Originally Posted by
wrench1
The alternate power source (plus a few other items) was from back before they revised Part 27 in the late 90s and was dealt with by a 2nd gen on the engine. The revised Part 27 required a "1 in a Billion" failure rate for any critical systems which was different than Part 23 airplane IFR requirement of "1 in a Million" failures. This high ratio required dual hyd, dual/triple navs, etc. and basically killed any new single IFR platforms. The original Bell SPIFR kits predated that revision. Fortunately the discussion of single IFR came to the fore front around 2015 or so and laid the ground work for the recently approved 407 and AW119 IFR STCs.
Thanks for update , I have been out of industry for many years so my experience is also a little dated.