Seems some operators can treat mda as a da, for some non prec approaches. The following taken from
http://www.faa.gov/about/office_org/...004-02-258.pdf
The meat of which I have posted below
"This Bulletin provides the applicable
procedures, operating criteria, and revisions to the operator’s operations specifications
(OpSpecs), if applicable, to permit additional use of Vertical Navigation (VNAV) capability of
Flight Management Systems (FMS) for instrument approach. This bulletin defines a new
term, “decision altitude” (DA(H)) for the use of VNAV in conducting certain instrument
procedures. Additionally criteria and procedures are provided to authorize the use of the
minimum descent altitude (height) (MDA) as a decision altitude (height) [DA(H)] for certain
existing instrument approach procedures meeting specified obstacle assessment provisions"