By David Shepardson

WASHINGTON (Reuters) -U.S. President Joe Biden’s nominee to head the Federal Aviation Administration (FAA) is withdrawing his nomination after Republican criticism that he was not qualified to serve as the top aviation regulator, sources familiar with the matter told Reuters on Saturday.

Last year, Biden nominated Denver International Airport CEO Phil Washington to serve as FAA administrator.

The agency has faced questions in recent months after a series of close-call safety incidents and the Senate Commerce Committee earlier this week delayed a vote on his nomination citing outstanding questions by some lawmakers.

One of the sources, a White House official, told Reuters that “an onslaught of unfounded Republican attacks on Mr Washington’s service and experience irresponsibly delayed this process, threatened unnecessary procedural hurdles on the Senate floor, and ultimately have led him to withdraw his nomination today.”

Senator Ted Cruz, ranking Republican on the Senate Commerce Committee, and other Republicans had said Washington, who retired from the U.S. Army in July 2000, must have a waiver from rules requiring civilian leadership to head the FAA. The Transportation Department’s general counsel said in a letter this month that Washington was fully qualified and did not need a waiver.

Sources told Reuters Republicans had threatened to use parliamentary tactics to object to Washington’s lack of a waiver.

The White House official added “politics must not hold up confirming an Administrator to lead the FAA, and we will move expeditiously to nominate a new candidate for FAA administrator.”

The FAA has had a number of recent safety issues.

In January, the FAA halted all departing passenger airline flights for nearly two hours because of a pilot messaging database outage, the first nationwide ground stop of its kind since the Sept. 11, 2001, attacks.

On Wednesday, the FAA issued a safety alert to airlines, pilots and others about the “need for continued vigilance and attention to mitigation of safety risks” after a series of high-profile near collisions.

Six serious runway incursions have occurred since January that prompted the agency to convene a safety summit last week.

Some industry official think the White House could name acting FAA Administrator Billy Nolen as a new nominee. Nolen, who was named head of the FAA’s aviation safety office, has been the acting FAA administrator since April 2022 and has received backing from many Republicans in Congress.

Washington had won support from a wide range of groups, including a number of aviation unions and a group of family members of some killed in a 2019 fatal Boeing 737 MAX crash.

The FAA has been without a permanent administrator for almost a year.

(Reporting by David Shepardson, editing by Deepa Babington and Marguerita Choy)