WASHINGTON (Reuters) - United Airlines can take delivery of new airplanes as U.S. aviation regulators review the carrier, the head of the Federal Aviation Administration said Thursday.

"We are permitting them to take deliveries of aircraft. Most of those aircraft have been one-on-one replacements for missing aircraft," FAA Administrator Mike Whitaker told reporters at a briefing. "Some of it has been growth. They have provided us with their growth plan, and we're working with them on that growth plan going forward."

Some airline certification activities were halted after the FAA said in March it was increasing its oversight of United following recent safety incidents.