This surprises me and I find it hard to believe. Why don't they just add 50ft like they do in NZ and Australia if they are going to treat an MDA as a DA?
The point is to
reduce minimums when safe practices allow it.
Examples:
1. FAA OpSpec C073 VNAV MDA as DA:
"The certificate holder is authorized to use minimum descent altitude (MDA) as a decision altitude (DA)/decision height (DH) with vertical navigation (VNAV) on a Nonprecision Approach (NPA)."
8900.183 - OpSpec/MSpec/LOA C073, Vertical Navigation (VNAV) Instrument Approach Procedure (IAP) Using Minimum Descent Altitude (MDA) as a Decision Altitude DA)/Decision Height (DH) ? Document Information
2. Transport Canada Special Exemption from 602.128(2)(b)
"The purpose of this exemption is to permit pilots-in-command of IFR aircraft operated by holders of an air operator certificate or a temporary private operator certificate to descend below the minimum descent altitude (MDA), when conducting a non-precision approach ... following a stabilized constant descent angle (SCDA) non-precision approach."
EXEMPTION FROM PARAGRAPH 602.128(2)(b) OF THE CANADIAN AVIATION REGULATIONS - Transport Canada
(SCDA is the Canadian term for CDFA).