The Federal Aviation Administration (FAA)'s move comes after the aircraft had been grounded since a mid-air blowout on an Alaska Airlines jet on Jan. 5.

Here is what regulators and airlines are doing as a result of the incident:

AIRLINES WITH THE AFFECTED PANEL:

ALASKA AIRLINES

The airline grounded all 65 of its Boeing 737 MAX 9 planes and cancelled hundreds of flights since the incident.

It said on Jan. 8 that initial reports from its technicians indicated some "loose hardware" was visible on some aircraft in the relevant area.

Alaska Airlines said it expects inspections to be completed over the next week after the FAA green lit the resumption of MAX 9 flights. It aims to begin returning the planes to service on Friday.

UNITED AIRLINES

The only other U.S. airline operating the jets that suspended service on all 79 of its 737 MAX 9 aircraft.

The carrier said on Jan. 8 its preliminary checks found bolts that needed tightening on several panels.

After receiving final approval from the FAA to complete the process to return its 79 MAX 9 fleet to service, United Airlines aims to begin flights on Sunday.

The company has 100 MAX deliveries scheduled for this year, according to a regulatory filing in October.

COPA AIRLINES

The Panamanian carrier said on Jan. 9 that 21 Boeing 737 MAX 9 planes remained grounded while authorities and the manufacturer defined inspection instructions.

AEROMEXICO

The airline said on Jan. 12 that the 19 Boeing 737 MAX 9 jets in its fleet remained grounded awaiting inspection.

Aeromexico added it had launched a flexible flight-change policy for affected travellers, but did not specify how many flights had been cancelled.

TURKISH AIRLINES

The airline said on Jan. 7 it had withdrawn five 737 MAX 9 aircraft from service for inspection.

AIRLINES THAT LACK THE AFFECTED PANEL:

ICELANDAIR

Icelandair said the issue is related to equipment that's not a part of the configuration of its four 737 MAX 9 aircraft.

FLYDUBAI

The airline said its three 737 MAX 9 planes, which use a deactivated mid-aft exit door configuration, were not affected.

CORENDON DUTCH AIRLINES

Corendon Dutch said it has two 737 MAX 9, but the airline uses the extra door, so inspections are not needed.

AIR TANZANIA

Air Tanzania has one 737 MAX 9, but its CEO said Boeing had told the airline its aircraft was not of the type that needed inspection.

REGULATORS:

U.S. FEDERAL AVIATION ADMINISTRATION (FAA)

The FAA has allowed MAX 9 planes to resume flying once inspections were completed. The regulator had launched a formal investigation into the aircraft on Jan. 11 after it had instructed 40 of the 171 grounded planes to be reinspected.

In an unprecedented move, the FFA has, however, barred Boeing from expanding production, following "unacceptable" quality issues.

"We will not agree to any request from Boeing for an expansion in production or approve additional production lines for the 737 MAX until we are satisfied that the quality control issues uncovered during this process are resolved," FAA Administrator Mike Whitaker said.

U.S. NATIONAL TRANSPORTATION SAFETY BOARD (NTSB)

The independent U.S. agency opened an investigation into the incident, and it appointed International Associations of Machinists and Aerospace workers (IAM) to the investigation.

The NTSB said the plane's cockpit voice recorder was overwritten, renewing long-standing calls for longer in-flight recordings.

BRAZIL

Brazil's aviation regulator ANAC said on Jan. 7 the FAA ruling automatically applies to all flights in Brazil.

In Brazil, only Copa Airlines operates the plane, it said.

BRITAIN

The UK Civil Aviation Authority said on Jan. 6 that no UK-registered planes were affected. It will require any 737 MAX 9 operators entering its airspace to comply with the FAA directive.

CHINA

Chinese airlines do not have the MAX 9 model in their fleet, only MAX 8 which do not have the panel involved in the Alaska Airlines incident.

China's foreign ministry said on Jan. 25 that Boeing has permission to resume deliveries of its 737 MAX 8 to Chinese customers as authorities completed a design approval of the aircraft.

EUROPEAN UNION

The EU Aviation Safety Agency (EASA) adopted the FAA directive, but noted no EU member state airlines operate aircraft with the affected configuration.

INDIA

India's Directorate General of Civil Aviation (DGCA) said on Jan. 8 that one-time inspections it had ordered of 737 MAX 8 aircraft had been performed satisfactorily. None of the country's airlines fly the MAX 9 model.

INDONESIA

Indonesia temporarily grounded three MAX 9 planes operated by Lion Air on Jan. 6, a transport ministry spokesperson said, adding that the planes had different configurations from the Alaska Airlines plane.

PANAMA

Panama's civil aviation authority said on Jan. 11 it had grounded 21 of Copa Airlines' 737 MAX 9 planes. The carrier has 29 in its fleet, but only 21 have the affected panel.

SOUTH KOREA

South Korea's transport ministry said on Jan. 11 it will conduct inspections of maintenance procedures of the country's airlines operating 737 MAX 8 aircraft.

The ministry said five South Korean airlines operate 14 MAX 8 airplanes. This comes after the ministry said no problems had been detected after inspections on Jan. 9.

TURKEY

Turkey's Directorate General of Civil Aviation on Jan. 8 noted the FAA's actions and said it was coordinating with stakeholders regarding affected aircraft belonging to airlines in Turkey and those using Turkish airspace.

UNITED ARAB EMIRATES

The civil aviation said on Jan. 7 that none of its national carriers have planes affected by the order.

(Reporting by Reuters bureaus; Compiled by Josephine Mason, Marleen Käsebier, Luca Fratangelo, Lisa Barrington and Kylie Madry; Editing by Jamie Freed, Matthew Lewis and Milla Nissi and Miral Fahmy)