Classic avionics stack (KMA, KX, KT, KAP style)

The classic stack of a 172 in one standing 2 x 3 rack: a KMA 24-style audio panel, two KX 155A-style NAV/COMs with orange gas-discharge digits, a KT 76C-style transponder and a KAP 140-style autopilot. Every unit is its full working module.

Modeled on: Bendix/King KMA 24 / KX 155A / KT 76C / KAP 140-style stack
Category: Avionics stacks
Size: 2 × 3 cells
Version: 1.0 · 2026-10-19
Plan: Pro
Simulators: MSFS 2020 · MSFS 2024 · X-Plane 11 · X-Plane 12

Variants

Unitsv1.0

KMA 24 audio, KX 155A NAV/COM 1, KX 155A NAV/COM 2, KT 76C transponder, KAP 140 autopilot (fixed order)

Fixed

Night lightingv1.0

Each unit lights its own parts: faceplates in the red flood light with their key and label printing backlit (Labels and keys dimmer) and the glareshield's warm light over them; displays keep their colors, dimmed (Displays dimmer), and go dark when the aircraft's avionics power is off

Panel lights: day / night / auto, and the lighting dimmers

Features

Five working classic units: KMA 24-style audio, two KX 155A-style NAV/COMs, KT 76C-style transponder, KAP 140-style autopilot
Classic faceplates: black in thin silver frames, gas-discharge (orange) digit windows, light gray keys, smooth black knobs
All units the same width, each at its faceplate's proportions
Units fill the cell: each may be drawn up to 15% taller or shorter than its faceplate's proportions; any space left is spread evenly
Each unit lights itself at night: faceplate in the red flood with backlit keys and labels and the glareshield's light, displays dimmed (dark without avionics power)
Used by the 'Radio Stack' view preset (the C152's)

On the iPad

Each unit works as on its own: drag the dual knobs (skirt or inner knob) to tune, tap a knob to push it, tap the keys (see the KMA 24, KX 155A, KT 76C and KAP 140 entries)

Settings

None of its own: each unit keeps its own controls; panel lighting applies

Keys and controllers

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

Transmit on COM 1
Transmit on COM 2
Audio NAV 1
Audio NAV 2
Audio DME
Audio ADF
Audio MKR
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
COM 2 MHz +
COM 2 MHz -
COM 2 channel +
COM 2 channel -
COM 2 swap
NAV 2 MHz +
NAV 2 MHz -
NAV 2 channel +
NAV 2 channel -
NAV 2 swap
Transponder IDENT
Transponder STBY
Transponder ALT
Autopilot AP
Autopilot FD
Autopilot YD
Autopilot HDG
Autopilot NAV
Autopilot APR
Autopilot BC
Autopilot ALT
Autopilot VS
Autopilot FLC
Autopilot LVL
Autopilot UP / DN +
Autopilot UP / DN -
Altitude +
Altitude -
Altitude sync
CDI: next source

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
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`
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`
Marker beacon: 0 none, 1 outer, 2 middle, 3 inner (enum)	`MARKER BEACON STATE (number)`	`sim/cockpit2/radios/indicators/outer_marker_litsim/cockpit2/radios/indicators/middle_marker_litsim/cockpit2/radios/indicators/inner_marker_lit`
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`
Transponder code as its four digits (e.g. 1200) (code)	`TRANSPONDER CODE:1 (number)`	`sim/cockpit2/radios/actuators/transponder_code`
Transponder mode: 0 off, 1 standby, 2 test, 3 on, 4 altitude (enum)	`TRANSPONDER STATE:1 (number)`	`sim/cockpit2/radios/actuators/transponder_mode`
Pressure altitude (ft)	`PRESSURE ALTITUDE (feet)`	`sim/flightmodel2/position/pressure_altitude`
Autopilot modes, one bit each (ApBit: ap, fd, yd, hdg, nav, apr, bc, alt, vs, flc, lvl, gs, vnv) (bitfield)	`AUTOPILOT MASTER (bool)AUTOPILOT FLIGHT DIRECTOR ACTIVE (bool)AUTOPILOT YAW DAMPER (bool)AUTOPILOT HEADING LOCK (bool)AUTOPILOT NAV1 LOCK (bool)AUTOPILOT APPROACH HOLD (bool)AUTOPILOT BACKCOURSE HOLD (bool)AUTOPILOT ALTITUDE LOCK (bool)AUTOPILOT VERTICAL HOLD (bool)AUTOPILOT FLIGHT LEVEL CHANGE (bool)AUTOPILOT WING LEVELER (bool)AUTOPILOT GLIDESLOPE HOLD (bool)`	`sim/cockpit2/autopilot/servos_onsim/cockpit2/autopilot/flight_director_modesim/cockpit2/switches/yaw_damper_onsim/cockpit2/autopilot/heading_statussim/cockpit2/autopilot/nav_statussim/cockpit2/autopilot/approach_statussim/cockpit2/autopilot/backcourse_statussim/cockpit2/autopilot/altitude_hold_statussim/cockpit2/autopilot/vvi_statussim/cockpit2/autopilot/speed_statussim/cockpit2/autopilot/roll_statussim/cockpit2/autopilot/glideslope_status`
Autopilot vertical speed target (fpm)	`AUTOPILOT VERTICAL HOLD VAR (feet per minute)`	`sim/cockpit2/autopilot/vvi_dial_fpm`
Selected altitude (ft)	`AUTOPILOT ALTITUDE LOCK VAR (feet)`	`sim/cockpit2/autopilot/altitude_dial_ft`

Sends

When you…	MSFS	X-Plane
KMA 24: MIC selector	`COM1_TRANSMIT_SELECTCOM2_TRANSMIT_SELECT`	`sim/cockpit2/radios/actuators/audio_com_selection (6 = COM1, 7 = COM2)`
KMA 24: COM receive keys	`COM1_RECEIVE_SELECTCOM2_RECEIVE_SELECT`	`sim/cockpit2/radios/actuators/audio_selection_com1sim/cockpit2/radios/actuators/audio_selection_com2`
KMA 24: NAV / DME / ADF / MKR / SPKR keys	`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`
KX 155A #1: COM knobs and transfer	`COM_STBY_RADIO_SET_HZCOM_STBY_RADIO_SWAP`	`sim/cockpit2/radios/actuators/com1_standby_frequency_hz_833sim/radios/com1_standy_flip`
KX 155A #1: NAV knobs and transfer	`NAV1_STBY_SET_HZNAV1_RADIO_SWAP`	`sim/cockpit2/radios/actuators/nav1_standby_frequency_hzsim/radios/nav1_standy_flip`
KX 155A #2: COM knobs and transfer	`COM2_STBY_RADIO_SET_HZCOM2_RADIO_SWAP`	`sim/cockpit2/radios/actuators/com2_standby_frequency_hz_833sim/radios/com2_standy_flip`
KX 155A #2: NAV knobs and transfer	`NAV2_STBY_SET_HZNAV2_RADIO_SWAP`	`sim/cockpit2/radios/actuators/nav2_standby_frequency_hzsim/radios/nav2_standy_flip`
KT 76C: code entry	`XPNDR_SET`	`sim/cockpit2/radios/actuators/transponder_code`
KT 76C: the mode selector knob	`SimVar write: TRANSPONDER STATE:1`	`sim/cockpit2/radios/actuators/transponder_mode`
KT 76C: IDT	`XPNDR_IDENT_ON`	`sim/transponder/transponder_ident`
KAP 140: mode keys	`AP_MASTERTOGGLE_FLIGHT_DIRECTORYAW_DAMPER_TOGGLEAP_PANEL_HEADING_HOLDAP_NAV1_HOLDAP_APR_HOLDAP_BC_HOLDAP_ALT_HOLDAP_PANEL_VS_HOLDFLIGHT_LEVEL_CHANGEAP_WING_LEVELER`	`sim/autopilot/servos_togglesim/autopilot/fdir_togglesim/systems/yaw_damper_togglesim/autopilot/headingsim/autopilot/NAVsim/autopilot/approachsim/autopilot/back_coursesim/autopilot/altitude_holdsim/autopilot/vertical_speedsim/autopilot/level_changesim/autopilot/wing_leveler`
KAP 140: UP / DN	`AP_VS_VAR_SET_ENGLISHAP_SPD_VAR_SETAP_PITCH_REF_INC_UPAP_PITCH_REF_INC_DN`	`sim/cockpit2/autopilot/vvi_dial_fpmsim/cockpit2/autopilot/airspeed_dial_kts_machsim/autopilot/nose_upsim/autopilot/nose_down`
KAP 140: altitude knob	`AP_ALT_VAR_SET_ENGLISH`	`sim/cockpit2/autopilot/altitude_dial_ft`
KAP 140: altitude knob push	`AP_ALT_VAR_SET_ENGLISH`	`sim/cockpit2/autopilot/altitude_dial_ft`