CLEVELAND (WJW) — The FOX 8 I-Team has uncovered a series of investigations by the Federal Aviation Administration at Cleveland Hopkins International Airport.

So, we asked what it means to airline passengers, especially now with the start of holiday travel.

Since March, the FAA has issued three letters of investigation. All raise questions about what’s happening at Hopkins airport on the ground — in particular, on the runways and taxiways.

Back in March, the feds started asking about training for winter operations, operating ground vehicles and airport firefighting.

Then in June, the FAA raised questions after a report that said a “construction vehicle under escort failed to yield to a taxiing aircraft.”

And last month, more questions came after a report of an airport vehicle entering a runway without clearance from air traffic control.

We asked a Hopkins airport manager what he’d say to travelers about that.

“We have thousands and thousands of movements of vehicles and aircraft on the airfield in a given week,” said Assistant Manager for Operations Dejan Radosavljevic.

He argued there’s no need to be alarmed by the investigations, since they can lead to more safety.

“So, we take lessons learned from incidents. Try to implement that into our next training,” he said. “And we make sure that we learn from any type of mistakes that may have happened.”

We checked with the FAA. What’s going on with the letters of investigation?

The FAA told the I-Team two of the cases were investigated and closed with no penalties or fines. One case remains open. That is the one looking into training.

We also spoke to veteran commercial pilot and flight instructor Robert Katz.

“What we’re talking about here is the human factor that is never perfect. This is why we train. This is why we educate. And, this is why we practice. To prevent these things from happening,” he said.

Those letters of investigation serve as a reminder that what happens on the ground affects travelers like you taking to the air.

One traveler told us, simply: “Safety is my concern.”

Another said: “I’m just really trying to get to my destination and hope I have a safe flight.”

We will let you know the outcome of the one investigation that’s still ongoing.

We have also requested records showing how the city has responded to the FAA in all of these matters.