linco22
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BA 747/777 Cruising Altitudes

Fri May 23, 2008 12:38 pm

Hi all,

Was listening to a discussion at the lunch table in work today and the this topic popped up. One of the guys from work who usually claims to know everything about everything, says that his friend works for BA on transatlantic flights and the 747 cruises at 33,000ft and the 777 at 38,000 on LHR - USA routes.

Can anyone confirm the altitudes on these routes. I'd imagine they do vary given certain conditions and certainly didnt think the 747 would cruise that low.

Thanks

Colin
 
kappel
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 12:51 pm



Quoting Linco22 (Thread starter):
I'd imagine they do vary given certain conditions

You'd imagine right  Wink

Quoting Linco22 (Thread starter):
didnt think the 747 would cruise that low.

Like you said, depends on conditions, like how heavy is the aircraft, is there any other traffic on the other flight levels, winds, etc. The 747 can easily cruise much higher, especially in the later stages of the flight. As will the 777 not immediately climb to 38,000 at the start of a long flight.
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N104UA
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 12:52 pm

They cruise between FL 330 and FL410 but when they are fully loaded thier first altitude is about FL290 and then they go up after they speed up and burn fuel
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linco22
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 12:53 pm

Thanks guys, keep bringing the info. I knew that fuel and other loads influence this.

Cheers

Colin
 
seattleflyer
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 5:00 pm

Just as an example pull up the track logs in flightaware.com for BA flights 48 and 49 (LHR-SEA). This route flies a combination of 772s and 774s. Their cruise levels are comparable for both aircraft types though they do vary - presumabley for the reasons stated above. You'll notice that the eastbound flights seem to be lower, but I think that's just because it showing the earlier part of the flight when heavy with fuel versus the westbound where the track is showing the later part of the flight.

If memory serves, I've been on that route in the 744 at 41,000 ft
 
Mir
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 5:03 pm

There is no one set cruising altitude for a specific plane. A 747 and 777 have pretty much the same range of operating altitudes.

The next day it could have been the 747 at FL380 and the 777 at FL330. It all depends on winds, loads, other traffic, etc.

-Mir
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B747forever
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 5:12 pm

Always when I fly to LAX it cruise first at FL320 to burn some fuel, at the end of the flight it usually goes up to FL 380. I really doubt that a 744 cruise all the flight on FL330.
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BA380
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 5:13 pm



Quoting SeattleFlyer (Reply 4):
Just as an example pull up the track logs in flightaware.com for BA flights 48 and 49 (LHR-SEA).

how do you do that, exactly? I can see flights in flightaware, but can't work out where to see altitudes or access the track log?
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FlyCaledonian
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 5:13 pm

Recently flew a BA 744 SYD-BKK-LHR. We flew FL390 for a lot of the flight from SYD-BKK, but on BKK-LHR never got above FL360.
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seattleflyer
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 5:39 pm

After you enter a flight number, a number of past and future occurances of that flight number appear in the bottom section of the screen. Click on one of the past flights and it's detail will appear above. On the right hand side of the screen you will see the Status and will say something to the effect of "Arrived over xx hours ago" at the end of that it should have "(track log)". Click on this and it will give you a list of fixes and altitudes throughout the flight. Areas of the flight outside of US ATC tracked airspace will not be recorded.

Hope that helps.
 
787EWR
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 6:22 pm

I have flown to SYD from LAX on numerous occasions. During the first two hours, the flight climbs slowly and sits between 31 and 35. By the time the flight is approaching the Australian coast, the -400 is normally at 390 thru 410. Along with the loads, the status of the winds are a big factor. If you have major headwind at a certain level, you might want a lower level where they aren't so bad.
 
ChiGB1973
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 6:46 pm



Quoting BA380 (Reply 8):
how do you do that, exactly? I can see flights in flightaware, but can't work out where to see altitudes or access the track log?

http://flightaware.com/live/flight/B.../20080522/1429Z/EGLL/KSEA/tracklog

http://flightaware.com/live/flight/B.../20080520/0218Z/KSEA/EGLL/tracklog

From what I can tell, the flight must be completed and have a definite outcome in FlightAware. If it has an "unknown" or "result unknown," I cannot get the log.

M
 
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Starlionblue
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 11:32 pm

Quoting Linco22 (Thread starter):
One of the guys from work who usually claims to know everything about everything, says that his friend works for BA on transatlantic flights and the 747 cruises at 33,000ft and the 777 at 38,000 on LHR - USA routes.

Never trust someone who claims to know everything about everything and has a friend. I would treat anything he says with suspicion. It always amazes me how people like me will then come with the actual truth (in this case "it depends") and get beaten down by Mr Know-it-all. If we then stick to our guns they try to turn everyone against us. In the end, people start saying "I don't care, let's talk about something else". So not only has the truth not come to light, most people are too lazy to be interested in the truth. They just like flashy facts.

I am soooo cynical. Nowadays I just say, "you're wrong", and leave it at that for a bit. Leave the crowd wanting more.´Get them to ask why. Don't give the whole explanation at once. Use some salesmanship.If Mr. Know-it-all continues with his "Well my friend who works at BA," tell him to call his friend, right now. Also ask him if this was one flight or on average. Get Mr. Know-it-all off balance.

Never argue with an idiot. They will drag you down to their level and beat you with experience


BTW all of you giving anecdotal example about "When I fly blabla". That's nice but it is only anecdotal info and would not help in beating down Mr. Know-it-all.

[Edited 2008-05-23 16:35:37]
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PhilSquares
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RE: BA 747/777 Cruising Altitudes

Fri May 23, 2008 11:56 pm



Quoting Linco22 (Thread starter):
Can anyone confirm the altitudes on these routes. I'd imagine they do vary given certain conditions and certainly didnt think the 747 would cruise that low



Quoting Linco22 (Thread starter):
They cruise between FL 330 and FL410 but when they are fully loaded thier first altitude is about FL290 and then they go up after they speed up and burn fuel

I can't speak for the 777, but on the 744 at MTOW 310/320 is generally the optimum altitude. So 290, is a little low unless there are other ATC restrictions.

On the UK-US routes the 744 isn't anywhere near it's MTOW. A LHR-JFK flight should be able to make 340 as the initial level off depending on OAT. The LHR-SFO would be closer to MTOW but again it 320 should be no problem at all.
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thegeek
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RE: BA 747/777 Cruising Altitudes

Sat May 24, 2008 3:16 am



Quoting Starlionblue (Reply 12):
Never argue with an idiot. They will drag you down to their level and beat you with experience

That's probably about right. lol


Back to aviation, do you run the engines at maximum thrust until some fuel is burned off on long haul flights? I would think that would be the most efficient if you can't reach the altitude you would like. They certainly don't do it that way for short haul.
 
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Starlionblue
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RE: BA 747/777 Cruising Altitudes

Sat May 24, 2008 5:04 am



Quoting Thegeek (Reply 14):

Back to aviation, do you run the engines at maximum thrust until some fuel is burned off on long haul flights? I would think that would be the most efficient if you can't reach the altitude you would like.

Goodness no. If you ran the engines at max in cruise you would end up in an overspeed condition.

- Take-off: Take-off thrust. This may often be de-rated based on weight, runway length and temperature.
- Climb: Climb thrust. Less than take-off thrust.
- Cruise: "Cruise thrust", which of course is rather widely variable but is not as much as climb thrust.
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thegeek
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RE: BA 747/777 Cruising Altitudes

Sat May 24, 2008 5:54 am



Quoting Starlionblue (Reply 15):
Goodness no. If you ran the engines at max in cruise you would end up in an overspeed condition.

So, why don't you just dial up more thrust and fly higher? Do aerodynamics in the thinner air make that tough?

Quoting Starlionblue (Reply 15):
- Take-off: Take-off thrust. This may often be de-rated based on weight, runway length and temperature.
- Climb: Climb thrust. Less than take-off thrust.
- Cruise: "Cruise thrust", which of course is rather widely variable but is not as much as climb thrust.

I understand the need for a distinction between TOGA power and normal power, but I don't see the need for a distinction between climb and cruise. i.e. isn't it possible to have a derated climb and a full power one engine cruise?
 
PhilSquares
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RE: BA 747/777 Cruising Altitudes

Sat May 24, 2008 6:14 am



Quoting Thegeek (Reply 16):
So, why don't you just dial up more thrust and fly higher? Do aerodynamics in the thinner air make that tough?

Max and optimum altitudes are governed by a few factors and thrust available vs. thrust required is another. Another factor is wing loading. Depending on the values used by the airline some airlines use an optimum altitude of 1.3 VSO. Meaning that at your max cruise altitude you have a 1.3 stall margin. That takes into account turbulence at altitude, enroute turnd where the wing loading increases with bank angle. If you went all the way up to the 0 margin, you'd stall at the first sign of turbulence or anytime you turned.

Quoting Thegeek (Reply 16):
I understand the need for a distinction between TOGA power and normal power, but I don't see the need for a distinction between climb and cruise. i.e. isn't it possible to have a derated climb and a full power one engine cruise?

The distinction is really between TOGA, CLIMB and MCT. Normally, CLIMB and MCT (max continious thrust) are the same but they can be different. But TOGA is a thrust setting that is limited to 5 or 10 minutes depending on the aircraft, engine maker and airline. MCT is just that. There is no real "cruise thrust". The thrust required to maintain level, unaccelerated flight is someplace between idle and MCT. The FMC or performance charts will give a "nominal" cruise EPR/N1 setting but it will vary because of differences in airframes, engine wear, OAT.
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tdscanuck
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RE: BA 747/777 Cruising Altitudes

Sat May 24, 2008 6:32 am



Quoting Thegeek (Reply 14):
Back to aviation, do you run the engines at maximum thrust until some fuel is burned off on long haul flights?

Somewhere, a GE field rep just shivered in his sleep.

Engines are not built to produce maximum thrust for more than a few minutes per cycle. You would drastically curtail the engine's life if you ran it at maximum thrust for very long.

Quoting Starlionblue (Reply 15):
Goodness no. If you ran the engines at max in cruise you would end up in an overspeed condition.

This might happen on a direct controlled engine, but a FADEC engine shouldn't overspeed unless something breaks.

Tom.
 
thegeek
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RE: BA 747/777 Cruising Altitudes

Sat May 24, 2008 7:30 am



Quoting Tdscanuck (Reply 18):
Somewhere, a GE field rep just shivered in his sleep.

I didn't mean TOGA power, I meant maximum continuous.

Quoting Tdscanuck (Reply 18):
This might happen on a direct controlled engine, but a FADEC engine shouldn't overspeed unless something breaks.

I think the over speed he was referring to was of the aircraft, not the engine. (I read it as engine at first too.)

Quoting PhilSquares (Reply 17):
Another factor is wing loading. Depending on the values used by the airline some airlines use an optimum altitude of 1.3 VSO. Meaning that at your max cruise altitude you have a 1.3 stall margin. That takes into account turbulence at altitude, enroute turnd where the wing loading increases with bank angle. If you went all the way up to the 0 margin, you'd stall at the first sign of turbulence or anytime you turned.

Thanks for your lucid explanations. It sounds like SFC improvements have a much bigger effect than I had previously appreciated. For the 747 and A388, they had to decide whether or not to have a wing too big in the last part of the flight, or too small in in the first part of the flight. The 747 choose the former, and the A380 chose the latter. That's probably a bit simplistic, but I see how ULH dies - it's not just the part where you burn fuel to carry fuel.
 
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Starlionblue
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RE: BA 747/777 Cruising Altitudes

Sat May 24, 2008 8:02 am



Quoting Tdscanuck (Reply 18):

This might happen on a direct controlled engine, but a FADEC engine shouldn't overspeed unless something breaks.

Well ok. But if it was at full throttle you would overspeed no? I was sorta ignoring the fact that there are various safety systems.  Wink

Quoting Thegeek (Reply 16):
So, why don't you just dial up more thrust and fly higher? Do aerodynamics in the thinner air make that tough?

Higher and higher, until you reach coffin corner, where the air is thin so stall speed is too high and mach buffet speed is too low. Baaaaad. Captain Squares explains it very well. If you have no margin and need to maneuver or experience some turbulence you're toast.
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tdscanuck
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RE: BA 747/777 Cruising Altitudes

Sat May 24, 2008 4:49 pm



Quoting Thegeek (Reply 19):
Quoting Tdscanuck (Reply 18):
This might happen on a direct controlled engine, but a FADEC engine shouldn't overspeed unless something breaks.

I think the over speed he was referring to was of the aircraft, not the engine. (I read it as engine at first too.)

OK, that makes a lot more sense. My bad.

Quoting Starlionblue (Reply 20):

Quoting Tdscanuck (Reply 18):

This might happen on a direct controlled engine, but a FADEC engine shouldn't overspeed unless something breaks.

Well ok. But if it was at full throttle you would overspeed no? I was sorta ignoring the fact that there are various safety systems.

If you mean "full throttle" = "fuel metering valve full open" then yes, definitely. However, no FADEC engine actually has a throttle control anymore (i.e. no direct control of fuel input)...the thrust lever tells the engine what thrust level (either as EPR or N1) the the flight crew wants and the FADEC does whatever it needs to do to achieve that. So the flight crew can ram the thrust lever to the firewall on a FADEC engine and the engine will say "Oh, you want 100% N1 (or whatever the EPR equivalent is on that engine)" and go to that speed. It's not so much a safety system as a control philosophy. A throttle and a thrust lever are controlling different engine parameters.

Tom.
 
thegeek
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RE: BA 747/777 Cruising Altitudes

Sat May 24, 2008 10:35 pm



Quoting Tdscanuck (Reply 21):
"Oh, you want 100% N1 (or whatever the EPR equivalent is on that engine)"

Aren't both those things a little indirect? The way I see it, what your asking for when you dial up maximum thrust, you're selecting maximum EGT.
 
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Starlionblue
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RE: BA 747/777 Cruising Altitudes

Sun May 25, 2008 12:30 am

Fair enough Tdscanuck.  Wink
.
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tdscanuck
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RE: BA 747/777 Cruising Altitudes

Sun May 25, 2008 5:07 am



Quoting Thegeek (Reply 22):
Aren't both those things a little indirect? The way I see it, what your asking for when you dial up maximum thrust, you're selecting maximum EGT.

Nope. You really never want to have your engine up at max EGT. The difference between current maximum EGT and maximum allowable is the EGT margin. It's a very common measure of engine health. You always want to have positive EGT margin.

When you ask for maximum thrust you're asking for the maximum N1 (GE/CFM) or EPR (P&W/RR) that the engine is rated for. The FADEC will take you there as long as it can...that could mean an EGT well below maximum for an engine that's in really good shape, or over maximum EGT for one that's really worn down. Over maximum EGT, obviously, isn't an option for very long.

Tom.
 
PhilSquares
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RE: BA 747/777 Cruising Altitudes

Sun May 25, 2008 6:53 am



Quoting Tdscanuck (Reply 24):
When you ask for maximum thrust you're asking for the maximum N1 (GE/CFM) or EPR (P&W/RR) that the engine is rated for. The FADEC will take you there as long as it can...that could mean an EGT well below maximum for an engine that's in really good shape, or over maximum EGT for one that's really worn down. Over maximum EGT, obviously, isn't an option for very long.

Just a little technical issue. On a FADEC/EEC engine, as long as one channel is working you will always have the N1/EGE/EPR protection. So, you should never see an overspeed, overboost or overtemp when the thrust levers are firewalled.
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tdscanuck
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RE: BA 747/777 Cruising Altitudes

Sun May 25, 2008 7:28 am



Quoting PhilSquares (Reply 25):
Just a little technical issue. On a FADEC/EEC engine, as long as one channel is working you will always have the N1/EGE/EPR protection. So, you should never see an overspeed, overboost or overtemp when the thrust levers are firewalled.

Thanks for the clarification. I knew that most FADEC's implement N1/EPR protection, but wasn't sure about EGT protection.

Tom.
 
linco22
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RE: BA 747/777 Cruising Altitudes

Mon May 26, 2008 9:25 am

Just logged in this morning to find these responses, and some very interesting ones too. Thanks to everyone for answering, I know now that the know-it-all was only about 5% correct!  Wink

Cheers

Colin

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