(CNN) — The dramatic engine failure on a United Airlines flight flung debris across neighborhoods outside Denver and caused the airline to ground more than 20 planes out of caution.

It’s the second time in three years that the right engine failed during a United Airlines flight.

In 2018, a Boeing 777 bound for Honolulu lost the cover to its right engine mid-flight. Though the plane safely landed, the passengers onboard were terrified.

Like the plane involved in Saturday’s engine failure, the Boeing in 2018 was headed for Hawaii, too. Both were powered by engines from the same company.

Investigators haven’t yet determined the cause of Saturday’s engine failure. If the outcome is the same as in 2018, the engine’s fan blades may have played a part.

The 2018 flight to Honolulu

In February 2018, United Airlines Flight 1175 took off from San Francisco toward Honolulu. More than 370 people were on board.

Less than an hour away from the Hawaii capital, passengers heard pieces of metal rattling loudly, and the plane started to shake. Outside, the plane’s right engine was exposed, its cover lost over the Pacific Ocean.

The plane landed safely in Honolulu, though the remainder of the flight was tense. One passenger called it the “scariest flight of [her] life.”

The planes were powered by similar engines

The Boeing 777 involved in the 2018 incident was powered by Pratt & Whitney’s PW4000 112-inch engines. The engine damaged on Saturday outside Denver was also a Pratt & Whitney engine, the PW4077.

In its final report of the 2018 incident, the National Transportation Safety Board (NTSB) found that an engine blade failed and United mechanics didn’t have the proper training to inspect blades.

It’s too early to tell if issues with fan blades caused Saturday’s engine failure. But an initial examination by the NTSB did find that two fan blades were fractured, and the remaining blades exhibited damage “to the tips and leading edges.”

Pratt & Whitney said Monday it’s sending a team to work with NTSB investigators to figure out what went wrong.

Another aircraft with a Pratt & Whitney engine was grounded on Saturday: A cargo-carrying Boeing 747’s engine failed in the Netherlands. It, too, was powered by a PW4000.

Countries restrict planes with the same engine

Boeing recommended suspending operations of all Boeing 777 aircraft with the Pratt & Whitney 4000 engines, and several countries have since banned, grounded or opened investigations into planes with the same engine.

United said Sunday it would immediately pull 24 planes from flying “out of an abundance of caution.” The company said its move was voluntary and temporary and should disrupt only “a small number of customers.”

The United Kingdom said Monday it will temporarily ban Boeing 777s with PW4000 engines from entering UK airspace. Also on Monday, Japan ordered all domestic airlines to halt all Boeing 777s with the same engines, which impacts a combined 32 aircraft.

South Korea’s Asiana Airlines has also grounded its fleet of Boeing 777 planes, which are also powered by PW4000 engines.

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