Jan 11 (Reuters) -

Boeing's top-selling 737 MAX aircraft is being investigated following an incident on Friday when a panel blew off an Alaska Airlines plane, forcing pilots to make an emergency landing.

U.S. regulators ordered a temporary grounding of 171 Boeing 737 MAX 9 jets installed with the same panel, while investigations and safety checks take place.

There are about 215 737 MAX 9 jets in service globally in total, according to aviation analytics firm Cirium.

Carriers offering denser seating configurations have an exit door at that position instead of the panel and are not affected by the grounding order.

In Boeing's first public acknowledgment of errors since the incident, CEO Dave Calhoun on Tuesday said an accident like the panel blowout "can never happen again". In a separate meeting, Boeing told staff this was being treated as a "quality control issue" and checks were under way at Boeing and fuselage supplier Spirit Aerosystems.

Here's what regulators and airlines are doing as a result of the latest incident:

AIRLINES WITH THE AFFECTED PANEL:

ALASKA AIRLINES

The airline grounded all 65 of its Boeing 737 MAX 9 planes.

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

Alaska Airlines has cancelled hundreds of flights since the incident. On Wednesday, it said it would cancel Boeing 737 MAX 9 flights through Jan. 13.

UNITED AIRLINES

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

The carrier said on Monday its preliminary checks found bolts that needed tightening on several panels. It was awaiting final approval for full inspection processes of the grounded aircraft.

United cancelled 225 flights, or 8% of its total schedule, on Tuesday. On Wednesday, 167 MAX 9 flights were cancelled, with the airline expecting "significant" cancellations on Thursday as well.

COPA AIRLINES

The Panamanian carrier said on Tuesday that 21 Boeing 737 MAX 9 planes remained grounded while authorities and the manufacturer defined the inspection instructions necessary for their safe and reliable evaluation and return to operation.

AEROMEXICO

The airline said on Sunday it had grounded 19 affected 737 MAX 9 jets for inspection.

TURKISH AIRLINES

The airline said on Sunday it had withdrawn five 737 MAX 9 aircraft from service for inspection.

AIRLINES THAT LACK THE AFFECTED PANEL:

ICELANDAIR

Icelandair said on Monday its aircraft were not affected by the FAA grounding. "It has been confirmed that the issue is related to equipment that is not a part of Icelandair's Boeing 737 MAX 9 configuration," said a spokesperson for the airline, which operates four of the aircraft.

FLYDUBAI

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

CORENDON DUTCH AIRLINES

Corendon Dutch said on Monday 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 on Sunday that Boeing told the airline its aircraft was not of the type that needed inspection.

REGULATORS:

U.S. FEDERAL AVIATION ADMINISTRATION (FAA)

The FAA issued a directive on Saturday temporarily grounding certain 737 MAX 9 planes.

The FAA said on Tuesday that Boeing was revising its instructions for inspections and maintenance, which the regulator must still approve before checks can begin.

The FAA said it "will conduct a thorough review" and public safety will determine the timeline for returning the MAX to service.

U.S. NATIONAL TRANSPORTATION SAFETY BOARD (NTSB)

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

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 Sunday 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 Saturday there are no UK-registered planes affected. It will require any 737 MAX 9 operators entering its airspace to comply with the FAA directive.

CHINA

China's regulator has sought details on the incident, a person familiar with the matter said on Saturday. Bloomberg reported that China, the first country to ground MAX flights in 2019, was considering whether to take action.

Chinese airlines have not yet resumed delivery of any MAX models and analysts said the Alaska Airlines incident could cause further delays.

EUROPEAN UNION

The European Union 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 Monday that one-time inspections it had ordered of Boeing 737 MAX 8 aircraft had been performed satisfactorily. None of the country's airlines fly the 737 MAX 9 model.

INDONESIA

Indonesia temporarily grounded three 737 MAX 9 planes operated by Lion Air on Saturday, a transport ministry spokesperson said, adding that the planes had different configurations from the Alaska Airlines plane.

The ministry will coordinate with the FAA, Boeing and Lion Air to monitor the situation, adding that "operational safety will be our priority".

PANAMA

Panama's civil aviation authority

said on Thursday

it had temporarily grounded 21 of Copa Airlines' Boeing 737 MAX 9 planes. The carrier has 29 in its fleet, but only 21 have the affected panel, the authority said.

SOUTH KOREA

South Korea's transport ministry said on Thursday 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 aircrafts. This comes after the ministry said no problems had been detected after inspections last Tuesday.

TURKEY

Turkey's Directorate General of Civil Aviation on Monday 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 Sunday that none of its national carriers have planes affected by the order.

(Reporting by Reuters bureaus; compiled by Josephine Mason, Luca Fratangelo, Marleen Käsebier, Lisa Barrington and Kylie Madry; Editing by Jason Neely, Louise Heavens, Jamie Freed, Milla Nissi)