The pilot of the parked Cessna 500 reported that he and his co-pilot had just re-entered the airplane at the airport in Fort Lauderdale, Florida, and were having a conversation when he felt the airplane shake and heard a loud noise.
He looked out of the right window and saw a Piper PA-34 with its propeller hitting the right wing.
The airplane sustained substantial damage to the right wing.
The pilot of the other airplane reported that, after engine start and before taxi for takeoff, he was looking at his navigation communications and did not notice the airplane rolling forward. The airplane rolled forward and collided with the airplane in front of it.
The pilot further reported that he was unaware of the airplane’s forward movement and that the thought that the hand brake was fully engaged. The Piper sustained minor damage.
Probable cause: The pilot’s failure to ensure that the brake was fully engaged and his subsequent failure to notice that his airplane was rolling forward, which resulted in it hitting another airplane.
NTSB Identification: GAA16CA454B
This August 2016 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

It’s common practice when an aircraft engine is operating to keep feet on the toe brakes when not taxiing. There is no excuse for this incident.