Garmin Gotchas: GNS 530 GPS

Stuff I Learned the Hard Way

by Dave Touretzky

Vectoring and Course Specification

VTF (Vectors to Final) doesn't take you direct to the FAF; it sets the DTK to the final approach course. So somebody had better be vectoring you onto that course, because the GPS is not providing navigation guidance to get you to the FAF!
Selecting "Activate VTF" from the PROC menu replaces the approach loaded into the flight plan page with the version of the approach for the "vectors" transition. So if you had some other version loaded (say, for example, the GPS-B at Pottstown Muni (N47) with the PTW transition) you will lose that version if you activate VTF. If you simply activate the approach and then manually select the appropriate leg, you can avoid this.
On the ILS 28 approach to KAGC, VTF takes you to the Miffy OM, omitting the MKP beacon. However, the Pittsburgh controllers will always vector you to the beacon and will often ask you to "switch to tower at McKeesport". Selecting the MKP-IA transition instead of "vectors to final" will work, but will introduce a hold (in lieu of a procedure turn) at MKP. You must either manually delete the hold in the flight plan, or wait for the SUSP annunciator and then hit OBS to exit the hold.
Approaching AGC from due North, I selected the ILS 28, MKP-IA, set course direct MKP. The course was about 90 degrees to the FAF. When I got closer, ATC vectored me and got me onto the localizer just fine; I was no longer paying attention to the DTK value since I was flying vectors and had intercepted the localizer needle. When I crossed MKP, the Garmin did not sequence to the next waypoint. I'm guessing this is because my heading on the localizer was roughly perpendicular to the selected DTK to MKP. I think what I needed to do was re-select "direct MKP" once I was established on the localizer, so that the DTK value would be reasonably close to the final approach course. Gotcha!!! Will have to verify this on a later flight.
Hitting OBS in GPS mode takes the course from the HSI needle; you can rotate the knob on the HSI and watch the course line on the 530 move. This becomes the new DTK, so this is one way to fly a specific course to a waypoint. Here's the gotcha: popping out of OBS mode does not alter the modified DTK, so you may see "direct to XYZ" on the display, but the DTK won't take you there. You must use the Direct button to restore the DTK to an automatically calculated value.
If you're in GPS mode and want to intercept and fly a 280 degree course, e.g., to fly a straight-in final to runway 28 at a strange airport, hit OBS and rotate the HSI until the course reads 280, then cancel OBS. You could also manually set the CRS in the Direct dialog box. Hitting OBS in VLOC mode pops up a dialog box to ask for the CRS; it ignores the HSI setting.
If your flight plan contains the waypoint sequence ALPHA-BRAVO-CHARLIE, and you're flying the ALPHA-->BRAVO leg when you're cleared direct CHARLIE, hit Direct and scroll over to the waypoint field in the dialog box. The field will say BRAVO, but the inner knob will let you select CHARLIE. This is faster than going to the Flight Plan page. (This trick is actually in the manual, but easy to overlook.)

Departure and Arrival Procedures
On IFR departure from KAGC a common clearance is intercept AGC VOR 073^o radial to HOMEE. No way to enter that in the 530's flight plan, though. Solutions: (1) enter an AGC-->HOMEE leg (not KAGC-->HOMEE, which you get by default when starting up at AGC), which will put you on the correct radial. Or, (2) enter HOMEE as the first waypoint, then, when route is complete, hit Direct, select HOMEE, and you can enter a CRS value of 073^o in the dialog box.
Vector departure procedures, like the Capital 5 at Dulles, are not included in the database. Only RNAV departures are available in the database.

Approaches
Can't shoot an ILS/DME or LOC/DME approach because the procedure doesn't provide a way to measure mileage from the localizer antenna? Someone named "Doug" on rec.aviation.ifr pointed out that you can get mileage by selecting "direct to" the localizer identifier, if there is an associated DME, e.g., direct IAFJ works for Washington County's LOC/DME approach. (I found this works on the 530, but not the 150XL. Another reader reports it works on the 430 too.) Then you can select VLOC mode so the HSI is actually showing localizer guidance. Now you're not flying the IAP (as far as the GPS knows), but you can fly the procedure manually. You'll have to do the missed approach manually too.
Another rec.aviation.ifr reader points out that none of this should be necessary, since the 530 knows the approach procedures, and stepdown fixes expressed as DME values on the plate can also be interpreted as distance from whatever the next waypoint is in the Garmin's encoding of the procedure, usually the MAP but possibly a stepdown fix. Discuss amongst yourselves.
Failure to sequence: I was approaching AGC from the south, and told to expect the ILS 28 approach. I selected the approach on the Garmin, with the MKP IA transition, and activated it. This set my DTK to MKP to 351 degrees. As I got closer in, ATC began vectoring me, initially turning me right to 030 degrees, then left to 300 degrees to intercept the localizer, which I did. I flew the localizer and crossed MKP on a heading of around 280. The Garmin did not sequence to the next waypoint (MIFFY OM)! I'm guessing that this was because my heading was 70 degrees off the DTK it had computed to the waypoint, so it figured this crossing didn't "count".
Take home lesson: be aware that the Garmin computes its own course to an IA fix when you load (or activate?) the approach, and this becomes part of the flight plan; if the actual heading on which you reach the IA fix is going to differ significantly from the computed heading due to vectoring, you might need to hit the Direct button to recompute the course in order to get the 530 to sequence properly.
DME Arc: the Garmin will guide you through a DME arc as part of an approach, but the manual does not provide much guidance on how this works. DME arcs are covered only briefly, on pp. 71-73, and the example given in the manual does not look like what I experienced when I tried to fly a DME arc in the airplane. Approaching Erie, Pennsylvania (KERI) from the south, I requested the DME arc transition for the ILS 24 approach. This is a 61 degree arc at a 19 mile radius off the ERI VOR. The Garmin offered a choice of several IAFs for the ILS 24. The correct one, OMIRY, is not shown by name on the government plate for the ILS 24 approach! Fortunately it is shown on the VOR/DME OR GPS 24 plate. So I selected OMIRY as my IAF, which is located on the 121^o radial off ERI, and the Garmin set up the following curious flight plan:

OMIRY-ia 143^om 16.9 nm

dme arc ERI 19.0 nm

D066S 033^om 18.2 nm

CF24

WAILS-fa 242^om 7.5 nm

RW24-ma 243^om 4.5 nm

click for
larger version
1. The first line was a mystery. At the time I hit the PROC button to select the approach and transition, I was south of OMIRY, heading north. Why was the course shown as 143^o? It turns out that my en route flight plan had me flying direct to KERI. So when I selected the approach and the OMIRY transition, the Garmin calculated the course from KERI to OMIRY, not from my present position to OMIRY.
2. The second line indicated a DME arc segment flown at a radius of 19 miles from the ERI VOR.
3. The third line indicated the intersection of the DME arc with the lead radial for the turn onto the localizer: D066S means a waypoint at 066^o and 19 miles (because S is the 19th letter of the alphabet) from the VOR. But what were those two other values? Notice that 033^o is 88 degrees counterclockwise from the radial that defines OMIRY. The 033^o course is the initial heading along the DME arc at OMIRY, and has nothing to do with the lead radial that marks the end of this segment. And eventually I figured out that the 18.2 nm distance is the length of the DME arc segment from OMIRY to the lead radial waypoint. You can verify this by calculating (121-066)/360 * 2*pi * 19 = 18.2.
4. The fourth line, CF24, is the waypoint marking the beginning of the final approach segment, with a course of 242^o. (CF is apparently short for CNF, which the AIM says stands for Computer Navigation Fix.) It's only a short distance (but a large heading change) from the lead radial intersection to the extended final approach course; no values are given for this segment.
5. The fifth line shows WAILS, the FAF. The segment from CF24 to WAILS is 7.5 nm.
6. The sixth line shows the runway 24 threshold as the missed approach point. The distance from the FAF to the threshold is 4.5 nm.
"Viperdoc" on rec.aviation.ifr says the 530 will automatically change from GPS to VLOC mode on an ILS approach, but will not do so on a LOC or LOC/BC approach and requires manual switching. Haven't verified this myself yet.
On the VOR 28 approach to KBVI, there is an unnamed 5.0 DME stepdown fix off the Ellwood City VOR. The Garmin named this fix 50VOR.

Holding
To hold at a random GPS waypoint, hit the OBS button and input the inbound course for the holding pattern.
When holding, you will see two time values on the display. One is the ETA to the holding fix, and will be counting up or down depending on whether you're heading toward or away from the fix. Above and to the left is the holding timer, which always counts up, and gets reset each time you across abeam the fix.
Reset of the holding timer as you go around the racetrack is done automatically by the box.

Map Display
The green V thingie at the top of the Nav-1 compass rose is an RMI indicator. It switches to < or > at edge of display when RMI bearing is off screen.
On the Nav-1 page, the mileage scale goes from "5.0nm" to "5.0nm-A" during an approach. I think this is to indicate approach-mode decluttering; not documented in the manual. Hitting the CLEAR button cycles through other decluttering modes but you cannot get back to the -A mode.
If you're approaching an unfamiliar airport with a complex runway pattern and want to use the map to figure out your position with respect to your assigned landing runway, you should go to the Nav-2 page, because you can zoom in much closer on that page. The Nav-1 page won't zoom in closer than 5.0 nm and won't zoom out past 200 nm.

Miscellaneous
To enter maintenance mode, hold down ENT key on power-up; you still have to go through the two OK confirmations. To set comm parameters, use frequencies 118.0, 127.0, and 136.95. But you should probably not mess with any of this maintenance mode stuff. Frank Stutzman (who has a 430) says on rec.aviation.ifr that holding down CLEAR during power-up will reset everything to factory defaults, and wipe out all your customizations, flight plans, etc. I don't plan to test this.
When you creat a user waypoint by hitting ENT on the map page with the map cursor enabled, the Garmin will assign a computer-generated name starting with +001. If you don't want that name, move the cursor back to the name box and enter a new name. If you confirm the waypoint creation without changing the name first, then you must use the "rename waypoint" procedure: see next item.
You cannot rename a user-defined waypoint from the "Modify Waypoint" dialog box, which is unintuitive and stupid. Editing the waypoint name in that dialog box moves you to a different waypoint to modify. The only way to rename an existing waypoint is to go to the "list of waypoints" page, put the cursor on the waypoint you want to rename, and then twist the small knob to begin editing the waypoint name.

Dave Touretzky

Last modified: Mon Dec 12 02:26:58 EST 2005

Garmin Gotchas: GNS 530 GPS

Stuff I Learned the Hard Way

by Dave Touretzky

Vectoring and Course Specification

Departure and Arrival Procedures

Approaches

Holding

Map Display

Miscellaneous