Here's a short story:

(CNN) -- The surviving pilot of Virgin Galactic SpaceShipTwo told authorities he was unaware the feather system had been unlocked early by his co-pilot. 

The spaceship disintegrated 45,000 feet above the Mojave Desert on October 31, killing co-pilot Michael Tyner Alsbury and injuring co-pilot Peter Siebold, who managed to parachute to the ground. 

Siebold was interviewed last week by the National Transportation Safety Board. He described being "extracted from the vehicle as a result of the break-up sequence and unbuckled from his seat at some point before the parachute deployed automatically," according to a release from the NTSB. 

Earlier this month, the NTSB tweeted that Alsbury "moved the lock/unlock handle into unlock position." 

...the copilot, who was in right seat, moved the lock/unlock handle into unlock position; he did not survive accident. #SpaceShipTwo 

But that mishap alone doesn't explain why the feathering started, since no one moved the feathering handle. 

During feathering, two pieces on the back of the vehicle -- the "feathers" -- lift up perpendicular to the spaceship, making the vehicle look as though it's arching its back as it descends. 

The wreckage has been recovered and will be used for follow-up examinations. 

Test pilot's workplace a cold, harsh environment 

 (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: How many feet above ground did the spaceship disintegrate?
Guess: 45,000 feet

Question: Who survived the accident?
Guess: Peter Siebold

Question: Who was killed?
Guess: Michael Tyner Alsbury

Question: When did this happen?
Guess: October 31

Question: Who moved the lock/unlock handle according to the NTSB?
Guess: Alsbury

Question: What system was unlocked?
Guess: Feather system

Question: What does NTSB stand for?
Guess: National Transportation Safety Board

Now answer the following question in the same format.

Question: What happens during feathering?

Two pieces on the back of the vehicle lift up