On a recent morning, Delta Air Lines Flight 435 pushed back early from the gate at New York's John F. Kennedy International Airport. Passengers watched the safety video and settled in for a six-hour trip.

Then they waited. And waited.

Still within sight of the gate, their jet sat motionless due to airport congestion. It wasn't until 30 minutes after passengers buckled in that they were finally in the sky.

It's a scene playing out across the country. According to an Associated Press analysis, airplanes spent 23 minutes and 32 seconds, on average, taxiing between gates and runways during the first nine months of the year. That's the longest it has been since the Bureau of Transportation Statistics started tracking taxi times in 1995 and a 50-second increase over last year's average.

For passengers, the rising delays add to the frustrations of travel. A plane might land early but then sit waiting for a gate to open up. Flights are still arriving "on time" but only because airlines have increased scheduled flying times to account for the added taxi times. The Delta flight made it to the gate in San Francisco 10 minutes ahead of schedule despite the takeoff delays.

The creep in taxi times is attributed to a series of changes: massive runway construction projects at some of the nation's busiest airports; schedule changes that increase the number of flights at peak hours; and new, distant runways that relieve congestion but require more time to reach.

"It's death by a thousand cuts," says Vikram Krishnan, a partner in the aviation practice of consultancy Oliver Wyman.

The problems on the ground are costing airlines dearly.

"Two, three, four, five minutes in a fleet of 500 planes a day is significant amounts of money," says aviation consultant Mike Boyd.

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That translates into hundreds of millions of dollars extra in operating costs so far this year, according to AP calculations factoring in average operating costs including pilot and flight attendant salaries.

Airlines say the longer taxi times are baked into schedules, so planes generally still arrive on time. So far this year, 79 percent of flights have been at the gate within 15 minutes of their scheduled time, the best performance since 2012.

Passengers might be spending more time on planes, but airlines are better managing their expectations by increasing scheduled times for flights. That masks some of the problems, like taxi delays.

For instance, ten years ago the average scheduled time from gate to gate between Chicago and San Francisco was 4 hours and 32 minutes. Today, flights are scheduled for an extra 11 minutes, according to PlaneStats.com - even though airports in the two cities are the same 1,846 miles apart.

All it takes are a few problems at some of the country's busiest airports to drive up the national taxi time average.

The top offender in the past year was Chicago's O'Hare International Airport. Of all the additional taxi time minutes in the nation, one of out of five extra minutes can be traced back to delays at O'Hare.

A United Airlines jetliner lands on Chicago O'Hare International Airport's newest parallel runway on Oct. 15 in Chicago, shortly after the airport opened the runway and an air traffic control tower, completing the latest piece of a nearly $9 billion overhaul of its outdated airfield. Bob Chwedyk / Daily Herald via AP

Planes in Chicago this year spent an average of 1 minute and 18 seconds extra navigating the taxiways. And taxi times are up 3 minutes and 24 seconds from five years ago, a 20-percent increase. Those delays add up considering that O'Hare had 227,358 flights during the first nine months of this year.

Most of the problems at O'Hare stem from a construction project that is reconfiguring taxiways and runways. The long-term goal is to reduce congestion but delays are being racked up during the construction. A new runway did just open, but further away from the airport's terminals. Longer trips from that runway are not yet reflected in government data.

In an email to the AP, O'Hare officials note that taxi times "will fluctuate as construction phases are started or finished" and that the work is helping to reduce delays in the sky around the airport.

Delays have also been climbing at the two main airports in Dallas, but for different reasons.

At Dallas Love Field, taxi times are up two minutes, or 13-percent, so far this year. That's the highest percent gain of any major airport. Home to Southwest Airlines, Love Field saw the number of scheduled flights during the first nine months of this year spike 41 percent to 47,438 after the repeal of a federal law restricting most long-distance flights from that airport.

Terry L. Mitchell, the airport's assistant director for operations, says the increase in flights, construction projects and the use of a farther runway to reduce noise concerns of neighbors all led to the run up in taxi times. Now that construction is complete and the airport at capacity, he expects no further growth in taxi times.

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Across town at Dallas-Fort Worth International Airport, taxi times climbed two and a half minutes, or 11.7 percent. In this case, the increase was due to new scheduling procedures by American Airlines, which carries 82 percent of the passengers at the airport.

American groups together large numbers of flights in Dallas - and its other hubs - to allow passengers easy connections. In March, the airline reconfigured its schedule so more flights arrive and depart in a narrower band of time. That meant shorter layovers in the airport, more connection options for passengers and more revenue opportunities for the airline. However, the adjustments also extended taxi times. American accounted for those increases in its schedule.

"When they try to cram as many flights as possible into their hubbing complexes," says airline consultant Paul Sterbenz, "they create logjams."