Hello

Is it possible to add/modify the GTN 750 for an ADF radio similar to Nav?

 

No, the real unit does not have this function and that is what the RXP is modelled on.

You can navigate with GPS to radio beacons that are still active, such as VOR's and NDBs, so in a GPS equipped aircraft, especially one with dual GPS (for backup) what is the need?

thanks for the info; yes, I know ADFs are old and outdated.  I do have an AP3000 that I do use to quickly tune an ADF if needed.  The particular airport I use a number of times, only has an ADF transmitter which is also why the FAA is asking the real airport to upgrade to GPS.

6 hours ago, cesdash8 said:

which is also why the FAA is asking the real airport to upgrade to GPS.

???  GPS is not dependent on radio beacons.  It is based on coordinates.  What is the airport at issue?  Are you aware that if needed you can establish and store your own GPS user-defined waypoints?  Those could be established based on the location of the radio beacon.

The GTN will have the coordinates all own known VOR's & NDB's in its database, but in the case of NDB's you cannot tune them as there is no ADF receiver.

Frank

Thanks for the info; I am aware that GPS is based on coordinates and not radio beacons.  The airport in question CQX only has an ADF beacon, and as I understand it, they were required to hold a public info meeting to add GPS (although there is an RNAV for runway 24) which would necessitate the removal of a number of trees and require easements from some homeowners around the airport.  Of course, the public thought that instead the runway was going to be lengthened (not), etc. etc. thereby permitting larger/more aircraft into this small airport.  Here is a recent article for your perusal from a local newspaper https://capecodchronicle.com/en/5439/chatham/4980/Airport-Meeting-Moved-Amid-Controversy-Over-Master-Plan.htm

The airport already has an existing RNAV/GPS B approach. Although the approach course appears to be directly aligned with runway 24, it is considered to be a circling approach with 600 foot minimums, similar to the NDB approach. If there are trees in the approach path, that may be what is preventing the FAA from creating a straight-in GPS approach with (possibly) lower minimums.

Looking at the airport in a satellite view, there appears to be a line of trees not far beyond the threshold of runway 24. 

1 hour ago, JRBarrett said:

The airport already has an existing RNAV/GPS B approach. Although the approach course appears to be directly aligned with runway 24, it is considered to be a circling approach with 600 foot minimums, similar to the NDB approach.

Jim. I believe the similar circle diagram you see on the RNAV approach is the missed approach course.  The approach itself is pretty much a standard RNAV GPS based approach.

2 hours ago, cesdash8 said:

I understand it, they were required to hold a public info meeting to add GPS (although there is an RNAV for runway 24)

The current RNAV 24 is a GPS based approach. Chatham already has, and-has-had a RNAV 24 approach for some time.  It has been in place since at least 2014.  See the revision date (extreme bottom left corner of the approach plate). It is Sept 2014 based on the approach plate at Airnav.com (click here): https://aeronav.faa.gov/d-tpp/1913/05247RB.PDF. 

What I see is an NDB approach where the beacon is at the airport but offset from the runway.  Basically it is used to cross the beacon and then circle back to it on a heading near the runway heading.  That only applies to 24. With both an NDB and an RNAV 24, if you are GPS equipped you should not need the NDB approach.

I assume the current controversy is likely about establishing an additional RNAV approach to 06.  Extending 06 runway vector via Google Earth shows that it would bring in IFR approach traffic over neighborhoods and businesses that do not currently "entertain" instrument approaches.   Certainly those areas are already overflown by departing traffic.

The initial approach path from west-northwest to the NDB appears to be over a much less populated area.  The subsequent final approach course from both the NDB-A and RNAV already overfly areas to the E & ENE of the airport.  The RNAV 24 final approach course flies over the same area as the NDB.

From the notams you can see that noise abatement is an issue.  The avoid INTXN DEPS means to avoid circling back over the beacon after takeoff.  TGL OPNS (touch and gos) are also discouraged.

Notams:
-     NOISE ABATEMENT RWY 6/24. USE FULL RWY & AVOID INTXN DEPS. MINIMIZE /AVOID TGL OPNS. CLIMB OUT ON RWY HDG TIL 1000 FT OVR WATER THEN PROCD ON CRS. REDUCE PWR AS SOON AS PRACTICAL.
-     RWY 6/24, FLY PAT DOWNWIND LEG 1/2 TO 1 MILE OUT FM RWY AS PRACTICABLE.
-     AVOID RESIDENTIAL AREAS AS MUCH AS PSBL.