Originally Published: 12 JAN 24 06:35 ET

Updated: 12 JAN 24 12:12 ET

By Ramishah Maruf, Ross Levitt and Pete Muntean, CNN

New York (CNN) — Winter weather combined with the grounding of the 737 Max 9 planes is causing major disruptions for air travel.

There are more than 1850 flight cancellations Friday morning, the highest number since July 2023, data from the tracking site FlightAware show.

Only a handful of days in all of 2023 had more cancellations than Friday’s total.

Most of the cancellations are due to a winter storm that is pounding the Midwest. Chicago’s two major airports are seeing the bulk of the cancellations, with nearly 40% of departing flights at O’Hare, and more than 60% of departing flights at Midway are cancelled, according to FlightAware.

O’Hare airport posted on social media that more than 650 flights have been “proactively canceled” by the airlines. Denver and Milwaukee flights are also being hard hit by the storm. Nearly 40% of Milwaukee’s flights are also cancelled.

Cancellations due to the grounding of the 737 Max 9 planes are also contributing to the totals. More than 200 United and Alaska Airlines flights have been cancelled each day this week due to the FAA-mandated grounding. The FAA and Boeing are still trying to settle on an inspection protocol that would allow those planes to resume flying.

FlightAware shows Southwest, which doesn’t fly the 737 Max 9, cancelling nearly 400 flights, the most of any airline.

737 Max 9 delays

Passengers on Alaska Airlines and United Airlines have been marred by hundreds of flight cancellations this week.

The Federal Aviation Administration grounded more than 150 Boeing 737 Max 9 aircraft after a piece of the fuselage blew off an Alaska Airlines flight last Friday. It left a gaping hole in the side of the plane and ripped headrests off seats as the plane flew at 16,000 feet shortly after taking off from Portland, Oregon, carrying 177 people.

The troubles are still ongoing for the airlines, which are the two largest US carriers that use the Boeing 737 Max 9 aircraft. On Friday, United canceled 10% of its operations and Alaska Airlines canceled 21%, according FlightAware data.

Alaska Airlines said in a statement Wednesday that it canceled all flights on 737-9 MAX aircraft through Saturday, January 13 – that’s about 110-150 flights per day.

Both Alaska and United Airlines say they found loose hardware or bolts in the assembly of door plugs – the part of the plane that flew off last week’s Alaska flight – on their Boeing 737 Max 9s.

The FAA has grounded affected Max 9s for inspection for days, and neither airline has has hinted that flights on those planes will resume soon.

Max 9s Grounded

On Saturday, the FAA ordered the grounding of 171 Boeing 737 Max 9 aircraft that have “a mid-cabin door plug installed.” It’s the model of the Boeing plane involved in the Alaska Airlines blowout incident.

The FAA said the planes must be parked until emergency inspections are performed, which will “take around four to eight hours per aircraft.”

The planes remain grounded pending details on FAA-mandated inspections. The FAA is still reviewing guidance on the inspections from Boeing.

As of Wednesday, Alaska’s latest update said that the airline is still waiting for documentation from Boeing and the FAA to begin inspection of its 737-9 MAX fleet. Alaska Airlines has also said it is working with Boeing to understand what happened on Flight 1282.

“We regret the significant disruption that has been caused for our guests by cancellations due to these aircraft being out of service. However, the safety of our employees and guests is our highest priority and we will only return these aircraft to service when all findings have been fully resolved and meet all FAA and Alaska’s stringent standards,” the airline said in the Wednesday statement.

Alaska said it has implemented a flexible travel policy, and that guests can change, cancel, or if the flight has been canceled, rebook.

United Airlines said it had canceled 167 Boeing 737 Max 9 flights on Wednesday as it awaits “final approval on the full inspection process… We expect significant cancellations on Thursday as well.”

On Thursday, the airline canceled an additional 175 Max 9 flights. By switching to other planes, it will avoid 35 additional cancellations. United uses more Max 9s than any other carrier.

“Since we began preliminary inspections on Saturday, we have found instances that appear to relate to installation issues in the door plug – for example, bolts that needed additional tightening. These findings will be remedied by our Tech Ops team to safely return the aircraft to service,” the airline said Thursday.

FAA investigation

FAA on Thursday said it is opening an investigation into Boeing’s quality control due to the failure of the door plug.

In a statement, the FAA said the dramatic in-flight blowout on Alaska Airlines 1282 “should have never happened and it cannot happen again.”

The FAA says the investigation will focus on whether Boeing “failed to ensure completed products conformed to its approved design and were in a condition for safe operation in compliance with FAA regulations.”

Boeing said it “will cooperate fully and transparently with the FAA and the NTSB on their investigations” in a statement Thursday.

On Wednesday, Boeing CEO Dave Calhoun admitted in an interview with CNBC that the door plug failure was a “horrible escape” of its manufacturing and quality control processes.

When asked what exactly happened, Calhoun told CNBC, “What happened is exactly what you saw, a fuselage plug blew out. That’s the mistake, it can never happen.”

In that interview, Calhoun emphasized that he is “confident” in the FAA’s ongoing work to “inspect each and every one of the airplanes” and make “certain that they’re in conformance with our design, which is a proven design.”

National Transportation Safety Board Chair Jennifer Homendy told CNN’s “Anderson Cooper 360” that the fuselage plug that blew out of the plane mid-flight Friday and was recovered from an Oregon backyard Monday has “quite a lot” it can tell investigators and “really was the missing piece in the investigation.”

The NTSB is conducting its own investigation, separate from the FAA.

A class action lawsuit was filed on Thursday in Washington state against Boeing on behalf of the passengers aboard last week’s Alaska Airlines flight 1282.

“Boeing is responsible for the safety of design and maintenance instructions as well as continuing airworthiness of the aircraft,” the lawsuit said.

More troubles for United

It was a difficult 2023 for United. The carrier canceled thousands of flights last summer, stranding hundreds of thousands of passengers in a widespread service meltdown. Beyond the bad weather, the problems were also human-made.

United CEO Scott Kirby largely blamed the FAA and inadequate staffing at airline control centers. But Transportation Secretary Pete Buttigieg, who oversees the FAA, pushed back, noting United was struggling relative to other US carriers.

– CNN’s Marnie Hunter, Forrest Brown, Paradise Afshar, Elizabeth Wolfe, Gregory Wallace, Pete Muntean and Chris Isidore contributed to this report.

The-CNN-Wire