An 8-inch knife found on board a Horizon flight that landed at Portland International Airport Monday has exposed airline security concerns.

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A Horizon Airlines plane.

Officials with the Transportation Security Administration said a passenger handed the knife to a flight attendant as passengers were getting off the plane and said he found it between two seats.

The TSA said it’s possible that an employee working on the plane had left it behind after working on the plane. According to TSA spokeswoman Tina Burke, it appeared to be a kitchen knife.

However, such knives aren't typically used by employees working on the plane.

“Eight-inch knives are not in the toolbox for our mechanics, flight attendants or pilots,” said Jen Boyer, a spokeswoman for Horizon Air.

Jennifer Currier, president of the flight attendants' union for Horizon Airlines, said the knife incident is just one example that airline security needs to be tightened.

Currier said she has heard of numerous prohibited items, including butane lighters, getting past security and onto planes.

“A lot of people are granted access to the aircraft area that are not going through security, everybody from the maintenance, the rampers, the aircraft groomers, they have full access to all parts of the aircraft yet they are not having to go through security,” Currier said.

The Horizon Airlines plane landed at the Portland International Airport just before 5 p.m. from Ontario, California.

The investigation continued.