As of July, the Bureau of Transportation Statistics stopped reporting on US Airways, in light of its merger with American. All former US Air flights will now be reported as American.

In July, the percentage of delayed flights for all carriers taken together was 20.9%, which is a drop from June which was the worst month so far this year. With over 30% of its flights delayed, Spirit Airlines retained its crown as the worst performing airline. Frontier, Southwest, and United (!) all had more than 25% delayed flights.

Here is the summary report for this month.

• Total flights: 520,718
• Busiest day of week: Thursday
• Slowest day of week: Saturday
• Busiest airport: Atlanta
• Most popular route: San Francisco (SFO) to Los Angeles (LAX)
• Airline with the most flights: Southwest
• Number of delayed flights: 107,627 (20.92%)
• Airline with highest % delayed flights: Spirit
• Airline with lowest % delayed flights: Hawaiian

Not many surprises there, so I will continue on last month’s theme of delays. We saw from last month’s data that about 65% of all delayed flights involved a delay of less than an hour. This month’s data is along the same lines. In fact, July’s data shows a slight improvement, with over 67% of flights arriving within an hour.

The graph below shows the distribution of the delay data. I have ignored the 454 flights that were delayed by over 6 hours from this graph.

As you can clearly see, the number of delayed flights drops exponentially as time progresses. The dashed red line is the average time delay for all flights, but we can clearly see that this is a right-skewed distribution, whose median is around the 30-minute mark.

I came up with this hypothesis in last month’s post, but I have checked this against data from the beginning of the year, and the data bears this out: if you want to minimize your chances of missing a connecting flight, leave at least one hour between the two flights. Your chances of missing a flight will be less than one in three in this case.

Extending this further, we see also that almost 89% of delayed flights are delayed by less than two hours, and over 95% of delayed flights are delayed by less than three hours.

Of course, even with a three-hour gap, you may end up missing a connection, but the data offers you jumping off points. If I were traveling by myself, I would be OK with leaving just an hour’s gap between connections. But if I were traveling with family, I might be more comfortable picking flights that are two hours apart.

You can download the IPython notebook for this month’s analysis from here. Happy flying!