Jump to Content

Analysis

Summary

The fractured fan blade and several liberated portions of the blade were examined by the ATSB and by the engine manufacturer. The other 39 fan blades were returned to the engine manufacturer for review.

The blade had fractured about 470 mm above the blade platform, just inboard of the mid-span shroud. About one-quarter of the blade had been liberated. The fan blade had fractured as a result of fatigue crack growth. The failure had originated at a foreign object damage impact site 2.54 mm aft of the blade leading edge on the rear (concave) face of the blade. Traces of mineral debris were detected at the crack origin, indicating that the foreign object damage was the result of stone ingestion. Fatigue crack growth, from a crack depth of 1.5 mm, probably occurred over about 35 flight cycles. The blade had no material abnormalities at the fracture site. No evidence of a birdstrike was found.

The fractured blade had an eroded leading edge in the mid-span shroud region of the fan blade. The engine manufacturer reported that all of the fan blades had eroded leading edges in front of the mid-span shroud (about 152 mm above and below the shroud), and that the shroud hardfaces showed signs of possible lockup. It could not be determined whether the shroud lockup had occurred before or after the fan blade fracture.

The cracking and fracture of the fan blade appeared to be the result of high stress at a foreign object damage impact location in combination with vibratory stress and possible locked shrouds. The manufacturer reported that an adverse combination of these items could produce stresses high enough to fracture a fan blade. The eroded leading edge evident on all fan blades would have contributed to the blade fracture by affecting the vibratory characteristics of the fan blades.

The engine manufacturer said there had been only one other reported fracture of this type of fan blade. This was also due to fatigue crack growth starting at a foreign object damage impact site at a similar radial location to this fracture.

Findings

  1. A fan blade of the right engine fractured as a result of fatigue crack growth during aircraft climb, resulting in shutdown of the engine.
  2. The crack originated at a foreign object damage impact site on the rear face of the blade near the mid-span shroud.
  3. All fan blades of the right engine had significant leading edge erosion/blunting in the mid-span shroud region.
  4. The fan blade shroud hardfaces showed signs of shroud lockup.
  5. High stress at the foreign object damage impact site, vibratory stresses due to blade leading edge erosion and possible locked shrouds caused the crack to grow.
  6. Liberation of one-quarter of the fan blade and the resulting fan imbalance damaged the fan case, nose cowl and other fan blades.
 
Share this page Comment