North American NA265-65 N651MK

Summary

On 10 May 1998 at about 19:20 local time, a North American NA265-65 registered N651MK was involved in an incident near Palm Springs, California, United States. 8 people were on board and nobody was injured. The aircraft was slightly damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

10 May 1998 at 19:20

Classification

Incident

Location

Palm Springs, California, United States

Nearest airport

Palm Springs Regional (PSP)

Coordinates

33.8492, -116.5604

Aircraft

North American NA265-65

Registration

N651MK

Category

Airplane

Engines

2

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Executive/Corporate

Phase of flight

Not recorded

Route

Unknown → St Louis

Aircraft damage

Minor

Weather

VMC

Light

Day

NTSB number

LAX98IA158

Nobody was injured.

the fatigue failure and uncontained separation of the high pressure impeller in the No. 2 engine during the takeoff roll. While the impeller showed evidence of a subsurface fatigue origin, the percipient cause of the separation was not definitively determined.

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

Read the full NTSB narrative

An uncontained engine failure occurred during the takeoff roll. The high pressure centrifugal impeller disk had burst, with one chunk exiting through the engine cowling. The melt and forging records for the disk were reviewed and met the required specifications, including alloy chemistry. Metallurgical examination of the disk revealed subsurface primary and secondary fatigue cracks near an area that had been reworked to remove LCF stresses in accordance with a Service Bulletin. The cracks were located opposite of each other in the seal relief undercut area. The primary fatigue origin was below the shot-peened surface near a high stress area and the secondary fatigue origin remained subsurface, with the propagation of both cracks running parallel to the surface until overload separation. The primary fracture surface could not be definitively analyzed due to plasticity and the presence of an oxide layer. No melt, forging-related or heat-treating defects were found in the vicinity of the fatigue origins; however, subsurface LCF was present. No significant hardness difference was found either in or away from the fatigue origins. There was no evidence of a subsurface occlusion. A physical resemblance between the fatigue origin and the zones of crystallographically aligned phase (texture zones) was observed in the microstructure. The shape and orientation of the origin macrostructure and/or texture may have been a contributing factor to crack initiation; however, no precipitating event or cause for the fatigue initiation was identified. Analysis reverified the Service Bulletin rework specifications, confirming that residual stress was negligible at the depth of crack initiation.

Quoted verbatim from the NTSB record.