N101PG

HISTORY OF FLIGHTOn April 27, 2012, about 1430 Pacific daylight time, a Cessna Citation 560XL, N101PG, 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 airplane was registered to and operated by Pape Group Inc., as a cross country corporate transportation flight under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and an instrument flight plan had been filed. The flight originated from Cleveland-Hopkins International Airport (CLE), Cleveland, Ohio, with an intermediate stop at Centennial Airport (APA) in Denver, Colorado.

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. The flight crew both verified that all cockpit indications showed the landing gear in the down and locked position. The airplane touched down smoothly on the main landing gear followed by the nose gear. The PIC had his hand on the thrust reversers (he was unsure if he started to deploy them or not) when the flight crew heard the landing gear unsafe horn; 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 it came to rest on the runway. PERSONNEL INFORMATIONPilot in Command (PIC)

The PIC, age 44, held an airline transport pilot certificate with ratings that included airplane single- and multi-engine land, and instrument airplane. At the time of the accident, he had accumulated about 5,600 hours of flight experience, about 250 of which were in the accident airplane. His most recent FAA second-class airman medical certificate was issued on April 14, 2012, with the restriction that he must wear corrective lenses.

Second Pilot

The second pilot, age 45, held a commercial pilot certificate with ratings that included airplane single- and multi-engine land, and instrument airplane. At the time of the accident, he had accumulated about 2,519 hours of flight experience, about 15 of which were in the accident airplane. He also held a FAA second-class medical with no limitations or waivers. AIRCRAFT INFORMATIONThe airplane was a Cessna Citation 560XL, serial number 560-5590, and was manufactured in 2005. The airplane was maintained under a manufacturer's inspection program and its most recent maintenance occurred on December 21, 2011. At the time of the accident, the airplane had a total time of 1,937 hours.

The airplane has a tricycle landing gear system that is controlled electrically and actuated hydraulically.

The landing gear control panel in the cockpit contains a landing gear handle, three gear indicator lights, a red gear unlocked indicator, and an audible warning system. The landing gear handle can be positioned either up or down, with the two positions separated by a detent. Therefore, if the handle is in the up position the pilot must pull the handle out to clear the detent before positioning it in the down position. There is also a locking solenoid within the gear handle that physically restricts the handle from being moved while the airplane is on the ground. This solenoid is activated by a squat switch on the left main landing gear, which indicates if there is 'weight on wheels' or 'no weight on wheels'.

The hydraulic system contains a bypass valve, a manifold assembly that houses the control valves for all hydraulic components, and landing gear actuators. The bypass valve opens and closes on command to pressurize and depressurize the system. The landing gear control valve, which is secured to the manifold assembly, receives an electrical signal to either an extend or retract solenoid, which directs fluid through an internal spool to either the extend or retract side of the hydraulic system. When the control valve is not in use, it is spring loaded to a neutral position. Finally, the landing gear actuators, one at each gear, raise and lower the gears. When the gear is retracted, mechanical uplocks hold the gear in place; and when the gear is extended, an internal lock within the actuators hold the gear into the extended position.

In summary, if the pilot wants to retract the landing gear: with weight off of the left landing gear squat switch, the landing gear handle solenoid unlocks, and the pilot can move the handle to the up (retract) position. The pilot then receives a GEAR UNLOCKED indicator light; an electrical signal is sent to close the bypass valve, and to energize the landing gear control valve. The hydraulic fluid pressurizes and routes through the landing gear control valve to the retract side of the hydraulic system. The fluid then flows to the landing gear actuators which raise and mechanically lock the gear. Once all three gears are in the up position the bypass opens to reduce pressure, the control valve is positioned to neutral, and the GEAR UNLOCKED indicator light extinguishes.

To extend the landing gear, the system works identical with the exception that the landing gear control valve routes fluid through the uplocks to release them before going to the extend side of the actuating cylinders. Also, when the landing gear is down and locked the pilot will get three green gear safe lights. METEOROLOGICAL INFORMATIONAt 1441, the weather reported at EUG was wind from 200 degrees at 9 knots, 10 statute miles of visibility, scattered clouds at 3,300 feet above ground level (agl) and 4,300 feet agl, broken clouds at 5,000 feet agl, temperature 13 degrees C, dewpoint 6 degrees C, and an altimeter setting of 30.32 inches of mercury. AIRPORT INFORMATIONThe airplane was a Cessna Citation 560XL, serial number 560-5590, and was manufactured in 2005. The airplane was maintained under a manufacturer's inspection program and its most recent maintenance occurred on December 21, 2011. At the time of the accident, the airplane had a total time of 1,937 hours.

The airplane has a tricycle landing gear system that is controlled electrically and actuated hydraulically.

The landing gear control panel in the cockpit contains a landing gear handle, three gear indicator lights, a red gear unlocked indicator, and an audible warning system. The landing gear handle can be positioned either up or down, with the two positions separated by a detent. Therefore, if the handle is in the up position the pilot must pull the handle out to clear the detent before positioning it in the down position. There is also a locking solenoid within the gear handle that physically restricts the handle from being moved while the airplane is on the ground. This solenoid is activated by a squat switch on the left main landing gear, which indicates if there is 'weight on wheels' or 'no weight on wheels'.

The hydraulic system contains a bypass valve, a manifold assembly that houses the control valves for all hydraulic components, and landing gear actuators. The bypass valve opens and closes on command to pressurize and depressurize the system. The landing gear control valve, which is secured to the manifold assembly, receives an electrical signal to either an extend or retract solenoid, which directs fluid through an internal spool to either the extend or retract side of the hydraulic system. When the control valve is not in use, it is spring loaded to a neutral position. Finally, the landing gear actuators, one at each gear, raise and lower the gears. When the gear is retracted, mechanical uplocks hold the gear in place; and when the gear is extended, an internal lock within the actuators hold the gear into the extended position.

In summary, if the pilot wants to retract the landing gear: with weight off of the left landing gear squat switch, the landing gear handle solenoid unlocks, and the pilot can move the handle to the up (retract) position. The pilot then receives a GEAR UNLOCKED indicator light; an electrical signal is sent to close the bypass valve, and to energize the landing gear control valve. The hydraulic fluid pressurizes and routes through the landing gear control valve to the retract side of the hydraulic system. The fluid then flows to the landing gear actuators which raise and mechanically lock the gear. Once all three gears are in the up position the bypass opens to reduce pressure, the control valve is positioned to neutral, and the GEAR UNLOCKED indicator light extinguishes.

To extend the landing gear, the system works identical with the exception that the landing gear control valve routes fluid through the uplocks to release them before going to the extend side of the actuating cylinders. Also, when the landing gear is down and locked the pilot will get three green gear safe lights. ADDITIONAL INFORMATIONOn April 15, 2008 a Cessna 560XL, N613QS was substantially damaged during an uncommanded gear retraction while landing at the Westchester County Airport in White Plains, New York [NTSB accident number NYC08LA162]. The subsequent investigation was not able to determine the cause of the gear collapse. This investigation differed in the fact that a landing gear extend hydraulic line was compromised consistent with overpressure. FLIGHT RECORDERSReview of the cockpit voice recorder (CVR) revealed that the flight crew read through the landing checklists. The recording also captured the sound of the landing gear extending and the flight crew verifying "three green." After touchdown, a thump and another thump was heard followed immediately by the gear warning horn. The airplane rolled down the runway for a few seconds and the recording captured the landing gear collapse, followed by the sound of the airplane sliding. [Additional information can be found in the CVR group chairman's report located in the public docket.] TESTS AND RESEARCHExamination at Ma...