UNITED Airlines Holdings Inc said it can begin the process to add new planes and routes again after the Federal Aviation Administration (FAA) indicated it would ease restrictions, a sign of progress after a series of safety issues led to a clampdown on the carrier's operations.

The agency will allow the carrier to start work to resume those certification activities "after a careful review and discussion about the proactive safety steps United has taken to date," the airline said in a message to employees recently that was seen by Bloomberg. The FAA review is ongoing, the carrier said.

"There is more work to do, and we remain open to their perspective on things that can make us an even safer airline," United said.

The FAA said in a statement that it has not yet approved "any expansion of United Airlines' routes or fleets," but didn't specify whether certification work for future growth plans can resume. The agency said that "safety will determine the timeline for completing" its review.

Authorities took steps to temporarily limit the carrier's growth in recent months and review its safety procedures following a series of headline-grabbing incidents. Among them, a wheel fell off a plane just after take-off, an aircraft veered off a runway and a piece of a fuselage came loose in flight. Airline safety throughout the US has been under heightened scrutiny since a fuselage panel broke off an Alaska Airlines flight on January 5.

United earlier had to delay two new routes set to start this summer and at least three Boeing Co 737 Max 9 deliveries because they could not be added to the carrier's operating certificate during the FAA review.

CEO Scott Kirby said recently that the Chicago-based carrier was "embracing" the FAA evaluation as an opportunity to improve what it considers to be an already high level of safety. United simultaneously has been conducting an internal review to determine if its safety procedures or training need to change.