Atlanta, GA, USA
N857AS
BOMBARDIER INC CL-600-2B1
While configuring the airplane for landing, the left main landing gear light indicated that it was not down and locked. The flight crew accomplished the landing gear abnormal procedures, including recycling the landing gear once. The left main gear continued to indicate unsafe, and the captain landed the airplane. After touching down on the right main and the nose gear, 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 came to a stop at the runway’s left edge. During recovery of the airplane, the left main gear was partially extended, and no physical obstructions were observed that would prevent the gear from extending. Loosening a hydraulic line to the left main gear actuator allowed the gear to fall into the extended and locked position. The airplane was examined and the landing gear was cycled numerous times using the normal and alternate extension methods. The examination failed to duplicate the incident conditions; the gear extended and retracted normally without hesitation or binding. All major components of the main landing gear system, including the left main landing gear, left gear door, hydraulic pumps, valves and actuators were examined at the manufacturers’ facilities. Although some minor anomalies were noted, no evidence was found to explain the failure of the gear to extend. Analysis of fluid from the numbers 2 and 3 hydraulic systems revealed that the fluid exceeded the maximum particle contamination limits. The system 3 sample also contained metallic particles. Hydraulic system 3 powers gear extension and retraction. After the incident, the operator enhanced its maintenance procedures for testing hydraulic fluid to include contamination. The operator also added verbiage to its pilot procedures to further explain that, in certain cases, it is appropriate to make several attempts at normal gear extension and provided more explanation and guidance regarding the use of the back-up (freefall) system.
HISTORY OF FLIGHT On June 11, 2009, about 1840 eastern daylight time, a Bombardier CL600-2B19, N857AS, operating as Delta Connection flight 5414, landed with the left main landing gear partially extended at Hartsfield Jackson Atlanta International Airport, Atlanta, Georgia. The airplane was operated by Atlantic Southeast Airlines (ASA). The airline transport-rated captain, commercial-rated first officer, one flight attendant, and 19 passengers were not injured. The airplane received minor damage. Visual meteorological conditions prevailed at the time, and an instrument flight rules flight plan was filed for the 14 Code of Federal Regulations Part 121 flight. The flight originated at Columbus Metropolitan Airport (CSG), Columbus, Georgia at 1725. While configuring the airplane for landing, the flight crew observed a landing gear disagree message, and the left main gear indicated that it was not down and locked. The Quick Reference Handbook (QRH) procedures were accomplished, which included cycling the landing gear handle once and the use of the alternate gear extension (manual release) system. The left main gear continued to indicate that it was 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 the airplane 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 came to a stop at the runway’s left edge. The captain commanded an evacuation and all passengers departed the airplane using the left and right forward doors. PERSONNEL INFORMATION The captain was a certificated airline transport pilot with multi-engine and instrument airplane ratings. He held a first class medical certificate that was issued on March 12, 2009. He reported a total of 4,200 flight hours with 2,101 hours in the Bombardier CL-600-2B19. The first officer was a certificated commercial pilot with multi-engine and instrument airplane ratings. He held a first class medical certificate that was issued on August 12, 2008. He reported a total of 1,700 flight hours with 929 hours in the Bombardier CL-600-2B19. AIRCRAFT INFORMATION The airplane was a Bombardier CL-600-2B19, serial number 7411, equipped with two General Electric CF34-3B2 engines. The airplane seated 53 and had a maximum gross weight of 53,000 pounds. The last continuous airworthiness inspection was conducted on June 1, 2009. The airplane had a total time of 22,266 hours. A review of the airplane maintenance records revealed that on June 8, 2009, an anomaly with the left main landing gear was reported by a flight crew. A left main gear disagree message was noted on landing and subsequently cleared itself. The corrective action was the removal and replacement of the left main landing gear side stay actuator. Also, the left main landing gear proximity downlock sensor was removed and replaced. On June 9, 2009, a flight crew reported the left main landing gear indicated “up” with the gear lever down. The anomaly remained until the gear was recycled 3 times. The maintenance corrective action was to tighten the number 2 main landing gear downlock proximity backshell. The system checked satisfactorily and the airplane operated without further landing gear anomalies until the incident flight. METEOROLOGICAL INFORMATION The 1852 weather observation for ATL included the following: few clouds at 3,500 feet, broken clouds at 25,000 feet, surface winds from 280 degrees at 7 knots, 10 statute miles visibility, temperature 28 degrees Celsius, dew point 21 degrees Celsius, and an altimeter setting of 29.88 inches of mercury. FLIGHT RECORDERS The cockpit voice recorder (CVR) was sent to the National Transportation Safety Board’s (NTSB) Vehicle Recorder Division Audio Laboratory for download. The CVR recorded 30 minutes of cockpit voice communications. A summary of key events recorded on the CVR follows: At 18:10:30 - Start of recording. At 18:11:48 - Captain briefs passengers on landing gear situation. At 18:12:53 - Captain attempts to depressurize the aircraft. At 18:14:18 - Captain calls for flaps 30 and to slow to 160. At 18:14:54 – Captain confirms zero pressurization, closes left and right tenth stage bleed valves, and turns emergency lights on in accordance with the Landing Gear Up/Unsafe Landing Procedure checklist. At 18:15:17 – Captain briefs flight attendant on brace procedure. At 18:15:39 – ASA5414 is cleared for visual approach to runway 27R. At 18:15:49 – Captain takes over the controls from the first officer. At 18:16:14 - AirTran flight informs tower that ASA5414’s main gear is not down. At 18:17:48 – Tower clarifies that the left main gear is not down. At 18:18:01 - Captain decides to go around and make another approach. At 18:20:48 – Captain talks with maintenance again and is told maintenance cannot offer any further advice than what is in the QRH. At 18:23:29 – Captain notes they are down to 3,300 pounds of fuel. At 18:25:02 – Captain retraces the Landing Gear Up/Unsafe Landing Procedure checklist. At 18:25:43 – Captain requests turn back toward the airport. At 18:27:51 – Captain rejects ATC’s suggestion to land on runway 28 due to surrounding obstructions. At 18:31:16 – Captain briefs 132 knots as reference speed. At 18:32:33 – ASA5414 is cleared for the ILS 27R approach and is switched to tower. At 18:33:58 – Tower clears ASA5414 to land runway 27R. At 18:34:24 – Crew briefs remaining items on Landing Gear Up/Unsafe Landing Procedure checklist. At 18:34:58 – Captain confirms positioning of rescue equipment. At 18:36:08 – Captain calls for flaps 45 and landing checklist. At 18:39:12 – First officer calls, “brace brace brace,” over PA system. At 18:39:14 – Flight attendant shouts, “heads down stay down,” until 18:40:43. At 18:40:00 – Sound of touchdown. At 18:40:14 – Sound of short tone. At 18:40:28 – Sound of engine rpm decrease. At 18:40:43 – Captain calls evacuate over PA system and flight attendant begins evacuation process. At 18:40:59 - End of recording. The flight data recorder (FDR) was sent to the NTSB Vehicle Recorder Division for download. The data indicated that, consistent with the initial attempt to lower the gear for landing, the left gear uplock parameter transitioned from “up and locked” to “not up and locked.” Concurrently, the left gear downlock parameter remained “not down and locked,” while the right and nose gear transitioned to “down and locked.” The data then showed the recycling of the landing gear. All landing gear momentarily transitioned to the “up and locked” indication, followed by the right and nose gear transitioning to the “down and locked” position while the left gear remained “not down and locked.” The landing gear remained in this configuration through the landing. WRECKAGE AND IMPACT INFORMATION Runway ground scars and airport surveillance video showed the airplane touching down approximately 3,600 feet down the 11,890-foot long runway, adjacent to taxiway Juliet. The airplane traveled approximately 3,000 feet and came to rest with the nose gear and left wing tip in the grass on the left edge of the runway, adjacent to taxiway Sierra. Examination of the airplane by NTSB prior to recovery revealed that the left main landing gear was partially extended from the wheel well, with the outboard tire visible and the inboard tire inside the well. Scraping damage was noted on the left wing flaps, flap fairings, flap actuation arms, and the left wing tip. A recovery team from Delta Air Lines assisted in removing the airplane from the runway. As the airplane was lifted with air bags, the left main gear remained stationary in the partially extended position. The gear could not be lowered by manually pushing on the gear, and there were no physical obstructions 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 was towed to the ASA maintenance hangar for further evaluation. On June 12 through 18, 2009, an examination of the landing gear system was accomplished at the ASA maintenance facility in Atlanta, Georgia. All components of the left main landing gear system were examined for deformation, discoloration, wear, and excessive play. No abnormal conditions were noted that would result in a failure of the landing gear to extend. Functional checks of the normal and manual gear extension and retraction system were accomplished, including multiple gear up/down cycles. The examination failed to duplicate the incident conditions; the gear extended and retracted normally without hesitation or binding. TESTS AND RESEARCH Following the functional check of the landing gear, numerous components were removed for examination at their manufacturers’ facilities. Oversight of the examinations was provided by Federal Aviation Administration or Transport Canada inspectors. The results of the examinations are summarized below. On July 9, 2009, the engine-driven hydraulic pump (part number (P/N) 887055, serial number (S/N) MX600003A) was examined at the Eaton Aerospace facility, Jackson, Mississippi. A visual inspection of the unit revealed no anomalies. There was some fluid staining on the mounting adapter. The pump was tested per the acceptance test procedure and passed all test requirements with the exception of minor shaft seal leakage. After the functional test, the pump was disassembled and exhibited normal internal wear. On July 9, 2009, three alternating current (AC) electric motorpumps (P/N 848847; S/N MX625410, P/N 848847; S/N MX625415, and P/N 848847; S/N MX640163) were examined at the Eaton Aerospace facility. The MX625410 pump passed all acceptance test procedure test requirements. Disassembly of the pump revealed minor internal wear. The MX625415 pump was tested to the acceptance test procedure and passed all requirements except for compensator pressure. The MX640163 pump was tested to the acceptance test procedure and passed all requirements except for compensator pressure. Disassembly of the pump revealed the front motor bearing, P/N 887290, was installed upside down. There was minor wear on the bearing due to the incorrect installation. On August 19 through 20, 2009, the following left main landing gear components were examined at the Messier-Dowty facility, Ajax, Ontario, Canada: the main landing gear assembly (P/N 17002-111, S/N DCL364/99), main landing gear side brace (P/N 17008-113, S/N 00962), auxiliary actuator (P/N 17319-105, S/N DH0432/99), and the uplock assembly (P/N 17051-101, S/N NGL0582/99). No defects or damage were observed on the landing gear assemblies and all functional tests were acceptable. Oil sampled from the components showed high water content. On September 18, 2009, the left main landing gear door and hinge attachment (P/N 601R31178-169 and 601R31599-11, S/N P43895) were examined at the Bombardier facility, Mirabel, Quebec. X-ray, visual examination, and dimensional checks were performed. The forward and aft hinges and hinge pins exhibited mechanical damage in several areas. Some deformation and shearing was observed on some of the metal washers, and the Teflon® washers showed compression damage. On September 22 through 23, 2009, the main gear selector valve (P/N 750005000, S/N 0638) was examined at the Tactair Fluid Controls facility, Liverpool, New York. The acceptance test procedure was performed with all tests passed within acceptable limits with the exception of the proof pressure test and the pressure drop test to the return port. During the pressure drop test, 750 psig was supplied to the pressure port (500 psig was required for the test). There was an initial hesitation in the unit when solenoid “A” was energized. This was indicated by no pressure reading to the C2 port. The C2 port on the valve supplies pressure for both landing gear actuators. The pressure was increased to 1,200 psig and the valve then functioned normally. The valve continued to function normally when the supplied pressure was subsequently lowered to 500 psig. Tactair reported that the unit was drained of all fluid prior to testing and trapped air was not bled from the unit prior to the test, which is called for in the proof pressure and external leakage tests. Tactair personnel stated in their Engineering Investigation Report that, “With the potential for air to be entrapped in the valve, that could explain the hesitation the valve displayed at the lower pressure as trying to overcome the pressure buildup from the air. At the higher pressure it was believed that the hydraulic pressure was strong enough to push the entrapped air out of the valve causing the valve to behave properly from there on.” The main gear selector valve was then disassembled. Upon removal of the end cap under solenoid “B,” the spring guide was fractured around the rim portion. The function of the spring guide is to be the point of contact with the spring and spool. The spring pushes the spool back to the neutral position when either solenoid becomes de-energized. According to Tactair, “approximately 41 percent of the surface area the spring would make contact with was still intact allowing the spring guide to still be able to perform its function.” The fractured spring guide was re-installed in the unit and re-tested. The unit was cycled 140 times at supply pressures ranging from 375 to 3,000 psig; no subsequent anomalies were observed. On September 22 through 23, 2009, the by-pass and runaround valve (P/N 750004000-003, S/N 677A) was examined at the Tactair Fluid Controls facility. The acceptance test procedure was accomplished and all tests passed within acceptable limits except for the internal leakage and pressure drop tests. The internal leakage test revealed excessive leakage across the up side to the down side of the valve. The pressure drop tests showed a high pressure drop through the down side of the valve. According to Tactair, “If this valve malfunctions, both main gear actuators should not function, not just one actuator.” Disassembly and visual inspection of the interior of the valve showed no anomalies. On September 22 through 23, 2009, the manual selector landing gear valve (P/N 400017000, S/N 646) was examined at the Tactair Fluid Controls facility. Functional testing of this component revealed no anomalies. On September 28, 2009, a high watt jet (P/N JEHX0501400A) was examined at The Lee Company facility, Westbrook, Connecticut. A visual inspection of the unit revealed no anomalies. The high watt jet, which is a precision micro-hydraulic component, tested and flowed within the limits prescribed by The Lee Company. On November 25, 2009, a check valve (P/N 1C3308, S/N 0071) was examined at the Crissair, Inc. facility, Palmdale, California. Visual inspection revealed that the unit appeared to be dirty, and the remains of an insect could be seen in the unit without magnification. The check valve was functionally tested and successfully passed the requirements of the manufacturer’s acceptance test procedure. Internal examination of the unit revealed no mechanical anomalies. On February 23, 2010, a priority valve (P/N 4619-3, S/N 925) was examined at the PneuDraulics, Inc. facility, Rancho Cucamonga, California. Visual inspection of the valve revealed normal installation tool marks and the safety wire was loose. The unit was functionally tested as received and then with established torque. The unit passed all tests in accordance with the manufacturer’s acceptance testing procedure requirements. On March 4, 2010, a relief valve (P/N P44-771, S/N 91021131) was examined at the Circor Aerospace facility, Corona, California. The valve was manufactured in October, 1999 by Circle Seal Controls. The valve was fitted to a test bench to perform the manufacturer’s acceptance test procedure. The valve tested within acceptable limits during three of four tests (“Proof,” “Crack Pressure” and “Flow Rat
The failure of the left main landing gear to extend due to high levels of particulate contamination in the hydraulic fluid.
Source: NTSB Aviation Accident Database
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