McDonnell Douglas DC10 N386FE

Summary

On 4 April 2006 at about 22:45 local time, a McDonnell Douglas DC10 registered N386FE, operated by Fedex Express, was involved in an accident near Memphis, Tennessee, United States. 3 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

4 April 2006 at 22:45

Classification

Accident

Location

Memphis, Tennessee, United States

Nearest airport

Memphis International Airport (KMEM)

Coordinates

35.1499, -90.0494

Aircraft

McDonnell Douglas DC10

Registration

N386FE

Category

Airplane

Engines

3

Operator

Fedex Express

Operating rule

Part 121: Air Carrier

Phase of flight

Not recorded

Route

Memphis → Seattle

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

DCA06FA033

Nobody was injured.

The rupture of a fatigue crack in the forward air seal tooth serration of the No. 3 engine low pressure turbine stage 1 disk that initiated due to an improper weld repair performed during original manufacture. The improper weld repair changed the material properties of the disk near the weld feature, resulting in an accelerated crack propagation rate that allowed the crack to grow to rupture before the next inspection interval. Contributing to the severity of the accident was the inability of the flight crew to shutdown the engine as a result of the damage caused by a liberated piece of the low pressure turbine stage 1 disk when it punctured the right wing.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

As the airplane climbed through about FL260, the No. 3 engine low pressure turbine (LPT) stage 1 disk burst when a fatigue crack that initiated in the forward seal tooth serration arm ruptured. Fragments from the burst disk partially severed the LPT case and struck the fuselage in multiple locations. The airframe vibration increased to a severe level until the LPT rotor separated from the engine, about 14 minutes 30 seconds after the uncontained LPT stage 1 disk burst, when the high pressure turbine aft shaft and the fan mid shaft failed due to contact damage and torsional loading. Metallurgical examination of the portion of the LPT stage 1 disk that was imbedded in the right wing found that the disk burst due to a mixture of high cycle and low cycle fatigue. The fracture was located in the vicinity of the forward seal tooth serration, although the exact fracture origin could not be identified because the entire seal tooth and part of the seal tooth arm were missing at the fracture location. Examination of the forward seal tooth serration revealed the presence of two previous weld repairs that extended into the forward arm. Review of the manufacturing records revealed that the disk had been dabber weld repaired twice to correct anomalies and non-conformances found during the original manufacturing process. The dabber weld procedures did not authorize welding in the forward seal tooth serration, therefore, the weld repair performed on the failed LPT stage 1 disk did not conform to the approved repair instructions. Based on testing and analysis of sample, post-manufacture dabber weld repaired disks, the suspect population of CF6 disks was confined to those that had been repaired at original manufacture. Records indicated that, in addition to the accident disk, four other disks had been dabber weld repaired at original manufacture to correct forward seal tooth serration anomalies and non-conformances. None of these disks are any longer in service. Based on the estimated crack propagation rate, it is likely that either no crack existed at the last inspection of the disk or the crack size was below the reasonably detectable threshold. After the disk burst, the flight crew completed all required checklists; however, the crew could not manually shutdown the affected engine because the burst disk fragments had severed the fire shutoff valve cable, the power off cable, and the emergency shutoff cable. The engine eventually shutdown on its own due to airflow disruptions within the engine. The flight crew’s procedural coordination and use of available resources, consistent with cockpit resource management best practices, helped to ensure the safe landing of the airplane.

Quoted verbatim from the NTSB record.