Continuing the discussion from Fuel factor:
When I am flying with the 773ER I have to plan for a fuel factor of P15
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Then you’re flying the 77W sub-optimally. I’ve done pretty extensive testing and Benny is correct.
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Wait when you say that I’m not flying it optimally, do you mean that I’m Not doing step climbs and stuff like that or I’m travelling too fast and using too much fuel?
Because When I’m flying the 77W I do step climbs, and Maintain my speed in the right way and everything as well… any advice?
By my math:
JFK-ORD, ZFW 461k lbs, Simbrief says 51k lbs block, I have 37k, roughly 27% less.
YYZ-LHR, ZFW 446k lbs, Simbrief says 114k lbs block, I have 86k, roughly 24% less.
IST-LAX, ZFW 447k lbs, Simbrief says 260k lbs block, I have 186k, roughly 28% less.
It gets a little muddier if you want to copy IRL altitudes exactly but it seems like you can lose like a maximum of 2k lbs an hour flying really high (and that’s really pushing it) before you go to serious stall risk. If you apply that then the numbers fall to 20%, 14%, and 18%.
If you’re holding M 0.84, try the above altitudes (it’s loads on the left side and optimal altitudes going east in Green and west in Blue) and see what happens. If you’re still having issues then something else is going on.
I saw a case a few weeks ago where the person as flying with the flight spoilers extended because they thought “Spoilers Flight” meant use them in flight. Could that be the case?
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My numbers are checked to within about 1% margin of error so I am fairly confident in my math.
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Based on that, you are either cruising too high, or too fast, or both.
Or you have spoilers in flight mode, someone did that recently…
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Not the least understandable mix-up to be fair, they do say FLIGHT spoilers.
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True - maybe just “down/off”, “up”, and “armed” would be less confusing.
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Thanks heaps for the breakdown—it makes more sense now! I’ve actually got the opposite problem though. On recent 777-300ER flights in Infinite Flight (ICN–DXB and SIN–LHR), I’ve run out of fuel well before arriving, even when following the planned cruise speeds and using no spoilers mid-flight.
Based on SimBrief’s numbers, I was short by around 14–18% on both flights, so I’ve been testing higher fuel factors (currently trying P18–P20) to compensate. I do follow proper step climbs and cruise around Mach 0.84, so I don’t think it’s an altitude issue.
Have you seen anything like that happen in IF before—where fuel burn is higher than SimBrief’s plan instead of lower? Just curious if it might be a model-specific issue or weight-related.
Appreciate the help! Thanks heaps for the breakdown—it makes more sense now! I’ve actually got the opposite problem though. On recent 777-300ER flights in Infinite Flight (ICN–DXB and SIN–LHR), I’ve run out of fuel well before arriving, even when following the planned cruise speeds and using no spoilers mid-flight.
Based on SimBrief’s numbers, I was short by around 14–18% on both flights, so I’ve been testing higher fuel factors (currently trying P18–P20) to compensate. I do follow proper step climbs and cruise around Mach 0.84, so I don’t think it’s an altitude issue.
Have you seen anything like that happen in IF before—where fuel burn is higher than SimBrief’s plan instead of lower? Just curious if it might be a model-specific issue or weight-related.
Appreciate the help!
Well, for example, I recently tried to do a flight from South Korea to Dubai and this is where I ran out of fuel around an hour and a half Before landing… Or at least I was at around 20 minutes of fuel left when I still had about an hour and a half of flying to go.
Throughout the flight I was doing on average M0.86 and I was at cruising altitude of FL342
M0.86 is too fast. Depending on your cruise altitude you probably would’ve been at or near 100% N1, which uses considerably more fuel then a typical cruise N1 in Infinite Flight of 85-91%.
Also I put that route into Simbrief. It didn’t recommend FL340 till 6-7 hours in at a cruise speed of M0.83/.84. If you climbed to FL340 straight away at M0.86 that would’ve used a fair bit more fuel, particularly if you encountered stronger headwinds as a result.
That’s really interesting. Nothing off the top of my head stands out. 0.86 over 0.84 is a bit of an increase and an average of 340 is maybe a little high? But regardless, this is a difference of about 1000-1500 lb/hr which is like 6%, nowhere near the 30-40% you’re getting undercut by.
Do you have the exact numbers you used on these flights? See if you can check the Simbrief history. I’m wondering if maybe less fuel was loaded than you thought. I’ve never had a 77W fuel issue before so I’m just speculating.
It happens, but not with the 77W. Mostly older jets.
When I Simbrief’d ICN DXB right now it gave me a block fuel of 195k lbs. If that was short 15% then you would’ve needed 230k just to complete the 10.3 hour flight, which would mean burning roughly 22k lbs per hour which is just insane. For reference, that’s about how much you’d burn trying to fly 0.89-0.90 at an optimal altitude.
I have a theory. It is a very outlandish theory and I don’t know the Simbrief integration tool well enough to know if this is debunkable from the start but regardless. From the way you type I’m going to assume you aren’t American. Are you somehow loading in fuel in lbs in game when Simbrief has kg? My spreadsheet says you’d need roughly 115k lbs to complete ICN-DXB. The Simbrief came out to about 90k kilos, so if you loaded 90k lbs instead of 90k kilos you would indeed come up about 20% short. Probably a long shot but I’ll throw it out there.
On your next 77W flight try this:
Do whatever preflight you need, and then before pushing back manually reset the fuel to what Simbrief tells you. Then, follow these altitudes at 0.84 and see if you still end up running out of fuel.
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That’s interesting, and thank you for putting the route in yourself because while I did A step climb at the start and I didn’t go to FL340 straight away, I was headed to bed at around 1-1.5 hours into the flight and I set it to FL340 before then so that could have been a slight issue and yes I did have extreme headwinds (around 80-110knots) for the first hour.
Regardless of this specific flight, I did my step climb properly for the flight from Singapore to London and I still ran out of fuel 2 hours before arriving in London (had to land early). So Whilst I completely agree with the South Korea to Dubai flight, It seems to be inconsistent even when I’m following the proper step climb and speeds for other legs of the 77W
That’s a decent theory tbf…and works out maths-wise with pretty much any flight.
Imma test it.
It’s a little short to be honest…but I’ve got no other leads so I gotta throw it out there. Considering you burn more at the start of the flight I think you’d probably be 25% short distance wise. However, I don’t know how OP is deriving the 18% number so maybe?
Also my question is, is that even possible to do? When you load from Simbrief does it just load based on your current IF units and current Simbrief units without checking the units? I haven’t used the tool at all so I don’t know. Though I suppose they could just be manually loading without checking.
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Just did a test run. Simbrief in kg, Infinite Flight in lbs, and it converted it appropriately. So that’s not it.
Now this is vexing - how is OP using that much more fuel…
If altitude and speed are reasonable there are like three factors that it could be: gear, flaps, or flight spoilers. OP already mentioned the spoilers were down and I find it hard to believe that you’d leave flaps or gear out on multiple flights without noticing it.
Very strange indeed.
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P15? That’s way too much try to keep it under P06. Can you share the pdf of your flight plan? Also do you add extra fuel for MEL and WXX? And what about contingency fuel? Remind you simbrief does not account for wind factors in long haul routes.
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Where are you getting this from? ICN-DXB currently is an extra 60k in block fuel over DXB-ICN on account of winds