History of Flight
On February 19, 2011, at approximately 0900 central standard time, a Mooney model M20J airplane, registration N888DF, experienced a collapse of its left main landing gear during landing at Lewis University Airport (KLOT) in Romeoville, Illinois. The airplane was substantially damaged. The pilot and his passenger were not injured. The airplane was registered to DLM Holding Group, LLC, and operated by a private pilot under 14 Code of Federal Regulations Part 91. Day visual meteorological conditions prevailed for the cross-country flight, which was operated without a flight plan. The flight departed Southwest Michigan Regional Airport (KBEH) in Benton Harbor, Michigan, at 0930 eastern standard time.
The pilot reported that while on the downwind leg for runway 2, he reduced engine power, lowered the landing gear, and selected 15 degrees of flaps. He stated that the landing gear extended without issues and the position indicators showed the gear in an extended position. He further reduced power after turning onto final approach, selected 33 degrees of flaps, and the airplane touched down above stall speed. Shortly after touchdown during the landing roll, the left wing suddenly dropped and the propeller contacted the runway. The airplane swerved left and struck a runway edge identifier light, then slid across the grass infield, crossing another runway before coming to rest.
Personnel Information
According to Federal Aviation Administration (FAA) records, the pilot, age 29, held a private pilot certificate originally issued on May 22, 2008, with an airplane single land rating. His last aviation medical examination was completed on March 3, 2008, when he was issued a third-class medical certificate with no restrictions or limitations. He reported 183 hours total flight time, of which 30 hours were in the accident airplane make/model. He had accumulated 17 hours at night and 6 hours in simulated instrument conditions. In the last 90 days he had flown 30 hours, in the previous 30 days 15 hours, and about 30 minutes in the previous 24 hours. His most recent flight review was completed in a Grumman American AA-5B on August 28, 2010.
Aircraft Information
The accident airplane was a 1992 Mooney M20J, serial number 24-3254. It was a low-wing, all-metal, single-engine, four-place monoplane with a certified maximum takeoff weight of 3,200 pounds. It was equipped for instrument flight rules. The engine was a Continental IO-550-A4B reciprocating engine, serial number 280368-R, producing 300 horsepower through a Hartzell PHC-C3YF-2UF/FC7382 constant-speed, three-blade, metal propeller. The airplane was issued a standard airworthiness certificate on February 19, 1992. DLM Holding Group, LLC, purchased the airplane on October 7, 2010. The airframe had 2,119.9 hours total service time, and the engine had 1,617.1 hours. The last annual inspection was completed on September 23, 2010, at 2,068.6 hours airframe time, with no mechanical anomalies found in the landing gear extension/retraction system. Postaccident review of maintenance records found no history of unresolved airworthiness issues.
Meteorological Information
At 0903, the airport's automated surface observing system reported wind from 030 degrees at 5 knots, clear skies, visibility 10 miles, temperature -01 degrees Celsius, dew point -09 degrees Celsius, and altimeter setting 30.39 inches of mercury.
Airport Information
Lewis University Airport, located about 2 miles south of Romeoville, Illinois, has two runways: 2/20 (6,500 feet by 100 feet, concrete) and 9/27 (5,696 feet by 75 feet, asphalt). The airport elevation is 679 feet mean sea level. Runway 2/20 is equipped with a medium intensity runway lighting system, and runway 2 has a 4-light precision approach path indicator system.
Wreckage and Examination
An on-site examination revealed substantial damage to the left wing leading edge and left horizontal stabilizer from impact with the runway edge identifier light. The aft fuselage bulkhead and forward bulkhead of the articulating empennage were crushed upward and impacted with dirt. The left main landing gear had partially collapsed into its wheel well, while the nose and right main landing gear remained fully extended.
Inspection of the landing gear extension system showed that both push-pull tubes associated with extension/retraction of the main landing gear were buckled, consistent with compression failure. The left push-pull tube was deformed more than the right. The damage prevented the left main landing gear from extending fully into a locked position. The damaged push-pull tube was removed, and the left gear was manually placed into the fully extended (down-and-locked) position. The airplane was towed to a hangar for further examination.
On March 21, 2012, an examination by the National Transportation Safety Board, an FAA Airworthiness Inspector, and an airplane mechanic confirmed that the airframe damage was consistent with collapse of the left main landing gear during landing roll. With the damaged tubes removed, the main landing gear were swung into the fully extended position, where the down-lock assemblies functioned as designed. The damaged tubes were straightened and reinstalled to verify rigging; no additional mechanical or rigging anomalies were found. The landing gear position warning horn, instrument panel indicator lights, and floor-mounted visual/mechanical indicator functioned properly, providing correct indication when the gear was fully extended.
According to the airframe manufacturer, the main landing gear down-lock assemblies incorporate an over-center design that isolates side-loading under normal landing conditions. However, excessive side-load to a main landing gear can result in slight damage to the push-pull tubes, which can prevent full extension into a down-and-locked position on subsequent flights. During retraction, the same push-pull tubes are in tension, so prior compression damage would not inhibit normal retraction. Review of postaccident photos of the damaged push-pull tubes led the manufacturer to note that the extent of damage was likely attributable to the final collapse of the landing gear during the accident sequence.