, fully correct, my mistake
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
Armadillo1
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Re: New queen v old queen max alt

Sun Aug 11, 2019 7:21 pm

Varsity1 wrote:
L/D ratio on the new wing is better, getting down is more difficult.


spoilers, interceptors?
 
Armadillo1
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Re: New queen v old queen max alt

Sun Aug 11, 2019 7:26 pm

SteelChair wrote:
In reality, what percentage of the time did the 744 ever spend at FL450? .

on return cargo flight? a lot

funny to read about L/D and other out of topic thing.

its all about speed limits (both)
any drag can be added by spoilers, but speed limit really limit you in descend
 
Armadillo1
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Re: Boeing 747 Max Altitude Changes

Mon Aug 12, 2019 7:19 am

interesting is actual long 748 flights going at FL360
https://www.flightradar24.com/data/flig ... 0#2197c597

with few flights ended at FL380
 
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747classic
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Re: Boeing 747 Max Altitude Changes

Mon Aug 12, 2019 9:24 am

Armadillo1 wrote:
interesting is actual long 748 flights going at FL360
https://www.flightradar24.com/data/flig ... 0#2197c597

with few flights ended at FL380


Flight Level is determent by actual aircraft weight (incl pax, cargo, fuel), wind, availabilty (ATC) and sometimes temperature (e.g fuel freezing temp at the end of your flight.)
All above mentioned factors are already included in the flightplan, but if the actual situation (temps, wind or available FL) may differ, you have sometimes to select an off -optimum altitude.

I operated the 747-200/300 series at FL 450, especially at the last part of (allmost empty) freighter positioning flights, to obtain direct routings due no interfearing traffic at that altitude.
But with any turbulence reported we never would climb to that altitude (cofin corner of your flight envelope)
Also some short pax flights (IAH-MEX) we sometimes made it to Fl 450 (fuel was cheap at that time )
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
vikkyvik
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Re: Boeing 747 Max Altitude Changes

Tue Aug 13, 2019 7:14 pm

Armadillo1 wrote:
any drag can be added by spoilers, but speed limit really limit you in descend


And why would the airplane overspeed? Because there's not enough drag...
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
Armadillo1
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Re: Boeing 747 Max Altitude Changes

Wed Aug 14, 2019 8:19 am

vikkyvik wrote:
Armadillo1 wrote:
any drag can be added by spoilers, but speed limit really limit you in descend


And why would the airplane overspeed? Because there's not enough drag...

you need more time to lower speed and more time to descent on lower speed.
 
Armadillo1
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Re: Boeing 747 Max Altitude Changes

Wed Aug 14, 2019 8:20 am

interesting how its doing on bizjets and possible high altitude planes - supersonic for example.
 
GalaxyFlyer
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Re: Boeing 747 Max Altitude Changes

Wed Aug 14, 2019 12:55 pm

No, the bizjets have large spoilers and descend at MMO/Vmo and those speeds, while high in some models are subsonic. The G7500 has an MMO of .995.

GF
 
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747classic
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Re: Boeing 747 Max Altitude Changes

Fri Aug 16, 2019 10:57 am

ICAO Doc 7030 directs the following actions in the event that an aircraft experiences a sudden decompression or a (similar) malfunction requiring an emergency descent:

•Initiate a turn away from the assigned route or track before initiating the descent (note that in very congested airspace, this may not be advisable and that in some regions, such as the North Atlantic, there are specific contingency procedures to be followed. Certain regions of Europe have, in their AIPs, denoted that an emergency descent should be conducted on their cleared track unless an immediate conflict exists)
•Advise the appropriate air traffic control unit as soon as possible of the emergency descent
•Set the transponder code to 7700 and select Emergency Mode on the Automatic Dependent Surveillance (ADS) / Controller Pilot Data Link Communications (CPDLC) equipment as appropriate
•Turn on all exterior lights
•Watch for traffic both visually and with reference to ACAS/TCAS (if equipped)
•Coordinate further intentions with the appropriate ATC unit

Ensure that altimeters are set to local QNH or QFE as appropriate. An initial target altitude which is the higher of MEA or a specified Company/manufacturer value (often 10,000') will be selected. In mountainous terrain, specific escape routes may be required. Temperature corrections should be applied as appropriate.

Unless structural damage is suspected, the aircraft should be descended at or near maximum speed (Vmo/Mmo) with thrust at idle and flight spoilers or speed brakes extended. If structural damage is suspected, the aircraft should be flown at, or close to, the indicated airspeed (IAS) at which the failure occurred.
Operating a twin over the ocean, you're always one engine failure from a total emergency.
 
Armadillo1
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Re: Boeing 747 Max Altitude Changes

Fri Aug 16, 2019 11:03 am

747classic wrote:
If structural damage is suspected, the aircraft should be flown at, or close to, the indicated airspeed (IAS) at which the failure occurred.[/b]

because any change in speed may require rebalance and may be impossible due to damage?
 
GalaxyFlyer
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Re: Boeing 747 Max Altitude Changes

Fri Aug 16, 2019 1:32 pm

No, because the plane may start coming apart as the IAS increases the dynamic pressure on the structure. There was a bombing of a PAA (?) B707, crew did the standard as trained descent only to lose the tail. A C-141 had an aft door fail, damaging the tail and causing a near explosive decompression. Crew did nothing but idle power and successfully descending at or below the existing IAS. Lockheed determined the structure would have failed in a emergency descent profile.

GF
 
Armadillo1
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Re: Boeing 747 Max Altitude Changes

Fri Aug 16, 2019 1:54 pm

GalaxyFlyer wrote:
No, because the plane may start coming apart as the IAS increases the dynamic pressure on the structure. There was a bombing of a PAA (?) B707, crew did the standard as trained descent only to lose the tail. A C-141 had an aft door fail, damaging the tail and causing a near explosive decompression. Crew did nothing but idle power and successfully descending at or below the existing IAS. Lockheed determined the structure would have failed in a emergency descent profile.

GF

maintain speed means not only "don not increase", but "do not decrease" too.
article said not "speed not above " but "maintain speed" (in another words)
 
GalaxyFlyer
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Re: Boeing 747 Max Altitude Changes

Fri Aug 16, 2019 2:00 pm

That wording was all added after incidents in the old days where there was ONLY one procedure, drag devices and Mmo to Vmo. It was drilled in—get down.

GF

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