Cessna 560XL N498AB incident near Birmingham, Alabama

Probable cause

The manufacturer's inadequate initial design and inadequate subsequent modifications of the tailcone, which allowed moisture to collect and freeze around rudder cables during operations in subfreezing temperatures, resulting in a loss of rudder authority during landing.

NTSB analysis

During approach and landing, the pilots noted that the airplane had stiff rudder operation. A postflight examination of the airplane found ice in its tailcone stinger, through which the rudder and elevator control cables run. Further investigation discovered that other Cessna 560XL airplanes had encountered the same problem. The design of the airplane was such that water could enter the tailcone, collect there, and freeze around the rudder cables during operations in subfreezing temperatures. The manufacturer had issued a service letter (SL) in 2005 to add a drain hole in the tailcone stinger for in-service airplanes and added a drain hole to production airplanes; this incident airplane had a drain hole in its tailcone that was consistent with the SL. Therefore, the drain hole specified in the SL was not sufficient to correct the problem. In addition, the investigation discovered that some production airplanes had drain holes that were smaller than the size specified in the SL. The manufacturer subsequently issued an alert service letter (ASL) in January 2011 to inspect the existing drain holes to ensure they were the right size, seal an existing drain hole, and add another drain hole in the aft canted bulkhead; however, in March 2011, an airplane modified in accordance with the ASL experienced stuck rudder controls; ice and water were found in its tailcone stinger. The manufacturer subsequently issued a mandatory service bulletin (SB) in October 2011 that specified additional modifications intended to reduce the amount of moisture that can enter the tailcone stinger and to improve the drainage. The Federal Aviation Administration (FAA) district office that oversees the production certification of the Cessna 560XL and the manufacturer's issuance of associated SLs and SBs did not detect the improper-sized holes on some production airplanes. The manufacturer subsequently implemented a specific inspection to verify the drain hole installation on production airplanes, and the FAA has followed up.

Text from the NTSB. Open the NTSB docket for CEN11IA111 for the full record.