Sixteen People Fatally Injured When Propeller Blade Separated And Impacted The Fuselage

The U.S. Marine Corps has released a report from an accident which occurred on July 10, 2017 that fatally injured all 16 people on board the airplane.

The report found that a corrosion problem on the propeller worsened as it went neglected over several years and eventually led to the blade separating from the propeller hub, sending it through the fuselage of the airplane. The failure of the blade, identified as the #4 blade on propeller 2, (P2B4) initiated the catastrophic sequence of events resulting in the midair breakup of the aircraft and its uncontrollable descent and ultimate destruction.

According to the report, post- mishap analysis of P2B4 revealed that a circumferential fatigue crack in the blade caused the fracture and liberation. This fatigue crack propagated from a radial crack which originated from intergranular cracking (IGC) and corrosion pitting. The analysis also revealed the presence of anodize coating within the band of corrosion pitting and intergranular cracking on the blade near the origin of the crack. This finding proves that the band of corrosion pitting and intergranular cracking was present and not removed during the last overhaul of P2B4 at Warner Robins Air Logistics Complex (WR-ALC) in the fall of 2011.

The investigation concluded that the failure to remediate the corrosion pitting and intergranular cracking was due to deficiencies in the propeller blade overhaul process at WR-ALC which existed in 2011 and continued up until the shutdown of the WR-ALC propeller blade overhaul process in the fall of 2017.

The investigation also examined whether any operational or intermediate level maintenance inspections or maintenance actions exist which could have detected the underlying causal conditions prior to the mishap. The investigation concluded that while these inspections exist, it cannot be quantifiably determined that these inspections would have detected the causal condition.

The investigation arrived at this conclusion due to the fact that the growth or propagation rate of an IGC radial crack cannot be predicted. Though no evidence exists to determine when the radial crack had grown to a detectable area, beyond the bushing, there exists a distinct possibility that it could have been detected if the radial crack had grown past the bushing and the off wing eddy current inspection was performed.

The blade sliced through the left (port) side of the fuselage, and impacted the interior of the right (starboard) side, initiating the catastrophic sequence of events of this mishap. This impact caused the skin of the aircraft to separate along the starboard side.

The energy transferred from P2B4's impact through the structure of the airframe also caused an overload condition. of propeller three's drive shaft. This resulted in its associated reduction gearbox assembly (RGA) failing and the separation of propeller three from the aircraft. Propeller three then momentarily embedded into the upper right section of the fuselage. After which, it continued over the aft starboard section of the fuselage and impacted the starboard horizontal stabilizer separating a significant portion of the stabilizer from the aircraft.

As a result of these events, the C-130 split into three primary sections: the cockpit, the rear fuselage, and the 19' 4" section in between (where the passengers were sitting), which explosively disintegrated into multiple pieces.

The report concludes that "negligent practices, poor procedural compliance, lack of adherence to publications, an ineffective QC/QA program at WR-ALC, and insufficient oversight by the USN, resulted in deficient blades, being released to the fleet for use on Navy and Marine Corps aircraft from before 2011 up until the recent blade overhaul suspension at WR-ALC occurring on 2 September 2017."

Among the recommendations from the report are for the USAF to investigate key personnel and all others for historical and current noncompliance of NAVAIR publications and procedures at Warner Robins Aviation Logistics Complex. Shortcomings exist in the areas of proper supervision, verification and understanding of critical safety of flight repair processes. The culture at WR-ALC from 2011 to 2017 resulted in gross negligence of depot level maintenance personnel and practices that are the direct causal factor for this mishap.

(Image from file. Not accident aircraft)

FMI: Redacted report