CHICAGO, April 17 (Reuters) - United Airlines on

Wednesday said it has been prevented from putting new aircraft

into service due to an ongoing review of its operations by the

U.S. Federal Aviation Administration (FAA).

The review was ordered following several safety emergencies

involving the Chicago-based airline in recent weeks.

A small number of aircraft previously scheduled to enter

into service in the current quarter will be pushed into the

quarter through September, the company said. The change is

expected to have a minimal impact to its growth plans for this

year, it added.

United has delayed the start of two new international

routes, citing a pause in some certification activities by the

FAA. It also postponed its investor day, which was scheduled for

early next month, due to the review.

The FAA has said the formal evaluation is aimed at ensuring

the airline's compliance with safety regulations, identifying

hazards and mitigating risk, and effectively managing safety.

United told its employees last month they would see more of

an FAA presence in its operations over the next several weeks as

part of the agency's review of the carrier's "work processes,

manuals and facilities."

On a call to discuss company results on Wednesday, United

CEO Scott Kirby declined to predict when the review would

conclude. He said the review does not stop the airline from

promoting pilots to captain.

"The main focus has been less about changing the policies

and processes," he said, "but really making sure that everyone

keeps safety as a top of mind awareness."

Last month, an external panel was missing from a United

aircraft when it landed in Oregon. Before that incident, a

United Airlines-operated Boeing 737 MAX rolled onto the grass in

Houston.

A United-operated Boeing 777-200 bound for Japan also lost a

tire after takeoff from San Francisco and was diverted to Los

Angeles, where it landed safely.

"Through the FAA review, I'm confident that we'll uncover

opportunities to make our airline even safer," Kirby said.