N386FE

HISTORY OF FLIGHT

On April 4, 2006, at about 16:45 central standard time, FedEx Express flight 597, a McDonnell Douglas MD-10-10F, N386FE, experienced a No. 3 (right-hand) engine uncontained failure of the low pressure turbine (LPT) stage 1 disk while climbing through about FL260. About 8 minutes after the engine failure, and while the airplane was returning to Memphis International Airport (MEM), Memphis, Tennessee, the airplane experienced severe vibration that stopped when the entire LPT rotor separated from the engine. There were no injuries to the two flight crewmembers or one passenger onboard and the airplane received substantial damage. The flight was operating under the provisions of 14 Code of Federal Regulations (CFR) Part 121 from MEM to Seattle-Tacoma International Airport (SEA), Seattle, Washington.

The captain was the flying pilot. The takeoff and initial climb phases of the flight were normal and uneventful.

According to pilot interviews and recorded information, about 19 minutes after takeoff, as the airplane was climbing through FL260, a loud bang was heard and the airplane yawed to the right. An amber “X” appeared on the No. 3 engine instrumentation and the captain called for the Engine Fire and Severe Damage checklist.

The first officer called for the passenger, a qualified MD-11 first officer who was in the courier compartment, to come to the cockpit to assist with the emergency. The first officer declared an emergency with air traffic control (ATC) and then completed the Severe Damage checklist, including shutting down the No. 3 engine and pulling its respective fire handle. The captain turned the airplane back towards MEM and the crew began dumping fuel.

About eight minutes after the engine failure, the moderate airframe vibration that started when the engine failed, began to increase. This vibration intensified to a severe level over about a 6-minute period and then stopped abruptly about 14 minutes 38 seconds after the engine failure. In addition to the engine failure indications, the crew received No. 3 hydraulic pressure low, slat disagree, and right main gear unsafe warnings. The crew performed the checklists applicable to each of these warnings.

The crew continued the descent and requested vectors for an extended final and visual approach to runway 36C at MEM. Due to the slat disagree warnings, the captain conducted a no slat, Flaps 22 approach with an approach reference speed (Vref) of 199 knots.

After stopping on the runway, the aircraft rescue and firefighting (ARFF) personnel communicated that there was no fire present. As a result, the pilots shut down the No. 1 and 2 engines and started the auxiliary power unit while waiting for stairs to disembark. About 11 minutes after stopping, the ARFF personnel advised the flight crew that there was an increase in smoke around the No. 3 engine at which point, the captain ordered the crew to evacuate via the L1 (forward left) door slide.

DAMAGE TO No. 3 ENGINE

After landing, the LPT rotor was found to have separated from the No. 3 engine and a piece of the LPT stage 1 disk was lodged in the upper skin of the right wing. The LPT rotor wreckage was recovered from a field near Weiner, Arkansas. The flight data recorder (FDR) and cockpit voice recorder (CVR) data indicated that the LPT stage 1 disk failed over a forested area near Ravenden, Arkansas. An alert was issued for public assistance with finding the remainder of the disk, and a physical search was conducted of the forested area. No additional portions of the disk were recovered.

There was no evidence of fire on the No. 3 engine, its respective cowling and thrust reverser, or on the right-hand wing. The aft engine mount beam and links were intact with no apparent cracks and were not distorted or twisted. The LPT case was fractured circumferentially and torn just aft of the LPT stage 1 nozzles where the LPT stage 1 disk would have normally been located. All the LPT case-to-turbine mid frame (TMF) attachment bolts were intact and the entire LPT case front flange remained attached to the rear flange of the TMF; however, the flange was fractured at three separate locations. Portions of the LPT case body, ranging from about 1-inch to 5-inches, remained with the front flange. Visual examination of the TMF did not reveal any damage, breaches, or signs of fire.

With the aft end of the engine missing, the “C” sump housing, the LPT nozzle support, the static pressure balance seal, the LPT stage 1 interstage seal, and the LPT stage 1 nozzles were all exposed. All of the LPT stage 1 nozzles were intact, in place, and the airfoil trailing edges exhibited impact marks, tears, missing material, and were pushed forward. The inner ends of three nozzle segments, located at approximately the 2:30, 4:00 and 5:00 o’clock positions, were found disengaged from the LPT stage 1 interstage seal aft flange. The LPT stage 1 interstage honeycomb seal was intact and exhibited a deep trench along the middle of the seal down to the backing strip. The aft half of the honeycomb seal was also heavily worn, but not down to the backing strip. The rear flange of the LPT stage 1 interstage seal was distorted around the attachment bolts and exhibited circumferential contact wear and three radial impact marks located at approximately the 7:00, 8:30, and 10:30 o’clock positions. Damage at the 7:00 and 10:30 o’clock position consisted of a straight impact slash across the honeycomb material while the damage at the 8:30 o’clock position was a combination of a straight slash across the seal and aft flange, continuing into a spiral slash along the aft flange.

The static pressure balance seal is comprised of an outer and inner seal land that works in conjunction with the rotating pressure balance seal attached to the LPT rotor to balance the pressure load of the HPT rotor and works with the No. 4 ball bearing to axially position the HPT rotor correctly within the engine. The outer seal land portion of the pressure balance seal was torn from the rest of the structure aft of the stiffener ring and exited the engine with the rest of the LPT rotor. This piece was recovered with the LPT rotor and turbine rear frame (TRF). The inner seal land remained attached to the support and was intact but was heavily distorted, flared outwards, compressed and exhibited material transfer, bluing, and heat distress. The inner seal land was also canted in relation to the engine’s longitudinal centerline – at the 6:00 o’clock position the seal was approximately 1.0 inch farther forward than at the 12:00 o’clock position.

The “C” sump aft stationary air and oil seal is a single piece seal that works in conjunction with the rotating air and oil seal attached to the LPT rotor to prevent oil from leaking out of the bearing compartment and to provide pressure balancing throughout the bearing compartment. The oil-seal portion of the “C” sump seal is comprised of a “wind back” knife edge seal (forward most seal) and a nickel graphite seal land. The knife edges of the “wind back” seal were heavily damaged and flattened, and in some areas were completely rubbed away. Both oil-seal locations were heavy distorted, blued, missing, and exhibited heat distress. The airseal portion of the “C”-sump seal is comprised of a seal land and it was distorted, flattened forward, missing material, and exhibited bluing, material transfer, and heat distress.

The outer race of the No. 6 bearing, which is located within the “C” sump, was fractured into several pieces, incomplete, and what remained was not oil wetted. Those pieces of the No. 6 bearing outer race that remained installed exhibited impact damage but no thermal distress or bearing roller material transfer. Fractured pieces of the No. 6 bearing cage were recovered loose within the bearing compartment and they exhibited heavy impact damage; however, no significant thermal distress or bluing was noted and the silver plating was still present.

The LPT rotor (minus the stage 1 disk) and the TRF, along with various loose LPT blade and vane material, were recovered together in the same 3.5 foot deep crater near Weiner, Arkansas. The outer seal land of the static pressure balance seal was recovered approximately 190 yards from where the LPT rotor was found. The recovered LPT rotor was comprised of the stages 2, 3, and 4 disks, the LPT front shaft, No. 6 bearing inner race, the “C” sump aft air/oil seal, the aft portion of the fan mid shaft (FMS), the rotating pressure balance seal, the “D” sump air and oil seals, the LPT rear shaft, and the No. 7 bearing inner race. Some blades from each stage were missing and those that remained were fractured at various lengths. Forty-five degree shear lips, bluing, heat discoloration, and areas of melting/plastic flow were noted on the FMS fracture surfaces.

The turbine rear frame (TRF) was comprised of a portion of the LPT turbine case (bottom half) still attached to the TRF outer case, the LPT stage 5 disk, the “D” sump housing, the center body, and exhaust nozzle.

DAMAGE TO AIRCRAFT

As a result of the engine failure, the airplane sustained numerous impact marks, holes, and punctures in the right-hand wing, the right-hand slats and flaps, the right-side of the fuselage, the No. 3 engine pylon, and the No. 3 main landing gear door. An airplane damage scatter pattern diagram was produced to map the approximate trajectory angles of debris as it was shed from the engine.

The No. 3 engine pylon was intact, remained attached to the wing, and exhibited no holes or penetrations (thru holes). It did, however, exhibit scuffmarks and impact damage. Two sets of “train track” marks were noted on the outboard vertical skin of the pylon. The size, shape, and spacing of the “train track” marks were consistent with the size, shape, and spacing of the LPT stage 1 disk rim blade retaining fir tree slots. The pylon heat shield was severely impact damaged, torn, and th...