Cessna 560XL N580QS incident near Traverse City, Michigan

Probable cause

The inoperative galley drain tube heater, which allowed water within the tube to freeze and led to its failure; the tube’s failure allowed water to drain onto the rudder cables and freeze and resulted in the rudder binding during landing.

NTSB analysis

The flight was conducted at flight level 400, and the entire flight was 3 hours 17 minutes long. During the landing at the destination airport, the flying pilot noted that the rudder pedals were hard or frozen; however, he was able to make an uneventful landing. The nonflying pilot then took the flight controls and confirmed the rudder pedal situation. Once slowed to a safe speed, the flight crew was able to break the rudder pedals free and to taxi the airplane to the ramp. After the airplane was parked and shut down, the rudder still felt stiff and required more input than normal to operate.

Postaccident examinations confirmed compliance with an alert service letter and service bulletin related to control cable icing. Examinations also revealed witness mark consistent with a water line in the fuselage area, and a liquid consistent with pooled deice fluid, staining, and moisture was found in the tailcone compartment. Water was also found where the galley drain exits the pressure vessel and enters the fairing area. Water was observed draining from the black foam wrap around the drain tube's heating element, and the black foam exhibited deformation consistent with the expansion of frozen water. Removal of the foam revealed an opening in the drain tube. Testing of the galley drain heating element revealed that it was inoperative. Black foam deposits were observed on a rudder cable, but no rudder system anomalies were detected.

Laboratory tests revealed that an opening in the drain tube caused the rudder cables to freeze to the drain mast, and some additional force above a baseline was needed to break the simulated rudder pedals free from a static position. At the time of the incident, the airplane's approved inspection program did not specify that the galley drain tube or heater should be inspected. Additionally, the failure of the galley drain heater is not annunciated to the flight crew nor to maintenance personnel.

It is likely that the undetected failure of the galley drain tube heater allowed the water within the galley drain tube to freeze, which led to the tube's failure. Once the tube failed, water was allowed to drain from the tube onto the rudder cables; this water also froze due to the inoperative heater and caused the rudder to bind during landing.

Text from the NTSB. Open the NTSB docket for CEN14IA172 for the full record.