NEW YORK, May 13 (Reuters) - United Airlines may

not take delivery of the Boeing 737 MAX 10 until 2027 or

2028 because of uncertainty about when the plane will be

approved for use, an executive said Tuesday.

Boeing ( BA ) has faced significant delays in getting the smaller

MAX 7 certified, which must be approved before the Federal

Aviation Administration can then certify the larger MAX 10.

United Chief Commercial Officer Andrew Nocella told

reporters on the sidelines of an event the airline is taking MAX

9 airplanes as it waits for the certification of the 10.

"In supply chain terms, we want to make sure we get our

aircraft," Nocella said. "Until we know the MAX 10 is going to

be delivered, we don't want to have an aircraft that doesn't

arrive."