Panel Planner 101: Round-Gauge Bonanza

Drop-in electronic round gauges avoid cutting a well-kept traditional panel. A WAAS navigator and audio panel upgrade add new utility.

This month’s panel for planning is on a 1962 Beech P35 Bonanza. It’s a panel that was once nicely reworked (before the glass age) into a logical arrangement of traditional six-pack and round engine instruments.

Top of the food chain in the late 1990s, there’s a first-generation, non-WAAS Garmin GNS 430 GPS that feeds a UPS-AT MX20 MFD. ADS-B traffic and weather are on the standalone stack-mounted L3 NGT9000 ADS-B transponder. 

Audio comes from a Narco CP136 audio panel and PS Engineering PM1000 intercom. A TKM comm radio, Narco NAV122, King DME and (an oldie but goodie) Avionics West stereo/cassette player finish off the radio stack. It has an S-TEC 60-2 two-axis autopilot with GPS steering, a small-display engine monitor and Electronics International 2-inch digital tachometer, manifold pressure and fuel totalizer instruments. 

There is good attention to detail, plus useful accessories on the clean, old-school instrument panel—a huge upgrade from the one it had in 1962—and one you might think twice about cutting into. Let’s go shopping.


Wisely, owner Aram Basmadjian goes into this upgrade with a realistic view of prices, plus a plan for future upgrades. A flagship Garmin glass, autopilot and engine monitoring retrofit will be an $80,000-plus investment, so he’s breaking this into stages. After a good demo at AirVenture last summer, he settled on Garmin’s GI 275 drop-in electronic flight instruments—one to replace the vacuum AI and another in place of the DG. Out comes the vacuum system.

While the S-TEC 60-2 is a capable autopilot, Basmadjian’s long-term goal is upgrading it with Garmin’s GFC 500. It’s a weight-saver over the multi-box and aging S-TEC system. For flight displays, the three-screen Aspen Avionics Evolution 2500 MAX PFD/MFD suite was an attractive option (roughly $13,000) to the $8800 Garmin GI 275 instruments, but the Aspen was a deal breaker because it won’t work with Garmin’s GFC 500. But it’s compatible with the NGT9000 ADS-B transponder, displaying traffic and weather on the Aspen’s MFD.

 In a future upgrade (likely a Garmin G3X Touch or Dynon HDX big-screen suite), the GI 275 AI can be used for backup. The two-instrument GI 275 portion of the installation was quoted at $13,880.

Over in the avionics stack, it’s time to remove the old stuff for current-day real-world utility. But all is not lost. The GNS 430 and GI-106A indicator will serve as a secondary nav/comm/GPS system. While Basmadjian, a former airline captain, is more than comfortable flying into big airfields where ILS approaches are still the norm, it’s time to add RNAV GPS approach capability to the panel.

“Just this week, the ILS went down at my home airport (Lehigh Valley International in Pennsylvania), and the non-WAAS GNS 430 had me relegated to LNAV minimums on the RNAV approach,” he said. The path of least resistance might be to remove the GNS 430 and slide in an Avidyne IFD440. That would require a GPS antenna (and antenna cable) change and minimal wiring. Basmadjian gets along better with buttons and knobs when the air gets bumpy, and Avidyne’s hybrid IFD has both touch and hard controls. Still, he’s comfortable with Garmin’s touch-only GTN 650 and 750 touch navigators, but prefers the larger GTN 750 because of more screen real estate. I’d suggest considering Avidyne’s IFD550 when deciding on which navigator to go with. Basmadjian has time to sort it out because his shop told him it can’t touch the project until May 2023. 

A worthy upgrade to the old Narco audio panel and PS Engineering intercom is the PS Engineering PMA450C Bluetooth audio system. At $2600, plus installation, it’s worlds ahead of the old Narco. Add a good ANR headset—maybe a Lightspeed Delta Zulu with CO detecting or Bose A20—and the result is a pleasing cabin audio experience.

As for the old MX20 MFD that’s on the pilot’s panel, removing it will leave a big hole in an otherwise clean layout. But since it’s out of horsepower, and Basmadjian just happens to have a later-model GMX 200 display that will fit in its location, it’s a good temporary solution with reasonable amounts of mapping utility.

Not counting a GPS upgrade, the proposal is just shy of $19,000, and it will be every bit of $30,000 with one. But that’s better than $80,000, while offering good utility and preserving a good-looking panel.

Editor in Chief Larry Anglisano has been a staple at Aviation Consumer since 1995. An active land, sea and glider pilot, Larry has over 30 years’ experience as an avionics repairman and flight test pilot. He’s the editorial director overseeing sister publications Aviation Safety magazine, IFR magazine and is a regular contributor to KITPLANES magazine with his Avionics Bootcamp column.