© Anthony Pecchi European Aviation Safety Agency (EASA) has granted certification to the redesigned vertical bevel gear shaft for Airbu...
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| © Anthony Pecchi |
The certification will enable production and installation of redesigned shaft on all affected helicopters in operation globally, as well as those under production.
The redesign involved extensive investigation into the main gear box shaft failures of two EC225 helicopters in the North Sea in 2012.
The new design eliminates all the three factors that, in combination, had caused two unexpected vertical shaft ruptures resulting in two controlled ditching.
It provides corrosion resistance, compensates for residual stress and eliminates stress hot spots.
The new design features:
1. A smooth shape of the shaft to avoid any collection of moisture.
2. An improved inner side of the bevel shaft splines lubrication by two additional holes into the shaft
3. A different type of surface finish (better roughness) and design to prevent corrosion.
4. An improved strength and thickness to eliminate stress factors and ‘hot spots’.
EC225 fleet were grounded following the controlled ditchings. Initial visual investigation found a 360° circumferential crack on the bevel gear vertical shaft (which drives the two Main Gear Box (MGB) lubrication pumps), in the vicinity of the weld that joins two sections of the shaft.
During the two ditchings, the emergency lubrication system was activated by the pilots and operated properly. However, a warning light, indicating a system malfunction, came on and resulted in the crew making the decision to perform a controlled sea landing, as required in the flight manual.
The warning light was later found to be a false alarm resulting from a wiring discrepancy.
The 11-ton-class helicopter is mainly employed in offshore transportation to oil rigs
