yerongard

Can anyone provide the exact reference for being able to use GPS in lieu of an ADF on an NDB approach? (as long as it is a retrievable procedure from the database and uses an overlay of course)

I've seen this in various publications and articles online, but none provide an exact reference.

EMAW

The info you are looking for is in the AIM, chapter 1. 1-1-18 e. F. And g. And other info thereabouts. Probably info in the TERPS to.

Flyhayes

Intstrument Procedures Handbook 4-26

GPS Overlay of Nonprecision Approach
The original GPS approach procedures provided authorization to fly non-precision approached based on conventional, ground-based NAVAIDs. Many of these approaches have been converted to stand-alone approaches, and the few that remain are identified by the name of the procedure and “or GPS.” These GPS non-precision approaches are predicated upon the design criteria of the ground-based NAVAID used as the basis of the approach…

http://www.faa.gov/regulations_polic.../Chapter_4.pdf

cougar

From AIM, 1-1-19 g.)

g. GPS Approach Procedures

As the production of stand−alone GPS approaches has progressed, many of the original overlay approaches have been replaced with stand−alone procedures specifically designed for use by GPS systems. The title of the remaining GPS overlay procedures has been revised on the approach chart to “or GPS” (e.g., VOR or GPS RWY 24). Therefore, all the approaches that can be used by GPS now contain “GPS” in the title (e.g., “VOR or GPS RWY 24,” “GPS RWY 24,” or “RNAV (GPS) RWY 24”). During these GPS approaches, underlying ground− based NAVAIDs are not required to be operational and associated aircraft avionics need not be installed, operational, turned on or monitored (monitoring of the underlying approach is suggested when equip-ment is available and functional).

If the approach has NDB in the title only, then the navaid must be functioning and GPS cannot be used as substitute means of navigation. 90-94 was rescinded in 2009.

If your company has Op Spec C300, then you can use GPS as a substitute means, even if the underlying navaid is inop.

There is also a current notice regarding C300 removing the restriction to have WAAS if the approach is to be used as an alternate.

PerfInit

All the above are good for general information and theory, but when it comes to you operating a specific make/model/series of aircraft, the FAA Approved AFM or AFM Supplement and OPSPECS (if an air carrier) are the governing documents. The AFM / avionics AFM supplement will tell you exactly what the "box" is certified for.

Also, TSO-C146 is the technical standard order which deals with RNAV/GPS I believe.

PerfInit

Minor correction to my previous post- TSO C129 deals with GPS standards for lateral navigation. TSO C146 deals with WAAS GPS capability (vertical Nav).

cougar

TSO C146 and TSO-C145 are the standards for SBAS (WAAS) receivers, either stand alone systems (TSO-C146) or FMC integrated systems (TSO-C145).

Most commercial aircraft were certified under TSO-C129, ABAS (RAIM) receivers usually as part of an MMR and FMC integration. TSO-C129 was cancelled and TSO-C196 is the current equivalent.

Regardless of which TSO an aircraft is certified under has nothing to do with vertical guidance or flying a GPS overlay.

Each type of RNAV approach has it's own Advisory Circular for approach requirements, AC 90-105, AC 90-101 or AC 90-107.

PerfInit

Cougar said:

"If the approach has NDB in the title only, then the navaid must be functioning and GPS cannot be used as substitute means of navigation. 90-94 was rescinded in 2009."

I think this is incorrect, but I don't have the time and energy to research it right now. Why would this be true? If it were, it actually reduces the level of safety. Onboard, certified IFR FMS/GPS systems can and should be used as a substitute means of navigation to NDB's. For one thing, the FAA is in the process of decommissioning numerous NDB's.

I will defer to BILSCH and/or USMCFLYER, but I believe that it is legal and recommended to use an IFR approved GPS with a current database (TSO C129) for navigation as a substitute to ground based NDB's.

JamesNoBrakes

Um, that's like one of the #1 rules of approaches, have to have the equipment in the title (and any required in notes).

CBreezy

You can use GPS for any approach up until the final segment. Once you pass the FAF inbound, the required Navaid, as identified in the title MUST be operational and used as the primary source of navigation. The overlay can be used for situational awareness but not navigation. The only time you can substitute GPS for a nonfunctional NDB or ADF is if the approach title says "NDB or GPS RWY 19." Another exception is DME. The GPS derived DME may be used in leiu of traditional DME. So, an aircraft with VOR only receiver with a GPS certified for IFR can fly a VOR/DME approach. (AC 90-108).