How do BA calculate flight distance?

Old Oct 24, 17, 3:13 am
  #1  
Original Poster
 
Join Date: Mar 2014
Location: Reading UK
Programs: BA Silver, Accor Gold
Posts: 112
How do BA calculate flight distance?

I've wondered for a while why the Avios I'm awarded always seems to be a little bit less than the minimum actual distance flown between two airports. Last week when we boarded at ATH, the screen display showed a distance of 1,509 miles to LHR. This corresponds pretty well with a "great circle" distance calculator on my computer which gives 1,511 miles. In fact BA award me 1,494 miles (exclusive of any bonus) for the journey. Although I don't have the figures to hand, I had a similar experience on the route to HEL recently too.

As the "great circle" distance is the minimum possible one between any two points, my question is whether BA have found some secret way of taking a slice through the earth's surface to calculate a shorter distance???
IanAsiaTraveller is offline  
Old Oct 24, 17, 3:23 am
  #2  
 
Join Date: Dec 2014
Programs: BAEC Silver, Flying Blue Petroleum
Posts: 164
Ground miles compared to miles flown at ~35,000 ft? The latter will be slightly further because of the curvature of the earth
St Elmos Fire is offline  
Old Oct 24, 17, 3:24 am
  #3  
 
Join Date: Aug 2010
Location: München, Germany
Programs: BA GGL (no longer CCR), Hertz PC, Hilton Diamond
Posts: 5,716
Do they do it from city centre to city centre?

I guess in some cases it could work in your favour, e.g., LCY-ORY is 5 miles further by the great circle than LON-PAR.
Cymro is offline  
Old Oct 24, 17, 3:24 am
  #4  
Original Poster
 
Join Date: Mar 2014
Location: Reading UK
Programs: BA Silver, Accor Gold
Posts: 112
Originally Posted by St Elmos Fire View Post
Ground miles compared to miles flown at ~35,000 ft? The latter will be slightly further because of the curvature of the earth
Exactly. So how on earth can you get a distance LESS than ground miles??
IanAsiaTraveller is offline  
Old Oct 24, 17, 3:29 am
  #5  
FlyerTalk Evangelist
 
Join Date: Aug 2002
Location: London
Programs: Mucci. Nothing else matters.
Posts: 36,428
Originally Posted by Cymro View Post
Do they do it from city centre to city centre?
This seems plausible, as ATH-LCY is 1,492 miles great circle.

Also, ATH-LON (using the LON metro area code) is 1,500 miles great circle, and ATH airport is about 12 miles to the far side of the city centre of Athens.
Globaliser is offline  
Old Oct 24, 17, 3:30 am
  #6  
 
Join Date: Jul 2010
Location: London, UK
Programs: BA Gold, AirBnb 700x Platinum, AC (never again)
Posts: 285
Originally Posted by IanAsiaTraveller View Post
As the "great circle" distance is the minimum possible one between any two points, my question is whether BA have found some secret way of taking a slice through the earth's surface to calculate a shorter distance???
For flights under a certain distance, we can assume BA ignores the GC and just measures a straight line through the earth connecting the two city centres.
YacozA is offline  
Old Oct 24, 17, 3:31 am
  #7  
 
Join Date: Dec 2014
Programs: BAEC Silver, Flying Blue Petroleum
Posts: 164
Originally Posted by IanAsiaTraveller View Post
Exactly. So how on earth can you get a distance LESS than ground miles??
Good point! Circumference of the earth is 24,901 miles, the circumference of an orbit at 35,000 ft is about 20 miles more. I can see why the miles flown quoted onboard would be longer than the shortest ground distance.

The calculator you used may assume an average ground altitude above sea level, BA may assume sea level.
St Elmos Fire is offline  
Old Oct 24, 17, 3:38 am
  #8  
Original Poster
 
Join Date: Mar 2014
Location: Reading UK
Programs: BA Silver, Accor Gold
Posts: 112
Originally Posted by Globaliser View Post
This seems plausible, as ATH-LCY is 1,492 miles great circle.

Also, ATH-LON (using the LON metro area code) is 1,500 miles great circle, and ATH airport is about 12 miles to the far side of the city centre of Athens.
Yes this does sound the most likely explanation, thank you. I will have to check on my next flight.
IanAsiaTraveller is offline  
Old Oct 24, 17, 4:03 am
  #9  
 
Join Date: Sep 2014
Location: Brexile in ADB
Programs: BA, TK, HHonours, Le Club, Best Western Rewards
Posts: 6,248
Perhaps it's which ever "London" airport is closest. London Oxford heading west, London Southend heading east. Gatwick heading due south.
Worcester is offline  
Old Oct 24, 17, 4:51 am
  #10  
 
Join Date: Nov 2007
Location: SW London
Programs: BAEC Gold; Hilton Diamond;a miscellany of other hotel non-statuses
Posts: 3,223
The Avios / TP calculator gives the same 1494 miles whether you fly LHR-ATH or LGW-ATH, so it looks like it's measured from Charring Cross or similar .
EsherFlyer is offline  
Old Oct 24, 17, 5:04 am
  #11  
 
Join Date: Nov 2007
Location: SW London
Programs: BAEC Gold; Hilton Diamond;a miscellany of other hotel non-statuses
Posts: 3,223
Originally Posted by EsherFlyer View Post
The Avios / TP calculator gives the same 1494 miles whether you fly LHR-ATH or LGW-ATH, so it looks like it's measured from Charring Cross or similar .
If you ask gcmap.com to plot LCY, LGW and LHR whilst drawing radii for [email protected],[email protected] in the Ranges box the place where those paths cross looks north of all the airports (and Charring Cross). It looks more "in the middle" if STN is added.
EsherFlyer is offline  
Old Oct 24, 17, 5:36 am
  #12  
 
Join Date: Jun 2009
Location: MME (midway between NCL and LBA)
Programs: BA Gold, AF/KL Gold, Hilton Gold, Nordic Choice Gold
Posts: 622
There is no logic to it.

ARN-LCY (when BA flew the route) used to give 891 miles but ARN-LHR comes in at 890 miles despite probably 20 miles further to fly.

Great circle gives 894 for ARN-LCY and 911 for ARN-LHR so I guess Charing Cross would be around 900 miles so BA are short-changing me either way!

My guess would be that there is a table somewhere in BA's IT systems that has all the route distances hardcoded into it. When a new route is added, the award mileage has to be included but over the years this has been done by different people using slightly different calculation methods.
tigertanaka is offline  
Old Oct 24, 17, 7:12 am
  #13  
 
Join Date: Nov 2010
Location: Oxford, UK
Programs: BA GGL, Asiana Diamond
Posts: 612
There's also that oddity where BA thinks the distance to a destination is different to the distance back to LHR. I know that Boston flights have given me 1 less Avios for the return flight, and I think there may be a couple of other destinations thst are like this too.

Edit: tigertanaka got there before me!
crazyanglaisy is offline  
Old Oct 24, 17, 9:08 am
  #14  
 
Join Date: Jun 2009
Location: MME (midway between NCL and LBA)
Programs: BA Gold, AF/KL Gold, Hilton Gold, Nordic Choice Gold
Posts: 622
Originally Posted by crazyanglaisy View Post
There's also that oddity where BA thinks the distance to a destination is different to the distance back to LHR. I know that Boston flights have given me 1 less Avios for the return flight, and I think there may be a couple of other destinations thst are like this too.

Edit: tigertanaka got there before me!
ARN-LON got you 891 miles each way for LCY and 890 for LHR no matter what direction you went.

BA's systems are seriously weird if you get a different amount for one way compared to the other.
tigertanaka is offline  
Old Oct 24, 17, 2:25 pm
  #15  
Suspended
 
Join Date: Jun 2017
Programs: BAEC
Posts: 325
Originally Posted by tigertanaka View Post
My guess would be that there is a table somewhere in BA's IT systems that has all the route distances hardcoded into it. When a new route is added, the award mileage has to be included
Yes, almost... only the table and the logic are owned by Avios Group, not BA.
LordBuckethead is offline  

Thread Tools
Search this Thread
Search Engine: