Anti-stall hollow tip treatment bars for damage limitation

A gas turbine engine fan or compressor casing includes a cavity 10 separated from the main flow 12 through the engine by an annular array of tip treatment bars (16, fig 2) which delay the onset of stalling. The tip treatment bars 16 are hollow having internal passages 22 which enables the bars to deform or break upon impact by a shed blade 4 or blade fragment so that the blade or blade fragment may be contained within the cavity 10, or embedded in the casing 2, so causing the minimum of damage. The bars 16 may be a metallic or composite material, and are mounted on annular end supports 18,19 through which passages 22 may extend. Bar wall thickness may be between 0.5-1.5 mm. The interiors of the tip treatment bars may be filled with a damping material, to minimise high cycle fatigue failure.