Gourette Les Bosses english summary
On Saturday 2 February 2013, at 11.30, at the Gourette ski area in Eaux-Bonnes in the département of Pyrénées-Atlantiques, car No 53 of the Bosses cable-car, which was going up, got stuck at the level of pylon P14 located immediately upline from the top station. After having swayed, it became unhooked from the cable and fell three metres and sank into the fresh snow at the foot of the pylon. The top station’s supervisor saw this car fall from a distance and immediately shut the installation down.
The fallen car’s two passengers were very slightly injured. They broke the Plexiglas window and managed to get out on their own. The evacuation of the 79 other passengers travelling on the cable-car at the time of the accident was completed at 14.30.
The direct cause of this accident was the breakage of two metallic flanges on one of the intermediate bogies on the sheave train of pylon P14 in the upwards direction. This breakage caused one of the bogie’s two wheels to fall, the cable to rub against its axle and then, after four cars had passed the damaged sheave train without mishap, the seizing and tearing out of car No 53’s detachable grip.
The rupture of these two flanges resulted from the fatigue cracks that had developed in them quickly, in just a few months, very certainly under the effect of the lateral forces generated on the sheave train by the passing of the cable strands and cable grips.
Three factors contributed to this situation :
- vagueness of the standards and rules that apply to the sizing of the sheave trains installed on cable-car pylons that do not take into account all the lateral forces that their components may be subjected to in operation ;
- difficulty, without any precise procedure, in detecting cracks in the bogies of sheave trains, whether at the time of the annual inspections or of the checks performed in operation, which are carried out without disassembly ;
- absence on the intermediate bogies on the Bosses cable-car sheave trains of a device making it possible to immediately detect the loss of a sheave wheel.
Further to this accident, the Cableways and Guided Transport Technical Service (STRMTG) asked all the operators concerned to replace, by 2019, all the twowheel bogies of the same type as those equipping the Bosses cable-car – which are currently installed on single-cable installations with detachable grips – with bogies ensuring a better resistance to the lateral forces they are subjected to. In the meantime, the STRMTG also defined a formal procedure for monitoring the bogies awaiting their replacement.
In the light of the above, BEA-TT made three recommendations :
- strengthen the design standards for sheave trains installed on cable-car and chairlift pylons in order to take into account all the lateral forces that these parts may be subjected to in operation ;
- extend the implementation of specific visual procedures to every type of bogie equipping sheave trains such as these, in order to monitor their condition and enable the detection of any cracks that could develop there ;
- equip the chairlifts and cable-cars with safety devices enabling automatic shut-down in the case of partial or total breakage of a bogie on a sheave train.