Speeding up
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Speeding up
Scenario:
Long haul flight, many pax with onward connections at the far end, and you have a delayed start.
Are you able to "put the foot down a bit" to try and make up time?
Pro- you get to the destination having made up time, hence less pax are affected (which in turn may mean less costs to the airline having to deal with the dealys eg. re-booking, hotels, etc.
Con- More fuel burn, more stress on the engine and airframe, etc
Long haul flight, many pax with onward connections at the far end, and you have a delayed start.
Are you able to "put the foot down a bit" to try and make up time?
Pro- you get to the destination having made up time, hence less pax are affected (which in turn may mean less costs to the airline having to deal with the dealys eg. re-booking, hotels, etc.
Con- More fuel burn, more stress on the engine and airframe, etc
Join Date: Sep 1999
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Have you heard of "Cost Index"? Its a computerized means of calculating operating costs versus time, the airline/crew can then decide to fly faster or slower in order to minimize costs, some flight planning systems will allow the process to calculate delayed passenger costs and have the speed chosen accordingly.
Mutt
Mutt
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Most airliners already cruise at a speed that is close to the maximum cruising speed, and although there is still an element of margin available, it is probably much less than you realise.
On top of this there are other factors to consider such as ATC constraints, as well as those things you have already touched on, such as fuel consumption.
So while there is a little bit of scope in this regard, any advantages are often outweighed by the ATC requirements to maintain a filed constant airspeed, turbulence, airport arrival times, gate availability etc.
On top of this there are other factors to consider such as ATC constraints, as well as those things you have already touched on, such as fuel consumption.
So while there is a little bit of scope in this regard, any advantages are often outweighed by the ATC requirements to maintain a filed constant airspeed, turbulence, airport arrival times, gate availability etc.
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Are you able to "put the foot down a bit" to try and make up time?
Paid...Persona Grata
Most airliners already cruise at a speed that is close to the maximum cruising speed, and although there is still an element of margin available, it is probably much less than you realise.
However it seems that it doesn't apply on short-haul. On a few recent flights I was pleasantly surprised to hear announcements such as "80 knot head wind" coupled with "twenty minutes early arrival". OK we were 5 mins early leaving, but how did the pilot gain the extra 15 mins (on a flight less than an hour)? The answer seems to be that the flights were scheduled at well below the aircraft maximum speed - the figure I remember hearing on the occasion mentioned above was 325mph, which is well short of the maximum speed for the 738.
Not surprising that the airline concerned can boast a magnificent punctuality record with that much speed in hand!
Cheers
UFO
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Not really. The schedule is normally based on the average gate to gate time with an element built in to allow for delays at either end. This has the dual advantage of both a built in schedule buffer, and minimizes the number of occaissions that a flight is seen to be arriving late.
Flights are generally filed at a constant mach number. Straight in arrivals and direct routings will obviously shave a few minutes off the planned flight time here and there.
Bear in mind that most delays occur either on the ground, or during holding/spacing vectors prior to landing, and the schedule is constructed to acccomodate a significant element of that.
Flights are generally filed at a constant mach number. Straight in arrivals and direct routings will obviously shave a few minutes off the planned flight time here and there.
Bear in mind that most delays occur either on the ground, or during holding/spacing vectors prior to landing, and the schedule is constructed to acccomodate a significant element of that.
Supercharged PPRuNer
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Regarding short haul operations, I can think of some routes with overly generous schedules, and others where we consistently struggle to keep to time. Going flat out helps less than you might expect, as the difference between our economy cruise and ‘full speed ahead’ is a whopping 10 knots. On a 1 hour sector, that amounts to a few minutes at best.
What does help are things like expeditious departures when traffic is light (taxy times at Gatwick range from 90 seconds to 35 minutes+) short cuts from ATC, favourable winds (a 100kt tailwind being better than 100kt headwind) and straight in approaches at the other end. Add them all together, and we could easily arrive 15-20 minutes early on a one hour sector.
As Bealzebub says, the schedules are based on an average block to block time, including a ‘factor X’ as a cushion against delays. Occasionally it’s not enough - most of the time it’s more than sufficient, and we’re on stand a few minutes ahead of schedule.
What does help are things like expeditious departures when traffic is light (taxy times at Gatwick range from 90 seconds to 35 minutes+) short cuts from ATC, favourable winds (a 100kt tailwind being better than 100kt headwind) and straight in approaches at the other end. Add them all together, and we could easily arrive 15-20 minutes early on a one hour sector.
As Bealzebub says, the schedules are based on an average block to block time, including a ‘factor X’ as a cushion against delays. Occasionally it’s not enough - most of the time it’s more than sufficient, and we’re on stand a few minutes ahead of schedule.
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The Cost Index as mentioned above is normally determined by accountants in hangers and entered into Flight Management Systems prior to departure.
To make up time enroute, the normal method is to just increase speed via the autopilot, other ways as mentioned are taking advantages of jet streams above/below by changing levels or begging ATC for shortcuts . . . . .
To make up time enroute, the normal method is to just increase speed via the autopilot, other ways as mentioned are taking advantages of jet streams above/below by changing levels or begging ATC for shortcuts . . . . .
Paxing All Over The World
Non pilot speaking.
The last time I left JFK, the taxi time from push to turning onto the active was 55 minutes. All airlines do now build in 'delay' time to their schedule. on a short domestic route I used to take three times a year (LTN~IOM) the wheels-to-wheels time was usually 45 minutes and with usually short taxi's either end, so the sector was always marked as 60 minutes.
As to time in long haul, the supporters of Boeing used to make much that the 744 was a lot faster than the A343. On the LHR~JNB route which I know well, the difference allowed by VS, who operate both types on the route, is just on half an hour. That is: across some 5,000 route miles and 10.5 hrs, the Airbus would only take some 30 mins longer (to be fair, the company point out how much more economical it is on fuel).
Lastly, this change in schedules started because (1) the carriers wanted to minimise pax delays at the gate by bringing the scheduled departure time forward to get people to the airport earlier. (2) they lengthened the scheduled time when various govt and consumer organisations started to publish the on-time statistics. In the past decade, the UK train companies have all done the same thing!
So the room for making up time? They make sure that the time is already there before they rotate. I'm going LTN~MAD this evening and the advertised time is 2.5hrs. I expect we shall leave 'late' and arrive on time.
The last time I left JFK, the taxi time from push to turning onto the active was 55 minutes. All airlines do now build in 'delay' time to their schedule. on a short domestic route I used to take three times a year (LTN~IOM) the wheels-to-wheels time was usually 45 minutes and with usually short taxi's either end, so the sector was always marked as 60 minutes.
As to time in long haul, the supporters of Boeing used to make much that the 744 was a lot faster than the A343. On the LHR~JNB route which I know well, the difference allowed by VS, who operate both types on the route, is just on half an hour. That is: across some 5,000 route miles and 10.5 hrs, the Airbus would only take some 30 mins longer (to be fair, the company point out how much more economical it is on fuel).
Lastly, this change in schedules started because (1) the carriers wanted to minimise pax delays at the gate by bringing the scheduled departure time forward to get people to the airport earlier. (2) they lengthened the scheduled time when various govt and consumer organisations started to publish the on-time statistics. In the past decade, the UK train companies have all done the same thing!
So the room for making up time? They make sure that the time is already there before they rotate. I'm going LTN~MAD this evening and the advertised time is 2.5hrs. I expect we shall leave 'late' and arrive on time.
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I remember being on a Qantas flight several years ago from Singapore to Sydney, on a 747-400. We were delayed leaving Singapore for some reason, and the captain came on the intercom after take-off to apologise for the delay. He said we would fly faster than usual to try to make up some of the time, adding that "we've got the fuel". I don't know how much faster a 744 can fly than its optimum cruising speed, but I guess even 20kts or so would make a difference over an 8-hour sector. (I can't remember how much time we did make up in the end - and anyway, I wouldn't know what was due to the higher speed cruise, and what was due to tailwinds, or ATC shortcuts around Sydney.)
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i remember a few years ago, having flown overnight JFK - LHR, we were sat on the 757 shuttle ready to come back upto manchester. there was confusion with the number of bags in the hold, and this led to a 2 hour delay. eventually when we did set off - the 1 hour scheduled flight ended up being 23 minutes runway to runway. i seem to recall there was very little turning, so we might have gone in the most direct route possible, and when the engines roared on take off - they never seemed to throttle back until ready for approach at manchester.
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speeding up................not so fast.
Tb10er,
When you embark on a journey with your automobile you have a very wide range of speeds available to you. The longer the distance the greater the opportunity to arrive sooner; you could drive at 50 km/hr or 100 km/hr. The latter could cut your time in half. Not so with transport jets, at higher altitudes and heavier weights the airspeeds available to us are much more limited. Fly too slow and we approach stalling speed, fly too fast and we approach maximum certified speed, and the difference between the two is often not very much. We simply do not have as wide a range of speeds to choose from as you do driving your automobile on the autobahn/freeway.
Once we are airborne a simple delay vector by ATC, a slower speed assignment due to traffic ahead of us, or added time incurred while navigating away from enroute storms will negate virtually any advantage gained by having flown a few knots faster. The best way to ensure an on time or early arrival is to get off the gate and into the air as expeditiously as possible.
For more information Google aviation+coffin corner.
Respectfully,
When you embark on a journey with your automobile you have a very wide range of speeds available to you. The longer the distance the greater the opportunity to arrive sooner; you could drive at 50 km/hr or 100 km/hr. The latter could cut your time in half. Not so with transport jets, at higher altitudes and heavier weights the airspeeds available to us are much more limited. Fly too slow and we approach stalling speed, fly too fast and we approach maximum certified speed, and the difference between the two is often not very much. We simply do not have as wide a range of speeds to choose from as you do driving your automobile on the autobahn/freeway.
Once we are airborne a simple delay vector by ATC, a slower speed assignment due to traffic ahead of us, or added time incurred while navigating away from enroute storms will negate virtually any advantage gained by having flown a few knots faster. The best way to ensure an on time or early arrival is to get off the gate and into the air as expeditiously as possible.
For more information Google aviation+coffin corner.
Respectfully,
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If I could have a pound for every time I've got away early had a quick taxi, good route and landed early only to find the stand occupied, no guidance or no steps (if on remote), I would be a very rich man.
On time at LHR is best!
6
On time at LHR is best!
6
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If you can fly at a slightly faster Mach speed in the cruise on a long flight to make up a little time, I've always wondered whether you also cruise slower on short-haul routes (e.g.one-hour flights between UK airports) to 'maximise' your time in the cruise?
