Incident Overview
On June 11, 2009, about 1840 eastern daylight time, a Bombardier CL600-2B19, registration N857AS, operating as Delta Connection flight 5414, landed with the left main landing gear partially extended at Hartsfield Jackson Atlanta International Airport. The airplane was operated by Atlantic Southeast Airlines (ASA). The flight crew consisted of an airline transport-rated captain and a commercial-rated first officer; one flight attendant and 19 passengers were aboard. No injuries occurred. The airplane received minor damage. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed for the 14 CFR Part 121 flight. The flight originated at Columbus Metropolitan Airport, Georgia, at 1725.
Flight Crew Actions
While configuring for landing, the flight crew observed a landing gear disagree message and the left main gear indicated it was not down and locked. The Quick Reference Handbook (QRH) procedures were completed, including cycling the landing gear handle once and using the alternate gear extension (manual release) system. The left main gear continued to indicate not down and locked. A flight crew on a parallel approach confirmed that the left main gear was not extended. The captain declared an emergency and landed on runway 27R. The captain used right aileron to keep the left wing up as long as possible. The left wing eventually dropped to the runway, and the airplane stopped at the left runway edge. The captain commanded an evacuation; all occupants exited via the left and right forward doors.
Aircraft and Crew Information
The airplane, a Bombardier CL-600-2B19, serial number 7411, was equipped with two General Electric CF34-3B2 engines. It had 53 seats and a maximum gross weight of 53,000 pounds. The last continuous airworthiness inspection was on June 1, 2009; total time was 22,266 hours. The captain reported 4,200 flight hours, with 2,101 hours in type. The first officer reported 1,700 flight hours, with 929 hours in type.
Maintenance History
On June 8, 2009, a flight crew reported a left main gear disagree message on landing that cleared itself. Maintenance replaced the left main landing gear side stay actuator and the left main landing gear proximity downlock sensor. On June 9, 2009, another crew reported the left main gear indicated “up” with the gear lever down; the anomaly cleared after cycling the gear three times. Maintenance tightened the number 2 main landing gear downlock proximity backshell. The system checked satisfactorily and operated without further anomalies until the incident flight.
Post-Incident Examination
Runway scars and video showed the airplane touched down about 3,600 feet down the 11,890-foot runway, near taxiway Juliet. It traveled about 3,000 feet and came to rest with the nose gear and left wing tip on the grass at the left runway edge, near taxiway Sierra. Examination revealed the left main landing gear partially extended; the outboard tire was visible, the inboard tire inside the well. Scraping damage was found on left wing flaps, flap fairings, flap actuation arms, and the left wing tip. When the airplane was lifted, the left main gear remained stationary; no physical obstructions were noted. A hydraulic line to the landing gear actuator was disconnected, and the gear lowered into the extended position. The gear was then pinned and the airplane towed to an ASA maintenance hangar. Between June 12 and 18, 2009, all components of the left main landing gear system were examined; no abnormal conditions were found that would prevent extension. Functional checks, including multiple gear cycles, could not duplicate the incident; the gear extended and retracted normally.
Component Tests and Findings
Numerous components were removed and examined at manufacturers' facilities under FAA or Transport Canada oversight. The engine-driven hydraulic pump passed all tests except minor shaft seal leakage. Three AC electric motorpumps were tested; one passed all tests, two failed compensator pressure tests, and one had a bearing installed upside down. Left main landing gear components (main gear assembly, side brace, auxiliary actuator, uplock assembly) had no defects; oil samples showed high water content. The left main landing gear door and hinge attachment exhibited mechanical damage on hinges and pins. The main gear selector valve initially hesitated at low pressure, which was attributed to trapped air; a fractured spring guide was found but did not prevent function. The by-pass and runaround valve passed all tests except internal leakage and high pressure drop; it was noted that if it malfunctioned, both main gear actuators would be affected. Other valves (manual selector, high watt jet, check valve, priority valve, relief valve, miniature restrictor check valve) showed various anomalies: one had insect remains, one had loose safety wire, one failed internal leakage tests. Analysis of hydraulic fluid from systems 2 and 3 after the incident revealed particle contamination exceeding limits, particularly in system 3 (which powers gear extension). After the airplane returned to service, all three hydraulic systems were re-tested and found satisfactory. The investigation did not identify a definitive single cause for the partial gear extension.