Let's say I'm going to work. Usually the drive takes me one hour at my usual pace of 60mph. One day, I'm leave the house late by about 10 minutes. But I can still make it to work on time by driving a little faster, say around 70mph.

When travelling a bunch recently, I noticed that whether the airline takes off on time or not, the arrival time is still about the same as scheduled.

I know that there are jet streams and such that can allow the airplane to fly faster.

But dumb question: in general, do the departure and arrival times assume some airspeed (ie - like 60mph above) for normal flights and then use some higher speed (ie - 70mph) if takeoff is delayed for some reason to avoid late arrivals?

If so, why not just fly at the higher speed all the time? Do airlines fly slower normally to save gas or something? And then just fly faster if takeoff is delayed for some reason?

This is from a non airline pilot who got it secondhand from buddies who fly for carriers, but the airlines try to save as much as they can on fuel and still make their schedules if possible. The schedules are generally conservative. I’d guess that while they probably do occasionally burn a little extra fuel and go a little faster to make up time, it is probably more common that they slow down and save some fuel whenever they can do it and still make their scheduled arrival time. It is not uncommon for crews to negotiate shortcuts when they can. Making the route a little shorter is a more efficient way to save time than turning more fuel into noise.

The routes are usually calculated on averages based on seasonal winds and loads. Fuel savings is a paramount concern...mostly.

Yes, we can fly faster, but at jet speeds and route lengths, going faster vs going the efficient speeds doesn't usually make that much of a difference except on longer routes (meaning 3-4 or more hours in my experience. Even then, it's an equation between the extra fuel burn and the loads. Airplanes can carry mas payload or max fuel, but not both, so it's a real balancing act.

Honestly, trying to shorten up time is at the discretion of the pilot. Dispatch doesn't generally worry to much about it. Occasionally, we will get the word from "higher up" to goose it, but not that often. Delays are delays, and it's just the reality of the job. The best I have ever managed is with winds much stronger and in different directions than normal.

I'm sure others will chime in with much more detailed explanations, but that's the quick and dirty.

The airlines schedule arrival times based upon the particular airport. Lets say you are flying a round trip from Okc to ORD and back the next day. The scheduled flight time from OKC to ORD might be 2 hrs. However, the return leg might be scheduled for 2 hrs and 10 minutes.

The reason?

Each airport has different levels of volume. So, sometimes flying from a less busy airport could mean almost no delay in departing (no long departure cues at the runway). Conversely, flying into a busier airport also means the chance of Traffic Management Initiatives that could delay your flight. Airlines know the averages of this, and thus, it is built into the schedule. Now, there are other factors that will blow all of that out of the water (weather being the main thing) and cause you to experience extensive delays.

Next time you book a flight, see if the the outbound leg has the same flight time as the inbound leg. Depending upon the airport pairs involved, they times are different.

The question was addressed to airlines. I'm not an airline pilot, but I am a commercial pilot and have done a good bit of corporate, charter, and air taxi flying.

My experience has been that variations in flight times have been caused by wind and weather, much more so than by how busy the departure and arrival airports are.

As far as varying the power to compensate for delays and meet a schedule, I don't do that much, but I might change power settings for lower fuel burn with a tailwind, and more power with a headwind. I generally do this for flight efficiency / cost, rather than for trying to meet a schedule.

Headwind/tailwind seem to be a big factor. I've flown BOS->Shannon, Dublin, Heathrow, Amsterdam a lot. Usually up to an hour or more longer into the wind going west. I've also arrived in Europe as much as 45 minutes early because of a stronger than expected tailwind.

Thanks guys.

Ok, sounds like:
1) schedules are influenced by some nominal speed assumptions that are less than some higher but reasonable speed to save costs.
2) arrivals can be modulated by env factors without cost
3) higher speeds can make up for late departures

quote:

Originally posted by konata88:


But dumb question: in general, do the departure and arrival times assume some airspeed (ie - like 60mph above) for normal flights and then use some higher speed (ie - 70mph) if takeoff is delayed for some reason to avoid late arrivals?

If so, why not just fly at the higher speed all the time? Do airlines fly slower normally to save gas or something? And then just fly faster if takeoff is delayed for some reason?

Flights are conducted on the basis of a "cost index," which takes into account speed vs. fuel consumption, and are seldom flown at the maximum speed; there is a point at which efficiency rapidly diminishes, fuel consumption goes up, and more fuel must be carried, which also increases fuel burn; for the very minor increase in speed, the increase in fuel burn isn't worth it. Generally one burns 4% of any additional fuel just to carry that fuel. Weight is a big issue on any flight, and any more weight than necessary restricts climb altitude, which restricts efficency further, keeps the flight from having options in the event of turbulence and wind, and may restrict the routing. Therefore, keeping a particular speed, as much as possible, is important.

A flight is predicated on a planned and filed routing. The flight may or may not be assigned that routing, but it's picked for traffic flow and efficient altitudes, and weather. Becuase of the high volume of traffic in flight at any given time, giving everyone direct from one point to another isn't possible, any more than it's possible do drive your car in a straight line to your destination. There are roads in the skies, some made up of actual "airways" and "jetways," and others that are simply made up of a series of "waypoints," or points in space.

Enroute, it's not uncommon to request, and get, direct to a particular waypoint downrange. This may decrease the enroute time, or in some cases, it might increase it. A week ago, I had a routing that took me 200 miles more than our original planned distance. This meant changes in our alternate choice of airports, as well as a change in our fuel load, planned altitude, etc. At one point air traffic control offered us direct and a shorter routing, but we elected to take a longer distance and higher fuel burn, due to weather.

Small increases in speed make a noticeable difference in fuel burn on long trips. On oceanic legs, we operate using what's called a "constant mach technique" for traffic spacing; sometimes it's a slower speed than we want, sometimes a bit higher, and it can quite a difference in fuel burn over a seven hour flight or more. Typically I operate at .83 or .84 Mach, but bumping it up just .1 mach produces a large drag increase, which takes a lot more thrust, and a lot more fuel. This interfers with fuel reserves and optiosn in the event I need to divert.

You may sometimes hear the flight crew say "we'll try to make it up enroute," but this is usually lip service, as the option doesn't really exist. It may be that winds will be better, or that air traffic control may shave a bit off with more direct routing, but beyond that, there's not a lot that can be done. The faste you go, especially at the upper end of the speed range, drag rises very rapidly, and small increases over cruise speeds affect the flight planning and fuel burn/reserves a LOT more than slightly slower speeds might. Much of the time, given winds, temperatures aloft, weather, and payload and weights, it's not practical or possible to increase speed for the flight.

Back in 2008 - 2009 I had a consulting gig in NJ that lasted 12 months, flying into Newark. Every Monday I flew out of Denver and every Thursday I flew back. Approximately 3 out of 4 departures, when we pushed back from the gate in Newark we sat on the tarmac in line for about 45 minutes before we took off. I noticed we always landed on time in Denver. Occasionally we would push back, taxi and takeoff. No sitting for 45 minutes. When that happened we landed 45 minutes early in Denver.

I figured out Continental's schedule (now United) had a built in "normal delay" of 45 minutes leaving Newark. I am sure some of the other busy airports have similar built in delays during peak times.

“Why not fly at higher speeds all the time...?”

$$$$$$$$$$$

There was a time back in the day of dirt cheap oil where airlines did "fly faster". Basically it was red line (balls to the wall) all day every day. Nowadays fuel is 20% more or less of an airline's operating budget so they pay much closer attention to fuel usage. We hear constantly how just reducing APU (aux power unit) usage by a few mins per aircraft per leg translates to millions of dollars a year in savings.

Another thing to consider re speed is that many aircraft inspections and parts life is hour based, so flying slower than normal means an airplane accumulates more flight time in a shorter calendar period, and that impacts the maint cost and downtime over the life of the plane(s).

Generally expect some breadth of knowledge in any given forum.

The depth of knowledge on any given topic here on SF still always amazes me

Remember, this is the airlines end goal.



Getting you places on-time is part of making that happen, but 5-30 min late doesn't matter a bit (likely even more than that). Their scheduling is organized madness that they have some control over, with the rest (delays, weather, ATC, etc) being out of their control.

As mentioned, I've seen some 'built in' extra time as I fly around the country - a route I know takes between 50-60 min advertised as 75-80 min right up until takeoff.

But often times weather, winds, etc pushes those numbers back and forth a good bit. Generally wind blows west to east, but that can change a good degree depending on the fronts as they swing through the country. So that has to be written into the route times, planned, etc.

Just be glad you live in a time you can pay several hundred to a couple thousand dollars today and be nearly anywhere in the WORLD tomorrow - a trip that only 100 years ago would have taken weeks or months, cost a ton more in money (and potentially lives).

I think a thesis could be written with all the info in the responses.

As an aside, I had the pleasure of late departures/arrivals and almost missed connecting flights. Because people got violently ill all over the seats.

I don’t want to seem alarmist but with all the stuff in the news these days of measles outbreaks and other previously uncommon diseases, this is the first time in all my years that I’ve been uncomfortable flying with so many sick people on board.

quote:

When travelling a bunch recently, I noticed that whether the airline takes off on time or not, the arrival time is still about the same as scheduled.

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I wish this were the case when I fly. I have missed many a connecting flight because of time delays. Unless it is a long haul I would prefer to drive.

quote:

Originally posted by konata88:
I don’t want to seem alarmist but with all the stuff in the news these days of measles outbreaks and other previously uncommon diseases, this is the first time in all my years that I’ve been uncomfortable flying with so many sick people on board.

I have a N95 mask and a pair of gloves in my carry on after having a kid of some foreigners start coughing up blood on the jetway.

Never had to use them, but not all of us have the option of driving everywhere.

For layovers, I never accept anything less than 1-hr on the ground and prefer to sit for an extra hour than have to stress / race / potentially miss a connection. And I only connect through Atlanta, so worst case I can get in a rental car and drive home if things go really really sideways.

quote:

I have a N95 mask and a pair of gloves in my carry on after having a kid of some foreigners start coughing up blood on the jetway.

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Not enough protection from Ebola.LOL

quote:

Originally posted by ZSMICHAEL:

quote:

I have a N95 mask and a pair of gloves in my carry on after having a kid of some foreigners start coughing up blood on the jetway.

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Not enough protection from Ebola.LOL

Yeah, but it lays flat folded in the carry on suitcase and takes zero room. Every laughs until the person next to them pukes or shits themselves

Then you know they'll be like "You got another one of those???", to which the response will be a gloved middle finger.

Problem is by the time you get on your mask and gloves you are already exposed and screwed. There was a story yesterday about a 14 year old who sat down in a wet seat which happened to be covered in vomit. Her mother did not handle the situation well and Frontier kicked her off the flight and local authorities locked the mom up for 12 hours.



Gloves can have tiny holes and masks have limited effectiveness. I would suggest a plastic splash shield to go over the mask. LOL

See here: https://www.universalmedicalin...p3rmBxgaAg_8EALw_wcB

When the airlines wanted to get more on time arrivals, they started adding 20 to 30 minutes to the published flight times, depending on where you were going, NE coast usually 30 minutes for e ample. It also depends if it’s the crews last lag of the trip, and trying to catch a commuter flight. If so, you are passing SR71’s, meteorites,ICBM’s, etc, to get in early.