Cessna TU206 N9493Z accident near Ellsworth, Maine

Probable cause

The pilot’s decision to operate the airplane with a known deficiency of the floats, which resulted in an accumulation of water in the forward compartments of the floats, a forward center of gravity, and subsequent nose over during a water landing.

NTSB analysis

The pilot of the amphibious airplane reported that he and a passenger had departed earlier that morning from the lake where the airplane was based and flew to a local airport to meet with a mechanic where they discussed future work to the airplane. Afterwards, they departed and flew back to the lake and conducted a normal water landing. As the airplane settled into the water, the pilot reported a more than normal nose down tendency. As the airplane slowed to nearly a full stop with idle power, the forward section of the floats continued to sink, and the airplane subsequently nosed over resulting in substantial damage to the fuselage.

The pilot reported that he had noticed on previous flights that the floats seemed to accumulate a large amount of water in the forward three to four compartments of each float. He stated “I feel like it was gallons of water per compartment,” but he had not measured the exact quantity of water that he had pumped from each compartment. The pilot described some steps he took to determine the nature of the issue and tried to learn, “what is considered [a lot] or too much water per compartment.” Following the accident, he reported that upon righting the airplane the forward 5 compartments of the floats were “completely flooded” and the aft 2 compartments contained no water. According to an advisory circular regarding seaplane safety published by the Federal Aviation Administration, “A small amount of water, e.g., a cupful, is not unusual and can occur from condensation or normal seepage.” It also stated, “Finding an excessive amount of water should cue the pilot to look for the source of the leak.” Based on this information, the pilot should have discontinued flying the airplane from water until the nature and source of the leaking floats had been appropriately addressed. Additionally, it is likely that the excessive water accumulation in the forward portion of the floats moved the airplane’s center of gravity forward such that it resulted in the noseover during landing.

Text from the NTSB. Open the NTSB docket for ERA25LA285 for the full record.