Qantas Delays/Cancellations

[Himeno]

Suggesting different performance characteristics - cruise speed?. Or airframe differences wrt to despatch efficiency

I understand 2 engine vs 4 engine w.r.t to ETOPS but the 777 is 2 engine and MEL-SIN is not really an ETOPS affected route

Compare the scheduled block times for QF11 A380 vs QF11 on Tuesdays (a 747), or QF93 vs QF95 MEL-LAX.

 

[jb747]

What's the practical difference between CI60 and 130.

About .02 to .03 mach.

 

[Quickstatus]

About .02 to .03 mach.

CI higher for the DXB /LHR flights due to scheduling pressures? or prevailing headwinds?

Ill ask more about this in the usual ATP thread.

In order to repair a delayed flight, can a different CI be used (I understand that previously you have said such attempts might be futile due to fuel limitation and degree of actual time saved)

 

[flychrisfly]

Your flight is waiting for the 747 coming in from JFK (QF12 transcontinental). That aircraft is expected to arrive at 2349 hrs.
It is currently overflying DEN.

The root cause was a late departure of the outgoing QF11 transcontinental LAX-JFK 2 hours 15 minutes late

I suspect that you will be waiting past 00:55 hours as that departure time seems a bit optimistic. Flightaware suggests a 0128 departure


Can you discern whats happening to QF94 to MEL and perhaps comment on the general level of service recovery by the airline?

QF94 got away on time as far as I know.

Service recovery? Wait in the terminal. I'm travelling in F but am on Nee York time so trying not to have too many reds...

 

[jb747]

CI higher for the DXB /LHR flights due to scheduling pressures? or prevailing headwinds?

It's a tight schedule, so it's planned fast to maximise the available turnaround/transit time.

In order to repair a delayed flight, can a different CI be used (I understand that previously you have said such attempts might be futile due to fuel limitation and degree of actual time saved)

If you want to increase the speed then you can. But, fuel is always a consideration. Generally we'll have a play with a couple of FMC options, and see whether the time gained is worth the fuel lost. That relationship varies from day to day, and flight to flight.

Options for increasing the speed vary. You can increase the CI. Or you can program a fixed mach number. You could even enter a target time at a point, and have the FMC continually vary the speed to make that time.

 

[Melburnian1]

Amending previous discussion a page or two back on AFF, the Sunday 3 July delayed B744 on QF12 departed JFK at 2116 hours, three hours and six minutes behind time, arriving LAX at 2351, two hours and 46 late, thus picking up 20 minutes on a gate-to-gate basis.

 

[Quickstatus]

It's a tight schedule, so it's planned fast to maximise the available turnaround/transit time.

So using an example if a MEL-DXB 380 service needs to make up some time what "ball park" time saving could a doubling of the CI input achieve? (Fuel on this route would obviously be the main limitation)

 

[Melburnian1]

QF1/2/9/10 at times have tight turnarounds, especially QF10 to QF9 in Melbourne, but to suggest that the timetables - not the turnarounds - are 'tight' ignores how often some of these sectors see the aircraft regularly picking up time on a gate-to-gate basis. These gains on the timetables appear to occur during much of the year, not just in three months of a year.

For instance a few days ago QF2 departed DXB at 1049, 94 minutes late, yet arrived SYD the next morning at 0551 hours, only 41 minutes late - a pushback to on blocks gain of 53 minutes on the schedule.

In the other direction, QF9 on Saturday 2 July departed MEL at 2317, 22 minutes late, arriving DXB on Sunday 3 at 0640 hours, 25 minutes early. The onward sector then pushed back at 0901, four minutes ahead of time, arriving LHR 45 minutes early - a gain of 49 minutes gate-to-gate on this shorter sector.

The Friday 1 July QF1 departed SYD 25 minutes late at 1615 but arrived at the DXB terminal at 0009, 16 minutes early - a 41 minute gain on the timetable. It then departed DXB on time at 0210 hours but arrived LHR 24 minutes early at 0631.

The Saturday 2 July QF10 departed LHR five minutes ahead of time at 1300, arriving DXB's terminal at 2253, 27 minutes early - a gain of 22 minutes on the schedule. Continuing on, it departed the Middle East at 0137, two minutes late but arrived in MEL at the gate at 2031 hours, 24 minutes early - a net gain of another 22 minutes on the timetable.

It isn't just QF that does this, although it slowed the LHR timetables last October (2015) as prior to that the punctuality had been appalling, particularly with QF9 and QF10. My sense is that it has improved somewhat since then.

Adding extra time like this makes airlines' timekeeping look good.

 

[jb747]

So using an example if a MEL-DXB 380 service needs to make up some time what "ball park" time saving could a doubling of the CI input achieve? (Fuel on this route would obviously be the main limitation)

Going from 60 to 130 might bump the initial mach number from .83 to about .85. It will slow down as it burns fuel, but if you assume an overall increase of .02, then that would get you about 12 knots groundspeed, for 12 hours, so a saving of about 18 minutes. On that flight it can be done, as the fuel loading will be for the higher CI. But, if I just bumped it up by the same amount on a random flight, it would cost about 3 tonnes, which is probably a cost I can't afford. You can have a higher overall gain by using fixed mach numbers, but at the expense of even more burn.

 

[jb747]

Adding extra time like this makes airlines' timekeeping look good.

The flight times are based on what is achieved 90% (or thereabouts) of the time. They try to allow for the average holding, and arrival procedures, which at Dubai can be very lengthy. If you get no holding, you can be miles ahead. The original schedules did not make adequate allowance for any of this.

 

[Melburnian1]

The delayed Sunday 3 July 2016 QF12 has just pushed back in LAX at 0106 on Monday 4 July, two hours and 36 minutes (156 minutes) late. SYD arrival is estimated at 0800 on Tuesday 5, 90 minutes late. Sometimes QF adjusts the latter after it becomes clear what time takeoff occurred. At this stage there are no shown delays to QF1/7/11 tomorrow (Tuesday).

 

[Quickstatus]

18 minutes is easily lost with the myriad of issues that may beset an airline's punctuality.

If it takes substantial fuel to get back 18 minutes, I would speculate then that a clawback of 1 hour would be impossible on a long haul route by utilising faster flight envelope speeds

So when pilots say they will try to make up time, really the substantial time savings is to be found either end at the departure and arrival airports. Going faster seems limited in its time saving potential but at significant fuel cost.

Thanks JB747 for this additional insight

 

[Melburnian1]

Updating what I contributed two posts above, QF has indeed altered the forecast arrival time of QF12 in SYD from 0800 hours to 0930 hours. This is more realistic.

The Sunday 2320 hours late night QF16 (LAX - BNE) is showing as forecast to push back at 0155 hours on Monday 5, that is, in a few minutes.

UPDATE: QF16 departed at 0208 from LAX. Ot is showing as arriving in BNE at 0825 on Tuesday 5 July, 135 minutes late.

 

[jb747]

18 minutes is easily lost with the myriad of issues that may beset an airline's punctuality.

Each run around the holding pattern costs about 7 minutes.

If it takes substantial fuel to get back 18 minutes, I would speculate then that a clawback of 1 hour would be impossible on a long haul route by utilising faster flight envelope speeds.

You'd not be able to get anywhere near an hour, just by going fast. That 18 minutes would be very close to the maximum possible. Max mach number is .89, and the aircraft limits to .88. If you are cruising at high speed, you need to be aware that a wind change could result in a speed increase that could put you over the maximum speed. So, generally you'll find that pilots will keep their speed about .03 under the maximum, to ensure they don't exceed the limits. So, that puts you at .86. And that extra .01 would also have a disproportionate effect on the burn.

So when pilots say they will try to make up time, really the substantial time savings is to be found either end at the departure and arrival airports. Going faster seems limited in its time saving potential but at significant fuel cost.

Aircraft are already cruising at about 95% of their maximum speeds. There's not much room to play. You might be able to find some more time, by flying lower, where the mach number will equate to a higher TAS. Again fuel burn goes up. Descending late, at high speed, and with maximum speed brake can find 5 minutes just in the descent, but, it's uncomfortable and almost certainly won't be acceptable to ATC.

Savings on the ground are the cheapest, but you have no real control over them. It's why we try as much as possible to depart LAX from 24L, as it incurs virtually no delay, where going to 25L can take half an hour.

Very fast flights are simply the result of very favourable winds.

 

[Quickstatus]

Coming back to QF35 2Jul where the flight converted from late to early by shaving 40 minutes or so off the gate to gate time according to Flightstats.

A review of Flightradar did not reveal a fast ground speed which would have suggested a tailwind as Flightradar reports ground speed?
The time between gate and runway seemed the usual.

 

[Melburnian1]

It's why we try as much as possible to depart LAX from 24L, as it incurs virtually no delay, where going to 25L can take half an hour.

Is there any direct or indirect approved way for tech crew to 'request' this 'runway advantage' at (in this case LAX) from ATC, or do you simply take what you're allocated despite the possible time (and chewed up fuel) penalty? I often hear tech crew requesting (or agreeing to suggested by ATC) particular taxiways (and they do it in an easy going, quick conversational style) but cannot recall hearing a runway request. Maybe I have simply missed same.

Presumably the time and fuel savings over a year would be large.

 

[jb747]

Is there any direct or indirect approved way for tech crew to 'request' this 'runway advantage' at (in this case LAX) from ATC, or do you simply take what you're allocated despite the possible time (and chewed up fuel) penalty? I often hear tech crew requesting (or agreeing to suggested by ATC) particular taxiways (and they do it in an easy going, quick conversational style) but cannot recall hearing a runway request. Maybe I have simply missed same.

Presumably the time and fuel savings over a year would be large.

In LAX it's become the convention for the 12 and 94 to use 24L if they can. It helps ATC as we don't have to cross the active runway(s), and there's normally very little traffic moving on the northern side compared to the south. If we need 25L, we advise ground quite early in the piece (about 30 minutes before departure time, when we work to the performance data). It's just conversational..."Ground, Qantas 94, we'll require 25L tonight".

In Oz, ATC are pretty much used to us needing the long runways for departure, but you can specify it early in the piece (generally when you get your airways clearance, as they are runway specific). On arrival, if you need something other than the duty, you just tell approach that you 'require' whatever runway.

 

[suze2000]

That 18 minutes would be very close to the maximum possible. Max mach number is .89, and the aircraft limits to .88. If you are cruising at high speed, you need to be aware that a wind change could result in a speed increase that could put you over the maximum speed.

<snip>

Very fast flights are simply the result of very favourable winds.

These two statements seem to contradict each other? On the one hand you say you can't exceed a speed in case the winds take you over max. On the other, you say winds are the best way to go fast.

I was once on a PER-MEL flight (cannot remember if 737 or A330) and there were audible gasps throughout the plane when the Capt announced out arrival time, because it would mean our flight time was just over 2.5 hours. I'm willing to concede I'd had a few wines, but everyone else in the plane could not believe it as well. Is that even possible?

 

[Quickstatus]

These two statements seem to contradict each other? On the one hand you say you can't exceed a speed in case the winds take you over max. On the other, you say winds are the best way to go fast.

I was once on a PER-MEL flight (cannot remember if 737 or A330) and there were audible gasps throughout the plane when the Capt announced out arrival time, because it would mean our flight time was just over 2.5 hours. I'm willing to concede I'd had a few wines, but everyone else in the plane could not believe it as well. Is that even possible?

not a contradiction.

Tailwind increase ground speed - so destination arrived faster
headwinds reduce ground speed - so takes longer to get to destination. However if the aircraft is flying at maximum designed speed and suddenly there is a headwind, the apparent airspeed is greater than maximum design speed (but ground speed is now less) so the aim is to not fly at the boundaries but inside it allowing for variability in headwind

 

[suze2000]

Yeah understand about headwinds and tailwinds. Are you saying that when you set a speed on a plane, it's not determined by, say for example engine revs, but the plane attempts to maintain a ground speed? Feel like a complete nonce because that makes no sense to me.