New York (CNN Business) Boeing's Starliner spacecraft, which is designed to carry NASA astronauts to the International Space Station, encountered a second, previously undisclosed, software issue during a botched test flight in December.

The problem, revealed Thursday by a NASA safety adviser, adds to questions about when Boeing's spacecraft will be ready for its first crewed flight, which is already years overdue.

The space agency said Friday that it plans to launch a full-scale safety review of the company's work on Starliner, noting that there were "numerous instances where the Boeing software quality processes either should have or could have uncovered the defects." That review will attempt to determine why the software problems weren't detected during ground tests prior to the launch.

Starliner conducted an uncrewed test flight in December that was designed to show that the vehicle can safely dock with the International Space Station — but it didn't go as planned. Starliner's internal clock was off by 11 hours, which caused the spacecraft to misfire and stumble off course, NASA and Boeing officials told reporters at the time. Starliner was forced to make an early return to Earth.

Boeing BA Paul Hill, a member of NASA's safety adviser panel , disclosed a separate software problem during a public meeting on Thursday, saying it could have caused a "catastrophic failure," according to Space News . Hill saidwas able to identify and correct the error before it impacted Starliner's behavior.

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