Sierra said he and Leymeister noticed a flock of birds nearby.
"All of a sudden, one of [the birds] just came back and just kind of opened its wings facing backwards, and I think the wind picked it up and it came back straight into the windshield, mostly on [the instructor's] side," Sierra told KHOU-TV.
"We looked at each other and asked, 'Are you OK?'" Sierra said. "We just regrouped. We knew we had to get this [plane landed]. We looked out and obviously assessed the damage quickly. The window was almost all gone. I removed some glass at the top, because the wind was just blowing so hard, we didn't want any more glass coming in."
The pair safely made an emergency landing at Hooks.
Both men suffered cuts from the broken glass, but neither sustained any serious injuries.
