History of Flight
On April 27, 2012, about 1430 Pacific daylight time, a Cessna Citation 560XL, N101PG, operated by Pape Group Inc. as a cross-country corporate flight under 14 CFR Part 91, sustained substantial damage to the left wing and front pressure bulkhead following an uncommanded landing gear retraction while landing at Mahlon Sweet Field Airport (EUG), Eugene, Oregon. The airline transport pilot, commercial pilot, and one passenger were not injured. The flight originated from Cleveland-Hopkins International Airport (CLE), Ohio, with an intermediate stop at Centennial Airport (APA), Colorado, under visual meteorological conditions and an instrument flight plan.
The pilot in command (PIC) reported that the flight from APA was uneventful. During the visual approach into EUG, the PIC called for full flaps and final landing configuration. Both pilots verified that cockpit indications showed the landing gear down and locked. The airplane touched down smoothly on the main landing gear followed by the nose gear. The PIC had his hand on the thrust reversers when the landing gear unsafe horn sounded; the left main landing gear collapsed, followed immediately by the right and nose gears. The airplane slid on its belly for about 1,500 feet before stopping on the runway.
Personnel Information
The PIC, age 44, held an airline transport pilot certificate with ratings for airplane single- and multi-engine land and instrument airplane. He had accumulated about 5,600 total flight hours, with about 250 hours in the accident airplane. His most recent FAA second-class medical was issued on April 14, 2012, with a requirement to wear corrective lenses.
The second pilot, age 45, held a commercial pilot certificate with ratings for airplane single- and multi-engine land and instrument airplane. He had accumulated about 2,519 total flight hours, with about 15 hours in the accident airplane. He held an FAA second-class medical with no limitations or waivers.
Aircraft Information
The Cessna Citation 560XL, serial number 560-5590, was manufactured in 2005. The airplane was maintained under a manufacturer's inspection program, with its most recent maintenance on December 21, 2011. At the time of the accident, total time was 1,937 hours. The tricycle landing gear system is electrically controlled and hydraulically actuated. The landing gear control panel includes a handle with a detent and a locking solenoid activated by a squat switch on the left main gear. The hydraulic system consists of a bypass valve, manifold assembly, control valves, and actuators. The gear retraction sequence requires weight off the left squat switch to unlock the handle, then moving the handle to the up position.
Meteorological Information
At 1441, the weather at EUG was reported as wind from 200 degrees at 9 knots, visibility 10 statute miles, scattered clouds at 3,300 feet and 4,300 feet agl, broken clouds at 5,000 feet agl, temperature 13°C, dewpoint 6°C, and altimeter setting 30.32 inches of mercury.
Examination and Tests
Initial examination at the airport revealed that the left wing sustained scrape damage puncturing the fuel tank, and a communications antenna was pushed through the pressure vessel. The cockpit showed the landing gear handle in the down position, anti-skid on, flaps fully extended, and circuit breakers engaged except those intentionally pulled afterward. All landing gears were found fully retracted and engaged in their uplocks. The right wing skin and gear assembly had black circular marks; the left tire had linear abrasions. The nose landing gear doors were damaged. When manually released, all gears dropped but did not lock down.
The cockpit voice recorder captured the landing checklists, gear extension sounds, and after touchdown, thumps followed by the gear warning horn and the collapse. The enhanced ground proximity warning system showed no warnings or abnormalities before touchdown.
At the Citation Service Center, the landing gear handle passed acceptance test procedures (ATP) standards. One of three screws securing a PCB was loose but no anomalies affecting the flight were found. All three landing gear actuators functionally tested and passed ATP standards, with no leaks or anomalies. Electrical wiring was visually inspected and found continuous except for some rodent-chewed wires not associated with the landing gear system. The landing gear control PCB and monitoring PCB were visually inspected and passed ATP, though the monitoring PCB later showed a hard failure on an internally shorted transistor. Hydraulic lines were continuous and intact; system pressure testing showed no failures. Cockpit warning lights and sounds functioned normally. Hydraulic equipment was activated in normal and abnormal ways and operated as designed.
The manifold assembly, including a relief valve and control valves, was tested at PneuDraulics. Initial results showed internal leakage at the flap control valve, which was slow to respond and occasionally reversed command when the extend solenoid was energized. The manifold relief valve failed ATP due to low cracking pressure, high pressure drop, and poor reseat; debris was found in the fluid. Unusual wear marks were noted on internal components. A new relief valve was installed but the flap control valve still responded slowly. The flap control valve passed most ATP except two internal leakage requirements; the extend solenoid had excessive backpressure when de-energized. The retract solenoid showed higher than normal leakage when energized. Small debris was found in the retract solenoid. Scoring on the spool surface was noted. The gear control valve passed all ATP tests. Dimensional testing revealed no blockages or burrs. Attempts to recreate the command reversal were unsuccessful, but it was found that if the spool is not centered, it can favor either the retract or extend side.
Probable Cause
The investigation did not identify a specific cause for the uncommanded landing gear retraction.