Here is a collection of GPS tips from Tom Clements that appears on the 180/185 chat list.
I have a heckuva a lot of experience with many of the
latest GPS systems due
to my years of work as a King Air instructor. Thought it might me fun and
worthwhile to offer an ongoing "Tip of the Week" posting to present some of
the neat little ideas that I have learned -- a lot of which my students
showed me! -- on how to better utilize some of the most popular systems,
such as the Garmin 400/500 series and the Bendix-King KLN-90B. If this is
not a worthwhile function of the list, let me know and I'll shut up.
But maybe you'll find these little ideas helpful; I hope so.
When we set our (non-slaved) DG for the proper magnetic heading prior to
takeoff, how many people look at the compass? Of course we do -- and we
should! -- to make sure it is reasonable. But with the tail-low attitude, is
it in the best position to be really accurate? And when was the last time it
was swung?
Instead of setting your DG to the compass reading, try setting it to the
TRACK that your GPS is showing as you taxi. Unless you have some weird
crosswind gear installed and are taxiing in a crab angle, this is the exact
magnetic heading you are on. Even Lorans could provide Track fairly well,
but with GPS, Geez!, it is perfect! (If Track is not one of your normally
displayed parameters, it probably should be.)
So, Tip #1: Set your DG to the Track you are making while taxiing out,
nearing the takeoff runway. It will probably be more accurate than any
compass we have!
Tom Clements
N184TC
GPS Tip of the Week #2
Since I'll be at Reno for the Air Races this Friday, the GPS Tip of the Week
comes early.
You may recall that I said last week, If Track isn't one of your
normally-displayed parameters, it probably should be. Let's see why.
(For those of you blessed with the big-screen GNS 500 series, track is
always the number at the top of the HSI arc shown on Nav Page 1, so you have
it displayed automatically whenever you look at that page. Also, for both
the 400 and 500 series, Nav Page 2, the primary map page, can (and in my
opinion, SHOULD) be configured for a Track Up orientation, meaning that
again Track will always be represented as the top of the page. For the
KLN-90B, when Nav 5 is displayed on both sides of the screen to get the
Super Nav display, this can be configured in many ways, including Track Up
or, in some installations that are connected to a slaved-compass system,
Heading Up as well. So keep in mind that you may have Track information in
view, even when there is not a specific numerical value of Track being
displayed.)
Here's the Tip: Whenever you want to go direct to a waypoint, merely turn
the airplane so that Track equals Bearing. Voila! You are done! All
crosswind correction has been instantaneously applied and, so long as you
keep adjusting Track so that it stays with Bearing, you won't drift off
course.
I could be quite happy not having a DG nor a CDI/HSI display of the
airplane's course deviation so long as I have Bearing and Track. Yet I
observe many folks navigate with GPS just like they did with VOR: Namely,
center the needle and turn to that heading, fly that heading, watch which
way the CDI drifts, turn to a new corrected heading, wait for the CDI to
re-center, then try a new heading, etc., etc. In other words, Bracketing. Is
this wrong? Of course not! But why work so hard? Instead, when cleared
direct to ABC, make ABC the active waypoint, turn until Track is the same as
the Bearing to ABC, hit Direct and Enter as required to center the needle,
and off you go, occasionally making small heading changes to keep Track
equal to Bearing. You really only care about heading when you are curious
about what the wind is doing. Other than that, Track, not Heading, tells you
where the plane is going.
Remember to look out the window, too! In addition to looking for traffic,
one of the best ways to stay on Track is to have some distant aiming point
in view, perhaps that light-colored field, or the mountain saddle, or the
puffy little cloud. By keeping the nose aiming toward that reference, the
chance of staying on course and not wandering around unnecessarily is
greatly improved. Next time you find that you need to make a little Track
correction, find a new aiming point. (When in IMC, that's the time the DG
may provide the desirable aiming point a heading.)
Fly Safe, All!
Tom Clements
N184TC
GPS Tip of the Week #3
OBS vs. Leg Mode
I’ll bet that the difference between OBS and Leg modes of operation is one of
the most misunderstood aspects of GPS usage. Let’s see if I can shed a little
light on this topic.
Usually, GPS navigates on a great circle course, or leg, between two points,
either two waypoints in the database or between our present position and one
other waypoint. Also, once the “To” waypoint has been passed, the unit
automatically jumps ahead to the next leg, in which the old “To” waypoint
becomes the “From” waypoint for the new leg.
But in OBS (Omni Bearing Selector) mode, two significant changes occur. First,
the To waypoint will never change. Even when we pass it, we will still be
looking at our bearing and distance back to the point. Second, we can select any
course that we wish to fly relative to this waypoint, and we can fly the course
in either direction, either going To or From the waypoint…”just like a VOR.” In
fact, on the Garmin 295’s HSI page, when Menu is selected, one of the options
that shows up says “Set OBS and Hold.” That says it well…that we can set any OBS
course that we want and the To waypoint will be tenaciously held onto, with no
changes being made to a new waypoint. (And you thought that “Hold” word was
referring to an IFR holding pattern? Maybe yes, but probably no.)
So here is the Tip: When approaching any airport for a Visual landing (not
executing a published GPS approach) select OBS mode when about 10 miles out and
set the OBS course on the landing runway’s heading. (In the Garmin 400/500
series as well as with the KLN-90B, this is done by simply spinning the OBS knob
on the CDI or the Course knob on the HSI to the proper value. In other
manufacturer’s units, it may be done differently.) By so doing, we will always
have a picture of our position relative to the extended centerline of the
landing runway. Visualizing pattern entry becomes easier and lining up on an
incorrect runway becomes almost impossible if we check that we are close to the
selected course when on final.
There are some other neat uses of OBS mode, but we’ll talk about that later.
Tom Clements
N184TC
GPS Tip of the Week #4 -- Going Direct to
waypoints in the Active Flight
Plan
I know what you’re saying: “This is a no-brainer! I do this all the time.
It’s easy!” Yes, you’re right, but maybe I can show you a method that is
easier still.
To go direct to a waypoint that is already in the active flight plan, what
most of us do is to display the flight plan, turn on the cursor to highlight
the waypoint we want to activate, then hit Direct and Enter (once or twice,
it varies), and off we go. Agree? It works fine, and there is absolutely
nothing wrong with this technique…but there may be a simpler way.
For you Garmin 400/500-series folks, try this: Even though you haven’t
highlighted a waypoint in the flight plan -- in fact, you are probably
displaying your normal default Nav page -- hit Direct. Now look at the page
that shows up. There is a window on the center, left, side of the page
showing the current waypoint in the Flight Plan. Turn the big knob to
highlight that current waypoint. Now turn the small knob. See what happens?
There are all of your flight plan waypoints right there! Just select the one
you want and then hit Enter a couple of times. (Remember that you already
hit Direct, to start the process, so you don’t need to hit it again.)
For you KLN-90B folks, it’s even “cooler,” if that’s possible. With the
Super Nav page displayed, (that is, Nav 5 on both sides) pull out the small
right knob. Well, look what shows up now! The active waypoint appears like
magic in the lower right corner of the display. Now turn the small right
knob, still pulled out, and you can go forward or backward through all of
the waypoints of the active flight plan. When you have the one displayed
that you want to activate, hit Direct and Enter and off you’ll go. Now push
that knob back in to remove the clutter of displaying that waypoint on the
screen. But whenever you need to go to another waypoint in the plan, just
pull the knob out to find them. (This procedure only works for the –90B, not
for the –90A or the old –88 Loran.)
By the way, for you –90B users, unless you have the GPS coupled to a color
moving map, I suggest you make the Super Nav page your most common display.
Everything is here that you normally need, situational awareness is improved
by seeing the map, and it allows this neat trick you’ve just learned. On the
other hand, if your –90B is driving an Argus or an Avidyne or an MX20, then
the Super Nav page is redundant. Hence, like we said at the start, merely
displaying the flight plan page, using the cursor to select the new
waypoint, then going direct is as easy as anything else.
Y’all keep looking out the windows, too!
Tom Clements
N184TC
GPS Tip of the Week #5 -- Course Needle Sensitivity
(Warning! This is rather long and technical and a lot of it relates to IFR.
Delete and move on if you aren’t interested. It won’t hurt my feelings, I
promise!)
Unlike VORs and ILSs, deviation from a GPS-derived course is always
displayed as a function of the DISTANCE from the centerline, never as an
ANGLE off of the desired “radial.” (Radial is in quotation marks since it
correctly applies only to VORs, but I think it serves the explanatory
purpose here that I want.) Because GPS course deviation always shows LINEAR,
never ANGULAR, offset, we avoid any change in needle sensitivity as we get
close to a waypoint. “Zone of Confusion” over a station? No, never, with
GPS.
This makes for excellent autopilot tracking and permits even the hand-flyer
to nail the course centerline nicely. How much linear offset does it take to
peg the needle against the left or right side of the display?
All GPS units that are IFR-approach capable must have three different levels
of course needle sensitivity: Enroute, Terminal, and Approach. It takes 5.0,
1.0, and 0.3 nautical miles, respectively, to cause full needle displacement
in these three cases. (Thus, from side-to-side, the course widths would be
10, 2, and 0.6 nm). Non-IFR units may, and usually do, have different levels
of sensitivity, but 5.0 and 1.0 are very commonly available. (The Garmin 295
has 5, 1.25, and 0.25 choices. I wonder if these were chosen to emphasize
that this great little unit is NOT IFR-approved for primary navigation?)
Bendix-King, in the KLN-90B, uses different terminology for Enroute,
Terminal, and Approach. They show abbreviations for “Enroute,” “Approach
Armed,” and “Approach Active” instead, but it’s the same stuff.
Garmin automatically selects Terminal sensitivity whenever the airplane is
within 30 nm of the departure or the arrival airport, and annunciates it
appropriately. This is a good and correct benefit, helping to ensure more
accurate navigation when within the Departure and Arrival areas. However, if
you don’t have an airport as the starting point of the active flight plan –
for example, if you simply selected Direct to your destination when you
taxied out – then the Garmin units remain in Enroute sensitivity until you
get within 30 miles of the destination airport.
On the other hand, the KLN-90B never automatically leaves the Enroute level
of sensitivity unless a published Instrument Approach Procedure has been
called up out of the database and entered into the active flight plan. Even
if we are flying a published Departure Procedure or Standard Instrument
Arrival Procedure that comes from the KLN-90B’s database, the sensitivity
will be 5.0 nm, and that can make for rather sloppy course tracking in the
crowded terminal area.
So, at long last, here’s the Tip: You can change course needle sensitivity
whenever you want, and you should definitely make it 1.0 mile (Terminal) for
IFR Holding Patterns and IFR Arrival and Departure Procedures.
How? Well, like I said, the Garmin 400/500-series are way ahead of us --
selecting Terminal sensitivity automatically when near the departure or
arrival airport -- so about the only time we may wish to change the
sensitivity manually is when we are given an enroute Hold. In that case (or
just for the heck of it to see how it works) go to the “Aux” chapter, third
page, and select the “CDI / Alarms” function. There you will find a window
that is already highlighted by the cursor. Now use the small knob to select
the level of sensitivity that you want.
For the KLN-90B, use the large left knob to select the “Mode” chapter. There
you will find the current CDI sensitivity (plus or minus 5.0 miles, usually)
and by turning on the cursor, you may use the small left knob to select the
level that you want.
One last comment. Just for fun – and maybe as an ace-in-the-hole on some
dark and stormy night – you may wish to make a Present Position waypoint
while sitting on the landing zone(s) of your home base airport’s runway(s).
Also, learn exactly what the magnetic bearing of the runway(s) is by
observing your Track display as you roll down the centerline. Now, let me
emphasize: What I am talking about here is not a legal way to use the GPS
for IFR! It’s just a fun little exercise, OK? You aren’t gonna go out and
fly this when it’s below basic VFR weather, agreed?! But, by making that
end-of-runway waypoint active, by selecting the proper runway alignment as
an OBS course to it, and then manually selecting 0.3 nm sensitivity, I think
you will be amazed at how close this approximates a Localizer to that
runway.
Keep the little wheel behind you!
Tom Clements
N184TC
GPS Tip of the Week #6
Rejoining a Flight Plan Leg
So there we are, navigating on a flight plan that we’ve created, proceeding from
waypoint A to B to C to D to E to F. (I’ll label them this way for simplicity.)
As we are flying the “B to C” leg, either ATC (IFR) or our own initiative (VFR)
allows us to proceed direct to “E.” So, we highlight waypoint “E” and proceed
from Present Position direct to that waypoint. No big deal.
But then – and I realize that this scenario is rather unlikely, but it may
happen one in one hundred times – we must rejoin the appropriate leg of the
flight plan…the leg that we are currently abeam. How do we do this?
There are two ways, but one is better than the other. The first, less desirable
method, involves going direct to the end-of-leg waypoint (let’s call it waypoint
“D” in this example) and then selecting OBS mode. The course line on the IFR or
VFR chart shows that the proper inbound course to this waypoint is, let’s say,
“XYZ” degrees. You crank that setting into the CDI or Course needle, fly so as
to re-intercept that course, and then remember to switch out of OBS and back to
Leg mode before you arrive at “D.”
The other, preferred, method starts the same way, for you Garmin 400/500-series
users: Proceed direct to waypoint “D.” But then – Here’s the Tip – hit Direct
TWICE. Not once, but twice in succession. Look at what shows up. Instead of
proceeding from Present Position direct to “D,” now you are presented with the
option of flying the leg from C to D. You hit Enter to accept this option, set
up a heading to intercept the leg, and you’re on your way.
For the KLN-90-series, it is even easier. Hitting Direct – Clear – Enter, in
that order, is the trick. That is, to rejoin the leg of the flight plan that you
are currently abeam, depress three keys in succession, in the left-to-right
order that they appear at the bottom of your screen: Direct, Clear, then Enter.
Here’s what you’ve done. By hitting Direct, you told the computer to proceed
from present position direct to the current waypoint. But then, by hitting
Clear, you’ve told the computer, “No, I changed my mind. I don’t want to go
direct to that waypoint. Instead, you figure out what leg I am currently abeam
and set up that leg for me to follow.” Hit Enter to finish the command. Like
magic, the unit will re-create the appropriate leg.
( For the Garmin GPSMAP 295, when you are viewing the flight plan page and hit
the “Menu” key, one of the options is to “Re-evaluate” the Flight Plan. By
selecting this option, the same thing occurs: The unit “re-evaluates” where you
currently are on the flight plan and recreates the appropriate leg.)
So, no matter how far off course we may be and no matter what waypoint to which
we are currently heading, it is a relatively simple matter to rejoin the active
flight plan on the appropriate leg.
And remember, keep watching out for that other airplane that’s about ready to
nail you!
Tom Clements
N184TC
GPS Tip of the Week #7
Decluttering the Map
One of the very best features of the Garmin 400/500-series as well as the Bendix/King
KLN-90B is, of course, the moving map display. What a positive boon to improved
situational awareness! I suspect you may agree with me that there are times when
the moving map gets a bit too cluttered, too busy with waypoints, navaids, and
(for the Garmins) ground data. How can we get more out of the display by making
it show less?
Two basic methods are available. First, select a smaller range for the map
display. For example, try 30 miles instead of 50 miles. For the KLN-90B, this
will almost always remove some waypoints and declutter the display. For the
Garmins, we have the option of setting up our map to make it exactly like we
prefer, and, unlike the KLN-90B, we can select at what ranges certain items will
or will not be shown on the map. Hence, sometimes a smaller range actually adds
more screen clutter due to the fact that previously suppressed information may
now suddenly appears. So, with the Garmins, try a smaller range to aid in
decluttering, but be aware that it may not always serve the trick.
The second method involves clearing out unwanted information, regardless of the
range selected. In fact, the word “Clear” is the trick, and the Tip: For the
KLN-90B, whenever the Super Nav page (Nav 5 on both sides) is displayed, merely
depress the Clear key to eliminate all data except the current flight plan and
its waypoints. Depressing Clear a second time will return the display to its
original state. (Only Airports, VORs, and NDBs can be selected On or Off for
display on the Super Nav map. No matter what you may have selected for display –
maybe Airports and H(igh) and L(ow) Altitude VORs, for example – they’ll cycle
off and on by use of the Clear key.)
In a similar but slightly different fashion, hitting the Clear key on a Garmin
400 or 500-series unit allows the map to be progressively decluttered. When hit
the first time, a “-1” shows up to the right of the range mileage display. A
second hit causes a “-2” to appear. A third hit brings up – Yep, you guessed it!
– “-3.” Finally, a fourth hit brings us back to a fully capable display, showing
as much as it can.
Experiment with these decluttered displays to find what pleases you. As a
personal note, in most cases I do NOT de-clutter my GNS 530’s map, but I know
that the Clear key is always standing by to do the decluttering if I ever want
it.
Fly Safe!
Tom Clements
N184TC
P.S. My 530 seems to have suddenly died this week! When power is applied, a
faint pattern of lines appears on the screen, a few blinks occur, but that’s
all. I was working under the panel last week and maybe I bumped some critical
connection to the tray, but I don’t really think that I did. So the unit has
been pulled and will be checked out by a local Garmin dealer. Stay tuned for
further developments.
GPS Tip of the Week #8
Nearest Airport Criteria
I have been somewhat disappointed a number of times to notice that many of
the GPS units that I have observed installed in my clients’ airplanes have
never had their default Nearest Airport criteria changed. What good does it
do in a landplane to have seaplane bases show up in an emergency?! Gonna
glide to a seaplane base in the water instead of opting for the road or
field or land airport that may be just a tad farther? Why would a Learjet
want to be advised of airports that have their longest runway less than
2,000 feet?!
So, just in case you haven’t stumbled across the Nearest Airport Criteria
page yet, here’s where you’ll find it. For the Garmin 400/500-series, you’ll
find it in the Aux chapter. For the Bendix/King KLN-90B, it is under Setup.
Once you find the page, select the criteria that make sense to you: Runway
length, surface, land, sea, etc. For a King Air I would tend to go to,
maybe, hard surface, 3,000 feet minimum. For my 180 on wheels, maybe 1,500
feet, hard or soft, but no water runways. (Those little 1,000 foot farm
fields aren’t going to be in the database anyway!) You amphib pilots may
want ’em all listed.
I had a fellow suggest to me once that, with an engine failure, a glide to
an airport with a super short runway would still be preferable to a glide to
a farmer’s field that is longer but without any official airport “stuff.”
Although I didn’t really buy the idea totally, it did give me good food for
thought.
Also, for the KLN-90B, if you decide to have Airports displayed on the Super
Nav page – and I’d surely suggest that you do – the ones that don’t meet
your criteria won’t even show up on the map, so they won’t add unnecessary
clutter. I think this makes sense, but I haven’t yet discovered on the
Garmins if this is the case (but I don’t think it is).
So, Tip: Make sure you have reviewed how your Nearest Airport criteria is
configured and modify it as needed to suit what you want.
Also, just as a reminder: For the Garmins, Nearest airports are displayed in
the farthest “clockwise” chapter – Nav, Waypoint, Aux, Nearest. Remember
Obi-Wan Konobi from Star Wars? Well, now remember “N-Wan.” That is the order
of the Garmin chapters: Nav, Waypoint, Aux, Nearest.
For the KLN-90B, the shortcut to get the nearest airport(s) shown on the
right side of the window is to hit the two outermost keys below the screen,
left first, right second. That is, Message, followed by Enter. What you will
now see is the bearing and distance to the Nearest airport (NR 1), along
with the identifier and longest runway. By pulling out the small right knob,
the scanning knob, you will find the second nearest (NR 2), third (NR 3),
etc. up through NR 9.
Fly safe, y’all!
Tom Clements
N184TC
P.S. As a follow-up to my poor, dead, GNS 530 that I mentioned last week:
The panel wiring checked out OK, so we “knew” the problem was in the unit
itself. Westwind Aviation’s Avionics department at Deer Valley verified
this, and so my “baby” is on its way to Garmin for repair. Even though it is
a few months beyond the one-year warranty period, they have offered to fix
it free of charge. I only pay for the shipping. Garmin is one fine company
when it comes to customer support, as well as the innovative products they
create. Should take about two-weeks for turnaround.
GPS Tip of the Week #9
The Other Nearest Items
Last week I wrote about setting up criteria for the Nearest Airport feature and
reviewed how to find that listing of nearby airports. In an emergency – fire or
engine failure – it sure can be helpful to know immediately what the options are
for gliding to an airport. In that type of situation, we don’t care about the
nearest VORs or NDBs. However, it certainly is handy to have a list of the
nearby waypoints in other categories of the database, not just Airports. For
example, whenever I make a pop-up call to ATC, I prefer to give them my position
as a radial and distance from a VOR. Having that information quickly at hand
from the GPS makes life a little easier. Also, obsessive-compulsive pilot that I
am, I always want to have my VOR receiver tuned to a receivable VOR as I fly
cross-country, just in case the GPS has an unexpected outage.
Finding the nearest waypoints for categories other than airports is a snap in
the Garmin 400/500-series units. After we have accessed the Nearest chapter by
turning the large right knob fully clockwise (Remember N-WAN – Nav, Waypoint,
Aux, Nearest?), we can then use the small right knob to scan through all of the
pages of this chapter. The Airports page is followed by Intersections, NDBs,
VORs, User waypoints, ARTCC frequencies, FSS frequencies, and Airspace…in that
order. (I have always wondered why VORs aren’t second on the list instead of
fourth!) In each presentation, the bearing and distance are given from the
airplane’s position to the facility. So we need to do a reciprocal calculation
in our head to find the VOR radial that we are on. No big deal.
By the way, I forgot to mention last week the fact that anytime the Direct key
is hit, the page that shows up includes the nearest airport that may be
highlighted with the cursor. Once that is done, turning the small right knob
will scroll through the identifiers of the other nearby airports. If you find
one you want to go to, just hit Enter a couple of times.
For the KLN-90B unit, only nearest Airports, VORs, and NDBs are available, not
Intersections or Supplementary (user-created) waypoints. You already know how to
access the nearest Airport: Hit the Message key followed by the Enter key. That
action zips the right side of the display to the NR 1 airport. By pulling out
the small right knob, we can then scan through the next nearby airports until we
get to NR 9. At that point, one more clockwise click of the scan knob brings up
the first airport of the entire database, probably 00M, Bay Springs,
Mississippi. If you were exceedingly patient, you could then, click by click,
scan through the entire airport database, in alphabetical order: 0, 1 through 9,
then A through Z…over 15,000 airports!
See if you can follow me through on this explanation: As we maneuver the
airplane to various locations, the GPS computer always calculates the nearest
nine airports and copies them to the “head” of the airport alphabetical listing.
The “Message, Enter” key sequence jumps us to the start of this listing, but
even without that shortcut we could always find this nearest grouping by going
to the airport category of the database and then scanning backwards
(counterclockwise) until we can’t go any further.
In an identical manner, the KLN-90B does the same thing with VORs and NDBs.
Namely, it always copies the nearest nine to a listing that appears at the head,
or start, of the alphabet. Hence, to find the nearest VOR, merely select the VOR
chapter with the right large knob. Now pull out the right small, Scan, knob and
spin it rapidly counterclockwise a few times. Since this knob is rate-sensitive,
spinning it fast will leap through huge hunks of the VOR database and, in no
more than three or four spins, you will find yourself looking at the VOR that is
NR 1 (Nearest One). Now, clicking the knob clockwise, you’ll find NR 2, NR 3,
etc., up to the nearest nine VORs. After NR 9, the next clockwise click will
bring you to VOR “AA,” Auckland, New Zealand, the start of the alphabetical
listing of VORs.
NDBs work exactly the same way, but, like airports, there are some NDBs with
numbers in their name, so the list starts with 0 through 9, before it gets into
the A through Z list.
One additional comment about the KLN-90B: Although it doesn’t keep track of many
nearby ARTCC and FSS frequencies -- unlike Airports, VORs, and NDBs – it does
offer one of each. Look for these under the Other chapter on the left side of
the display.
Tip of the Week, then, is to realize that your situational awareness may be
improved by keeping track of the nearest VOR as you fly long legs, and that info
is readily available from your GPS.
Whether STOL-kitted or not, gap-sealed or not, big tail-wheeled or not, big-engined
or not…have fun with your own version of these classic airplanes, and fly safe!
Tom Clements
N184TC
GPS Tip of the Week #10
IFR Approaches
In a word, Don’t!
I know that statement is going to raise some hackles, and that is the shock
value I intend. Simmer down. Here’s what I am really saying: Don’t use your
marvelous GPS units to conduct non-precision IFR approaches in IMC until you
know what the hell you’re doing!
I have seen too many pilots – including lots of professional, competent pilots –
who have never made the effort to learn what a GPS approach is all about. Unless
you are familiar with the “T” pattern of the standard approach, know what TAAs
are about and why they’re not like MSAs, know how to set your unit up while
receiving radar vectors for the approach, know how to enter and leave holding
patterns, know how to make course reversals/procedure turns, know the difference
between Leg and OBS modes and when to use each, know what RAIM is, know about
the different levels of course needle sensitivity…unless these tasks are
commonplace and meaningful to you, then you aren’t yet ready to use your GPS for
IFR approach work.
Tip of the Week, then, is to acknowledge that using the GPS instead of a VOR or
NDB for an approach is not necessarily an easy thing to do, and should be
avoided until learning has occurred.
There. That was short, eh? Maybe not short and sweet, just short.
Next week I’ll give some ideas about how to get the learning that you need.
Tom Clements
N184TC
P.S. The final follow-up to the “death” of my GNS 530: Yes, the Garmin factory
did discover a “bad component” and repaired the unit free of charge. I only paid
for the freight, to and from. The unit came back with the latest Service
Bulletins and software complied with and installed, and, instead of the two-week
estimate, it was back in my hands in less than eight days. Wow! I am impressed
with this level of customer support! My only complaint is that the User
waypoints that I had created were now gone. (In the future I think I’ll
regularly write down the Lat/Long locations of my User waypoint list, just in
case the unit ever crashes again.)
GPS Tip of the Week #11
Learning How to Properly Execute GPS IFR Approaches
Last week I promised to offer some suggestions regarding how one could become
proficient in the use of the GPS for IFR approaches. Here, in no particular
order, are some thoughts about that topic.
First, read the book. That is easy to say and hard to do. No one enjoys plodding
through the large Operating Manuals that come with these units, but it must be
done. It is something that cannot be done just once. Read a little, go practice,
read some more, practice some more, etc. It is absolutely amazing how much more
you will glean from the book when you reread it after gaining operating
experience with your unit.
Second, having a method of practicing with your GPS at home is most worthwhile.
Lonestar Aviation, as well as some other companies, offers docking stations for
the various popular units that not only allow you to practice with the unit in
the comfort and quiet of your home, but also, if you choose, allow some of the
units to have their databases updated using a laptop after you have downloaded
the database from the internet. (This saves some bucks over giving the
cartridges mailed to you.) Try this website to see what is offered:
http://www.lonestaraviation.com/Product_type.asp?Product_Type=Docking%20Stations
For the Garmin units, you can obtain nearly identical practice using their free
PC-based simulator instead of purchasing a docking station. As of August 2002
their simulator has been updated to reflect the latest software changes, so even
if you have already downloaded this before, you may wish to do it again. Go to
http://www.garmin.com/aviation/index.html and download the trainer version you
want, either 430 or 530. Without a highspeed internet connection this may take
hours, so do it some night as you go to bed. Except for the fact you must click
and/or drag some buttons instead of twisting the actual knobs, this simulator is
superb. It even includes a miniature throttle quadrant and autopilot control
panel so that you may “fly” through whatever navigation maneuvers you want,
including radar vectors, procedure turns, and holding patterns! Remember: It’s
free! Get it!
I think there is also available a similar PC-based simulator for the KLN-90B,
provide by an outside vendor, but I have not used it so have no opinion as to
its usefulness. Perhaps some of the group can offer insights here?
Third, view a tutorial for your system. For the GNS 530, there is a fabulous
training discussion available, written by Mike Busch, that is available on the
Avweb site. It also includes info about the 430. It is loaded with tons of
actual pictures of the display screen during various phases of IFR operation.
Check it out at http://www.avweb.com/articles/gns530/ . This is such a useful
and excellent tutorial that it takes some significant amount of time to view and
learn from it. Set aside a quiet evening – cocktail in hand, preferably – and
log some computer time as you enjoy it. My hat is off to Mr. Busch. What a nice
job he’s done here!
For the KLN-90B, there is an excellent two-hour videotape available that covers
all aspects of the unit quite thoroughly. The tape was created by…me! A few
years ago I made this tape for use in my own King Air and Duke classes, but it
was so well-received and asked for, that we made it available to the public and
it has sold quite well ever sense. Go to http://www.flightreview.net/index.htm
to order, or email me direct. $30 is the cost, and I guarantee it will be money
well spent. It’s not fancy, but it’s mighty good for learning the Bendix/King
KLN–90B.
Fourth, get the latest version of the AIM (Aeronautical Information Manual) or
the Jeppesen equivalent and read under “Air Traffic Procedures” the information
about “Instrument Approach Charts.” (In my Jepp AIM, it is section 5-4-5.)
Again, I know this takes some effort and it is not overly exciting, but I think
you will be stunned by the amount of new information provided that you haven’t
realized was there, especially lots of new stuff about RNAV (GPS) approaches,
TAAs, and the like.
Fifth, get a safety pilot to watch for traffic, and do lots and lots of GPS
approach practice in Visual Meteorological Conditions. Do it all: Procedure
turns, radar vectors to final, full stop landings, missed approaches, holding
patterns, repeat approaches.
Sixth, get an instructor who knows your unit and practice with him or her. This
is sometimes not available, since not too many CFIs or CFIIs really have enough
experience with a particular brand of GPS unit to be considered expert. If you
are in the Phoenix area or schedule with me at a fly-in, I will be glad to help.
Avionics West, in Santa Maria, California, is now providing scheduled classes on
the Garmin units, and the feedback about them is good. Check out http://www.avionicswest.com
for more info.
Remember, these suggestions are in random order, not necessarily in order of
priority. Depending upon your background, some will be more helpful than others.
The main thing is, don’t get discouraged. There is a lot to learn, yes. But it
is certainly not an insurmountable task and, when you finally have the light
bulb of understanding illuminate, you’ll never do a pure VOR or NDB approach
ever again because the GPS is that much better!
Don’t forget to watch for traffic!
Tom Clements
N184TC
GPS Tip of the Week #12
Stepdown Fixes on the Final Approach Course
This discussion applies to the execution of published GPS approaches. Those VFR-only
pilots in the group may want to delete and move on.
A recent question was raised asking why all of the stepdown fixes aren’t shown
as waypoints in the mini-flightplan that constitutes a GPS approach. Before I
give my answer, let me emphasize the importance of comparing the waypoints that
show up after the GPS approach is loaded with the waypoints you see on the
Instrument Approach Plate. The FAA has some work left to do in this area,
because things are not nearly as clear as they should be. Sometimes, the plate
will give a name for a fix that is not identified by the same name in the GPS
database. Nevertheless, with some comparison and study of the plate vs. the GPS
waypoints -- before the approach begins -- we should be prepared and
knowledgeable about what is to come.
One of the requirements that must be met before the GPS unit will transition to
the Approach level of course needle sensitivity (0.3 nm center-to-side,
remember) is that Leg mode, not OBS mode, is active. Let’s take a quick poll.
Raise you hand if you have ever miss-set a course needle/OBS value. Have you
ever entered 107 instead of 113? How about 185 instead of 175? Yep, as I
thought, it is about unanimous: We’ve all made those little errors, and maybe
wondered off course a little before we (or ATC) caught our booboo. On the Final
Approach Course of a GPS approach, however, that type of mistake cannot be made.
Oh sure, we may still screw up and set the wrong value (unless our course needle
automatically slews, like on the Sandel and other EFIS units) but it won’t
affect our course deviation information. Why? Because we must be in Leg mode,
where the setting of the course needle/OBS value has no effect on CDI operation.
And what are the waypoints that make up the Final Approach Course, the course
where we need the 0.3 nm needle sensitivity? The starting waypoint is the Final
Approach Fix (FAF) and the ending waypoint is the Missed Approach Point
(MAP)…always!
Since the FAA/industry team that designed the rules for GPS approaches mandated
that the Final Approach Course must always be a leg from the FAF to the MAP,
there can never be a waypoint between these two fixes, since this would mess up
the leg we are on, making it into two or more legs instead.
So here is the Tip: Stepdown fixes will never show up between the FAF and the
MAP.
“But wait, Tom, you dingbat! There ARE stepdown fixes on the plate! I see ‘em!
Darn it, I need to know when I can safely descend!”
Yep, they sure do exist lots of time, and, yep, you can always figure out when
to leave one altitude for the next. How? By checking the distance to go to the
FAF. In every instance where a stepdown fix is shown, you can always determine
how far it is from the MAP. The mileage figures show up on the Profile View,
right above the line representing the “ground” (runway elevation) beneath us. In
a few cases, you may have to add a couple of numbers together. (“Let’s see now.
If the last stepdown is 1.3 nm from the runway and the one before that is 0.8
miles short of it, then that first one comes at 2.1 nm from the runway.”)
Also, for stepdown fixes prior to the FAF, either the fix will indeed be labeled
and shown or else you will always be able to “back it off” from a future fix.
Get out some approach plates and examine them closely, paying particular
attention to how you would determine the distance back from the MAP for stepdown
fixes between the FAF and the MAP. Not too hard, eh?
I happen to have the first book of my Jepp USA library in front of me and the
very first approach in it is the VOR or GPS-A to Alabaster, Alabama (KEET).
Without GPS, doing this only as a VOR approach, the FAF, named ALRIC, will come
when we are outbound on the 099 degree radial, 19.0 DME from the OKW VOR, or,
without DME, when we also are crossing the 176 degree radial of VUZ VOR. The
minimum altitude at that point is 2,300 feet. We then descend to 1,500 feet
until we get to 21.0 DME. Without DME (or GPS) that’s as low as we can go in IMC.
But, with the DME increasing past 21.0, now we can go on down to 1,340 feet (the
MDA for Category A aircraft). The MAP comes at a DME reading of 23.7 nm, or if
we are still at 1,500 feet without DME, we started the timer passing the FAF and
now the MAP comes in 3 minutes and 8 seconds if our average ground speed had
been 90 knots. That is the time required to cover a distance of 4.7 nm, from
19.0 to 23.7 nm.
Doing this same approach as a GPS approach, the final leg is from ALRIC to MACYI,
MACYI being the name given by the plate designers for the 23.7 DME fix on the
OKW 099 degree radial. As we cross ALRIC, the GPS jumps to the ALRIC – MACYI leg
and we note that we have 4.7 miles to go to the MAP. We descend to 1,500 feet
until the GPS says that we have 2.7 miles left to go to MACYI, then we step down
to the MDA. As the GPS distance hits 0.0, the To-From flag switches, the mileage
starts counting up, and we proceed either to circle for a landing (no
straight-in procedure here) or execute the missed approach procedure.
Even though I picked this airport at random, the approach illustrates a point I
feel strongly about: It will be easier when the VOR system is phased out and we
don’t have these “VOR or GPS...” mixes. How confusing it is when the DME is
counting up as we proceed to the airport but the GPS is counting down! Again,
you’ve got to examine the approach thoroughly beforehand to avoid last minute
surprises.
Tom Clements
N184TC
GPS Tip of the Week #13
Holding Patterns: Why time ’em?
A fact of life for the IFR pilot is the possibility that he or she may have to
execute a holding pattern at some time during the flight. Although they are
quite rare most of the time, it is still something that occasionally pops up.
Also, if a course reversal is required during a stand-alone (not a VOR or NDB
overlay) GPS approach, it will invariably be an entry to a published holding
pattern, never drawn as the traditional 45/180-degree procedure turn.
The classic method we were all taught about timing holding pattern legs –
adjusting the outbound leg time so that the inbound leg time would be as close
to 1 minute as we could make it – came about in the days before DME was readily
available. When DME is available, however, the AIM indicates that the timing of
holding pattern legs may be replaced, with ATC concurrence, by a DME leg length.
With GPS, we always have distance information available to the active waypoint.
Hence, the Tip is this: Don’t worry about timing holds any longer. Instead, use
an appropriate outbound leg length.
What airspeed are we going to fly during the hold? Certainly not cruise speed!
Why waste fuel? Instead, pull back to 15 inches and minimum RPM and loiter
around at 90 knots or so. At 90 knots, we cover 1.5 nm every minute. What if –
without even asking ATC! – we just flew outbound until we were about 1.5 nm from
the fix before turning inbound. Do you think the controller would know or care
that we weren’t diligently working at timing the hold? Of course not!
Better yet, especially if this hold is going to be a lengthy one, copy what the
airliners and other “professionals” do and ask for a leg length of 5, 10, or
even more miles. In my experience, a request for a reasonable leg length – I
usually use 5 nm for the 180 – will never be denied. So, once we have been given
the green light for this, now merely fly outbound until the distance back to the
holding fix is 5 nm, and then start the turn back in. A clearance for a 5 mile
leg does not mean that you must remain within 5 miles of the fix! No, it means
that you start back in at that distance. If the wind blows you out to 6 or 7
miles before you start converging back to the fix, so be it! And yes, the 5 nm
you see when you start turning is a diagonal measurement across the hold back to
the fix, not really a leg length, but that, too, has all been considered.
Now the Garmin 400/500-series units, when involved with a published holding
pattern (not one made up by ATC at some unexpected fix) even start and reset the
clock automatically as your track goes outbound and inbound during the hold. How
cool is that?! It is a great piece of additional information, but, again, why
worry much about it since you can fly by distance? Also, the holding pattern
that is drawn on the Garmin moving map is generic in size, so just making sure
the airplane stays on the oval track displayed won’t necessarily provide either
the correct timing nor distance.
One last comment: If you are using the holding pattern entry as the course
reversal of a published Instrument Approach Procedure, in lieu of another type
of procedure turn, and if the holding fix is also the Final Approach Fix (as it
usually is) then make sure that you extend outbound a minimum of 2 nm before
turning inbound and re-selecting Leg mode. If you cut in too early, your unit
probably won’t have time to conduct a RAIM check and activate Approach needle
sensitivity prior to reaching the FAF.
Tom Clements
N184TC
_____________________________________________
GPS Tip of the Week #14
Bulletin! Bulletin! Before I present this Tip, I want to let you know how much I
appreciate the responses that I have received from some of you, including the
good questions that you have raised. The GPS Tip of the Week has had a good run
but I have nearly exhausted my reservoir of ideas that I think are helpful.
Except for two or three more weeks, during which I will try to answer some
questions that were posed, this topic may be dead. I will be happy to continue
it in the form of responses to any questions, problems, hints, etc. that you
wish to propose. I believe in the adage that “There’s no such thing as a dumb
question.” Unless a question is asked, others aren’t challenged to think and to
provide/find an answer. I certainly don’t have all the answers but, as a group,
we probably can help each other a great deal! Jot down any GPS topics you can
think of and send them my way so that I can present my ideas and solicit group
response. Now we return to our regularly-scheduled broadcast…
Using OBS Mode to Fly From a Waypoint
In past discussions, we compared Leg and OBS modes of operation and talked about
one good use of OBS mode: Namely, to set up a course inbound to the landing
runway at the destination airport, when operating VFR.
Just remember this Tip: Whenever you want to fly an exact course of your choice
either to or from a waypoint, OBS is the mode to use.
Just the other day, I was flying in a King Air C90 from Scottsdale, Arizona (KSDL),
to Carlsbad, California (KCRQ), VFR at 16,500 feet, with flight following from
ATC. We had picked a route that would avoid the MOAs and Restricted Areas along
the way until we arrived at Blythe VOR (BLH). Then the flight plan went direct
to KCRQ, but this leg slightly entered a Restricted Area over the Salton Sea.
So, after BLH, I flew a heading slightly off course to the right, using the
moving map to avoid the Restricted Area. When we cleared the last corner of the
Restricted Area, we turned direct to Carlsbad and, after re-centering the
needle, I noticed a Desired Track of 240 degrees. I filed that number away in my
brain for future reference
When leaving Carlsbad later in the day, still VFR, I called up our KSDL-KCRQ
flight plan and activated it in the inverted format, from KCRQ to KSDL via the
intermediate waypoints. Once the flight plan was active, it showed us on the leg
from KCRQ to BLH. As before, this direct leg would cause us to infringe upon a
Restricted Area. So, I did the following: (1) I selected Direct to KCRQ, so that
it became the active waypoint. (2) I selected OBS mode and dialed in a course of
060 degrees, the reciprocal of the 240 course I had observed earlier. (3) Upon
departure, I adjusted my track so as to remain on 060 degrees, keeping the
needle centered as I flew outbound from KCRQ. (4) Watching the moving map, I
waited until I could see that I was clear of the Restricted Area and could turn
direct to BLH without any infringement. At that time, (5) I left OBS mode and
went back to Leg mode, did a Direct To BLH, and continued on to KSDL via the
flight plan routing.
I presume that most of you have experienced a similar situation in which you
know that a particular course going away from your departure airport will keep
you away from whatever you want to avoid: Restricted or Prohibited Areas, Class
B airspace, high terrain, other airports, etc. Remember that you can use OBS
mode to fly the course that you desire, the one that will avoid the stuff you
don’t want to hit. You may even want to sit down with a sectional chart and plot
a few outbound courses from your home airport, courses that will head you in the
general direction you wish to go but without interfering with the areas you wish
to avoid.
(Of course, I guess you could merely look out the window and “pilotage” your way
along the course…Nah! That’s not nearly high tech enough!)
Y’all be careful, hear?
Tom Clements
N184TC
GPS Tip of the Week #15
Vertical Navigation - VNAV
VNAV! Man, that is a formidable subject to discuss! Before I make a few
observations about how VNAV is addressed on the Garmin 400/500 series and on the
Bendix/King KLN-90B, let me tell you my “old fashioned” method of VNAV
calculation.
Usually our goal during descent planning is to hit a particular location at a
certain altitude, and to do it is such a manner that our and our passengers’
ears aren’t subject to unnecessary discomfort. For example, let’s say we are
cruising at 9,500 feet MSL and want to be at traffic pattern altitude (TPA) five
nautical miles before we arrive at an airport with an elevation of 500 feet.
Since the modern TPA for piston-powered airplanes is 1,000 feet above the
airport, that means we need to lose 8,000 feet (9,500 – 1,500). At 500 fpm, the
descent will require about 40 miles, so I will start the descent when 45 miles
from the airport.
How did I know that the descent would require 40 nm? Easy. I multiplied 8
(thousands of feet to lose) by 5. Why 5? Well, at 150 knots ground speed, we are
covering 2.5 nm every minute. Since we are losing altitude at 500 feet every
minute, that means that, as each two minutes elapses, we will lose 1,000 feet
and cover 5 nm. In other words, we need 5 nm to lose every 1,000 feet. I call
this 5 number our “Altitude Factor.” Of course, if the GS is less, then the
Altitude Factor will also be less if we maintain the 500 fpm descent rate. I’ll
do the math for you: 120 knots GS? Use an Altitude Factor of 4. 150? The factor
is 5, as has been shown. 180? Use 6. 210? (For Rob’s Wonder Wagon coming out of
the flight levels with a tail wind!) Then 7 is the factor. (By the way, with
pressurization and the ability to descend more rapidly without ear discomfort, a
very commonly used Altitude Factor is 3.)
Once learned and truly embraced, this Altitude Factor technique is so easy that
a quick “howgozit” check can be made often during the descent, and minor
corrections may then be made to the rate of descent. Let me show you how this
works,. Using our previous example, we needed 40 nm to lose 8,000 feet, so we
left 9,500 feet when 45 nm from the airport. Passing 7,500 feet, heading to the
TPA at 1,500 feet, we mentally say to ourselves, “OK, got 6,000 feet left to go.
6 times 5 equals 30. I need to be 35 miles from the airport. The GPS says that I
am 33 miles from the airport. I am two miles ‘behind’ my descent profile, so
I’ll tweak the descent rate just a little bit steeper.”
Later, passing, say, 3,500 feet, the thinking goes like this. “3,500 for 1,500.
2,000 to go. 2 times 5 is 10. I need to be 15 miles out. The GPS says I am 16
out. Hey! Close enough for government work!”
There are certainly other methods of descent planning. A very common one is
based on Estimated Time Enroute to the waypoint. At 500 fpm, a loss of 8,000
feet will require 16 minutes, so start down when the ETE shows that time to go.
The slight problem with this method, however, is that the 16 minutes showing on
the GPS will be to the airport, not to that TPA entry point five miles out.
Also, flying IFR, when the controller says something like, “Descend at pilot’s
discretion so as to cross 20 miles southwest of the Redding VOR at and maintain
3,000 feet” the ETE-based method becomes quite difficult since we are looking at
the ETE to the VOR, not to that phantom point 20 miles away from it. For myself
and many others, the Altitude Factor method is much easier and more flexible.
Then there’s always the LAR method: Looks About Right! Let’s start down now! And
NO method works very successfully when that big mountain is sitting between you
and the airport, right?!
Well, of course, the GPS units have been programmed to do the math for us and to
let us know how to descend to make any crossing restriction using any rate of
descent that we desire. Since I see that we have already rambled on into a
second page of this Word document, I think I’ll bid you adieu for now and we’ll
continue the topic next week.
G’Day, Mates!
Tom Clements
N184TC
GPS Tip of the Week #16
Vertical Navigation Continued
As we said last week, VNAV (Vertical Navigation) is a heckuva big topic. Using
an Altitude Factor, as we reviewed last week, is one method by which descent
planning is fairly easy and manageable. A nice back-up to that method is to
utilize the VNAV functions in the two GPS units we have been discussing, the
Garmin 400/500 series and the Bendix/King KLN-90B. The two different
manufacturers approach the VNAV task in quite different ways.
For Garmin, you start by accessing the VNAV page -- by hitting the VNAV key for
the 500-series or selecting the VNAV page in the NAV chapter for the 400-series.
Once there, you enter the parameters “asked” of you: The Target Altitude you are
descending to, the Target Position in terms of a waypoint name and a distance
back from that waypoint where you want to arrive at the altitude, and the
Vertical Speed Profile (rate of descent) desired. If the waypoint is an airport,
and since the unit knows the airport’s elevation, you can enter the final
altitude either as an MSL value or as a height above the airport (HAA). Once
these parameters are entered, then a number appears in the “VSR” field (Vertical
Speed Required). This field is always shown on the VNAV page and it also may be
displayed as a field on the Map page. In fact, on the second page of the Nav
chapter in my GNS 530, the Map page, I have the following five fields usually
showing on the right side, from top to bottom: Distance, Bearing, Track, Ground
Speed, and VSR. It is interesting that even though you perhaps entered a desired
VS of 500 fpm, the field will show whatever is currently required, no matter
whether it is a small value like 50 fpm or a steep profile like 2,000 fpm. It is
a very simple task to start the descent when the VSR is something you like, and
then adjust your rate of descent as necessary to keep it there.
I have been asked about using this VSR display to better plan descents to the
runway threshold during non-precision approaches. Here’s my answer; you may not
like it: Don’t do it!
Why? First of all, there are a lot of important parameters to watch and tasks to
perform while you properly execute any approach, especially a non-precision one
that may contain turns and step downs. Trying to make it like an ILS will merely
add to the workload and, perhaps, lull one into a false sense of security and
tempt one to continue down below MDA. Wait until WAAS (Wide Area Augmentation
System) gets approved in the next couple of years and until true
three-dimensional guidance becomes available. That will be the time to utilize a
glideslope-like function. The second reason for not doing it? Because you can’t!
The Garmin units are programmed to blank out the VSR field when you pass the FAF
and get on the Leg to the MAP! Guess the engineers agree with me that worrying
about VSR at this time is not wise.
Yes, I know, we could have a very lively discussion comparing two techniques:
(1) Utilizing a stabilized descent to MDA such that, if required visual inputs
are received in time, that we may then continue this descent to the runway,
versus (2) The classic “Dive and Drive” method. Let’s have someone start a new
thread on this if need be.
The KLN-90B presents VNAV information in a far different manner. The Nav
Chapter, Page 4, is where the desired parameters are entered: Target Altitude,
Waypoint, Distance back, etc. Altitude always has to be an MSL value, not an HAA.
However, now you need to specify not a desired Rate of Descent but a desired
Angle of Descent instead. For the Skywagons, an angle of 1.5 or 1.6 degrees
works quite well. (And by the way, the Calculator Chapter has a page on which
you can enter any ground speed and rate of descent and the angle this
combination yields will be calculated and displayed. Vice versa, you can also
enter a GS and Angle, and see what Rate is required.)
Once the information has been “typed in” on Nav 4, VNAV is now armed. Starting
ten minutes away from the Top of Descent, the top line of the Nav 4 page changes
from saying “VNAV Armed” to displaying a countdown clock. As the clock hits
0:00, it is replaced with an altitude readout. Your goal is simply to adjust
your vertical speed so that the altitude you are passing through is equal to the
altitude in the display. (I have heard this value called “Slope Altitude,” the
MSL height you should currently have to stay on the proper descent slope.)
As I have stated before, I spend 90 percent or more of my time with the Super
Nav Map (Nav 5 on both sides) displayed, when using a KLN-90B, because it is so
dang handy! On that page, by turning on the left cursor and moving the cursor
with the large left knob up to the third line from the bottom, the parameter
shown there can be changed from ETE (where mine is most of the time) to XTK
(Cross-Track Error, which I rarely ever display) to VNAV. So, once I have gone
to Nav 4 to enter the values, I then return to Nav 5 on both sides and change
that display line to show VNAV. Just like on Nav 4, a clock starts when ten
minutes out, counts down to zero, and then the Slope Altitude shows up. Match it
on the way down and – Voila! – there we are, right where we wanted to be as we
enter the Traffic Pattern or make the IFR crossing restriction.
Although both the Garmin and Bendix/King approaches to VNAV work just fine, I
must admit that this is one tiny area in which I prefer the –90B. One
interesting additional comment about the –90B method, however: Let’s say that
when you entered the descent parameters that you were at 11,500 feet, but later,
to avoid a lowering cloud base, you went down to 9,500 feet. As the countdown
timer starts, showing you how much longer until TOD, it will still be
calculating the descent based on your being at 11,500! You can handle this in
two simple ways. First, merely be patient, wait for the Slope Altitude to catch
up with you, then match it the rest of the way down. Second, once level at 9,500
feet, re-enter the desired parameters on Nav 4 to make the unit compute a new
VNAV profile.
And, guess what? I don’t even know for sure if the –90B will keep VNAV displays
going during the final leg of an IFR approach, but I suspect that it will.
However, I probably would be giving it little if any attention at this critical
time.
################
Well, friends, there you have it. It’s been challenging and fun writing these
Tips for the last four months, but now my brain is picked clean. Let me know if
questions arise as you use your units; perhaps I can help. But meanwhile, this
will be the last Tip that I plan to write. John Huft has been kind enough to
copy and display all of the Tips on his website, in case you wish to review them
at any time: http://www.lazy8.net/gps%20tips.htm
Aren’t we all blessed to fly these fine machines with this exciting equipment?
Amen!
Bye for now,
Tom Clements
N184TC