Ekfan
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High Altitude Flights By SAA

Mon Nov 21, 2011 1:43 am

I often fly to West Africa for work, and on a recent trip to Dakar, Senegal, I flew with South African Airways on their A340-300e service from IAD, which stops in Dakar and then continues on to Johannesburg, SA. During the flight to Dakar, the aircraft reached a maximum cruise altitude of 42,000 feet. On the return, the flight was at 41,000 for most of the cruise phase. This strikes me as a very high altitude - is this a normal flight level in this region? I would not imagine it's due to crowded airspace since the flight tracks over a remote part of the Atlantic ocean (in fact I have often wondered what the viable diversion points are in case of a problem). Is it due to the bad weather that can often occur in these southern parts of the Atlantic?

Thanks for any info.
 
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RWA380
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RE: High Altitude Flights By SAA

Mon Nov 21, 2011 1:50 am

The Azores come to mind, however the diversion points are few and far between, hence the 4 engined aircraft which dominates SAA's long haul fleet, however DL does it's non-stop to Jo'burg on the 777.
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ikramerica
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RE: High Altitude Flights By SAA

Mon Nov 21, 2011 2:07 am

I was under the impression that the higher you can fly, the better. Considering the flight is short in comparison to the range of the birds, climbing to this height would not be difficult from takeoff. In comparison, a 772 flying DFW-NRT must step up in altitude over time as fuel is burned off and the plane is lighter.

I know in the USA airlines try to get their 737s and A320s up to max efficient cruise on shorter missions as soon as possible, but ATC doesn't always let them because they want to flow them in their lanes. Over southern Africa, one imagines that the traffic is lighter than the USA.
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tdscanuck
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RE: High Altitude Flights By SAA

Mon Nov 21, 2011 4:36 am

Quoting Ekfan (Thread starter):
stops in Dakar and then continues on to Johannesburg, SA.

You've got a plane designed for 7400 nm on a flight that's only 3600 nm...you'd certainly hope, absent ATC restrictions, they can get up near maximum service ceiling.

Quoting ikramerica (Reply 2):

I was under the impression that the higher you can fly, the better.

Exactly. As long as you've got the performance and the route isn't so short that you never get to a steady cruise altitude, you want to be as high as you can. Optimum altitude for long range aircraft when they're lightly loaded is often at or near their maximum certified altitude.

Tom.
 
RyanairGuru
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RE: High Altitude Flights By SAA

Mon Nov 21, 2011 11:43 am

Quoting ikramerica (Reply 2):
a 772 flying DFW-NRT must step up in altitude over time as fuel is burned off and the plane is lighter.

Interesting. Thanks for that. I flew SYD-HNL on a 767 and LAX-MEL on a 744 in June/July on QF and both ways we started cruising at 28,000 and then about 2 hours into the flight started slowly rising until we got to 40,000 several hours later. I was wondering why, and this suddenly makes a lot of sense. Both flights would be pushing the range of the aircraft so they wouldn't want to burn a ton of fuel just getting up.
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rfields5421
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RE: High Altitude Flights By SAA

Mon Nov 21, 2011 1:38 pm

Quoting RyanairGuru (Reply 4):
Both flights would be pushing the range of the aircraft so they wouldn't want to burn a ton of fuel just getting up.

Usually the aircraft is not physically capable of climbing to the highest cruise levels until it burns off a lot of that fuel.
 
A342
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RE: High Altitude Flights By SAA

Tue Nov 22, 2011 12:12 am

Quoting Ekfan (Thread starter):
During the flight to Dakar, the aircraft reached a maximum cruise altitude of 42,000 feet.

Are you really, really sure about that? I'm quite sure that the entire A330/340 family is only certified for 41,000 feet.
Exceptions confirm the rule.
 
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Starlionblue
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RE: High Altitude Flights By SAA

Tue Nov 22, 2011 12:32 am

Quoting RyanairGuru (Reply 4):
Both flights would be pushing the range of the aircraft so they wouldn't want to burn a ton of fuel just getting up.

The fuel burn is not the issue. Weight is the issue. As rfields5421 says, the aircraft is not physically able to go that high at high weights because the wing can't carry it that high. It would fall below stall speed, or to be more precise it would fall out of the certified envelope and too close to stall speed.
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flymia
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RE: High Altitude Flights By SAA

Tue Nov 22, 2011 1:23 am

Quoting Starlionblue (Reply 7):
The fuel burn is not the issue. Weight is the issue. As rfields5421 says, the aircraft is not physically able to go that high at high weights because the wing can't carry it that high. It would fall below stall speed, or to be more precise it would fall out of the certified envelope and too close to stall speed.

Exactly. That is the purpose of a step climb. Go to the best optimal altitude for the weight of the aircraft is at. The FMC lets the pilots know what altitude they should be flying at. More fuel burned higher you can go.

As for the OP, as many have said the higher the better for fuel burn. That is a pretty short flight for the A340 so getting up there is no problem. When I fly AA on MIA-LAX the 777s get right up to around 39,000 feet usually, pretty short flight for a 777.

Quoting Ekfan (Thread starter):
(in fact I have often wondered what the viable diversion points are in case of a problem)

There are not many. With four engine A340s not much to worry about. Of course ETOPS twin engines can do the route also but the more the better of course 
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jetmech
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RE: High Altitude Flights By SAA

Tue Nov 22, 2011 2:59 am

Quoting Ekfan (Thread starter):

Earlier this year, I flew on a DJ 737-700 from SYD-MEL where we were cruising at 41,000ft even though the sector is only 381nm with a flight duration of about 1 hour. Even for such short sectors it seems worthwhile to get as high as possbile as soon as possible.


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474218
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RE: High Altitude Flights By SAA

Tue Nov 22, 2011 3:15 am

Quoting A342 (Reply 6):
Are you really, really sure about that? I'm quite sure that the entire A330/340 family is only certified for 41,000 feet.

Max altitude 41,450 with modification 52536?
 
A342
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RE: High Altitude Flights By SAA

Tue Nov 22, 2011 10:48 am

Quoting 474218 (Reply 10):
Max altitude 41,450 with modification 52536?

Yes, but that still doesn't explain FL420.
Exceptions confirm the rule.
 
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Starlionblue
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RE: High Altitude Flights By SAA

Tue Nov 22, 2011 11:02 am

Quoting jetmech (Reply 9):
Earlier this year, I flew on a DJ 737-700 from SYD-MEL where we were cruising at 41,000ft even though the sector is only 381nm with a flight duration of about 1 hour. Even for such short sectors it seems worthwhile to get as high as possbile as soon as possible.

41000 feet is peanuts compared to the distance traveled, only 6.75nm altitude. In this case of 381nm the maximum altitude is thus 1.75% of the distance. If you reduce the scale to a tabletop one meter long, the aircraft would be traveling 1.75 cm above it. The aircraft is practically grazing the ground.
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Rara
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RE: High Altitude Flights By SAA

Tue Nov 22, 2011 2:23 pm

Interestingly, on short haul, the most economical flight path is parabolic. In other words, it makes sense to climb as high as you can, even if you don't spend any time on your maximum altitude, and instead start the descend immediately. ATC won't like it though.
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andz
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RE: High Altitude Flights By SAA

Tue Nov 22, 2011 2:41 pm

I have flown SAA between South Africa and Europe many times and usually they will start around 37,000ft as an initial destination, more often than not when waking up in the morning the display showed 41,000ft. I don't recall ever seeing 42,000ft though (I'm sure I would remember as it would seem extraordinary to me).

Many years ago my wife and I were in the cockpit jumpseats on a 747SP between JNB and DUR (258nm according to Great Circle Mapper) and we climbed to FL410. When I asked the Captain why, he said "because we can".
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tdscanuck
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RE: High Altitude Flights By SAA

Tue Nov 22, 2011 2:44 pm

Quoting Rara (Reply 13):

Interestingly, on short haul, the most economical flight path is parabolic. In other words, it makes sense to climb as high as you can, even if you don't spend any time on your maximum altitude, and instead start the descend immediately. ATC won't like it though.

They will let you do a triangular profile in some parts of the world though...I used to fly HOU-MSY all the time. You climb all the way to your top-of-descent point then descend all the way back down. There's effectively no time in cruise.

Tom.
 
David L
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RE: High Altitude Flights By SAA

Tue Nov 22, 2011 3:00 pm

Quoting A342 (Reply 11):
Quoting 474218 (Reply 10):Max altitude 41,450 with modification 52536?
Yes, but that still doesn't explain FL420.

Could it be something simple, like the difference between pressure altitude and GPS altitude plus software rounding, for example?
 
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jetmech
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RE: High Altitude Flights By SAA

Wed Nov 23, 2011 1:15 am

Quoting Starlionblue (Reply 12):

I agree that the overall flight profile is quite shallow, but on the other hand, it probably takes around 15 minutes to get that high and 15 minutes to descend from that altitude, so at least half the flight time of such a short sector is spent getting to and from 41,000ft. It would take a fair amount of extra fuel consumption to get the extra altitude above a lower flight level such as 31,000ft for instance, so that half hour cruising at 41,000ft must really pay off.

Regards, JetMech
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Viscount724
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RE: High Altitude Flights By SAA

Wed Nov 23, 2011 1:26 am

Quoting ikramerica (Reply 2):
I know in the USA airlines try to get their 737s and A320s up to max efficient cruise on shorter missions as soon as possible, but ATC doesn't always let them because they want to flow them in their lanes.
Quoting jetmech (Reply 9):
Earlier this year, I flew on a DJ 737-700 from SYD-MEL where we were cruising at 41,000ft even though the sector is only 381nm with a flight duration of about 1 hour. Even for such short sectors it seems worthwhile to get as high as possbile as soon as possible.

I've been on 2 KLM 737-700 flights in the past month that reached 40,000 ft. on one hour flights (e.g. AMS-GVA 368 nm and AMS-MUC 359 nm).
 
tdscanuck
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RE: High Altitude Flights By SAA

Wed Nov 23, 2011 5:15 am

Quoting David L (Reply 16):
Could it be something simple, like the difference between pressure altitude and GPS altitude plus software rounding, for example?

Most IFE moving-map displays get their GPS and altitude data from the aircraft, and the aircraft doesn't use GPS altitude unless something has gone wrong. If the IFE is saying FL420 it's most likely because the aircraft it telling it that it's at FL420.

Tom.
 
jox
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RE: High Altitude Flights By SAA

Wed Nov 23, 2011 8:35 am

Very often on LLA-ARN (and back) if you are on a 73NG, at least SAS cruises on FL390-410. It is an hour flight, and usually the pattern is roughly like this: climb 20 min, cruise 20 min, descend 20 min.
 
David L
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RE: High Altitude Flights By SAA

Wed Nov 23, 2011 10:43 am

Quoting tdscanuck (Reply 19):
If the IFE is saying FL420 it's most likely because the aircraft it telling it that it's at FL420.


Fair enough, back to the drawing board on the FL420 thing then.
 
speedbird128
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RE: High Altitude Flights By SAA

Sat Nov 26, 2011 9:29 am

Quoting andz (Reply 14):
Many years ago my wife and I were in the cockpit jumpseats on a 747SP between JNB and DUR (258nm according to Great Circle Mapper) and we climbed to FL410. When I asked the Captain why, he said "because we can".

Hey Andz,

Seen 43 and I am sure 45 on that route too... Because they can, and fuel bill is not the crews problem  
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