Roy Halladay's Plane Climbing and Diving 2 Weeks Before Crash

New video has surfaced reportedly showing Roy Halladay performing concerning aerial maneuvers over water -- including extreme changes in altitude -- just 2 weeks before his fatal crash.

The video show's Roy's ICON A5 plane flying over the Gulf of Mexico on Oct. 20 -- it almost looks like he's practicing a water landing ... though he never lands on the water.

The person who shot the video told the NY Daily News he started recording because the plane was going so close to the water at a high rate of speed, he thought it was going to crash.

You can hear the man express concern as he watches Roy's plane.

Just 2 weeks later, the plane crashed near the very same area -- killing the ex-MLB star.

Multiple witnesses tell TMZ Sports Roy had been making similar changes in altitude -- just like in the video from Oct. One person described it as "aggressive flying."

Roy's family issued a statement saying he was not a reckless flyer -- and they're heartbroken over his death.