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 073o 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 073o 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 121o radial off
ERI, and the Garmin set up the following curious flight plan:
OMIRY-ia 143om 16.9 nm
dme arc ERI 19.0 nm
D066S 033om 18.2 nm
CF24
WAILS-fa 242om 7.5 nm
RW24-ma 243om 4.5 nm
click for
larger version
- 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 143o? 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.
- The second line indicated a DME arc segment flown at a radius of
19 miles from the ERI VOR.
- 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
066o and 19 miles (because S is the 19th letter of the
alphabet) from the VOR. But what were those two other values? Notice
that 033o is 88 degrees counterclockwise from the radial
that defines OMIRY. The 033o 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.
- The fourth line, CF24, is the waypoint marking the beginning of
the final approach segment, with a course of 242o. (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.
- The fifth line shows WAILS, the FAF. The segment from CF24 to
WAILS is 7.5 nm.
- 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