United AirlinesCEO Scott Kirby said that without additional gates, the airline would have to reduce or change flight schedules to handle frequent problems at its hub in Newark, New Jersey, news that came after mass flight delays spoiled July Fourth holiday travel weekend. The carrier gave away 30,000 loyalty miles to customers most affected by the chaos.

“This has been one of the most operationally demanding weeks I’ve experienced in my entire career,” Kirby said in a memo to staff seen by CNBC on Saturday.

He said the airline needs more gates at Newark Liberty International Airport because of frequent plane backups. “We will need to further change/reduce our schedule to have even more backup gates and buffers – especially during storm season,” he added.

A day earlier, Kirby apologized for taking a private jet out of Teterboro Airport in New Jersey while thousands of passengers were stranded, CNBC first reported Friday.

The problems began last weekend with a series of storms in some of the nation’s most congested airspace along the East Coast, cutting off aircraft routes. While most airlines recovered, United’s problems continued throughout the week, angering customers and crews alike. United and JetBlue Airways managers said air traffic control problems exacerbated the malfunctions.

Kirby explained the week’s difficulties and said long-term changes were needed. He said the heavily delayed departures that have piled up at his Newark hub since last weekend have hurt his operations. From Sunday to Tuesday, take-offs were delayed by up to 75% for more than 8 hours in some cases.

“Airlines, including United, are simply not designed for their largest hub to be severely limited in capacity for four days in a row and still operate successfully,” he wrote.

Aircraft and crews were then left out, which often happens during inclement weather and can cause a cascade of disruption for customers.

Unions have complained about hour-long waits for crew members to get assignments and get hotels, forcing them to stay longer at airports.

Kirby said the carrier needs to improve platforms to make it easier for crews to get assignments and accommodations on its app, and said what happened over the past week was unacceptable.

Kirby called for more investment in the FAA and air traffic control to avoid delays and staff shortages, some of which occurred after hiring and training were suspended at the start of the pandemic.

United sent 30,000 miles to customers who were delayed overnight or didn’t get to their destination at all, a spokeswoman said. She declined to say how many customers received the email.

Between last Saturday and Friday, more than 42,000 US flights were delayed and more than 7,900 were canceled — or more than 5% of airline schedules — more than triple the average so far this year, according to flight tracker FlightAware. FlightAware data shows that United fared worse than competitors, with about half of its main schedule arriving late and nearly a fifth canceled during the period.

United’s operations improved on Saturday, but disruptions persisted. About 11% of its main schedule, or nearly 300 flights, were delayed and 43 flights, or 1%, were cancelled, down sharply from 1,324 delays and 252 cancellations on Friday.