New grit for Boeing.
The 777s with PW4000 engines are to be "emergency inspected" and this will mean "probably some aircraft will be removed from service".
The order from the Federal Aviation Administration also resonates in Japan, where the authorities are asking national airlines to leave the 777s with PW 4000 on the ground until further notice.
The FAA's decision follows the United Airlines crash in Denver, when one of its aircraft - a 777 with PW4000 - was forced to return shortly after take-off due to a burning engine that caused a shower of debris in the area surrounding the city of Colorado.
An emergency landing that did not cause injuries among 231 passengers and 10 crew members, initially headed to Honolulu.
No one was injured on the ground either, where a lot of debris fell into the streets and gardens.
United has announced the temporary suspension of its 24 Boeing 777s with PW400 engines produced by Pratt & Whitney, a division of Raytheon Technologies.
"We are in contact with the authorities and will continue to work with them to determine further measures needed to ensure that our aircraft meet the highest safety standards and can fly again," says United.
For Boeing this is a new blow after the 737 Max scandal, left on the ground for a year.
The case is also a test for the FAA, overwhelmed by criticism of the 737 Max for its slow action and for not having conducted the necessary tests on the aircraft before being authorized to fly.
The Japanese Ministry of Transportation has ordered domestic airlines, All Nippon Airlines (Ana) and Japan Airlines (Jal), to temporarily suspend flights involving Boeing 777s. Ana and Jal own 19 and 13 777-200 aircraft respectively. of their own fleet, and they said they will comply with directives.
A similar incident involved another Japan Airlines Boeing 777 on December 4 during a flight from Tokyo Haneda to Naha, on the island of Okinawa.
Again the engine cover had detached from the fuselage leaving the turbojet uncovered and the aircraft had been forced to make an emergency landing.
Analysts are now wondering about the correct maintenance process by carriers globally, after the prolonged downsizing of air transport caused by the coronavirus, in a phase of heavy reductions in operating costs.