Amidst all the attention on GPS handhelds and all the confusion about the future of WAAS and its impact on existing approach-certified GPS receivers, II Morrow's new GX55 is the most exciting panel-mount GPS we've seen yet. Its highly-legible built-in moving map display puts the Bendix/King KLN-89 and -90 to shame. Best of all, the price is right (about $3000) and the unit is a simple slide-in replacement for older II Morrow Lorans and FlyBuddy GPSs (no tray or wiring changes, just a new antenna).
September 6, 1998
|About the Author ...
Tom Rogers is Avionics Editor for AVweb.
Avionics West, Inc. at Santa
Maria, California, one of the finest radio shops on the West Coast. Tom is an
instrument pilot, an FAA Designated Engineering Representative (DER) for
avionics, and has a Ph.D. in nuclear physics. (We're not sure why he got the
doctorate, but we call him "Dr. Tom," and he seems to like that.)
You can send Tom your avionics questions at
Tom's company, Avionics West,
is one of the worlds largest discounters of handheld and
panel-mount avionics for general aviation. They offer all leading brands of
aviation electronics at deep-discount prices. Every item sold by AWI is
covered by a 30-day no-questions-asked return privilege.
Avionics West features handheld GPS receivers from Garmin and Lowrance;
headsets from David Clark,
LightSPEED and Telex; and panel-mount GPS navigators from II Morrow. AWI
stocks these units and generally sells them at prices substantially below the
manufacturers' "Minimum Advertised Price" (MAP). Consequently, AWI is not
permitted to advertise these prices on its web site, but you can obtain them
by sending an email to the AWI auto-responder at
by telephoning AWI at 1-805-928-3601 (M-F, 8-5 Pacific Time).
|Ask Tom an Avionics Question
Nowadays, everyone wants a moving map along with their GPS. Up until now, you've had
- Install a Bendix/King KLN-89 or KLN-90 and make due with their extremely crude moving
- Install an Argus moving map costing thousands of dollars, and put up with the extra lost
panel space and yet another database that needs to be updated; or
- Rely on a yoke-mounted handheld GPS with moving map, and accept the resulting clutter of
wires and low-contrast liquid-crystal display.
Why doesn't someone come out with a good, high-resolution, easy-to-read moving map
integrated into a panel-mounted GPS? I'm happy to tell you that II Morrow has done exactly
that with their new GX55.
As if that wasn't enough, II Morrow went one better with the GX55: they made it
rack-compatible with their 600-series Lorans and their 800-series FlyBuddy GPS. The rack
is the same, the wiring is the same, so installation is a snap: just slide out your old
Loran, slide in the new GX55, and change the antenna. That's it! No change in wiring is
required. If your Loran drives your autopilot and/or your HSI, then the GX55 will do the
The GX55 display gorgeous. It's electroluminescent, which is nothing new in aviation
but you just don't see this type of display often offered in the price range of the GX55.
Display resolution is 160 by 80 pixels, which is comparable to that of the II Morrow
Precedus handheld (but of course with far better contrast). A photocell controls how
bright the display is, dimming it automatically for nighttime operations. Directly below
the display are five "smart" keys which do some great things that we will
discuss later. The main keypad features the same familiar push buttons that II Morrow has
used in its past GPS models, so if you've used any of them your learning curve will be
short. My favorite button is the "Direct" button. Push it, select the airport
and push "Enter." Now you're on your way to wherever you wanted to go.
The GX55 has a datacard that just pops out the at the push of a button, just like the
high-end GPS units. The datacard may be updated as often as every twenty eight days and
covers the Americas. The card has the airports, VORs, NDBs, intersections, and special use
airspace. The GX55 also allows you to store up to 500 user-defined waypoints, and up to 35
user-defined flight plans of up to 20 legs each (reversible).
The GPS engine is a parallel 8-channel design, which means it can normally track all
visible satellites at once, not just the four required for a 3D position fix or the five
required for RAIM. The unit has standard CDI outputs (left/right, to/from, and flag) so
it's easy to interface with any standard nav head or HSI. It also has a standard RS232
bidirectional data port for interfacing with your fuel totalizer, notebook computer, or
what have you.
The feature list is long, but you can read it in the brochures. Let's cut to the chase
and deal with the really important questions. Is it user friendly? Is it built well? Can
you see the display easily in bright daylight conditions? Will it wind up being an
obsolete lame duck like the Lorans it so neatly replaces? That's what I wanted to find out
when my shop, Avionics West, installed our first GX55 in a
customer's Cessna not long ago.
Inspecting the Merchandise
Time to tear open the shipping box and see what we've got. This is not a demo model,
it's one that we just received to be installed in a customer's aircraft. (I refuse to
write about products only using a demo model. Many products that demo well don't hold up
in a real field installation.) We find GX55 to be packaged well, making damage in shipping
extremely unlikely. The GPS receiver and installation materials are packaged in
anti-static bags. We inventory all the parts and find everything to be present, right down
to the Allen wrench used to lock and unlock the GX55 from its mounting tray.
The GX55 case is made totally of sheet metal, and even the front bezel is metal. We
check out all the buttons and knobs, and they feel just like buttons and knobs should
feel. (I've found this to be true throughout the II Morrow product line.)
Since this is our first GX55 installation, I can't stand the thought of putting it in
the airplane without first opening it up to see what's inside. My challenge is to
disassemble the GX55 without destroying it. Once the covers came off, I'm in for a real
shock: the inside of the GX55 is mostly air! Less than half of space inside is actually
utilized. One large printed circuit card, a small card and the display card. That's it!
Clearly the only reason the GX55 is so large is so that it will fit in the existing Loran
trays, otherwise it could be half-size. Another benefit of all this open space is that the
radio runs cool and no forced-air cooling is required.
Like all of the latest-generation avionics from II Morrow, the circuit boards are all
surface-mount. This makes them extremely compact and reliable, but if you ever have a
problem with the GX55 you'll want to send it back to the factory for repair. This is not
something you can work on with your Weller gun!
The 10-year lithium battery that keeps the memory alive when the unit is powered down
is not soldered to the board, so anyone can change it when it gets weak (if you still own
the airplane). Early GPS models had the battery soldered to the board and had to be
returned to the factory for battery replacement, but not so with the GX55. Examining the
circuit board, my only wish-list item is that they included a replaceable fuse.
The circuit boards and case represent high American-built quality. Fit and
finish are good. No jagged edges anywhere. Everything fastens together with machine
screws, again showing quality. I find three different Quality Assurance inspectors' stamps
just on the case alone. It appears someone is interested in quality. Another minor
complaint: the unit serial number is attached with a sticker instead of being etched into
or hard-mounted to the case. Granted, the GX55s serial number is in the software, but I
personally feel better when the serial number can't be removed from the case.
Having reassembled the radio apparently in one piece, I glance at the manual just to
see if it is written in plain English. I find the user's guide easy to read, and the
operation steps make sense. The manual even comes with a quick reference guide, what I
call a "cheat sheet." It also has a troubleshooting guide in the back, and II
Morrow's 800-number in case you come across something you can't figure out. Finally, after
all these years, the manufacturers seem to be letting pilots write the manuals, not
software engineers. From what I can tell, though, the only time you'll need the manual is
when you first initialize the GX55, and perhaps the first few times you use the flight
plan mode. Everything else is bone-head basic.
Let's Fire It Up
Now it's time to plug the GX55 into the power supply and light the thing up. By the way
you can order a cable/connector from II Morrow (p/n 500-4027) and plug it into any 10-40
volt DC power supply, so you can familiarize yourself with the unit (in simulation mode)
at home. The moving map operates in simulation mode also, and you will see fixes go by,
special-use airspace alerts come up, and so forth. I recommend doing this before using it
in flight, because I've found it's much easier to learn new equipment at home than in the
cockpit. In the flight simulator mode the GX55 will fly flight plans and warn you about
special use airspace just as if you were in the flying machine. The only things that don't
work at home are the remote lights and CDI outputs, of course.
I power up the GX55 on the bench for the first time, and already I like it. The display
is simply outstanding in the ambient light of this room. I hold the "Nav" button
as I turn on the GX55, which places it in the "Flight Simulation" mode. The GX55
lets you know in no uncertain terms that you are in the simulator mode as "NOT FOR
FLIGHT" appears on the display. It then asks you to push a couple buttons to set your
simulated groundspeed and altitude. Now all you do it tell the GX55 where you want to go
(using the "Direct" and "Enter" keys) and you're off.
The nav pages show you all the usual things such as a CDI indicator, groundspeed,
waypoint identifier, ETA, ETE, track, bearing, UTC and just about anything else you could
want. I found the on-screen UTC display to be a great tool in IFR conditions, no more
adding with the watch. There's even a page that shows you the minimum safe altitudes (MSA
and MESA). MESA is the altitude you'll need to fly to clear the terrain by 2,000' along
the flight-planned route. This can be very handy in flight planning: if the MESA is
16,500' for your trip and you are flying a Cessna 150, then you may want to plan a
Navigation Made Easy
Another neat feature of the GX55 is the ability to customize each nav page. You can
make each page show what you want to see. If you want the CDI, groundspeed and UTC on the
first nav page, then you can customize it that way. There is also an "autonav"
mode in which the unit automatically displays each nav page in rotation. While some II
Morrow users swear by this feature, I swear at it: I find it annoying because when I want
a particular piece of nav information, I can't stand waiting until the right page scrolls
by. I found I could get all the data I normally need on one customized nav page, so I
never have to change pages or resort to autonav mode.
The GX55 has a flight timer that can be programmed to start running once you've passed
a certain groundspeed (for example, 60 knots). In other words, once you exceed 60 knots on
takeoff, the timer starts; once you drop below 60 knots on your landing roll, the timer
stops. Neat, huh? (I wonder if the timer will run or stop if you're in a spin going
straight down at 120 knots?)
The "Direct-To OBS" function is really handy when you need to intercept a
particular radial from or bearing to a fix. To activate this feature, you press the
"Direct" key twice, then dial in the desired bearing using the concentric data
entry knobs, not unlike what you'd do with a normal OBS knob. Then you intercept the
bearing, much as you'd track a VOR radial. Of course, the fix needn't be a VOR, and this
function can be really handy for tracking extended runway centerlines.
Whenever you're navigating to a waypoint, you can press the "INFO" key to
display data about the waypoint: frequencies, identifiers, lat/lon, and (if the waypoint
is an airport) runway lengths, runway lighting, ILS frequencies, field elevation,
available fuel, and so forth. There's even a place to enter comments, so you could put in
the phone number of the local taxi or mention in the comment section no fuel is available
after 6:00 PM or whatever you want to remember about that waypoint.
Pressing the the "NRST" key brings up a list of the nearest 20 airports; if
you turn the large knob, you can see the nearest 20 VORs, NDBs, intersections and
user-defined waypoints. In each case, the fixes are sorted from nearest to farthest away,
and you'll see the distance and bearing to each from your present position. There's even
an arrow on the display to give you a general idea of which way the fix is, so you can
turn toward it quickly in an emergency. If you want more information about any of the
fixes on the "NRST" list, you can get it simply by pressing the "INFO"
button. To navigate to one of the fixes on the list, simply press "Direct" and
"Enter." It's very intuitive, and all of this also works in the simulation mode
so you can try it out at home.
While in NAV mode, the "Smart Keys" come into play. These are keys beneath
the display that have software-generated labels above them to show their function. For
example, by pressing the "DB" Smart Key you can create a waypoint defined by
radial and distance from any known fix, similar to the old rho-theta RNAV units. The
"DB" Smart Key also allows you to delete or modify your user-defined waypoints.
Pressing the "FPL" Smart Key puts you in the flight plan editor and lets you
create, modify, delete, and activate flight plans. The "SYS" Smart Key lets you
customize your nav pages, adjust CDI sensitivity, and set other system parameters. It also
lets you theft-proof your GX55 by entering your name and a password, if you wish. These
Smart Key functions are very powerful, but I suggest you learn to use them on the ground
before trying them out in the air.
Now That's A Moving Map!
Finally, we come to the piece de resistance, the GX55's MAP mode. I believe that
II Morrow should be required to placard the unit as follows:
GX55 CONSUMER WARNING:
If you try the MAP mode, you will buy this unit!
Friends, it's that good. The GX55 map is much like an Argus 3000
with a course line, except that in my opinion it's easier to read than the Argus. All you
do is keep the aircraft on the course line and maintain airspeed and altitude.
Now here's where things get even better. The Smart Keys in the MAP mode are labelled
APT, VOR, INT, NDB. I'm sure you know what they stand for. Here's how they work. Let's say
you push the "APT" Smart Key. The button lights up and airports appear on the
moving map display along with their identifiers. Now push APT again, only the outside
edges of the button are lit, and the airports remain on the screen but their identifiers
disappear, thereby decluttering the screen. Press APT again and now only the outline of
the button is lit and the airports disappear, further decluttering the display. The VOR,
NDB, and INT Smart Keys work the same way for fixes in those categories.
This is really slick. In most moving maps (including the Argus and all the handhelds
I've tried), you have to work your way through a bunch of menus in order to declutter the
map display, and that usually turns out to be more trouble than it's worth. With the GX55,
you can control what appears on the map with a simple press of a key. Special-use airspace
is always shown on the map.
While in MAP mode, you can adjust the scale of the moving map from 0.1 mile to 250
miles simply by just turning the small knob. Auto-range is also supported, but I wasn't
thrilled by it. You can configure the GX55 to warn you when you approach special-use
airspace. This is a great feature and easy to use. The "MSG" Smart Key will
flash if there is something you need to know, such as approaching or entering special-use
airspace or losing your GPS position.
By turning the large knob, you can put the GX55 into a split-screen mode with a moving
map on the left side of the display and nav information on the right side: waypoint ID,
distance, groundspeed, bearing, track, and off-course distance. The map is smaller in this
mode, but quite useable if you use the Smart Keys to declutter it. You can also remove the
course line on the moving map but I don't know why you would do that. Just keep the
aircraft on the line and look out the window for traffic, it's so simple.
With all this, I've only touched on about half the features of the GX55, but these are
the most important ones. To say this is a feature-rich radio is putting it mildly. But
enough fiddling around on the bench. Let's install this puppy in an airplane!
Installation Made Simple
II Morrow made the GX55 rack-compatible with the prior panel-mounted Lorans they built.
Of course, if you don't have an II Morrow Loran in your aircraft, you can purchase a
installation rack and have the GX55 installed. But our first GX55 sale is going into a
Cessna R-182 that had a II Morrow 618TCA Loran installed with a top-mounted antenna, so
installation should theoretically be a snap. I told the customer to allow three hours for
installation because this was our first GX55 installation and I wasn't really sure what I
was getting into. I learned long ago that things often aren't as easy as they seem.
We remove the 618TCA from the rack with a screw driver, slip the GX55 into the rack,
and tighten it down with the supplied Allen wrench. What a difference in weight! The GX55
only weighs 2.6 pounds (it's mostly air, remember?), while the Loran weighed over 4
pounds. Obviously the weight and balance will have to be updated.
Now for the antenna. Fortunately, this Loran antenna was top-mounted so we could put
the GPS antenna in the same location. (Bottom-mounted antennas don't work with GPS!) We
had to remove some of the headliner to get to the nuts that held the antenna mounting
screws on. Removing the old antenna is a two-person job, one to hold the nuts inside the
cabin and one to turn the screws outside. (How many avionics technicians does it take to
screw in a lightbulb?)
II Morrow was smart, they made the foot print of the GX55 GPS antenna exactly the same
as the Loran antenna, so no new holes have to be drilled. We install the GPS antenna with
new mounting screws and torque them down. The Loran antenna used what we call a BNC
connector at the end of the coaxial cable, but the GPS antenna requires a higher-quality
low-attenuation TNC connector, so we have to change the connector. The TNC requires
special tools to install, so you'll probably have to get your avionics shop involved. You
could use a BNC-to-TNC adapter but doing so defeats the purpose of the low-attenuation
connector, so it should be considered only as a last resort. We have the necessary tools,
so we install the TNC on the cable, connect it to the new GPS antenna, and reinstall the
Now for the exciting part. We pull the Cessna out onto the ramp, power-up the GX55,
initialize it with the current time and location, and within 4 minutes it is tracking
satellites and working fine. Now back inside the shop to revise the weight and balance and
complete the 337 form. We gain about 3 pounds of useful load. Total install time: less
than an hour, including the paperwork. (Had the Loran antenna been on the bottom of the
aircraft, the installation could have taken several more hours because the GPS antenna
must be on top of the aircraft, no exceptions.)
Flying the GX55
I tell the customer that I want to do a test flight with the new GX55. I explain that
this is necessary to verify that the GPS will work with his Cessna autopilot, but the real
reason is because I'm always looking for an excuse to fly and anxious to see how this unit
performs in flight. The customer agrees, so up and away we go. I select a destination
waypoint and press the "Direct" button and "Enter." The GPS gives me a
bearing of 335 degrees, and I set up the autopilot for nav-coupling and engage it. The HSI
needle centers up and the autopilot keeps it centered. So it appears the GX55 outputs will
work the same as the removed Loran did.
Now I turn the aircraft so the sun is directly on the display. I want to see if it will
wash out in bright light. It doesn't. I think the GX55 display is one of the best on the
market. LCD and LED units aren't even in the same league, and I'm not convinced CRT
displays (e.g., KLN-90, Argus) are any better (but they sure cost and weigh more).
I fly directly to an intersection and ask ATC to verify that they show me right at that
fix, which they do. I shoot an ILS in VFR conditions and watch the runway come up on the
moving map of the GX55. True, you can't use it for approaches, this is a VFR-only
installation. But seeing that runway in front of me on the moving map is a good feeling.
We land and I reluctantly turn over the keys to the owner. Later in the week, I call the
customer and ask what he thinks of his GX55. He tells me he loves it, and is still blown
away by the performance for the dollar.
The Bottom Line
I have subsequently installed a bunch of GX55's and all my customers have been ecstatic
about the unit. (If my customers aren't happy with a product, then I won't sell it.) When
they hand out the "product of the year" awards, I'd like to see II Morrow get it
for the GX55. It's easy to use, easy to read, and the customers love it. That's what it's
POSITIVES: Finally manufacturers are waking up and offering aircraft
owners what they want. Removing an outdated Loran and installing a GPS with a moving map
that slides in the same rack is great! It's easy to read and operate for under $3,000; by
comparison, installing an IFR-approved GPS plus an Argus moving map would cost more than
$8,000. The user's manual is in plain English. The radio has buttons and knobs that feel
like they should. The user interface is easy to learn and use, the map decluttering
features are the best I've seen, and the database can be updated by the owner simply by
changing plug-in datacard. And the GX55 is a high-quality made-in-USA product with
excellent factory support. What more could you ask for?
NEGATIVES: It's not certified for IFR approaches...but give me a
break: less than1% of the II Morrow Lorans that the GX55 is designed to replace were ever
certified for IFR-enroute, much less IFR-approach. Actually, the GX55 is TSO-C129 (Class
A2) certified for IFR enroute and terminal flight (not approaches). But to have it
installed as IFR-capable may not be just a slide-it-in affair; you'd need to add external
"Message" and "Parallel Track" annunciators, and a connection to a CDI
or HSI is required.
To install an approach-certified GPS, you'd have to re-wire the aircraft to meet the
IFR requirements, which could cost thousands of dollars. My advice to most owners is to
install an inexpensive VFR GPS like the GX55 and plan on waiting a few years until things
like WAAS sort themselves out before thinking about spending a small fortune on an
approach-certified GPS installation.
CAVEATS: If your Loran antenna is bottom-mounted, installation of the
GX55 will cost more because a completely new antenna installation on the top of the
aircraft will be required. Even with a top-mounted Loran antenna, the GX55 isn't quite
owner-installable because of the TNC connector (which requires special tools to install)
and the requirement to file a Form 337. And after reading this article, somebody's bound
to ask, "Tom, you said this unit is half-full of air, so why does it cost