NDB or Compass Locator on ILS

[100LL... Again!]

de727 brings up a good point here-

In my haste, i omitted the word PUBLISHED.

Why is this important?

135 and 121 operators are prohibited from descending after passing the FAF if the reported visibility is below minimums.

If you are past the FAF when you receive th report of lower wx, you may continue descent to MDA/DH, but may not land unless the required flight vis is present.

Okay, so why am I saying all this?

Since the FAF is defined as GS intercept at the PUBLISHED altitude, intercepting earlier and higher does not constitute an FAF.

EX: Publ GS intercept is 2500ft. Airplane intercepts a few miles earlier. Even though the airplane is on the GS, it is not considered to be past the FAF until it is past the published GS intercept alt.

Sorry for convoluted post.

 

[wheelsup]

GPS in lieu of ground based Navaids

It was my understanding that while you could use GPS to identify the ground based navaid position you could not shoot a NDB/VOR approach via your GPS unless you loaded the GPS approach for that particular approach. I.e. flying an NDB approach but loading the NDB into the GPS and selecting OBS mode and just intercepting the course is not sufficent...the GPS must go into ARMD mode for your to continue with the approach after the pseudo FAF. This only occurs if you've loaded the GPS overlay/standalone approach into the receiver. (AIM 1-1-21 (j) (3)).

Am I missing the boat here or is this the way everyone else has been trained?

~wheelsup

 

[Mmmmmm Burritos]

Nope, you're speaking of pure RNAV approaches there. A GPS approach is a type of RNAV approach. There are two types of GPS approaches- stand-alone and overlay. The overlay is what you speak of. Overlay approaches would be named something like VOR "or" GPS 25. Thus you can shoot either a VOR or GPS approach. If you choose GPS, you have to find the approach in the database and do all that stuff.

Now... pure NDB approach. Not "NDB or GPS" approach. You can use the GPS in lieu of the NDB and fly the NDB approach without even using the actual NDB! Just punch in "Direct to" and the NDB ID, then select OBS mode and dial in the final approach course. That's it. Just fly the NDB like it's a phantom VOR, which is what the GPS display shows. This works only if your GPS is IFR current, of course. It makes NDB holds a piece of cake too

You can also use the GPS for DME purposes, say an ILS DME approach. This works real well if you dont have DME in the plane. Just punch in the ID for the ILS/DME (I-UDL in the FLL ILS27R example) and if it comes up, viola! you have DME. If it doesnt come up, or asks for waypoints, then you cant use it. Not all of them are in the database yet.

 

[wheelsup]

I see your argument, that the AIM allows for the replacement of ground based navaids. Instead of shooting the NDB 29 using the NDB, you shoot the NDB 29, just with the GPS programmed for the same NDB. While I see what you are saying, you are shooting a GPS Approach if you use the GPS! It is no longer a NDB approach (it becomes an overlay approach if that is in the database).

Take a look at AC 90-94. I'll quote some info:

5. OVERLAY APPROACH.

In order to accelerate the availability of nonprecision instrument approach procedures that can be flown using certified GPS equipment, the FAA has authorized the GPS Approach Overlay Program. This program allows pilots to use GPS equipment to fly existing VOR, VOR/DME, NDB, NDB/DME, and RNAV nonprecision instrument approach procedures. The purpose of this program is to permit pilots to transition from ground-based to satellite-based navigation technology for instrument approaches. Approach operations are defined as that phase of flight from the Initial Approach Fix (IAF) to the Missed Approach Point (MAP) when flying an established nonprecision procedure. The approaches to be flown with GPS must be retrieved from the avionics database. (Refer to Section 2, "Airborne Navigation databases" for a more detailed description of the required database.) GPS equipment may be used to fly all codable nonprecision instrument approach procedures, except localizer LOC), localizer directional aid (LDA), and simplified directional facility (SDF) approach procedures. Any required alternate airport should have an approved instrument approach procedure (other than GPS or LORAN-C) which is anticipated to be operational at the estimated time of arrival.

Emphasis added by me. What you are doing by just selecting the NDB goes against the entire procedure of using GPS for an approach. You must have RAIM, you must select approach sensitivity, the entire procedure must be loaded, and the receiver must "arm" before using the GPS as a navigational device. All things that it does automatically if you load the approach contained in the GPS! What you speak of using it for (Direct to XXX) is simply for the enroute environment.

AIM 1-1-21 (f) (5) (a) through (f) allows the replacement of GPS for ground based navaids. HOWEVER, keep reading and under (f) you will find a "Note: This approaval does not alter the conditions and requirements for use of GPS to fky existing non-precision instrument approach procedures as defined in the GPS approach overlay program."



For your safety please read AC 90-94!!!

~wheelsup

 

[DAS at 10/250]

Mmmmmmmmmmmm Burritos

Your statement that you can use the GPS instead of an NDB for an NDB approach is not correct.

Aim 1-1-20 6. (f) clearly states:

Charted requirements for ADF and/or DME can be met using the GPS system, except for use as the principal instrument approach navigation source.

 

[Mmmmmm Burritos]

Sorry, momentary brain lapse there. I had a nagging feeling something was missing. I didnt have my FAR/AIM with me while typing and was too lazy to look it up online. I remit my post to simply stating:

You can use the GPS to do just about everything on an NDB approach except for using it as the primary means of navigation on the approach course. If the RAIM is good and you have it in terminal sensitivity mode, you can navigate to/from, determine your position to, and hold over, an NDB. To actually fly the approach procedure (inbound and outbound), you need to have the NDB tuned in, identified, and actually track it. But you can use the GPS as advisory information, which I highly recommend.

You can hold over and NDB with just GPS though I was partly right. And I have never flown an NDB approach with just GPS, I have always tuned in the NDB. I never bet my life on one box. Heck, I dial in the VOR or localizer into both NAV radios for redundancy.

Last time I try to argue without the AIM readily available. I've flown EFIS equipped aircraft where if you tune in an NDB, it displays it as a "phantom" VOR and you track it as such. Now that is cool.

 

[DAS at 10/250]

I second Mmmmmm Burritos procedure for tuning in both NAV's.

Wait, my #2 is inop. When are we going to the avionics shop boss? Next week. Riiiiiiight.