Cessna 560XL N588QS incident near Haynesville, Virginia

Probable cause

The manufacturer's inadequate design fix for previously known tailcone stinger water ingestion and retention.

NTSB analysis

After a flight earlier in the day, the airplane sat on a ramp in moderate rain for about 1 1/2 hours before departing. During the departure, the airplane encountered light to moderate rain, and, while climbing through about 28,000 feet, the crew found that the rudder was frozen in the neutral position. The crew continued the climb to 40,000 feet and, based on discussions with the company, diverted to an en route airport. Descending through 13,000 feet, normal rudder operation returned, and the subsequent approach and landing were uneventful. After the crew disembarked, they noticed water dripping from the belly of the airplane, and subsequently found ice in the bottom of the tailcone stinger, through which the rudder and elevator control cables ran.

About 4 months prior to this incident, two other airplanes had similar incidents that resulted in the manufacturer issuing an alert service letter (ASL). The ASL stated, in part, that the tailcone stinger may not drain water, which could allow ice to form around the rudder cables and pulleys. The ASL required inspection of the two existing drain holes to ensure they were the right size, sealing an existing drain hole, and adding another drain hole in the aft canted bulkhead. This incident airplane had incorporated the ASL prior to the incident.

Subsequent flight testing by the manufacturer revealed that, with the tailcone stinger drain hole sealed per the ASL, air could still enter the tailcone through seams at the bottom of the stinger with enough force to splatter water onto the rudder cables and pulleys, which could then freeze. Testing also revealed that air emanating from the new hole in the aft canted bulkhead also resulted in water splattering onto the rudder cables and pulleys and that, after large quantities of water were introduced, water would only drain forward through the new hole only if large quantities were introduced. As a result, the manufacturer issued a service bulletin, in addition to the ASL (which must be completed) that requires the installation of a seal and another drain.

Text from the NTSB. Open the NTSB docket for ERA11IA184 for the full record.