Its believed the pilot was killed in the crash, and authorities are still trying to figure out how someone could steal a commercial airliner and take off from a major US airport unauthorized.
The Q400 did a loop the loop and nearly crashed into Chambers Bay, and then flew further south chased by two F-15 Eagle fighter jets from the Air National Guard in Portland.
The 29-year-old man, who has not been identified, was suicidal and appeared to have acted alone, the Pierce County Sheriff's Department said on Twitter, adding the employee was probably killed in the crash. The pilot's identity has not been made public.
Instead, the sheriff's office said the cause of the crash could have been either the pilot's inexperience, or his decision to pull mid-air stunts during his short flight.
The aircraft was stolen at about 8 p.m. Alaska Airlines said it was in a "maintenance position" and not scheduled for a passenger flight.
The aircraft took off and began manoeuvering over Puget Sound.
It is unclear how the employee was able to taxi the plane on a runway and take off without authorization.
The man also said he had no flying experience - but had "played some video games before".
The Sheriff said the F15 military jets were not involved in the crash.
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Witnesses in the area posted videos to social media showing the 76-passenger plane, meant for short flights, doing unsafe ariel maneuvers while F-15 fighter jets scrambled behind it.
"I felt like we were on the ground and we were safe, we weren't in the sky while something was going on", he said after getting off the plane. F-15 fighter jets were sent from Portland to control the situation and, if necessary to intercept it. "We believe that it was taken by a single Horizon Air employee, and that no other passengers or crew were on board". He said the military planes were not involved in the crash.
A USA airline employee who stole an empty plane from an airport and crashed it into nearby island has been described by police as "suicidal".
The plane was a Q400, a Bombardier turboprop plane.
He also said he was "just a broken guy, got a few screws loose I guess". "I was kind of hoping that was gonna be it".
At another point, Rich said, "I've got a lot of people that care about me".
Then the passenger plane pilot "did a complete loop ..."
In one, the controller can be heard telling the pilot: "What we don't want to see is you get hurt or anyone else get hurt, so like I said, if you want to land, that's probably the best way to go". "Never really knew it until now".
His motive is not clear, but audio between the cockpit and air traffic control indicates the man was in emotional distress.
"My husband and I are recently former Boeing employees, and we were wondering why a jet was near the passenger airplane", she said.