Good day all

    I got the strangest of problems that popped up doing a flight today

So i did a flight from KSFO-YMML on the PMDG 777-300er     My trip distance was supposed to be 7,858 miles based on the flight plan i got but when i entered it into the FMC i get a distance of 6,957, that is about a

900 mile difference      and i am real confused 

I did the math adding up the legs and the 6,957 number was right

 

here is the flight plan i used

 

    GNNRR3 CINNY DCT 30N129W DCT 25N132W DCT 21N135W DCT 16N140W DCT 08N150W DCT 00N160W DCT WOOBY B581 NN DCT TANIL A579 UPSAD DCT ABARB DCT RIKNI DCT OMLAV Q15 WOL H65 RAZZI Q29 LIZZI DCT

 

any help with this would be great

 

thanks

 

13ifs40

On 1/14/2024 at 2:59 PM, 13ifs40 said:

Good day all

    I got the strangest of problems that popped up doing a flight today

So i did a flight from KSFO-YMML on the PMDG 777-300er     My trip distance was supposed to be 7,858 miles based on the flight plan i got but when i entered it into the FMC i get a distance of 6,957, that is about a

900 mile difference      and i am real confused 

I did the math adding up the legs and the 6,957 number was right

 

here is the flight plan i used

 

    GNNRR3 CINNY DCT 30N129W DCT 25N132W DCT 21N135W DCT 16N140W DCT 08N150W DCT 00N160W DCT WOOBY B581 NN DCT TANIL A579 UPSAD DCT ABARB DCT RIKNI DCT OMLAV Q15 WOL H65 RAZZI Q29 LIZZI DCT

 

any help with this would be great

 

thanks

 

13ifs40

Which tool did you use to calculate the trip distance of 7,858?

I assume both flight plan and fmc route had the same waypoints and SID/STAR, correct?

Maybe you can post the flight plan showing the incorrect distance? I threw your route into SkyVector and it comes close to what the FMC stated of 6,949.8 miles.

 

Another question-  any idea why that routing was selected? I would have thought picking up one of the routes out of KSFO (e.g R464) via Honolulu would be more appropriate?

900nm is not trivial, unlikely due to SID/STAR and map projection error.

I suspect 7858 is air distance, so that's 900nm due to headwind, but without seeing the plan you got it's just a guess.

4 hours ago, C2615 said:

900nm is not trivial, unlikely due to SID/STAR and map projection error.

I suspect 7858 is air distance, so that's 900nm due to headwind, but without seeing the plan you got it's just a guess.

Headwind won’t increase the distance flown. It only impacts the time required to fly the trip at a given true airspeed.

The shortest possible route - (the great circle distance direct from KSFO to YMML) - is 6826 nm. 

1 hour ago, JRBarrett said:

Headwind won’t increase the distance flown. It only impacts the time required to fly the trip at a given true airspeed.

The shortest possible route - (the great circle distance direct from KSFO to YMML) - is 6826 nm. 

The "Air Distances" is specific term for counting wind impact. My company's FPL show both DISTANCE and ESAD

Edited April 8, 20242 yr by C2615

2 minutes ago, C2615 said:

The "Air Distances" is specific term for counting wind impact. My company's FPL show both DISTANCE and ESAD

I have not seen that. Apparently they are calculating the “equivalent” distance you would fly caused by a headwind  as if there was no wind.

With most planners used by hobbyists - and that includes Simbrief and PFPX, as well as professional planners like Foreflight, “air distance” is exactly that - the distance the aircraft will actually fly through the air on the chosen route. It might be considerably longer than the direct (great circle) distance, especially if SIDS, STARS or airways are involved. Also,  sometimes airline  dispatch departments will route a trip quite far from the direct path if by so doing they can avoid a jet stream with strong headwinds.

I put the flight plan the OP posted into Foreflight and got the same distance as he did from the FMC: 6957 nm. I am curious what specific planner he used that gave a distance of 7858 nm