NTSB Factual Report

HISTORY OF FLIGHT

On August 6, 2011, at about 1142 EDT, a Delta Air Lines McDonnell Douglas DC9-51, registration N676MC, equipped with two Pratt & Whitney (P&W) JT8D-17 turbofan engines, rejected takeoff from Hartsfield-Jackson International Airport (ATL), Atlanta, Georgia after experiencing a No. 2 (right) engine uncontained failure. The flight crew reported that, during the takeoff roll, at about 80 knots, a "bang" was heard and the airplane shuddered. The captain rejected the takeoff and stopped on the runway. The airplane was unable to taxi due to a brake lockup. Passengers were deplaned and bussed to the terminal. The flight was being operated in accordance with 14 Code of Federal Regulations Part 121 as a regularly scheduled flight from ATL to Pittsburgh International Airport (PIT), Pittsburgh, Pennsylvania.

INJURIES

There were no injuries reported to passengers or crew.

DAMAGE TO THE AIRPLANE

A visual examination of the airplane identified a penetration in the No. 2 engine cowling and an impact scar on the outer pane of a window on the right side of the airplane fuselage, forward of the engine. One of the No. 2 engine fan blades was found separated below the platform and three small holes were observed on the compressor case.

TESTS AND RESEARCH

The engine was removed from the airplane and shipped to the Turbine Engine Center in Miami, Florida for inspection and disassembly from September 20-21, 2011. During the engine examination the separated fan blade was recovered in three pieces, the blade root that was still present in the fan hub blade slot and two sections of the airfoil that were recovered loose inside the engine. Damage was observed to the inlet guide vanes (IGV's), the remaining fan blades, the fan exit guide vanes (FEGV's), and visible low pressure compressor (LPC) stages aft of the fan. The separated fan blade pieces, seven additional damaged but intact fan blades, and the fuel oil cooler aft mounting bracket were shipped to the P&W materials lab for analysis.

Metallurgical analysis concluded that the separated fan blade failed due to a high cycle fatigue crack that originated approximately 0.9375 inch aft of the leading edge on the suction side of the blade. Replicas (molds) were taken on six fan blades at points along the leading edge that were undamaged during the event and then superimposed over a representative new fan blade profile to measure leading edge erosion. Four of the six replicas were taken at blade chord positions that are repairable in accordance with the JT8D-17 repair manual. The measurements collected from the four replicas confirmed that all four had material loss within allowable limits, but three of the four blades had chord loss greater than P&W's erosion estimate of 0.035 inches for engines that had accumulated 11,000 engine cycles. The erosion estimates were created using field data from P&W PW4000 series engines which has the same fan blade material as the JT8D-17.

ADDITIONAL INFORMATION

Fan blade fatigue fracture due to excessive leading edge erosion was addressed by P&W in maintenance advisory notice (MAN) MAN-JT8D-2-06, released on November 20, 2006. The advisory notice recommends fan blade refurbishment every 4,000 cycles to reduce fatigue fractures due to vibratory stress caused by leading edge erosion. The Federal Aviation Administration (FAA) subsequently released Airworthiness Directive (AD) 2010-21-17 for all JT8D engines on November 12, 2010, mandating fan blade leading edge overhaul after 4,000 cycles since the last blade overhaul was performed. The incident engine was overhauled prior to the AD release and blade refurbishment had not yet been performed in accordance with the P&W MAN. A MAN is supplemental information that is not covered in the engine manuals and compliance with the recommended actions is at the discretion of the engine operator.

NTSB Probable Cause

The probable cause of the No. 2 engine failure and subsequent aborted takeoff was the high cycle fatigue failure of a fan blade near the blade root that resulted in extensive low pressure compressor damage and compressor case breach.