GNC 255-style NAV/COM

A panel NAV/COM in the style of the GNC 255A, with its white-on-black dot-matrix display: COM and NAV active/standby with station names, an OBS page with a CDI, and a T/F line with radial, distance, ground speed and time to the VOR. Its FUNC menu gives recent, user and nearest frequency lists and a timer. Comes as NAV/COM 1 or NAV/COM 2.

Modeled on: Garmin GNC 255A-style NAV/COM
Category: Radios and panels
Size: 2 × 1 cells
Version: 1.0 · 2026-10-19
Plan: Pro
Simulators: MSFS 2020 · MSFS 2024 · X-Plane 11 · X-Plane 12

Variants

NAV/COM 1v1.0

Tunes and shows COM 1 / NAV 1, OBS turns the NAV 1 course

Picker: RADIO > NAV/COM 1

NAV/COM 2v1.0

Tunes and shows COM 2 / NAV 2, OBS turns the NAV 2 course

Picker: RADIO > NAV/COM 2

Features

Active and standby frequencies with the station on each (e.g. KSLE TWR, the VOR ident), found from the airports and navaids around
TX while transmitting, RX while receiving, SQ when squelch is open; ID on the NAV side while its ident audio is on
OBS page: the needle on five dots each side, a TO / FROM triangle, FLAG without a valid signal, the station and course, and the active COM (CM ACT)
T/F: the DST line with the radial FROM or the bearing TO the VOR, distance (NM), ground speed (KT) and time to the station
FUNC menu: COM lists (RECENT, USER, NEAREST APT / ACC / FSS / WX), NAV lists (RECENT, USER, NEAREST VOR), ICS, SYS and TMR configuration pages
Recent lists fill automatically as frequencies are made active; ENT stores the standby as a user frequency (up to 15)
Count-up / count-down (5 min) timer shown at the bottom right
Holding the swap key puts 121.5 into the COM active
COM / NAV volume bars on the bottom line (display only); MON shows MN instead of STB (display only)
Display dark without avionics power; dimmed at night with the faceplate under the red flood light

On the iPad

Drag around the TUNE knob: outer ring for MHz, inner knob for the channel of whichever (COM or NAV) is selected; in OBS it turns the course (outer 10 degrees, inner 1 degree); in menus and lists it scrolls
Tap the swap key to swap active and standby; in a list, puts the entry straight into the active; hold it for 121.5 on COM
Tap C/N to switch between the COM and NAV pages
Tap OBS for the OBS page (again to leave)
Tap T/F to cycle the DST line: off, radial FROM, bearing TO
Tap FUNC for the function menu; ENT opens an item; in a list ENT loads the standby; CLR backs out (on the main page, clears the timer)
Tap ENT on the main page to save the standby to the user list
Tap MON to toggle the monitor indication; push the COM knob for SQ; drag the COM / NAV knobs for the volume bars
Push the NAV knob (PUSH ID) to toggle the NAV ident audio

Settings

Which radio: NAV/COM 1 or NAV/COM 2 (picker variant)
In-unit SYS/ICS pages (COM spacing, sidetone, brightness, contrast, intercom) are shown but have no simulator effect

Keys and controllers

Map any of these to a key, a game controller's button or axis, or a MIDI knob (how):

COM 1 MHz +
COM 1 MHz -
COM 1 channel +
COM 1 channel -
COM 1 swap
NAV 1 MHz +
NAV 1 MHz -
NAV 1 channel +
NAV 1 channel -
NAV 1 swap

Simulator data

What the Hub reads from the simulator for this instrument, and what the instrument sends back. Names are the simulators' own: MSFS SimVars and events, X-Plane datarefs and commands.

Reads

Value	MSFS	X-Plane
COM1 active frequency (kHz)	`COM ACTIVE FREQUENCY:1 (MHz)`	`sim/cockpit2/radios/actuators/com1_frequency_hz_833`
COM1 standby frequency (kHz)	`COM STANDBY FREQUENCY:1 (MHz)`	`sim/cockpit2/radios/actuators/com1_standby_frequency_hz_833`
COM2 active frequency (kHz)	`COM ACTIVE FREQUENCY:2 (MHz)`	`sim/cockpit2/radios/actuators/com2_frequency_hz_833`
COM2 standby frequency (kHz)	`COM STANDBY FREQUENCY:2 (MHz)`	`sim/cockpit2/radios/actuators/com2_standby_frequency_hz_833`
NAV1 active frequency (kHz)	`NAV ACTIVE FREQUENCY:1 (MHz)`	`sim/cockpit2/radios/actuators/nav1_frequency_hz`
NAV1 standby frequency (kHz)	`NAV STANDBY FREQUENCY:1 (MHz)`	`sim/cockpit2/radios/actuators/nav1_standby_frequency_hz`
NAV2 active frequency (kHz)	`NAV ACTIVE FREQUENCY:2 (MHz)`	`sim/cockpit2/radios/actuators/nav2_frequency_hz`
NAV2 standby frequency (kHz)	`NAV STANDBY FREQUENCY:2 (MHz)`	`sim/cockpit2/radios/actuators/nav2_standby_frequency_hz`
COM transmitting: 1, 2, 0 none (enum)	`COM TRANSMIT:1 (bool)COM TRANSMIT:2 (bool)`	`sim/cockpit2/radios/actuators/audio_com_selection`
COM1 heard (1/0) (bool)	`COM RECEIVE:1 (bool)`	`sim/cockpit2/radios/actuators/audio_selection_com1`
COM2 heard (1/0) (bool)	`COM RECEIVE:2 (bool)`	`sim/cockpit2/radios/actuators/audio_selection_com2`
Audio panel keys lit, one bit each (AudioBit: nav1, nav2, dme, adf, mkr, spkr) (bitfield)	`NAV SOUND:1 (bool)NAV SOUND:2 (bool)DME SOUND (bool)ADF SOUND:1 (bool)MARKER SOUND (bool)SPEAKER ACTIVE (bool)`	`sim/cockpit2/radios/actuators/audio_selection_nav1sim/cockpit2/radios/actuators/audio_selection_nav2sim/cockpit2/radios/actuators/audio_dme_enabledsim/cockpit2/radios/actuators/audio_selection_adf1sim/cockpit2/radios/actuators/audio_marker_enabled`
NAV1 receiver course deviation, + = course right (dots (-2.5..2.5))	`NAV CDI:1 (number)`	`sim/cockpit2/radios/indicators/nav1_hdef_dots_pilot`
NAV1 TO/FROM: 0 off, 1 TO, 2 FROM (enum)	`NAV TOFROM:1 (enum)`	`sim/cockpit2/radios/indicators/nav1_flag_from_to_pilot`
NAV1 OBS course (deg)	`NAV OBS:1 (degrees)`	`sim/cockpit2/radios/actuators/nav1_obs_deg_mag_pilot`
NAV1 receiving a station (1/0) (bool)	`NAV HAS NAV:1 (bool)`	`sim/cockpit2/radios/indicators/nav1_flag_from_to_pilot`
NAV2 receiver course deviation, + = course right (dots (-2.5..2.5))	`NAV CDI:2 (number)`	`sim/cockpit2/radios/indicators/nav2_hdef_dots_pilot`
NAV2 TO/FROM: 0 off, 1 TO, 2 FROM (enum)	`NAV TOFROM:2 (enum)`	`sim/cockpit2/radios/indicators/nav2_flag_from_to_pilot`
NAV2 OBS course (deg)	`NAV OBS:2 (degrees)`	`sim/cockpit2/radios/actuators/nav2_obs_deg_mag_pilot`
NAV2 receiving a station (1/0) (bool)	`NAV HAS NAV:2 (bool)`	`sim/cockpit2/radios/indicators/nav2_flag_from_to_pilot`
Aircraft latitude (deg)	`PLANE LATITUDE (degrees)`	`sim/flightmodel/position/latitude`
Aircraft longitude (deg)	`PLANE LONGITUDE (degrees)`	`sim/flightmodel/position/longitude`
Magnetic variation, + east (magnetic = true - variation) (deg)	`MAGVAR (degrees)`	`sim/flightmodel/position/magnetic_variation`
Ground speed (kt)	`GPS GROUND SPEED (knots)`	`sim/flightmodel/position/groundspeed`

Sends

When you…	MSFS	X-Plane
TUNE knob on COM (com1 MHz, com1 + 1 channel), swap key (com1 + 2), list entries tuned into the standby as knob steps; com2 on NAV/COM 2	`COM_STBY_RADIO_SET_HZCOM_STBY_RADIO_SWAP`	`sim/cockpit2/radios/actuators/com1_standby_frequency_hz_833sim/radios/com1_standy_flip`
TUNE knob on NAV, swap, NAV list entries; nav2 on NAV/COM 2	`NAV1_STBY_SET_HZNAV1_RADIO_SWAP`	`sim/cockpit2/radios/actuators/nav1_standby_frequency_hzsim/radios/nav1_standy_flip`
TUNE knob on the OBS page (NAV/COM 1)	`VOR1_SET`	`sim/cockpit2/radios/actuators/nav1_obs_deg_mag_pilotsim/cockpit2/radios/actuators/hsi_obs_deg_mag_pilot (also, when HSI_source_select_pilot == 0)`
TUNE knob on the OBS page (NAV/COM 2)	`VOR2_SET`	`sim/cockpit2/radios/actuators/nav2_obs_deg_mag_pilotsim/cockpit2/radios/actuators/hsi_obs_deg_mag_pilot (also, when HSI_source_select_pilot == 1)`
NAV knob pushed (PUSH ID): the NAV 1 / NAV 2 audio bit	`RADIO_VOR1_IDENT_TOGGLERADIO_VOR2_IDENT_TOGGLERADIO_DME1_IDENT_TOGGLERADIO_ADF_IDENT_TOGGLEMARKER_SOUND_TOGGLETOGGLE_SPEAKER`	`sim/cockpit2/radios/actuators/audio_selection_nav1sim/cockpit2/radios/actuators/audio_selection_nav2sim/cockpit2/radios/actuators/audio_dme_enabledsim/cockpit2/radios/actuators/audio_selection_adf1sim/cockpit2/radios/actuators/audio_marker_enabled`