Zappbrannigan From Australia, joined Oct 2008, 247 posts, RR: 0 Posted (5 years 10 months 3 weeks 4 days 20 hours ago) and read 8753 times:
First off, my first post here, and thanks to all for some great forums. Quick intro, I'm a recently-instrument-rated CPL who will be shortly studying intently for my ATPL exams and will hopefully move into full-time professional flying in the near future. I love any and all tech discussion on aircraft (to the dismay of many of my friends), so this forum is golden.
I've done a ridiculous amount of long haul travel in previous jobs, and am wondering about the normal procedures and considerations for the selection of step climb levels during long sectors. For instance, I've flown LAX-MEL numerous times with Qantas, which is always flown on the 744ER, departing many times at MTOW (Captain has announced this) - it is standard for the initial cruise level out of LAX to be either FL280 or FL300. In some instances, the aircraft remains at this initial level for some time before it's stepped up to FL340 (skipping FL320). It's then generally stepped by 2000ft at a time, and in my experience normally arrives at TOD at FL380.
I have read somewhere that a 4000ft step is preferable than a 2000ft step for fuel burn reasons, but this does not seem logical to me, since surely the preference is to climb the 2nd block of 2000ft at a lower weight. I have also read in some manuals/textbooks that being above optimum altitude normally results in lower fuel burn than being below optimum altitude by the same amount. With this in mind, what are the reasons for selecting 4000ft steps, and not simply bracketing with a 2000ft climb every step? I imagine it's a combination of ATC requirements during Pacific ops, no RVSM available, favourable winds etc. etc.
Any answers would be great! Thanks again, cheers all.
PhilSquares From , joined Dec 1969, posts, RR:
Reply 1, posted (5 years 10 months 3 weeks 4 days 16 hours ago) and read 8704 times:
Quoting Zappbrannigan (Thread starter): With this in mind, what are the reasons for selecting 4000ft steps, and not simply bracketing with a 2000ft climb every step? I imagine it's a combination of ATC requirements during Pacific ops, no RVSM available, favourable winds etc. etc.
Normally, a 2000' step climb is much better than a 4000' step climb since it keeps you closer to your optimum altitude. However, there could have been traffic at the next FL or that FL could have been unavailable. In the NAT track system the FLs are 1000' apart so theoritically, you could get a climb every 1000' when your optimum allows.
LAXintl From United States of America, joined May 2000, 25058 posts, RR: 46
Reply 2, posted (5 years 10 months 3 weeks 4 days 14 hours ago) and read 8661 times:
From an operator I deal with, their SOP is that If its a choice of being above or below your optimum FL a bit, being above generally would be preferable as the optimum will rise into the higher FL as time goes on, while moving away from the lower FL leaving one being stuck ever farther below the optimum.
With often restricted FL in many parts of the world, suppose the thinking is take the FL when you can.
From the desert to the sea, to all of Southern California
Heinzmahrer From Switzerland, joined Feb 2008, 6 posts, RR: 0
Reply 3, posted (5 years 4 months 3 weeks 6 days 9 hours ago) and read 7703 times:
As in most things in life it is a question of what is desirable versus what is available. If you fly in RVSM airspace the flight levels are 1000 ft apart: 1000 ft above you there is opposite traffic and your next available level is 2000 ft higher. Once you reach the upper limit of RVSM (usually FL 410) then the separation becomes 2000 ft between levels and your next available level is 4000 ft above you.
GLEN From Switzerland, joined Jun 2005, 221 posts, RR: 2
Reply 4, posted (5 years 4 months 3 weeks 6 days 8 hours ago) and read 7670 times:
The availability of a level is one thing for the actual level you are flying. So in your example
Quoting Zappbrannigan (Thread starter): In some instances, the aircraft remains at this initial level for some time before it's stepped up to FL340 (skipping FL320).
it is also possible (just guessing) that an other aircraft at FL320 was blocking further climb. Once clear of the traffic you're optimum level may by so high in the mean time, that you're gona climb 4000 ft.
Furthermore optimum level is not only a question of weight. It would be, if there was no wind or constant wind at all levels. In fact windspeed and direction can quite differ at different levels. So you may stay longer or climb earlier to a level which wouldn't be optimal just considering your weight. Just in order to have more tail- or less headwind. Sometimes your optimum level could even become lower during a flight.
If you have the data from a wind prognosis model you can enter winds at different altitudes along your route into your FMS, preferably at waypoints with a significant change in either winddirection or -speed. It's a bit a fingerexercise to type in all these figures for a longhaulflight, but I don't care about 10 minutes typing on a 10 hour flight. FMS is then calculating the Optimum Level regarding weight and wind. And the result can be quite interesting and if you can fly such an optimised profile (depending on traffic) you sometimes save considerable amounts of fuel and time.
[Edited 2009-03-28 15:53:37]
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