SAN FRANCISCO — A United Airlines jetliner headed to Mexico City from San Francisco made an emergency landing in Los Angeles on Friday after the crew reported a hydraulics issue, in the fourth emergency involving a United Airlines flight this week.

The plane landed safely at Los Angeles International Airport around 4:30 p.m. and none of the 110 people on board were injured, United Airlines said in a statement.

Fire engines stood by at the airport but weren’t needed, said Nicholas Prange, a spokesperson with the Los Angeles City Fire Department.

The airline said passengers can travel to Mexico on another plane expected to depart later Friday.

United said the Airbus A320 has three hydraulic systems for redundancy purposes.

“Preliminary information shows there was only an issue with one system on this aircraft,” it said.

The Federal Aviation Administration said in a statement it will investigate the emergency landing Friday.

The emergency landing at LAX on Friday comes hours after passengers had to be evacuated from another United Airlines flight after the plane rolled off a runway and got stuck in the grass in Houston, Texas. No injuries were reported among the 160 passengers and six crew members, United Airlines said in a statement.

Video posted on social media taken after the landing in Houston showed the plane tilted to one side with one of its wings near the ground.

On Thursday, another United Airlines flight made an emergency landing in Los Angeles. It was a jetliner bound for Japan that lost a tire while taking off from San Francisco. No injuries were reported.

Video footage showed the plane losing one of the six tires on its left-side main landing gear assembly only seconds after takeoff. The tire landed in an employee parking lot at San Francisco International Airport, where it smashed into a car and shattered the back window before breaking through a fence and coming to stop in a neighboring lot.

Earlier in the week, a United flight from Houston to Fort Myers, Texas, was forced to turn around Monday after one of the plane’s engines caught fire. Several of the 167 passengers aboard the Boeing 737 took videos showing a line of flames shooting out of the engine. No injuries were reported.