Incident Description
During cruise at flight level 350 in light turbulence, the trailing half of the left-hand outboard trailing edge flap separated from the aircraft. The pilot declared an emergency and subsequently landed at Poughkeepsie, New York, without further incident.
Investigation Findings
The portion of the damaged flap that remained attached to the aircraft was removed and inspected at the NTSB Materials Laboratory. Inspection revealed that the flap drain/vent holes had been sealed with a filled material and paint. At the time of the incident, the aircraft had accumulated a total of 206 flight hours.
Regulatory Response
As a result of this incident, an emergency airworthiness directive was issued. The directive calls for the inspection of the drain/vent holes on the inboard end of each of the four flap panels on Cessna S550 aircraft.