United Airlines Flight Attendants say David Dao's Injuries Easily Preventable, Cops Should Know Better

United flight attendants are shocked David Dao was brutalized and bloodied because police could have prevented any injury if they had a clue about the plane they boarded.

We spoke to several United employees who say the officers should have known the armrests on those seats are movable. Remember, Dao's head slammed into the armrest, causing at least some of his injuries.

The flight attendants point out the cops could have effortlessly lifted the armrest before forcibly removing Dao ... who appeared to get hung up on the middle seat armrests before hitting the one on the aisle.

The employees we spoke to made it clear they believe Dao should've been removed, but they're fuming at how it was handled.

United's CEO says they're reviewing its procedures in these situations, but flight attendants think it's the police who need more training.