A portable speaker left on a floatplane at Duluth's Sky Harbor Airport ripped off the plane's propeller last year during takeoff, the National Transportation Safety Board concluded this month.
In its final report released May 5, the NTSB determined the 2020 incident's probable cause was "The pilot’s failure to remove an object from the airplane’s exterior, which impacted the propeller blades when he applied full power, causing them to fracture and damage the airplane."
No injuries were reported and the pilot and his passenger were able to put lifejackets on and escape the substantially damaged aircraft before it began to sink in the Duluth-Superior Harbor. A passing pontoon helped bring the plane, pilot and passenger to shore.
According to the NTSB, on June 3, 2020, the pilot of an Icon A5 amphibious airplane taxied on the water before facing into the wind for takeoff and applying full power. About 5 seconds later, the pilot "heard 'a loud bang.'" He shut down the engine, climbed out of the plane to look back, and saw all three of the propeller blades were gone, the NTSB said.
"It is likely that the audio speaker, which was left on the airplane, struck the propeller blades, which resulted in the propeller blades separating from the propeller and penetrating the fuselage," the NTSB said. There were also holes in the plane's hull.
It wasn't until the pilot sat down a few days later to fill out paperwork about the crash, and tried to listen to music while he did that, when he realized what had caused it: just a few days earlier, he set the speaker on top of his plane as he washed the aircraft.
"As I pondered all of this for the last few days, still nothing seemed to make sense as to what would cause the propeller blades to break off. It wasn't until I sat down and begin to fill out the NTSB paperwork at my computer, as I was going to listen to some music, that discovered what I believe had happened," the pilot wrote in the accident report. "While at the beach and before departing, I had a portable speaker sitting on top of the aircraft as we washed the aircraft. While boarding the aircraft for departure, I must have forgot to secure the speaker in the baggage area.
"Therefore when at full power and aircraft began to accelerate, that the speaker must have rolled back over the engine compartment, and into the propellers causing the separation and damage to the aircraft," the pilot continued.
The pilot told investigators he has not been able to find the speaker since the incident.