I guess I mean GA-level 'light heavy'---airline pilots must fly in almost anything...except into thunderstorm
- de-ice
- radar
- high altitude capability to get above organised IMC if possible
(FL250+)
- high performance (obviously)
- systems redundancy (2 alternators, 2 buses, 2 batteries, etc)
many twins have that -stuff/those capabilities
some twins are equipped with- real deice rarely
but trust me I know what you mean ...but ultimately the PIC is the last word on what s/he does... I've done some relatively nasty wx in light twins, in commercial operations--albeit a very well equipped Seneca...not fun...
But the minimum 'airline nasty' IMC is probably a Turbo-comander or BE-200
