Do Airline Delays Increase Average Flight Speed?

It seems to me that, on more than one occasion, I’ve found myself on a flight that lifted off far behind schedule, only to find myself arriving on time. Is it common for pilots to ‘make up time’ on flights that’ve been delayed on departure?

To help answer this question I used 2015 data on all commercial flight delays and cancellations, which I downloaded via Kaggle (this data set is also publicly available from the US Department of Transportation website). In addition to information on scheduled versus actual departure time for commercial flights, the data set also contains information about time in transit and distance traveled, which I used to calculate average airspeed.

Here’s what the distribution looks like, by month, for average air speed as it relates to departure delay. This excludes all flights that were cancelled outright, diverted, or had a transit distance of less than 300 miles.

From this, it’s not clear that average airspeed varies by departure delay. If anything, this suggests that average airspeed varies by month — but that’s a question for another day. Part of the problem with this density plot is that there are so many flights that leave on time or ahead of schedule.

Here’s the same style of plot, but limited to flights with a >30 minute delay:

The spread along the x-axis is much wider here, giving us a clearer picture. But no relationship really jumps out. The 90 degree tilted triangle in virtually every plot suggests there’s little relationship between these variables.

Here’s the same plot, with linear best fit lines drawn through each distribution, for good measure:

It would be interesting to further subdivide this by airline, or aircraft type (the former is possible with this dataset, the latter is not).

Reflecting on this, I suppose it’s not surprising that average flight speed isn’t correlated with departure delay. Airlines operate on paper thin margins of efficiency, and for every type of aircraft, there’s a combination of altitude and airspeed that maximizes fuel efficiency (not to mention safety) given the flight conditions of that day. To throw that all out in the interest of making up ground may be extreme on all but the most delayed flights.

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