DCA06FA058

The approach and landing were stabilized and within specified limits. Recorded data indicates that the loads experienced by the landing gear at touchdown were within the certification limits for an intact landing gear without any pre-existing cracks or flaws. The weather and runway conditions did not affect the landing. The application of braking by the accident crew, and the overall effect of the carbon brake modification did not initiate or contribute to the landing gear fracture. Post-accident modifications to the MD-10 carbon brake system were implemented due to investigative findings for the purposes of braking effectiveness and reliability. Post accident emergency response by the flight crew and ARFF was timely and correct.

The left main landing gear (LMLG) outer cylinder on the accident airplane had been operated about 8 ½ years since its last overhaul where stray nickel plating likely was introduced in the air filler valve hole. Nickel plating is a permissible procedure for maintaining the tolerances of the inner diameter of the outer gear cylinder, however the plating is not allowed in the air filler valve bore hole. Literature and test research revealed that a nickel plating thickness of 0.008" results in a stress factor increase of 35%. At some point in the life of the LMLG, there was a load event that compressively yielded the material in the vicinity of the air filler valve hole causing a residual tension stress. During normal operations the stress levels in the air filler valve hole were likely within the design envelope, but the addition of the residual stress and the stress intensity factor due to the nickel increased these to a level high enough to initiate and grow a fatigue crack on each side of the air filler valve hole. The stresses at the air filler valve hole were examined via development of a Finite Element Model (FEM) which was validated with data gathered from an instrumented in-service Fedex MD-10 airplane. The in-service data and FEM showed that for all of the conditions, the stress in the air filler valve hole was much higher than anticipated in the design of the outer cylinder. Fatigue analysis of the in-service findings and using the nickel plating factor resulted in a significantly reduced fatigue life of the gear cylinder compared with the certification limits. During the accident landing the spring back loads on the LMLG were sufficient to produce a stress level in the air filler valve hole that exceeded the residual strength of the material with the fatigue cracks present.

History of flight

On July 28, 2006, about 1125 central daylight time, FedEx Express (FedEx) flight 630, a Boeing MD-10-10F (MD-10), N391FE, experienced a left main landing gear failure immediately after landing at Memphis International Airport (MEM), Memphis, Tennessee. The left main landing gear (LMLG) collapsed after touchdown on runway 18R, and the airplane came to rest on the left side of the runway. After the gear collapsed, a fire developed on the left side of the airplane. The two flight crewmembers received minor injuries during the evacuation, and one nonrevenue FedEx pilot was not injured. The postcrash fire substantially damaged the airplane’s left wing and portions of the left side of the fuselage. Flight 630 departed from Seattle-Tacoma International Airport (SEA), Seattle, Washington, and was operating under the provisions of 14 Code of Federal Regulations (CFR) Part 121 on an instrument flight rules flight plan.

The crew stated that the takeoff and departure from SEA were normal with very little traffic that day, there were no issues with the airplane en route from SEA to MEM and there were no weather deviations. Approaching MEM, air traffic control (ATC) vectored the flight onto the runway 18R final approach course. The flight was then cleared for a visual approach to runway 18R. The visual approach was initially flown with the autopilot engaged and coupled to the instrument landing system (ILS). The airplane was established on the final approach course about 9 miles north of the airport. About 1,600 feet altitude, the airplane was configured for a flaps 35 landing and the approach was stable passing through 1,000 feet. The crew reported that gusty winds at altitude reduced to near calm, or a light tailwind, by this point.

The crew reported the final approach segment was smooth, and the first officer disengaged the autopilot at approximately 400 feet and manually flew the airplane appropriate to conditions. He noted that some crosswind correction was still required at approximately 50 feet, when the electronic altitude callout cadence began. He stated that the flare and touchdown were normal, with crosswind correction. The airplane landed with 122 knots airspeed and a descent rate of approximately 2 to 3 feet per second (fps). A Safety Board performance study concluded that the touchdown was within design limits for the main landing gear (see Tests and Research).

Approximately seven seconds after touchdown, FDR data and performance calculations indicated that the LMLG began to fail (collapse), which was coincident with the location of the ground scar marks on the runway. The first officer reported that while actuating the thrust reversers, he started to apply brakes and immediately experienced "a severe and violent shudder" much more violent than he had ever experienced. He released the brakes, and the shuddering continued, but less violently, and he then reapplied brakes and the shuddering increased again. At that time, the airplane rolled and yawed to the left. The first officer held full right yoke and full right rudder in an effort to counter the turning and listing. The captain tried to assist by using the tiller to keep the airplane on the runway. The airplane continued yawing and sliding to the left and came to rest close to taxiway M4.

Prior to the airplane stopping, a fire ignited beneath the left engine nacelle and spread to the inner portion of the left wing. The captain activated the left engine fire extinguisher and began shutting down the airplane. Airport fire crews responded almost immediately, and the fire was extinguished prior to spreading further.

The crew and nonrevenue pilot evacuated the airplane via the R1 door and slide. The crew reported that due to the leftward list of the airplane, the slide was at a steeper angle than normal.

Injuries to persons

The crew reported minor abrasions and sprains from the evacuation. No serious injuries were reported.

Damage to airplane

The airplane came to rest on the left side of Runway 18R at the M4 taxiway, about 6,050 feet from the approach end of the runway. The LMLG collapsed during the accident sequence and was folded aft with the strut in a horizontal position and the truck beam in a vertical position. The truck beam positioning actuator was fractured at the truck beam and the axles were in the normal positions. The aft tires of the LMLG impacted the left inboard flap, damaging it and deforming it upwards. The left side of the airplane was resting on the left nacelle, the left wing outboard flap hinge fittings, and the left wingtip while the right side was resting on the right main landing gear (RMLG) inboard tires. The left engine aft mount was fractured and the left engine was canted upwards about the forward mounts. The nose landing gear (NLG) was intact and turned to the right about 20 degrees and was resting on only the left tire. No tread remained on the left NLG tire, some of the reinforcing plies were showing, and there was cross-wise scuffing. The right NLG tire appeared essentially normal. The RMLG was intact with the two inboard tires contacting the ground. The RMLG forward, inboard tire tread was considerably worn while the other three appeared essentially normal. The rest of the airplane was undamaged. The flaps and slats were in the deployed position and the left engine thrust reverser was in the deployed position. The right engine thrust reverser was in the stowed position.

A post crash fire ensued on the left side of the airplane consuming the number 3 slat, the inboard end of the number 4 slat, the left and upper portions of the left nacelle, and the left side of the engine case. The remainder of the left wing and nacelle sustained moderate to heavy fire damage. There was some minor sooting to the left fuselage in the vicinity of the wing attach area. Memphis Airport Rescue and Firefighting responded to the accident within four minutes. Fire did not spread into the interior portions of the airplane.

The outer cylinder of the LMLG was fractured through the air filler valve boss on the aft side of the outer cylinder. The fracture continued around the circumference of the outer cylinder at the same level for about 240 degrees. The fracture then turned upwards and continued around the remaining circumference about 5 inches above the level of the filler valve on the forward side of the outer cylinder. A piece of the outer cylinder about 5 inches high by 8 inches wide was recovered on the runway. The LMLG lower side brace remained attached to the lower outer cylinder and the upper side brace was twisted about 90° along its length. The LMLG retract actuator was in the extended position and the rod end was fractured. The LMLG lock links were fractured.

Other damage

None

Personnel information

The two crewmembers had never flown together before this flight pairing, which began on July 26, 2006. On the first day, they flew MEM-SEA, followed by a layover at SEA. On the second day, July 27, 2006, they went SEA-Oakland, California-SEA, followed by another layover. The first flight on the third day, July 28, 2006, SEA-MEM, was the accident flight.

The Captain, age 57, held airline transport, flight instructor, and commercial pilot certificates, with multi-engine land and single-engine land ratings. She was type rated in the Falcon 20, Boeing 727, DC-10 and MD-10/11. The MD-10/11 type rating was issued in November 1993. She was hired by FedEx in February, 1979. Her total flight time was approximately 16,000 hours with 4,223 hours as pilot-in-command in the MD-10/11. She had flown 116 hours, 31 hours, and 6 hours in the last 90 days, 30 days, and 24 hours, respectively prior to the accident flight. Her last line check was in the MD-11 on July 19, 2006. The captain reported that she had served as a check airman on the MD-10/11 between 1997 and 2002. She held