UPDATE 2-United-operated Boeing 737 MAX rolls off Houston runway, says FAA

(Adds prior incidents this week, NTSB investigating)

By David Shepardson

WASHINGTON, March 8 (Reuters) - A United Airlines-operated Boeing 737 MAX rolled onto the grass and off the runway at George Bush Airport in Houston early on Friday, the Federal Aviation Administration (FAA) said.

The National Transportation Safety Board and FAA will investigate. The 160 passengers and six crew were not injured. They left the plane and were bused to the terminal, the FAA and United said. The plane had departed from Memphis.

United said it will move the aircraft from the taxiway as soon as it is able and will "work with the NTSB, FAA and Boeing to understand what happened."

This is the third incident this week involving a United Boeing airplane. Boeing and United shares were both down 1% on Friday.

A day earlier, a United-operated Boeing 777-200 bound for Japan lost a tire after takeoff from San Francisco and was diverted to Los Angeles where it landed safely. The plane had 249 people on board.

On Monday, a United Boeing 737 bound for Florida departing Houston returned to the airport shortly after takeoff after the engine ingested some plastic bubble wrap that was on the airfield prior to departure, the airline said.

Social media posts showed flames coming out of the engine.

Separately, the NTSB said on Thursday it is investigating a Boeing 737 MAX 8 flight last month that experienced "stuck" rudder pedals after it touched down on the runway for its landing.

(Reporting by David Shepardson and Katharine Jackson; Writing by Ismail Shakil, editing by David Ljunggren, Kirsten Donovan)