Tuning in Terra
A trim and tidy avionics stack.
BY MARK R. TWOMBLY (From AOPA Pilot, December 1994.)
AOPA's Better Than New 172 is equipped with a center stack of Terra Avionics radios. Why Terra? We've had plenty of experience with Brand K they were installed in the Good As New 172 last year and we wanted to play the field. We were intrigued by the light weight, compact size, and installation flexibility of the individual Terra units. Those are major considerations when panel real estate is precious, as it is in a 172.
Terra offers a top-of-the-stack-to-the-bottom complement of solid- state, digital-display gear including the TMA 230 D audio panel/marker beacon receiver, TN 200 D nav receiver with glideslope receiver, TX 760 D com transceiver, TGPS 400 GPS (manufactured by Trimble), TDF 100D ADF, and TRT 250 D transponder. Also, the company has a unique product in the Tri- Nav electronic course deviation indicator. Electronic CDIs are not new, but no company other than Terra currently offers one. Given the number of microprocessors busily controlling the many digital-display instruments across most of the rest of the Better Than New panel, the Tri-Nav seemed the logical choice.
Finally, Terra's prices are attractive. The stack of Terra avionics in the Better Than New 172, which includes everything listed above plus backup nav and com units but not the GPS (the airplane has a Garmin GPS certified for non-precision instrument approaches), lists for $10,270 uninstalled.
The decision to go with Terra was not without some hands-on experience. I have been flying with Terra radios in my Skyhawk for more than a year. Soon after buying the airplane, I added a Terra TMA 230 D audio panel/marker beacon, replaced a decrepit Narco unit with a TN 200 D nav receiver with glideslope and TX 760 D com transceiver, took out a conventional CDI and replaced it with a Tri-Nav, and added a Terra TGPS 400, which is the same as a Trimble TNL 1000 DC. Given the narrow confines of my avionics budget, I had to live with the remainder of the radio gear in the airplane: a Michels MX-300, an old but superb Bendix T12B ADF, and a Cessna 300A transponder that is close to getting the boot because it seems to prefer working a part-time schedule.
The Terra upgrade transformed the airplane. Although it had a current IFR certification with the old equipment, I wasn't keen on flying in the clouds with radios of questionable character, and no precision approach capability. With the new stuff, I launch into weather with confidence. The audio panel, which has toggle switches to select speaker or phones and a three-light marker beacon, works flawlessly. The nav and com displays are bright and crisp, and each has a standby frequency displayed plus a 10-frequency memory feature. I was skeptical about the usefulness of the memory function, but I took a few minutes one afternoon to read the manual and enter 10 com frequencies and 10 nav frequencies in the storage bins. I've been pleasantly surprised to find that it's a handy, useful feature.
I have become a fan of the Tri-Nav indicator. Terra readily admits that many pilots resist the change from a simple swinging needle CDI and analog glideslope indicator to an electronic presentation, but I think the electronic processing and presentation are a step forward. Full-scale deflection on the deviation bar is 10 degrees left and right, same as a conventional CDI, but the bar is composed of 14 light bars, each representing a 0.7 degree deviation. The larger scale on the electronic CDI means off-course indications appear sooner than on a conventional instrument, which makes for quicker course corrections and more precise flying. The same is true of the electronic glideslope deviation bar.
The indicator also has a lot more capability than a conventional one. It can display the active radial from a second VOR receiver or, in the case of the Tri-Nav C, a loran or GPS track. The signal source, whether a To/From radial, Localizer, ILS, or Backcourse, is displayed. The instrument also has a To/From radial-centering feature and a count-up electronic timer.
Terra's TGPS 400 is a GPS receiver with a front load slip-in Jeppesen NavData aviation database card. The 400 has a liquid crystal display that has proven to be perfectly satisfactory. The installing shop recommended the GPS be placed high in the stack for maximum readability, and that was good advice. The 400 has all the typical features of a state- of-the-art VFR GPS except special use airspace alert a lamentable omission, but one that enables a lower price. No surprise, the GPS is an incredible enhancement to a humble Skyhawk.
I did experience failure of the nav receiver display about a year after the radio was installed. The radio was shipped back to the Terra factory in Albuquerque for repair. A big plus for Terra is the three-year, no-cost warranty on all its equipment. The customer pays shipping charges only; Terra picks up parts and labor costs.
I've also had some difficulty tuning nav and com frequencies in turbulent conditions. The radios each have a single knob to scroll up or down through the frequency ranges. The knobs are hair-trigger sensitive, and when the airplane is bumping around it is difficult to tune the kilohertz frequencies precisely. Terra says a few customers have had similar complaints. The company is contemplating a survey of its customers to see if nav and com frequency tuning is indeed perceived as a problem.
Until recently Terra's digital transponder employed the same single-knob-scroll tuning system as the nav and com units. The company recently made a software change to the TRT 250 D that is now being field tested in a few units, including the one installed in AOPA's Better Than New 172. In the new version, the tuning knob controls one squawk code digit at a time. You push a button to move a cursor to the next digit to tune. It's a more accurate and faster method of inserting the proper transponder code.
The FAA earlier this year issued a proposed airworthiness directive that would require the 5,300 or so TRT 250-series transponders shipped from 1985 to March 21, 1994 be returned to the factory for modifications. It seems that the new ATC Mode S radars and airborne traffic alert and collision avoidance systems (TCAS) emit a unique pulse that momentarily jams the Terra transponder's circuitry. The transponder's original design met then-current FAA specifications, according to Terra officials. The company believes the FAA should pay for the changes. So far the FAA has refused. As it stands now, the fix costs the transponder's owner about $300. The comment period on the airworthiness directive closed in early November. A final decision from the FAA is expected soon.
AOPA's Better Than New is just beginning to build time with its spectacular panel. One nav reception problem has been reported. On a recent long cross-country trip the nav receiver did not pick up a good VOR signal until within about 40 miles of each station, even though the airplane was flying at relatively high altitudes. The source of the problem, which could be related to the antenna or installation, has not yet been identified. I have not had a nav signal reception problem with the TN 200 D in my Skyhawk.
The Terra upgrade has greatly enhanced an older, nowhere-near- good-as-new Skyhawk. I now have far more sophisticated avionics that weigh less than what they replaced. The much more extensive package in the Better Than New 172 is in harmony with the full panel's digital personality and capability. The eventual owner of the airplane will be able to fly it to its fullest potential.
3520 Pan American Freeway N.E.
Albuquerque, New Mexico 87107-4796