Spirit Airlines issued another apology on Thursday after four straight days of flight cancelations and service disruptions. Thousands of passengers have been stuck in long lines at airports in Newark, Las Vegas, San Jose, and Fort Lauderdale since the start of the week due to the disruptions.

Since Sunday, flight cancellations have continued to be at alarming levels. More than 19% of the airline's flight schedules were delayed or canceled on Sunday. The figure then jumped to 40% on Monday, up to 61% Tuesday, and 60% on Wednesday.

The low-cost carrier blamed the meltdown of its operations on the surge in summer passengers, problems with its computer systems, volatile weather, and staffing issues.

The company said that it was working to resolve the issues and assured the public that the cancelation numbers should "progressively drop" in the coming days. The airline advised passengers to first check their flight status and any notifications on their phones and email inboxes before heading to the airport.

The company said it has already rebooted its network and experts are now working to ensure that there would be no further issues. The airline claimed that resolving its computer problems should ease most of the operational challenges it is currently facing.

Spirit Airlines confirmed that it was facing serious issues with its online scheduling system, which had mostly contributed to the service disruptions. Some members of the Association of Flight Attendants previously told reporters that they had at times been unable to access the company's staff scheduling system for hours on end.

The timing of the issues couldn't have been worse as it is now the peak of the summer vacation travel season. Domestic and international travel is expected to surge this season as people are now traveling with a vengeance. Spirit Airlines said it is currently dealing with extremely high aircraft load factors, which is the same across the entire industry.

The airline said it has had to resort to enlisting staff members from other areas of the company to help with processing tasks because its systems could not cope with the influx of passengers. The airline also clarified that rumors of a possible worker strike were "completely untrue."