24
$\begingroup$

If you fly frequently there are chances you have seen some delays in departure where you end up waiting in the aircraft sometimes for multiple hours.

Almost every time that happened I remember the PIC announcing something in the lines of We will try to make up for the lost time...

And they manage to do a very good job at that. One of my recent flights was delayed 2 hours on departure but arrived only 1 hour late.

Its quite exciting when they say that, its like wow he/she will speed up! but how much leverage do they have to accomplish that? I'm sure there are commercial as well as regulatory requirements to remain within a range but how broad that range is for general commercial aircraft?

The aerodynamics and engineering part of this problem I know about, I'm mostly interested in the commercial aspect of it. Are the speed ranges set by commercial interests?

$\endgroup$
  • 3
    $\begingroup$ Most of the made up time comes from luck: Flying in a tailwind for hours has by far the biggest impact on travel time. $\endgroup$ – Peter Kämpf Dec 28 '16 at 10:01
  • $\begingroup$ Thanks! normally its always the case. But in this specific case it was headwind and still they managed to save some time $\endgroup$ – Hanky Panky Dec 28 '16 at 10:18
  • 8
    $\begingroup$ I suspect most of the time they "make up" is due to a buffer that was actually included in the schedule from the start and some help from the ATC like direct clearance and vectors to shorten the departure and approach. $\endgroup$ – Jan Hudec Dec 28 '16 at 11:46
  • 3
    $\begingroup$ Related: How can an airliner make up for time lost? $\endgroup$ – mins Dec 28 '16 at 11:49
  • $\begingroup$ I heard a better one recently: "We will make up for this lost time in flight." (of course, the delay was only ten minutes...) $\endgroup$ – Jasper Dec 28 '16 at 17:40
27
$\begingroup$

There is something called the "Cost Index" - it is basically how you choose between speed and fuel economy. Company dispatchers, after knowing that a flight has been delayed, will calculate this value, and the pilots simply input the updated value into the FMC (Flight Management Computer). That will instruct the autopilot to output more thrust, i.e. fly faster, but less fuel efficient.

$\endgroup$
  • 8
    $\begingroup$ Related (not a duplicate): What is Cost Index? $\endgroup$ – mins Dec 28 '16 at 11:49
  • 5
    $\begingroup$ In addition, they can request a more direct routing. $\endgroup$ – Burhan Khalid Dec 28 '16 at 15:15
  • 5
    $\begingroup$ The dispatchers also may be able to find an alternative route that is not more direct but has better tailwinds. But notice that "we" is not just the flight crew; there are things a dispatcher can do to reduce flight time that the pilot would not be authorized (or even have the ability) to do on his or her own. $\endgroup$ – David K Dec 28 '16 at 19:01
  • 1
    $\begingroup$ It might also be worth mentioning that the added cost is only worth it when compared with the cost of a delayed flight (with e.g. a bunch of passengers to re-route and so on), which is strictly out of the hands of the pilot in command. $\endgroup$ – E.P. Dec 28 '16 at 21:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.