ATL02FA113

A Bombardier CL6002B-19, N849AS, operated by Atlantic Southeast Airlines, Inc., as flight 4509, experienced a left main landing gear failure during landing on runway 26R, at the Atlanta Hartsfield International Airport, in Atlanta, Georgia. According to the flight crew, and confirmed by the FDR, the approach to landing was uneventful. Upon landing the pilot deployed the thrust reversers and the left main landing gear collapsed. Fracture of the main fitting for the left main landing gear was caused by a fatigue crack that emanated from multiple origins at the external surface of the wall at the shock strut radius run out area. No evidence of material anomalies, such as corrosion or gouge damage, was found at the fatigue origin area. Because the stresses leading to the fatigue crack of the main fitting have not clearly been identified, the root cause of the fatigue cracking has not been determined. During the investigation, Atlantic Southeast Airlines did a Fleet Wide inspection of all their Bombardier Inc., Model CL600-2B19 aircraft landing gear assemblies, which included visual and eddy current inspections. Their inspections found no additional cracked landing gear. Additionally, Transport Canada issued a revised AD, which eliminated the escalation of the eddy current inspection intervals as allowed in their previous AD. Also, the FAA issued an NPRM in response to Transport Canada AD, which requires repetitive detailed visual and eddy current inspection of the main landing gear main fitting. The NPRM if adopted would produce another AD that is applicable to certain Bombardier Model CL600-2B19 (Regional Jet Series 100 & 440) airplanes. The proposal would require repetitive detailed and eddy current inspections on the main fittings of the main landing gears (MLG) to detect discrepancies, and related investigative/corrective actions if necessary. The proposal also requires servicing of the shock strut of the MLGs; inspection the shock strut of the MLGs for nitrogen pressure, visible chrome dimension, and oil leakage; and servicing any discrepant strut. Transport Canada has also accepted Messier-Dowty’s redesign of the main fitting, on condition that the testing of the new design would be completed successfully. The testing is scheduled to commence in July 2004. Once the testing is completed Transport Canada will mandate the installation of the new design of the main fitting as the terminating action for the AD's.

History of flight

On June 2, 2002, at 2200 eastern daylight time, a Bombardier CL600-2B19, N849AS, registered to State Street Bank and Trust Company, and operated by Atlantic Southeast Airlines, Inc., as flight 4509, had the left main landing gear collapsed during landing on runway 26R, at the Atlanta Hartsfield International Airport, in Atlanta, Georgia. The airplane was being operated under the provisions of Title 14 CFR Part 121, and instrument flight rules. Visual meteorological conditions prevailed and an instrument rules flight plan was filed for the scheduled domestic passenger flight. The air transport pilot, first officer, flight attendant, and 50 passengers were not injured, and the airplane sustained substantial damage. The flight originated in Baltimore, Maryland, on June 2, 2002, at 1940.

The airplane landed on runway 26R at 2200. The airplane made an uneventful touchdown. During the landing roll at approximately 1000 feet down the runway at 110 knots and after the thrust reversers were deployed, the left landing gear collapsed. The left main wheel assembly remained attached to the side stay and was stuck between the fuselage and the inner edge of the inner wing flap. The flaps remained in the down position at 45-degrees and the flaps along with the flap actuator assemblies helped to support the wing when the airplane slid 4,000 feet down the center of the runway. The Captain was able to keep the airplane on the runway using rudder control, thrust reversers, right brakes, and the nose wheel steering system.

According to the flight crew, the approach to landing was uneventful. Upon landing the pilot deployed the thrust reversers and felt the airplane tilt to the left. At first he believed that he had a flat tire. However, as the aircraft continued down the runway he realized that the left main landing gear had collapsed. As the airplane began slowing the Captain notified the tower that he had a problem and ordered the first officer to contact the flight attendant to prepare the cabin for an emergency evacuation out the left entry door. After the airplane slid to a stop, the evacuation began. According to the flight attendant the evacuation progressed smoothly, with 40 passengers evacuating through the left main entry door and ten passengers evacuating through the right over wing exit.

Personnel information

A review of information on file with the Federal Aviation Administration (FAA) Airman's Certification Division, Oklahoma City, Oklahoma, revealed that the Captain held a commercial pilot certificate in airplane single engine land, and an Airline Transport Pilot certificate in Multi-engine land airplanes, with type ratings in the ATR-42, ATR-72, CL-65, and the EMB-120. A review of records on file with the FAA Aero Medical Records revealed the pilot held a first-class medical certificate issued on April 16, 2002, with a restriction that he must have available glasses for near vision. The pilot reported on his application for the medical certificate that he had accumulated 15,450 total flight hours.

A review of information on file with FAA Airman's Certification Division, Oklahoma City, Oklahoma, revealed that the First Officer held a private pilot certificate in airplane single engine land, commercial pilot certificate in rotorcraft-helicopter, and airline transport pilot certificate in airplane multi-engine land airplanes, with no type ratings listed. A review of records on file with the FAA Aero Medical Records revealed the pilot held a first class medical certificate issued on March 21, 2002, with no restrictions. The First Officer reported on his application for the medical certificate that he had accumulated 3,000 total flight hours.

Aircraft information

The Canadair Regional Jet (CRJ) CL600-2B19, Serial Number 7347, N849AS, was maintained by Atlantic Southeast Airlines, Inc., on a FAA approved continuous airworthiness inspection program. The airplane's most recent maintenance inspection was conducted on May 27, 2002. At the time of the accident, the airplane had accumulated a total time of 6,831 hours, and 5,584 cycles. Further review of the maintenance records found that the left and right main landing gears had been eddy current inspected 384 cycles prior to the accident. Bombardier Alert Service Bulletin A601R-32-079D Dated December 1, 2000, and Airworthiness Directive (AD) 2001-22-09, "Main Landing Gear - Repetitive Eddy Current Inspection of Left and Right MLG Fittings" requires that an eddy current inspection of the main landing gear fittings be repeated at every subsequent 500-flight cycles. The airplane's landing gear area had been inspected eight times prior to the accident.

Meteorological information

The nearest weather reporting facility at the time of the accident was Hartsfield International Airport, in Atlanta, Georgia. The 2153 surface weather observation was: Sky Clear, visibility 8 statute miles, temperature 25-degrees Celsius, dew point 21-degrees Celsius, wind 340-degrees at 7 knots, and altimeter 29.02. Visual meteorological conditions prevailed at the time of the accident.

Wreckage and impact information

The airplane came to rest in an overrun area near taxiway B3. Emergency response vehicles arrived at the accident site and there were no signs of a fuel leak and there was no fire. The following morning on June 3, 2002 the airplane was towed from the runway by the use of a tug truck, flat bed trailers and air bags to a Delta maintenance hangar on the airport for further examination.

Examination of the left trunnion main fitting found a three-inch area of discolored material, which had penetrated through the cross section of the main fitting. The area surrounding the fracture appeared to have sheared off rapidly, showing signs of overload. The left main landing gear assembly was removed and sent to the NTSB Materials Laboratory in Washington, DC for further examination.

Examination of the left wing found the inner and outer flaps ground down as a result of the collapsed left main gear and dragging on the runway. There was leading edge damage and a detached runway light lodged in the leading edge of the left inner flap. The left wing tip had a two foot by one foot oval shape grind pattern on the under side of the wing near the wing tip. There was damage to the inboard inner flap area where the left main gear had become lodged after the collapse. The collapsed wheel assembly also damaged the electric hydraulic pump located in the wheel well. The wheel assembly remained attached to the airplane by the side stay. The level of Nitrogen gas and hydraulic fluid from the left landing gear strut could not be measured due to damage. The left main tires showed excessive wear and one tire was completely cut in a circular pattern around the tire rim.

Examination of the right wing and main landing gear showed little damage as a result of the accident. However, the right main landing gear assembly was removed and shipped to the NTSB Materials Laboratory for further examination. The nose gear showed no signs of damage. However, the left nose wheel tire showed excessive wear that indicated the airplane was leaning heavily on the left side as it slid down the runway.

The airplane's Flight Data Recorder and Cockpit Voice Recorder were recovered from the airplane and sent to the NTSB Recorder Laboratory in Washington, DC for examination. Examination of the FDR found the accident landing to be within normal limits, and the CVR found nothing noteworthy on the recording.

The airplane had 1,600 pounds of fuel remaining in the left fuel tank and 1, 710 pounds of fuel remaining in the right fuel tank. There was no fuel leaks observed.

Special tests and research information

Metalurgical examination

Visual and bench binocular microscope examination of the upper fracture face of the left main landing gear revealed a discolored thumbnail fracture area typical of a preexisting