The Q400 is a turboprop aircraft with 76 seats.
"At this time, we believe he was the only one in the aircraft but of course, we haven't confirmed that at the crash site", said Jay Tabb, chief of the FBI's Seattle division.
Norad said the F15s were "working to redirect the aircraft out over the Pacific Ocean when it crashed on the southern tip of Ketron island", about 30 miles (48km) south of the airport.
The sheriff's department said "preliminary" information was that the plane's pilot was "a mechanic from unknown airlines" who "was doing stunts in air" or lacked flying skills. Witnesses report F-15s chasing plane then saw smoke, and loud boom.
This incident raises all sorts of questions about airport security.
Alaska Airlines and other planes sit on the tarmac at Sea-Tac International Airport Friday evening, August 10, 2018, in SeaTac, Wash.
The recordings were of radio communication between Russell and air traffic controllers.
"Got a few screws loose, I guess", Russell is heard saying in the recording.
Earlier this evening, traffic controllers could be heard speaking to a suspect identified only as "Rich", who they were urging to "land the plane safely and not hurt anybody".More news: Star Trek 4 in doubt as Chris Pine, Hemsworth drop out
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He then said: "I wouldn't know how to land - I wasn't really planning on landing it".
People on Twitter who were following the aviation audio reported that the man attempted a "barrel roll" with the plane at one point - or at least claimed he was going to do so.
"I want to share how incredibly sad all of us at Alaska are about this incident". Horizon Air is a division of Alaskan that flies shorter routes in the western US. Two f-15 fighter jets were scrambled from Portland to intercept the stolen aircraft. I don't know man!
Alaska Airlines said the plane was in a "maintenance position" when it was stolen and not scheduled for a passenger flight. "This is what we call the inside risk", he said, explaining that the security measures should not only be aimed at passengers, but also at employees.
Naturally, the errant plane disrupted air traffic control - but it also scared observers who had no idea what the aircraft was doing. "It's going to disappoint them to hear that I did this", Rich said.
The White House said Saturday that President TrumpDonald John TrumpKavanaugh once said president would likely have to testify before grand jury if subpoenaed: report Twitter says InfoWars account will remain online despite violating its rules Melania Trump family immigration lawyer praises so-called "chain migration" MORE, now staying at his Bedminster, New Jersey resort, had been briefed on the situation. This didn't turn out to be a terrorist incident, but we know that terrorists have had a very large interest in using airliners as guided missiles. "I would hope it is for a guy like me".
As federal agencies investigate, state and airline officials responded to the odd and tragic event with sympathy and thanks.
There was no connection to terrorism and no others were involved, said Troyer.
Only minutes after the plane made its freakish, unauthorized takeoff around 8 p.m., the North American Aerospace Defense Command (NORAD) scrambled two F-15s out of Portland to intercept it.