Recent travel hassles and airline cancelations may have been heightened this week as United Airlines canceled about 18 flights this week.

Some United planes were pulled from service when the carrier realized that some of its Boeing 777-200 planes had not undergone required inspections of the front edges of the wings.

The airline canceled flights Monday night and Tuesday morning, and said it's trying to rebook stranded passengers.

In all, the Federal Aviation Administration said United grounded 25 of the jets after discovering it had failed to inspect slats on the wing edges that are used during takeoffs and landings.

PILOTS UNION WARNS OF MORE FLIGHT DELAYS, CANCELLATIONS

A United plane on takeoff

A United Airlines passenger aircraft - Boeing 777 - arriving at Chicago O'Hare International Airport on a sunny morning. (istock / iStock)

As of late Tuesday afternoon, United said that it had inspected 10 of the planes and was working with the FAA to return the others to flying in the next two weeks without causing additional flight cancelations.

The matter was first reported by The Wall Street Journal.

United had grounded its Boeing 777-200s earlier this year because of the failure of a Pratt & Whitney engine on a flight that caused parts of the housing to fall on the Denver area.

United Airlines and American Airlines planes on DC tarmac

United Airlines and American Airlines planes sit on the tarmac as snow begins to fall at Ronald Reagan National Airport in Arlington, Virginia. (Samuel Corum/Bloomberg via Getty Images / Getty Images)

UNITED AIRLINES MAY END JFK SERVICE WITHOUT MORE FLIGHTS

Travel troubles have become a hallmark of post-pandemic flying.

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 So far this year, the rate of flight delays is up 23% from pre-pandemic levels, according to FlightAware, with the average delay time approaching an hour.

United Airlines plane

 A United Airlines passenger jet takes off with New York City as a backdrop, at Newark Liberty International Airport, New Jersey. (REUTERS/Chris Helgren/File Photo / Reuters Photos)

The rate of cancelations has increased 26% compared to 2019. With nearly as many people flying as before the coronavirus pandemic but fewer planes in the air, this means it is harder to book passengers on a new connecting flight.

The Associated Press contributed to this report.