I’ve been looking at AF flights from LAX to CDG recently, and I’ve noticed that the AF71 from Tahiti, operated by a 744 flies a great circle route over Greenland, Iceland etc, whereas the direct LAX-CDG AF65/69 operated by a 777 fly across the US to Boston and Newfoundland and then a normal NAT to CDG.
Why is there a difference in routing? Surely the 777 should follow the great circle route like the 744 for better fuel economy. Can anyone help out here?
Cheers,
Dan Biddle
May be taking advantage of different winds aloft at different times in the day. The 777 shouldn’t have any ETOPS issues with the great circle route.
It actually could be an ETOPS issue. ETOPS applies over isolated or rugged terrain as well as over water. Due to dozens of factors that relate to ETOPS, a twin-engine aircraft might take a longer route.
Long flights are sometimes filed as 2 flightplans. For example, LAX-HKG flights are often filed as LAX-ANC and ANC-HKG. If everything is OK approaching ANC, the first flightplan is cancelled and the second one started. This affects required fuel load, crews, etc. That might be what’s happening on the LAX-CDG flights.
Just speculation, though.
Id agree with mduells initial guess of better winds on that day on that particular route. The 777 has a ETOPS 207 min certification. 207 min is a weird number, but its a result of tha fact , that its pretty much the amount of ETOPS time needed to be able to fly pretty much anywhere point to point.
Kenish is right about the fact, that people assume ETOPS only applies over water.
The other thing Kenish is talking about is the procedure of “Reclearance Flight Plans”.
The airlines are required to carry (among other reserves…) 5% of their trip fuel (fuel calculated for use during the flight) as a reserve. On a 10 hour flight depending on aircraft type it could amount to 4000kg or more…
By declaring a destination closer to your departure airport you can save on the 5% rule. At the reclearance point you have to have (again among other reserves…) the remaining trip fuel plus 5% of that to your real destination, in order to continue. Your reclearance airport has to be somewhat close to your intended destination and the entire reclearance procedure only saves you from a couple of hundred to maybe 2000kgs of fuel or so. This procedure is usually only used if youre just a few hundered kgs over the maximum allowable take off weight in order to avoid offloading. Since its a little bit “tricking with the numbers” its usually at the discretion of the captain to accept it or to offload…