NTSB Factual Report

HISTORY OF FLIGHT

On February 19, 2011, about 0900 central standard time, a Mooney model M20J airplane, N888DF, was substantially damaged when its left main landing gear collapsed during landing at Lewis University Airport (KLOT), Romeoville, Illinois. The pilot and his passenger were not injured. The airplane was registered to DLM Holding Group, LLC, and operated by the private pilot under the provisions of 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 personal flight departed Southwest Michigan Regional Airport (KBEH), 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 any issues and the position indicators showed that the landing gear was in an extended position. He further reduced engine power after turning onto final approach, selected 33-degrees flaps, and the airplane touched down on the runway above stall speed. Shortly after touchdown, during the landing roll, the left wing suddenly dropped and the propeller contacted the runway. The airplane then swerved to the left and struck a runway edge identifier light. The airplane continued to slide across the grass infield, crossing another runway before coming to a rest.

PERSONNEL INFORMATION

According to Federal Aviation Administration (FAA) records, the accident 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.

The pilot reported having accumulated 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. The pilot had flown 30 hours during the last 90 days, 15 hours during the previous 30 days, and about 30 minutes during the previous 24 hours.

The pilot's most recent flight review was completed in a Grumman American model AA-5B airplane on August 28, 2010.

AIRCRAFT INFORMATION

The accident airplane was a 1992 Mooney model M20J airplane, serial number (s/n) 24-3254. The airplane was a low wing, all-metal, single-engine, four-place monoplane. The airplane had a certified maximum takeoff weight of 3,200 pounds. The airplane was equipped for operation under instrument flight rules. A Continental model IO-550-A4B reciprocating engine, s/n 280368-R, powered the airplane. The 300-horsepower engine provided thrust through a Hartzell model PHC-C3YF-2UF/FC7382 constant-speed, three-blade, metal propeller.

The accident airplane was issued a standard airworthiness certificate on February 19, 1992. The registered owner, DLM Holding Group, LLC, purchased the airplane on October 7, 2010. The airframe and engine had accumulated a total service time of 2,119.9 hours and 1,617.1 hours, respectively. The last annual inspection was completed on September 23, 2010, at 2,068.6 hours total airframe service time. No mechanical anomalies were found with the landing gear extension/retraction system during the annual inspection. A postaccident review of the maintenance records found no history of unresolved airworthiness issues.

METEOROLOGICAL INFORMATION

At 0903, the airport's automated surface observing system reported the following weather conditions: wind 030 degrees at 5 knots; clear skies; visibility 10 miles; temperature -01 degrees Celsius; dew point -09 degrees Celsius; altimeter setting 30.39 inches of mercury.

AIRPORT INFORMATION

The Lewis University Airport (KLOT) is located about 2 miles south of Romeoville, Illinois. The airport has two runways: 2/20 (6,500 feet by 100 feet, concrete) and 9/27 (5,696 feet by 75 feet, asphalt). The general airport elevation is listed as 679 feet mean sea level (msl). A medium intensity runway lighting system is installed on runway 2/20. Runway 2 is equipped with a 4-light precision approach path indicator system.

WRECKAGE AND IMPACT INFORMATION

An on-site examination of the airplane revealed substantial damage to the left wing leading edge and left horizontal stabilizer from the impact with the runway edge identifier light. The aft fuselage bulkhead and forward bulkhead of the articulating empennage were crushed upward and were impacted with dirt. The left main landing gear had partially collapsed into its wheel well. The nose and right main landing gear remained fully extended.

Further inspection of the landing gear extension system revealed that both push-pull tubes associated with the extension/retraction of the main landing gear were buckled, consistent with a compression failure. The push-pull tube that facilitated the extension of the left main landing gear was deformed more than the right push-pull tube. The observed damage prevented the left main landing gear from extending into a fully extended/locked position. The damaged push-pull tube was removed and the left landing gear was manually placed into the fully extended (down-and-locked) position. The airplane was then towed to a hangar for additional examination.

On March 21, 2012, an examination of the airplane was conducted by the National Transportation Safety Board (NTSB) Investigator-in-Charge, a FAA Airworthiness Inspector, and an airplane mechanic associated with the repair of the airplane. The observed airframe damage was consistent with the collapse of the left main landing gear during landing roll. With the damaged push-pull tubes removed, the main landing gear were swung into the fully extended position, where the respective down-lock assemblies functioned as designed. The damaged push-pull tubes were straightened and reinstalled in order to verify the rigging of the remainder of the landing gear extension/retraction system. With the exception of the repaired push-pull tubes, there were no additional mechanical or rigging anomalies found with the landing gear extension/retraction system. The landing gear position warning horn, instrument panel indicator lights, and floor-mounted visual/mechanical indicator functioned as designed, providing proper indication of when the landing gear was in the fully extended position.

TEST AND RESEARCH INFORMATION

According to the airframe manufacturer, the main landing gear down-lock assemblies incorporate an over-center design, which isolate side-loading from the remainder of the system under normal landing conditions. However, an excessive side-load to a main landing gear can result in slight damage to the push-pull tubes, which in turn, can result in the landing gear not fully extending into a down-and-locked position on subsequent flights. The same push-pull tubes are in tension during landing gear retraction, and as such, the existence of any previous side-load damage in compression would not inhibit normal landing gear retraction. After review of postaccident photos taken of the damaged push-pull tubes, the airframe manufacturer noted the extent of damage sustained to both push-pull tubes was likely attributable to the final collapse of the landing gear during the accident sequence.

NTSB Probable Cause

The collapse of the left main landing gear during the landing roll for undetermined reasons.