WPvsMW
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Adjusting flight plan en route for strong tailwinds

Tue Oct 30, 2018 5:19 am

In a thread in the civ av forum about QF's PER/LHR n/s, there was a report of a B789 having to hold for 30 minutes before landing at LHR (strong tailwinds en route). I understand the slot constraints at LHR, but why can't a flight plan be altered en route to avoid holding, and thereby save fuel? 30 minutes of fuel is huge, esp. at LHR prices.
 
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Starlionblue
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Re: Adjusting flight plan en route for strong tailwinds

Tue Oct 30, 2018 6:28 am

WPvsMW wrote:
In a thread in the civ av forum about QF's PER/LHR n/s, there was a report of a B789 having to hold for 30 minutes before landing at LHR (strong tailwinds en route). I understand the slot constraints at LHR, but why can't a flight plan be altered en route to avoid holding, and thereby save fuel? 30 minutes of fuel is huge, esp. at LHR prices.


Flight plans are typically made to avoid holding, and departures delayed, but sometimes unexpected things happen. The route hasn't been around that long, so statistics may not be quite solid yet, especially as season change.

In some cases you run into the issue of a curfew on both ends, so that you can't take off late enough to arrive after the curfew at the arrival. Similarly, you may want to go on time because if you wait half an hour, you might be subjected delays of a further 3 hours (for example) due to flow control. Better to go and hold at the destination for half an hour, than to sit on the ground for three hours and potentially delay beyond the duty time.

Either way once you're in the air you'd rather get there and hold, than take another route altogether just to extend your track miles. One thing that can be done if it looks like you'll be early is to decrease the cost index in flight.

BTW the fuel used for holding would be at PER prices, not LHR prices.
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zeke
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Re: Adjusting flight plan en route for strong tailwinds

Tue Oct 30, 2018 7:31 am

QF9 is scheduled to leave PER at 7:40 pm. They could easily just delay the departure by 20 minutes.

We regularly need to delay departures to achieve destination slot times at the scheduled arrival time.
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WPvsMW
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Re: Adjusting flight plan en route for strong tailwinds

Tue Oct 30, 2018 9:10 am

Thanks for the prompt replies... the gist of which is that if winds aloft decrease flight time, it's better to delay departure time, which would mean amending the flight plan before takeoff.

Starlionblue wrote:
BTW the fuel used for holding would be at PER prices, not LHR prices.

What I had in mind is topping off in LHR before the next segment, whether to PER or elsewhere. After a 30 min. hold for LHR, then landing, the a/c refueling is done at LHR prices (£££££).
 
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Starlionblue
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Re: Adjusting flight plan en route for strong tailwinds

Tue Oct 30, 2018 9:16 am

WPvsMW wrote:
Thanks for the prompt replies... the gist of which is that if winds aloft decrease flight time, it's better to delay departure time, which would mean amending the flight plan before takeoff.

Starlionblue wrote:
BTW the fuel used for holding would be at PER prices, not LHR prices.

What I had in mind is topping off in LHR before the next segment, whether to PER or elsewhere. After a 30 min. hold for LHR, then landing, the a/c refueling is done at LHR prices (£££££).


Ah. I see what you mean. However on such a long segment, tankering is very unlikely. The extra burn from carrying the tankered fuel all the way from PER would negate any savings.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
WPvsMW
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Re: Adjusting flight plan en route for strong tailwinds

Tue Oct 30, 2018 9:31 am

We're on the same page. The amended flight plan would avoid 'quasi-tankering'... not really tankering but using reserves for a 30 min. hold.
 
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Starlionblue
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Re: Adjusting flight plan en route for strong tailwinds

Tue Oct 30, 2018 9:34 am

WPvsMW wrote:
We're on the same page. The amended flight plan would avoid 'quasi-tankering'... not really tankering but using reserves for a 30 min. hold.


I take your point. In most cases, that 30 minutes for the hold would come out of contingency fuel which is carried anyway. And since they were early they probably didn't use the contingency en route.

But of course if you didn't use the contingency, you of course still have it in tanks on the ground. :)
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WPvsMW
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Re: Adjusting flight plan en route for strong tailwinds

Tue Oct 30, 2018 9:37 am

You're correct. I should have written "contingency fuel", not reserves.
 
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XAM2175
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Re: Adjusting flight plan en route for strong tailwinds

Tue Oct 30, 2018 6:09 pm

zeke wrote:
QF9 is scheduled to leave PER at 7:40 pm. They could easily just delay the departure by 20 minutes.
We regularly need to delay departures to achieve destination slot times at the scheduled arrival time.


QF regularly do this on flights to LAX based on the weather expected en-route - they show hideous on-time stats for departure but this is preferable to holding for their slot time on arrival.

Obviously though over such a long flight as PER-LHR it's entirely possible that the pre-departure estimates didn't quite match reality in the air.
 
MSJYOP28Apilot
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Re: Adjusting flight plan en route for strong tailwinds

Fri Nov 02, 2018 4:35 am

One thing to remember is that dynamic re-routing enroute based on winds is a relatively new concept. Some countries like the U.S. don't have the technology in place yet to allow for dynamic automated re-filings enroute by the airline. Dynamic re-routing for this would require manual coordination between the dispatchers or pilots and ATC which can be time consuming and this assumes the route change will even be approved.

On routes like PER-LHR that cross multiple time zones and countries, overflight permits are an issue. You can't just file any route you want. It is costly to maintain overflight permits when you rarely use them. Not to mention the cost for overflying each country is different. If you re-route into an expensive country, you might spend more money on overflight fees than simply burning fuel in holding waiting for the curfew to expire.

Also, weather can be a problem. You don't want to re-route yourself into turbulence or thunderstorms trying to make a flight plan longer.
 
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zeke
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Re: Adjusting flight plan en route for strong tailwinds

Fri Nov 02, 2018 6:33 am

Australia publishes new optimised flexible tracks daily via NOTAM based upon actual winds

https://www.airservicesaustralia.com/au ... xtrack.asp
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
744lover
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Re: Adjusting flight plan en route for strong tailwinds

Fri Nov 02, 2018 8:01 pm

If the flight is running a few minutes ahead of schedule, wouldn't it be prudent to use RTA (or the equivalent in Airbus) speed and guarantee the arrival slot? This way the FMC would reduce or increase speed based on the calculated time of arrival.


Thanks,
744lover
 
T54A
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Re: Adjusting flight plan en route for strong tailwinds

Mon Nov 05, 2018 1:50 pm

WPvsMW wrote:
You're correct. I should have written "contingency fuel", not reserves.


Contingency fuel is generally for en-route extra fuel requirements. Holding fuel is for what it says. Most operators will cater for holding into LHR as it is normal to hold there. If you don't use the contingency fuel en route, it will be available for extra holding at destination.
T6, Allouette 3, Oryx, King Air, B1900, B727, B744, A319, A342/3/6 A332/3
 
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MassAppeal
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Re: Adjusting flight plan en route for strong tailwinds

Mon Nov 05, 2018 2:58 pm

zeke wrote:
QF9 is scheduled to leave PER at 7:40 pm. They could easily just delay the departure by 20 minutes.

We regularly need to delay departures to achieve destination slot times at the scheduled arrival time.


Is this something that's feasible to predict after 17 hours of flight?
 
T54A
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Re: Adjusting flight plan en route for strong tailwinds

Mon Nov 05, 2018 3:28 pm

MassAppeal wrote:
zeke wrote:
QF9 is scheduled to leave PER at 7:40 pm. They could easily just delay the departure by 20 minutes.

We regularly need to delay departures to achieve destination slot times at the scheduled arrival time.


Is this something that's feasible to predict after 17 hours of flight?


Yes. Today’s flight planning and wind modeling is very accurate. I regularly fly 15-16hr ULR flights that end within a couple of minutes of the flight planned time. A flight plan is generally created about 2hrs before departure. On the a 16hr flight that’s 18hrs before scheduled arrival time.
T6, Allouette 3, Oryx, King Air, B1900, B727, B744, A319, A342/3/6 A332/3

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