Originally Posted by
showboats
Argument one is correct. If Cat III gets you down to 0/0 (not sure about that one since I'm a 135 guy...currently)
On page 259 in reference to IFR Takeoff Mins it states that FAR 121.617 requires a takeoff alternate if weather below IFR landing mins at departure airport. It goes on to break it down into aircraft with two engines or aircraft with two or more engines.
Next to that paragraph is a note stating, and I quote "The flight plan (or flight release) must specify a takeoff alternate if the weather at the airport is below landing minimums for the airport. Any landing minimums at the takeoff airport that are authorized for the certificate holder may be considered including Category II or III ILS approaches"
[91.175(f), 91.1039, 121.617, 121.619, 121.625, 121.651, 135.217, OpSpec C057 & C058 or C079]
T/O mins are predicated on CAT I landing mins in Part 121, and Ops Spex C will usually confirm this. Hence the need, if taking off from an airport that has below-Cat I wx for a "Take-Off Alternate". Why bother with an alternate if you can land Cat II/III? Some carriers cannot return to departure airport with an engine failure and fly Cat II/III with engine-out.
As always, depends on individual company SOPs, Ops Spex and GOM/FOM.