How could an airport ground crew employee steal and fly an airliner?

A picture of how an airliner was stolen from Sea-Tac International Airport on Friday evening is beginning to emerge.

Investigators and airline officials are tracing the sequence of events that led to a Horizon Air employee taking off without permission in one of the company's turboprop passenger planes.

Findings, when they come, will almost certainly lead to changes in aviation protocols.

[Report: Airline employee who stole Sea-Tac plane previously from Wasilla]

The plane crashed on Ketron Island, off the shore of Steilacoom, killing the pilot — the only person on board.

The alleged thief, identified in audio recordings as Rich, was not employed as a pilot. He was identified as a ground service agent Friday by Alaska Airlines, Horizon's parent corporation. On Saturday, Alaska said he handled baggage and towed aircraft at the airport.

The man used that tow knowledge to rotate the plane 180 degrees while it was parked in a cargo area Friday evening, Alaska officials said. After that, he started the plan, taxied to a runway and took off.

He appeared to be suicidal, based on his conversations with air traffic control. But the potential for a disaster, if Rich had wished to harm others, is sobering.

As the incident unfolded in the skies over Puget Sound, a Pearl Jam concert was being held at Safeco Field, and the plane traveled over highly populated residential and commercial areas.

Aviation consultant and retired airline pilot Dan Stratman told The News Tribune that it wouldn't have been unusual for an individual working in ground support to have access to the cockpit.

"Even just ground people working on the planes, they have access to inside the planes on ramp," Stratman said. "He could have just sat in the cockpit, and no one would have thought otherwise, being in the plane with a badge."

Stratman, author of aviation thriller "Mayday," said ground crews don't go through psychological screening.

Most ground crew members working at airports have a "basic knowledge" of how airplanes function, said Debra Eckrote, NTSB regional chief.

No records for a pilot license for the man thought to have stolen the plane could be found on the Federal Aviation Administration website. Alaska officials said, to the best of the airline's knowledge, the man did not have a pilot license.

A pilot who regularly flies in and out of Sea-Tac for a commercial carrier said on Friday that an employee who was "taxi qualified" could combine that knowledge with YouTube videos and easily purchased computer flight simulator programs to learn to fly an airplane.

Stratman agreed and said Microsoft simulators are available online with extremely accurate representations.

The commercial pilot, who was not authorized to speak to the media, said the Bombardier Q400 aircraft has the same autopilot systems used on Boeing and Airbus jets. It didn't appear Rich used autopilot Friday.

[Man who took Horizon Air plane from Sea-Tac was quiet and well liked, says former co-worker]

The stolen plane is a twin-engine turboprop designed for shorter distance flights. It can carry 76 passengers and has boarding doors in both the front and rear of the plane.

In conversations with a pilot on the ground, it appeared Rich wasn't fully knowledgeable with the plane's instruments yet knew enough about flying to perform aerobatics with the airliner.

The working commercial pilot said if the weather is clear, as it was Friday, instrument knowledge isn't as crucial to flying as it is at night or in poor weather.

At one point, Rich flew the plane upside down in a barrel roll, coming within feet of the water before pulling up. Rich complained of feeling lightheaded.

"I would like to get some, uh, make it pressurized or something so I'm not so light-headed," Rich told ground control.

A plane flying at low altitude doesn't need to be pressurized.

"He never got to high altitude, and there should have been no problem with pressurization," pilot Stratman said.

"More likely if he was lightheaded, that was caused by the aerobatics," Stratman said in a phone interview from Kansas City. "That can throw your inner ear out of balance, even for an experienced pilot it can make you dizzy and queasy."

Alaska said the plane was parked in a "maintenance position" in a cargo area of the airport and not involved with loading or unloading passengers.

There are no keys to an airliner. Planes are turned on using a variety of switches.

It will be up the FBI to get to the bottom of how he did it and why, Eckrote said.