A mid-air blowout aboard a Boeing 737-9 MAX passenger plane has led to dozens of aircraft worldwide being grounded while engineers try to establish what went wrong.
Six people aboard Alaska Airlines flight 1282 from Portland to California were injured after a window and chunk of fuselage blew out of the plane in mid-air shortly after takeoff on 5 January.
Questions around the safety of the jets are swirling and various airlines have come out with statements saying what actions they are taking, or seeking to reassure customers that they do not operate the same variant of plane.
What happened on board the Alaska Airlines flight?
Shocking scenes played out on board the aircraft, with passengers hearing a “big loud bang” and a “whooshing sound”.
Photos and videos from passengers showed a large hole in the side of the plane next to passenger seats, with oxygen masks deployed.
Alaska Airlines said the plane landed safely with 171 passengers and six crew members.
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Which part of the aeroplane was the problem?
The aircraft involved was a specific configuration of the MAX 9 variant of the popular Boeing 737, which is used by airlines around the world.
In the Alaska Airlines incident, a plug covering a spot left for an emergency door is believed to have torn off the plane as it flew 16,000 feet (4,800 metres) above Oregon.
These door plugs are inserted where emergency exit doors would be located on MAX 9s with more than about 200 seats. Planes like the one operated by Alaska Airlines have fewer seats, so the heavy doors are replaced with the plugs.
These panels can be opened for maintenance work. The bolts prevent the mechanism from moving upward on rollers when the plane is in flight.
On Alaska Airlines flight 1282, it is believed roller guides at the top of one of the plugs broke (for reasons unknown). This allowed the entire panel to swing upward and break away.
Jennifer Homendy, chair of the US National Transportation Safety Board (NTSB), said it was investigating whether four bolts that help prevent the panel from sliding up on rollers were missing when the plane took off from Portland or whether they blew off “during the violent, explosive decompression event”.
Are other 737-9 MAX planes being checked for issues?
Yes. The Federal Aviation Administration (FAA) grounded more than 170 737-9 MAX planes in its jurisdiction and other international aviation authorities and airlines have followed suit.
Alaska Airlines said initial reports indicate “some loose hardware was visible on some aircraft” following an inspection of its fleet of 737-9 MAXs.
It added that all aircraft were being “thoroughly inspected in accordance with detailed instructions provided by the FAA in consultation with Boeing”.
United Airlines, which also operates the same 737 variant, said its preliminary checks found bolts that needed tightening on several panels.
United Airlines has so far found close to 10 aeroplanes with loose bolts during its preliminary checks, a source told the Reuters news agency.
Which airlines are affected?
A handful of airlines have said they are looking at the 737-9 MAX planes in their fleets. There are believed to be 215 of the planes in service around the world.
Alaska Airlines says it has grounded its entire fleet of 65 737-9 MAXs for inspection and maintenance.
United Airlines, the world’s biggest operator of the aircraft in question, has grounded all 79 of its planes of the same type.
Copa Airlines, based in Panama, said it had suspended operations for 21 of the aircraft.
Turkish Airlines said it has pulled its five 737-9 MAXs from service.
Aeromexico has 19 737-9 MAXs in its fleet and has grounded them for inspection, it has been reported.
Icelandair and flydubai have 737-9 MAXs in their fleets but say they are not affected by the issue.
SCAT Airlines, Lion Air, Corendon Dutch Airlines and Air Tanzania have the plane in their fleets but it is not believed to be the configuration involving the door plugs. Sky News has approached the companies for comment.
Are any UK airlines operating 737-9 MAXs?
The UK’s Civil Aviation Authority, which oversees and regulates all aspects of civil aviation in Britain, has confirmed that there are no UK-registered 737-9 MAX aircraft.
“The impact on UK-operated aircraft and consumers is minimal,” the organisation said in a statement.
The CAA added that it has written to other “non-UK and foreign permit carriers” to ensure that inspections have been carried out before the aircraft can enter UK airspace.
Budget airline Ryanair, which is popular with UK jet-setters, said it operates different variants of the 737 MAX from the type grounded.
“The 737 is fine. But it doesn’t need these kind of short-term reputational issues,” chief executive Michael O’Leary told the Financial Times.
What has Boeing said?
Aircraft manufacturer Boeing is no stranger to dealing with grounded planes. A few years ago, 737 MAX aircraft of a different variant were kept on the tarmac around the world after fatal crashes in Indonesia and Ethiopia.
It said safety is its “top priority” and it “deeply regrets” the impact the incident has had on its customers and their passengers.
It added: “As operators conduct the required inspections, we are staying in close contact with them and will help address any and all findings.
“We are committed to ensuring every Boeing airplane meets design specifications and the highest safety and quality standards. We regret the impact this has had on our customers and their passengers.”