PbodyPhoto

I have recently noticed a discrepancy between the gcmap.com distance and what AA posts to my account for EQM.

SAL-MIA credited 12 short
FCO-LHR credited 1 short
DFW-HKG credited 12 short
HKG-SFO credited 13 short
MIA-LGA credited 1 short
JFK-MIA credited 1 short
SYD-DFW credited 9 short

On the plus side a few credit higher than the gcmap distance:
LHR-JFK credited 1 extra
DFW-EWR credited 4 extra
EWR-MIA credited 11 extra
VCE-PHL credited 1 extra

As you can see obviously more flights credit less than credit more miles. At the end of the year I will be out about 100EQM and maybe 300RDM, sure it is small numbers but it is really annoying!

Anyone know how they work their mileage out? Wonder if I should photograph the "distance to destination" part of the interactive map and fight for those miles to be honoured.

FAA1996

AA gives you the distance in miles of the flights before you purchase them (same way you can see fare codes and seat maps.) I don't know where they get these numbers from, but I would assume these are the ones you should make sure you get, not the ones on the GCM. Only downside is they only do this for AA flights, not including codeshares.

JDiver

Unfortunately, AA miles earned figures are somewhat dynamic because they creep with annoyingly and unpredictable periodicity.

Use Great Circle Mapper and figure there will be a little error; use the figures you're given on aa.com or the PDF schedule, you'll be closer - until they shift the pegs again.

CPRich

cgmap.com is a common source, but they aren't the be-all/end-all bible. Geography can be an inexact science, especially in the sub-1% range that most of your examples illustrate. They provide you their data up front, so you know what you're getting. If you don't like the deviation from another source, you can always try another airline.

Hasn't the "actual flight miles" vs. route planned miles credit been addressed - making photographs of actual flight mile calculations a moot point? It's at least covered in the T&C's of the program, so you'd need to sue to get it changed.

mAAine_flyer

For geography maybe, but geodesy is a much more exact science

While computations of the great circle distance can be laborious, they are not especially difficult. Key things to consider are rounding of the angular coordinates (nearest arc-second vs nearest arc-minute), and the choice of reference Earth model (ellipsoid vs sphere).

If AA's great circle calculator uses coordinates rounded to arc-minutes, then results will differ from gcmap. Likewise, AA's calculator might simplify the math by representing Earth as a sphere, whereas in reality Earth is an oblate spheroid or ellipsoid (gcmap uses the WG84 ellipsoidal model as a reference).

JDiver

Whatever AA uses, there's "mileage creep" in their stated mileage. I've had to change figures in my spreadsheet's lookup tables fairly regularly. Certainly greater changes than would result from continental drift.

mAAine_flyer

We don't call it "continental drift" anymore Plate tectonics is where it's at!

As for AA's mileage creep, the simple explanation could be that they've changed the reference Earth model (e.g., a sphere to an ellipsoid, or Clarke 1866 ellipsoid to WGS84 ellipsoid, or whatever) used in the great circle calculation.

PbodyPhoto

Not always. No figures are provided for FCO-LHR, HKG-SFO, or SYD-DFW.

djk7

I don't know why the larger discrepancies exist, but a mile or two is the difference between one end of a runway and the other. Those could be explained by where on the airport property the measurement is taken from.

jerry a. laska

If it is a flight that isn't operated by AA then the mileage is determined by the operating carrier.

Mwenenzi

gcmap.com is just 1 source/calculation. There are others

A similar topic http://www.flyertalk.com/forum/qanta...incorrect.html.

rcw

As mentioned in the Qantas thread, HKG moved in 1998 from Kai Tak to its present location at Chek Lap Kok. Per wikipedia, Kia Tak is at 22�19′43″N 114�11′39″E (which you can input into gcmap). This seems to account for the difference with respect to HKG-SFO. Similarly, SYD-DAL is 9 miles less than SYD-DFW so maybe they like, or rather love, the old airport. Some combination of the two likely explains DFW-HKG as well.

Below is a link to gcmap for the above airports:
http://www.gcmap.com/dist?P=hkg+-+sf...DM=&SG=&SU=mph

JDiver

Several times for each mileage pair pair? (AA systems are not up to plate tectonics; give it a decade or so. )