Incident Overview
On January 13, 2013, at 1818 eastern standard time, the flight crew of a Cessna 560XL (N662QS) experienced stiff elevator controls while climbing through FL350 near Debary, Florida. Both pilots and two passengers were not injured, and the airplane was not damaged. Instrument meteorological conditions prevailed, and the flight was operating under an IFR flight plan. The flight originated from St. Lucie County International Airport (FPR), Fort Pierce, Florida at 1752, destined for Dekalb-Peachtree Airport (PDK), Atlanta, Georgia, under Part 91 Subpart K.
The climb from FPR was uneventful until just before entering a cloud layer at FL320, when the crew activated engine and wing anti-ice systems and the pneumatic tail de-ice system. As the airplane climbed through FL350 at 1,000 feet per minute with autopilot engaged, it pitched nose-down and entered a 400-fpm descent. The crew disconnected the autopilot and leveled off at FL350.
Both crewmembers reported that "excessive" force was needed to change pitch. They notified ATC and requested descent. During descent, manual and electric pitch trim appeared normal, but any trim or manual elevator input resulted in exaggerated pitch response. After descending through FL180, a "broke loose" sensation was felt, and elevator controls returned to normal. The crew re-engaged autopilot and continued to PDK without further incident.
Examination of Aircraft
Two days after the incident, the airplane was examined on the ground at PDK using the operator's fuselage drain inspection procedure. The empennage inspection revealed multiple obstructed drains and evidence of standing water at various fuselage stations (FS). Key findings included:
- FS550: drain 50% obstructed, tidal mark 5 inches above belly.
- FS544: drain 100% obstructed, tidal mark at 8 inches, 1/4-inch standing water.
- FS496: drain 100% obstructed.
- FS479: drain 100% obstructed, 1.5-inch tidal mark.
- FS462: debris accumulation near control cable cutout, standing water.
- FS460: drain 100% obstructed, standing water to 1/4-inch at control cable cutout.
- FS449: elevator cable pulley mounting location; pulleys visibly saturated with water.
- FS421: drain 60% obstructed, 1/4-inch tidal mark.
Additionally, mechanics found that pulleys at FS528 had seized bearings and were not free to rotate. Water-saturated pulleys from FS449, a pulley from FS438, and debris samples were sent to the NTSB Materials Laboratory.
Mechanics noted that the tailcone stinger seals, installed per Cessna Service Bulletin SB650XL-53-16, were not trimmed to overlap as specified.
Findings
The NTSB Materials Laboratory examined pulleys from FS528, FS449, and FS438. The left pulley from FS528 showed partial staining and shiny grooves; its bearings had corroded balls and races. Pulleys from FS449 were uniformly darker, damp, and contained water and an unidentified silicon-based product on swabs. The debris sample contained fibrous material, beetles, a rivet shank, rubber seal portion, cotter pin, nylon wire tie, washer, and lock wire.
The incident airplane had complied with airframe manufacturer service bulletins and FAA Airworthiness Directive AD 2012-06-01, which mandated drain holes and seals to prevent moisture accumulation. The operator had also performed a one-time drain inspection procedure in May 2011.
After the incident, the operator updated its inspection program to include a recurring fuselage bilge drain inspection every 300 flight hours. The airframe manufacturer drafted a maintenance manual update requiring visual inspection and cleaning of the tailcone and bilge areas at intervals of 600 hours/12 months or 1,200 hours/24 months.