Douglas DC9 N671MC

Summary

On 15 June 2010 at about 01:45 local time, a Douglas DC9 registered N671MC, operated by Delta Air Lines, was involved in an incident near Minneapolis, Minnesota, United States. The number of people on board was not recorded. The aircraft was slightly damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

15 June 2010 at 01:45

Classification

Incident

Location

Minneapolis, Minnesota, United States

Nearest airport

Minneapolis - St. Paul Interna (KMSP)

Coordinates

44.0872, -93.2317

Aircraft

Douglas DC9

Registration

N671MC

Category

Airplane

Engines

2

Operator

Delta Air Lines

Operating rule

Unknown

Phase of flight

Not recorded

Route

Minneapolis → Minneapolis

Aircraft damage

Minor

Weather

Unk

Light

Day

NTSB number

ENG10IA037

Injuries not recorded.

The failure of the facility that overhauled the 1st stage fan blade to properly restore the leading edge, which caused a flutter mode resulting in a fatigue crack and fracture of the fan blade.

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

Read the full NTSB narrative

On June 4, 2010, a Delta Air Lines Boeing DC9-51, N671MC, had a case-uncontained, nacelle-contained 1st stage fan blade separation in the No. 1 (left) engine, A Pratt & Whitney (P&W) JT8D-17 turbofan, during a ground run for maintenance at the Minneapolis-St. Paul International Airport. Delta Air Lines maintenance personnel were conducting a trim run on the No. 2 (right) engine. After they had checked the No. 2 engine's power, they advanced the No. 1 engine's throttle to check its power when at about 1.7 EPR [engine pressure ratio], they heard a boom and felt a vibration. They shut down the engines and upon exiting the airplane, noticed the No. 1 engine's fan blades were damaged. One 1st stage fan blade was completely missing from the front compressor front hub's blade slot. Several pieces of the missing 1st stage fan blade were recovered from the engine's fan duct. The metallurgical examination of the fan blade pieces revealed a fatigue fracture on the blade's suction-side blade root bedding flank. In addition, there were fatigue fractures on the fractured fan blade's suction-side midspan shroud from the upper and lower surfaces of the shroud. A dimensional inspection of the fractured fan blade's leading edge revealed the radius was 0.035 inch in comparison to the required 0.009 inch. According to P&W, the leading edges of the 1st stage fan blades erode during normal operation. However, P&W also advised that the amount of wear observed on the separated blade would be associated with approximately 11,000 flight cycles rather than the engine's 2,685 flight cycles since the last overhaul, during which the 1st stage fan blades were overhauled. According to P&W, a worn and blunt leading edge can cause a flutter mode that can lead to increased stresses in the fan blade and cause fatigue fractures in the root and airfoil. The erosion of the fan blade leading edge was likely the result of faulty restoration of the leading edge profile or failure to restore the leading edge in a timely manner.

Quoted verbatim from the NTSB record.