Why published flight times are not always accurate: reasons and explanations

Flight times are something strange. Sure, it's on every flight - there's always a departure and arrival time that's published online months in advance. But if you fly frequently, you may have noticed that these times are almost never accurate.

The departure time may be pushed back due to a slow boarding process, and the arrival time may be shifted due to any delays during the journey, whether it's bad weather or heavy traffic. Therefore, no matter how hard the airline tries, it is almost impossible to calculate flights to the minute. This was reported by travelandleisure.com.

However, airlines certainly know and expect this, so they have sophisticated methods for formulating flight times, including a variety of data from previous performance in the National Airspace System. Ultimately, they do their best to accurately calculate flight times to keep things running as smoothly as possible - and that often includes adding extra time to the schedule in case of unexpected delays.

Here's what you need to know about how flight times are calculated, including what counts as an "on-time arrival."а

What is the departure and arrival time?

Although many passengers may assume that departure and arrival times refer to the moment of departure and landing, this is not the case. The "scheduled" part of air travel - from departure time to arrival time - is called block time and includes time spent on the ground.

"Blocking time is defined as releasing the brakes on the landing gate and setting the brakes on the arrival gate," says aviation expert Don Wolford.

This means that the published times you see online are not just the time spent in the air - they also include the taxiing time between the gate and the runway.

How do airlines determine blocking times?

Airlines are data-driven, so a complex algorithm takes various data and formulates a reasonable block time for a flight. "Factors such as average departures and arrivals, average travel time, chronic air traffic delays, etc. are taken into account when calculating block times," says Wolford.

And the results are different for every airport, every route, and every hour of the day. That's why different flights on the same route - even flights on the same airline - can have different published durations.

When is a flight considered on time or late?

The U.S. Department of Transportation (DOT) monitors airline performance and has determined that any flight that arrives within 15 minutes of its scheduled arrival time is actually "on time." So when you're planning a trip - say, booking a car from the airport in advance - think about adding 15 minutes to your arrival time just in case.

Are airlines supplementing flight times?

Airlines are cautiously reducing flight times, which is key to operational success. "There is such instability in the National Airspace System that airlines are forced to add blocking time to the schedule for almost all flights," Wolford says.

Reducing flight times also benefits passengers. Since most airlines in the U.S. operate on a hub-and-spoke model – passengers are routed from small airports to large hubs and then on to other hubs or smaller airports – change times are critical. "Up to 60 percent of passengers may change flights at a hub, so schedule integrity is important from that perspective," Wolford says.

But airlines don't want to increase flight times too much. While on-time arrival is a key metric for airlines, there is also a financial incentive to be as accurate as possible with lock-in times. "Airlines invest significant resources in operational analysis. When these analysts can find a way to reduce lock-in times by even a few minutes, the cost savings become enormous, just in terms of pilot and flight attendant pay, as well as under-the-wing labor at airports, such as on the ramp, gate, and maintenance crews," says Wolford.