Seattle-Tacoma (SeaTac)

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.

The Beech 1900C cargo aircraft was loaded with more than 4,962 pounds of cargo during an approximate 20 minute period. No scale was available at the aircraft, forcing loaders to rely on tallying either waybill weights or estimates of total cargo weight and center of gravity (CG) during the brief loading period. Additionally, a strike had shut down a major cargo competitor at the time with substantial cargo overflow to the operator. Post-crash examination determined the cargo load was 656 pounds greater than that documented on the pilot's load manifest, and the CG was between 6.8 and 11.3 inches aft of the aft limit. The airplane behaved normally, according to the pilot, until he initiated full flaps for landing approaching the threshold of runway 34L at the Seattle-Tacoma International airport. At this time, the aircraft's airspeed began to decay rapidly and a high sink rate developed as the aircraft entered into a stall/mush condition. The aircraft then landed hard, overloading the nose and left-main landing gear which collapsed. A post-impact fuel system leak during the ground slide led to a post-crash fire.

After departure, the airplane intercepted airway V-2, and appeared to climb normally until reaching 8,300 feet (9,000 assigned) while tracking approximately 110° magnetic. Radar analysis showed the airplane at 128 kias when it abruptly turned left 30° and then appeared to recover. Voice communication during this event was normal with no change in the pilot's level of anxiety. Immediately thereafter, the heading changed over 90° to the left (northbound), and a maximum 6,750 fpm rate of descent developed before the heading stabilized and the descent slowed. The airplane's ground impact site was approximately 1 nm southwest of the last radar target. Wreckage distribution was roughly parallel to V-2. The airplane impacted the mountainside in a steep nose low, left wing down attitude. The engines, propellers/governors were disassembled and inspected with no evidence of mechanical malfunction. Exam of the left propeller indicated low power on impact. There was no evidence of significant icing/turbulence. The pilot, sole on board, was killed.

ATI Flight 805 departed from Seattle at 23:20 for a flight to Toledo. The 1st officer was flying the ILS approach to runway 07. For undetermined reasons, he failed to properly capture the ILS localizer and/or glide slope during the approach. At 03:13 the captain decided to carry out a go-around. The aircraft was vectored onto a base leg and given a heading of 100° to intercept the final approach course again. With a 35 knots crosswind (at 180°) on the approach the 1st officer had trouble capturing the localizer/glide slope. At 03:24, as the 1st officer was attempting to stabilize the approach, 3 GPWS glideslope warnings and sink rate warnings sounded. The captain took over control at 03:24:17 and performed another missed approach manoeuvre. He became spatially disoriented and inadvertently allowed an unusual attitude to develop with bank angles up to 80° and pitch angles up to 25°. When in a nose-low and left bank angle attitude, control of the airplane was transferred back to the 1st officer who began levelling the wings and raising the nose of the airplane. Impact with the ground occurred before the unusual attitude recovery was completed. All four occupants were killed.