Flying Dogleg with NZ

[Cocitus23]

Hi All,

I recently (2 Dec 2016) flew NZ29 from Houston (IAH) to Auckland (AKL). It was a clear day with no weather problems over the US-Mexico border region. It's a long flight and I expected that we would take the Great Circle route SW from IAH across Mexico. For those of you who like precision in such matters, the initial bearing of the Great Circle is 237 degrees. But no! We started out somewhat north of due west. In fact, we were on a bearing of 285, as though we were headed for LAX. Initially I thought that this was for some local air traffic control problem, or else for some stray cloud. But for the next hour and a half on and on we went, decidedly off-track.

Eventually, when we were somewhere west of El Paso TX we wheeled left, entered Mexican air space, and headed for AKL. A good flight was had by all. My questions are: Does NZ29 always follow this route, and, if so, why? I calculate that the dogleg adds over 200 miles (320 km) to the journey. OK, I agree, that's only about 3% extra onto the total length of the trip, so it's no big deal. But, heck, the trip is long enough as it is, so why make it longer?

Does anyone have any insights or bright ideas?

Cocitus23

 

[RooFlyer]

FightRadar24 for some reason dates your flight as the 3rd ...



Randomly selecting dates before and after reveals that your flight was indeed not the usual way, which is this, give-or-take a few turns over Mexico.



Could be many reasons for the different route, but typically unfavourable winds would be a likely cause for them to change the normal route; perhaps a large storm cell or cells in the way?

 

[RooFlyer]

And here's your flight profile

 

[Cocitus23]

FightRadar24 for some reason dates your flight as the 3rd ...

View attachment 86525

Randomly selecting dates before and after reveals that your flight was indeed not the usual way, which is this, give-or-take a few turns over Mexico.

View attachment 86524

Could be many reasons for the different route, but typically unfavourable winds would be a likely cause for them to change the normal route; perhaps a large storm cell or cells in the way?

Many thanks, RooFlyer for your observations and for those great charts. Re the date, it's funny that it is listed as the 3rd, because it actually departed IAH on the 2nd and landed in AKL on the 4th. The 3rd went down the gurgler at the dateline.

Cocitus23

 

[Mattg]

Flights would generally take the quickest route (unless there's a good reason to deviate, e.g. due to weather). But due to the winds, the quickest route is not always the shortest.

I recall reading somewhere that flights between Australia/NZ and the USA often alter their flight paths slightly to either take advantage of (if travelling east) or avoid (if travelling west) strong winds around the equator. Perhaps that has something to do with it as well.

 

[Cocitus23]

Thanks for that, Mattg. A good example of the practice you refer to occurs on the Sydney - Johannesburg route. While the return journey, i.e coming back to Sydney, usually follows the Great Circle, which surprisingly perhaps brings it right over Melbourne, the forward journey usually swings way south of the Great Circle, right down to the coast of Antarctica. I have always assumed that this wide sweep is to avoid battling against the Roaring Forties. I have taken that flight many times, and it always astonishes me that the last point of Australia one sees is the southern tip of Tasmania.
Cocitus23

 

[Mattg]

Thanks for that, Mattg. A good example of the practice you refer to occurs on the Sydney - Johannesburg route. While the return journey, i.e coming back to Sydney, usually follows the Great Circle, which surprisingly perhaps brings it right over Melbourne, the forward journey usually swings way south of the Great Circle, right down to the coast of Antarctica. I have always assumed that this wide sweep is to avoid battling against the Roaring Forties. I have taken that flight many times, and it always astonishes me that the last point of Australia one sees is the southern tip of Tasmania.
Cocitus23

Yep - the winds also explain why the SYD-JNB flight takes more than 2 hours longer than JNB-SYD.

 

[neilmeister]

My last flight from WLG->SYD flew SW for about an hour before turning north, flight took 4.5 hours which is crazy long, around 1.5 hours longer than normal.

Most other Trans Tasman flights got cancelled so I imagine it was a mother of a storm that we flew around. I admit I was a bit frightened when we didn't get cancelled.