... which suggests to me that there is the possibility that there may be something to find in the tail rotor drive shaft department.
...in that case (fenestrone failure) pilot must put engines to IDLE and make an autorotation to the ground. Letīs say, with that height and (maybe) low speed, in night, over the congested area, you have very good chances to enter the last stage of autorotation low speed (which is unforgivable in 135), or to make a high flare (due to lack of suitable terrain), which will result with rapid loss of rotor RPM...