Takeoff Alternate Airport Requirement

[ckcrew]

Takeoff Alternate Airport is required when the takeoff airport weather is at or below landing minimum.”
Does it mean both VISIBILITY and/or CEILING (below DH) or just only the VISIBILITY applies?

[MarkerInbound]

"121.617 Alternate airport for departure.(a) If the weather conditions at the airport of takeoff are below the landing minimums in the certificate holder's operations specifications for that airport, no person may dispatch or release an aircraft from that airport unless the dispatch or flight release specifies an alternate airport located within ,,,.

(b) For the purpose of paragraph (a) of this section, the alternate airport weather conditions must meet the requirements of the certificate holder's operations specifications."

Most airlines will have OpSpec C55 which allows lower than standard alternate minimums. It has both ceiling and visibility minimums.

[flyboyike]

Takeoff Alternate Airport is required when the takeoff airport weather is at or below landing minimum.”
Does it mean both VISIBILITY and/or CEILING (below DH) or just only the VISIBILITY applies?

What type of operation?

[MarkerInbound]

Under FAA rules T/O alternates are only required for part 91k, 121, 125 or 135 operations. The OP posted the same tihing in Tech Log so I don't know if they are looking for US rules or to compare US rules to other CAAs.