What's going on with Boeing 737 Max 9 planes

• The increased scrutiny will include an audit of the 737-9 MAX production line to determine if the company has complied with quality procedures, the FAA said.
• The agency will also consider lining up an independent, third party to oversee Boeing's inspections and its quality system.

Driving the news: The oversight measures came shortly after the FAA announced an investigation into the company over whether it failed to ensure that the jets were safe.

• The FAA said the incident, which has set off a cascading effect throughout the airline industry, should have never happened and it cannot happen again.
• The agency added that the company's "manufacturing practices need to comply with the high safety standards they're legally accountable to meet."

Why it matters: Boeing is one of the largest aerospace manufacturers in the world and its planes are used by many major airlines.

• Boeing, a titan of commercial aircraft manufacturing, has only one major rival: Airbus.

What's going on with the Boeing 737 Max 9?

On Jan. 5, the Alaska Airlines Boeing 737 MAX 9 aircraft suffered a sudden depressurization when a "plugged" exit door flew off minutes after take off, leaving a gaping hole in the side of the plane as it reached an altitude of about 16,000 feet.

• The plane entered service in November 2023, per the flight tracking site Flightradar24, but had already been prohibited from traveling long flights over water due to a pressurization warning light going off during three previous flights, NTSB chair Jennifer Homendy said at a press briefing on Jan. 7.
• The Federal Aviation Administration ordered all Boeing 737 MAX 9 planes operated by U.S. airlines or in U.S. territory to be grounded on Jan. 6.
• In an update on Jan. 8, the FAA said the planes will remain grounded until "enhanced inspections" are completed.
• The FAA said in an update on Jan. 9 that Boeing was updating its instructions for inspections after receiving feedback on the initial set of instructions issued. The FAA will review the revised instructions after Boeing submits them.
• "The safety of the flying public, not speed, will determine the timeline for returning the Boeing 737-9 Max to service," the FAA added.

What they're saying: Transportation Secretary Pete Buttigieg did not give a timeline on when the 737 Max jets could resume flights during a meeting on Wednesday, saying "The only consideration for the timeline is safety."

• "Until it is ready, it's not ready. Nobody can or should be rushed in that process," he added, transportation news outlet Skift reported.
• During an address to staff Tuesday, Boeing CEO David Calhoun said the company was committed to approaching the issue by first and foremost "acknowledging our mistake," the Wall Street Journal reported.

Worth noting: United Airlines and Alaska Airlines are the only two U.S. airlines that operate Boeing 737 Max 9s. Both have grounded their fleets, pending the investigation into the Jan. 5 incident, per CBS News.

• Boeing said on Jan. 6 that it supports the FAA's decision to require aircraft inspections and that it supports the National Transportation Safety Board's (NTSB) investigation into the Alaska Airlines incident.

What have the inspections found?

United Airlines announced on Jan. 8 that it found loose bolts on the door plugs of several Boeing 737 Max 9s during inspections.

• Alaska Airlines also announced Monday that it had also discovered "loose hardware" during inspections.

What is an exit door plug?

The door plug that flew off Alaska Airlines Flight 1282 was later found in the backyard of a schoolteacher in Portland, Oregon.

• A door plug is used to seal unused exit doors on planes and is secured with bolts, cables and stop pads.

• The number of emergency exits a plane has is determined by the number of passengers a plane can hold.

• For an international flight operating at maximum capacity, an airline would use a Boeing 737 Max 9 with all its emergency exits in place — planes used for smaller flights with fewer seats might have some emergency exits plugged, the Los Angeles Times reported.

On the Alaska Airlines plane, the fittings at the top of the door plug fractured, enabling the door plug to move upward and outward, Homendy told ABC's "Good Morning America" on Jan. 9.

• "We don't know if the bolts were loose. We don't know if bolts were in there fractured or possibly the bolts weren't there at all," Homendy said.

Past safety concerns with 737 MAXs

This isn't the first time Boeing has faced safety concerns regarding its 737 Max jets.

• Two 737 MAX 8 crashes in Indonesia and Ethiopia in Oct. 2018 and March 2019 killed a combined 346 people, resulting in a temporary global grounding of the jets and igniting a flurry of questions regarding quality control and safety at Boeing.
• Notably, Boeing's 737 MAX was cleared to fly again in the U.S. by the FAA in November 2020.
• Yet last year, Boeing asked the FAA to exempt the 737 MAX 7 from certain safety standards related to its anti-ice system so the planes could be put into service.
• In December 2023, Boeing urged airlines to conduct inspections of their 737 Max jets for potential loose hardware in the aircraft's rudder control systems.

Boeing facing backlash

The problems faced by Boeing have sent the company shares plunging more than 8% on Jan. 8.

• One of its suppliers, Spirit AeroSystems, saw its shares drop by about 11%, CNN reported.
• The debacle with Alaska Airlines Flight 1282 has also attracted the attention of Congress. Sen. J.D. Vance (R-Ohio) on Tuesday called on the Senate Commerce Committee to hold a hearing to "evaluate the safety of 737 MAX aircraft."
• United Airlines and Alaska Airlines have both cancelled hundreds of flights this week as a result of the Max 9 grounding. Paired with cancellations due to extreme weather, the developments have snarled travel plans for customers.

Editor's note: This story has been updated with a statement from Transportation Secretary Pete Buttigieg and the FAA.