Assuming my aircraft's navigation equipment is a "Qualified/Suitable RNAV System," as defined by AC 90-108, is it legal for me to fly the LDA Y Rwy 19 IAP to DCA with ATC Radar out of service?
Here is a copy of FAA AC 90-108
Paragraph 7. a. (AC 90-108) states: (emphasis is mine)
Uses of Suitable RNAV Systems.
a. Usage of Suitable RNAV Systems. Subject to the operating requirements in this AC, operators may use a suitable RNAV system in the following ways.
(1) Determine aircraft position relative to or distance from a VOR (see first note in subparagraph 7b), TACAN, NDB, compass locator (see second note in subparagraph 7b), DME fix; or a named fix defined by a VOR radial, TACAN course, NDB bearing, or compass locator bearing intersecting a VOR or Localizer (LOC) course.
(2) Navigate to or from a VOR, TACAN, NDB , or compass locator.
(3) Hold over a VOR, TACAN, NDB, compass locator, or DME fix.
(4) Fly an arc based upon DME.
Here is the approach plate in question: