Originally Posted by
megan
The first failure I had the shrapnel was contained, in the second a lot of shrapnel exited tangentially, which could have had implications for the tail rotor drive as the shaft ran between the two engines.
One S-76 with Allison engines had a engine failure that severed the tail rotor drive shaft, severed the battery connection, and as result of the other engine being taken out as well, total electrical failure. We flew with a mod we called the BBQ plates, weighed some hundreds of pounds to contain the shrapnel until the engines could be modded.
Perhaps the standards are different for turboshaft engines used on helicopters, but it is a cert requirement for large commercial aircraft turbofan engines that the turbine case retains debris from failed turbine blades (same with the compressor case).
In addition, rotor burst analysis do both 'high energy' and 'low energy' debris and what shielding is needed (and can be taken credit for) for the 'low energy' debris - and shed compressor and turbine blades are considered 'low energy' debris (fan blades are treated differently for obvious reason).
OTOH, burst discs are considered to have infinite energy and no shielding credit can be taken - a burst disc is going to go wherever it's going to go and take out anything in its way. The rotor burst analysis is commonly known as a "1 in 20", since it's assumed that 5% of uncontained disc failures will be catastrophic.