WASHINGTON, June 18 (Reuters) -

Boeing Starliner's return to Earth from the

International Space Station with its first crew of astronauts

has been pushed back to June 26, a NASA official said on

Tuesday.

NASA astronauts Butch Wilmore and Suni Williams were

launched aboard Starliner June 5 and arrived at the ISS

following a 24-hour flight in which the spacecraft encountered

four helium leaks and five failures of its 28 maneuvering

thrusters.

Starliner's first flight with astronauts is a crucial last

test in a much-delayed and over-budget program before NASA can

certify the spacecraft for routine astronaut missions and add a

second U.S. crew vehicle to its fleet, alongside SpaceX's Crew

Dragon.

The new delay of the return of Starliner is intended "to

give our team a little bit more time to look at the data, do

some analysis and make sure we're really ready to come home,"

Steve Stich, NASA's commercial crew program manager, said during

a news conference.

NASA is targeting a departure no earlier than June 26,

leaving open an opportunity for further extensions of time at

the ISS. Starliner, while designed for future six-month

missions, can stay docked to the ISS for a maximum of 45 days

during its current mission.

The return to Earth is expected to last about six hours

and target a location in the desert of Utah, New Mexico or other

backup locations, depending on local weather conditions.

The latest in-flight problems follow years of other

challenges Boeing ( BA ) has faced with Starliner, including a 2019

uncrewed test failure where dozens of software glitches, design

problems and management issues nixed its ability to dock to the

ISS. A 2022 repeat uncrewed test had a successful docking.