diff --git a/libraries/AP_ADSB/AP_ADSB.cpp b/libraries/AP_ADSB/AP_ADSB.cpp
index dc0cb16b2ec8dc..02570a23050f1a 100644
--- a/libraries/AP_ADSB/AP_ADSB.cpp
+++ b/libraries/AP_ADSB/AP_ADSB.cpp
@@ -176,6 +176,13 @@ const AP_Param::GroupInfo AP_ADSB::var_info[] = {
     // @User: Advanced
     AP_GROUPINFO("OPTIONS",  15, AP_ADSB, _options, 0),
 
+    // @Param: MODE3_ONLY
+    // @DisplayName: Transmit in Mode 3A/C only
+    // @Description: Transmit in traditional Mode 3A/C only and inhibit Mode-S and ES (ADSB) transmissions. This is useful when an ATC (Air Traffic control) requests it in certain scenarios.
+    // @Values: 0:Transmit all Modes (3A 3C S ES), 1:Transmit Mode 3A/C only (no ADSB).
+    // @User: Advanced
+    AP_GROUPINFO("MODE3_ONLY",  16, AP_ADSB, out_state.cfg.mode3AC_only, 0),
+
     AP_GROUPEND
 };
 
@@ -958,6 +965,26 @@ bool AP_ADSB::Loc::vertical_accuracy(float &vacc) const
     return true;
 }
 
+uint8_t AP_ADSB::convert_maxknots_to_enum(const float maxAircraftSpeed_knots)
+{
+    if (maxAircraftSpeed_knots <= 0) {
+        // not set or unknown. no bits set
+        return 0;
+    } else if (maxAircraftSpeed_knots <= 75) {
+        return 1;
+    } else if (maxAircraftSpeed_knots <= 150) {
+        return 2;
+    } else if (maxAircraftSpeed_knots <= 300) {
+        return 3;
+    } else if (maxAircraftSpeed_knots <= 600) {
+        return 4;
+    } else if (maxAircraftSpeed_knots <= 1200) {
+        return 5;
+    } else {
+        return 6;
+    }
+}
+
 AP_ADSB *AP::ADSB()
 {
     return AP_ADSB::get_singleton();
diff --git a/libraries/AP_ADSB/AP_ADSB.h b/libraries/AP_ADSB/AP_ADSB.h
index 0ebf1b1ce413cc..e05d5af16aee08 100644
--- a/libraries/AP_ADSB/AP_ADSB.h
+++ b/libraries/AP_ADSB/AP_ADSB.h
@@ -207,6 +207,8 @@ class AP_ADSB {
     // confirm a value is a valid callsign
     static bool is_valid_callsign(uint16_t octal) WARN_IF_UNUSED;
 
+    static uint8_t convert_maxknots_to_enum(const float maxAircraftSpeed_knots);
+
     // Convert base 8 or 16 to decimal. Used to convert an octal/hexadecimal value
     // stored on a GCS as a string field in different format, but then transmitted
     // over mavlink as a float which is always a decimal.
@@ -311,6 +313,7 @@ class AP_ADSB {
             float       maxAircraftSpeed_knots;
             AP_Int8     rf_capable;
             bool        was_set_externally;
+            AP_Int8     mode3AC_only;
         } cfg;
 
         struct {
diff --git a/libraries/AP_ADSB/AP_ADSB_Sagetech_MXS.cpp b/libraries/AP_ADSB/AP_ADSB_Sagetech_MXS.cpp
index 67d3e73e25d8ce..de259927156b60 100644
--- a/libraries/AP_ADSB/AP_ADSB_Sagetech_MXS.cpp
+++ b/libraries/AP_ADSB/AP_ADSB_Sagetech_MXS.cpp
@@ -120,7 +120,7 @@ void AP_ADSB_Sagetech_MXS::update()
             (mxs_state.inst.icao != (uint32_t)_frontend.out_state.cfg.ICAO_id_param.get() ||
             mxs_state.inst.emitter != convert_emitter_type_to_sg(_frontend.out_state.cfg.emitterType.get()) ||
             mxs_state.inst.size != _frontend.out_state.cfg.lengthWidth.get() ||
-            mxs_state.inst.maxSpeed != convert_airspeed_knots_to_sg(_frontend.out_state.cfg.maxAircraftSpeed_knots)
+            mxs_state.inst.maxSpeed != (sg_airspeed_t)AP_ADSB::convert_maxknots_to_enum(_frontend.out_state.cfg.maxAircraftSpeed_knots)
             )) {
         last.packet_initialize_ms = now_ms;
         send_install_msg();
@@ -150,7 +150,7 @@ void AP_ADSB_Sagetech_MXS::update()
         last.operating_rf_select = _frontend.out_state.cfg.rfSelect;
         last.modeAEnabled = _frontend.out_state.ctrl.modeAEnabled;
         last.modeCEnabled = _frontend.out_state.ctrl.modeCEnabled;
-        last.modeSEnabled = _frontend.out_state.ctrl.modeSEnabled;
+        last.modeSEnabled = _frontend.out_state.cfg.mode3AC_only ? 0 : _frontend.out_state.ctrl.modeSEnabled;
 
         last.operating_alt = _frontend._my_loc.alt;
         last.packet_Operating_ms = now_ms;
@@ -358,7 +358,7 @@ void AP_ADSB_Sagetech_MXS::auto_config_installation()
     mxs_state.inst.sda = sg_sda_t::sdaUnknown;
     mxs_state.inst.emitter = convert_emitter_type_to_sg(_frontend.out_state.cfg.emitterType.get());
     mxs_state.inst.size = (sg_size_t)_frontend.out_state.cfg.lengthWidth.get();
-    mxs_state.inst.maxSpeed = convert_airspeed_knots_to_sg(_frontend.out_state.cfg.maxAircraftSpeed_knots);
+    mxs_state.inst.maxSpeed = (sg_airspeed_t)AP_ADSB::convert_maxknots_to_enum(_frontend.out_state.cfg.maxAircraftSpeed_knots);
     mxs_state.inst.altOffset = 0;         // Alt encoder offset is legacy field that should always be 0.
     mxs_state.inst.antenna = sg_antenna_t::antBottom;
 
@@ -511,7 +511,7 @@ void AP_ADSB_Sagetech_MXS::send_install_msg()
     mxs_state.inst.icao = (uint32_t)_frontend.out_state.cfg.ICAO_id_param.get();
     mxs_state.inst.emitter = convert_emitter_type_to_sg(_frontend.out_state.cfg.emitterType.get());
     mxs_state.inst.size = (sg_size_t)_frontend.out_state.cfg.lengthWidth.get();
-    mxs_state.inst.maxSpeed = convert_airspeed_knots_to_sg(_frontend.out_state.cfg.maxAircraftSpeed_knots);
+    mxs_state.inst.maxSpeed = (sg_airspeed_t)AP_ADSB::convert_maxknots_to_enum(_frontend.out_state.cfg.maxAircraftSpeed_knots);
     mxs_state.inst.antenna = sg_antenna_t::antBottom;
 
     last.msg.type = SG_MSG_TYPE_HOST_INSTALL;
diff --git a/libraries/AP_ADSB/AP_ADSB_uAvionix_MAVLink.cpp b/libraries/AP_ADSB/AP_ADSB_uAvionix_MAVLink.cpp
index bb510a738aa1d2..1a574ed23b2ebb 100644
--- a/libraries/AP_ADSB/AP_ADSB_uAvionix_MAVLink.cpp
+++ b/libraries/AP_ADSB/AP_ADSB_uAvionix_MAVLink.cpp
@@ -177,22 +177,7 @@ uint8_t AP_ADSB_uAvionix_MAVLink::get_encoded_callsign_null_char()
 
     uint8_t encoded_null = 0;
 
-    if (_frontend.out_state.cfg.maxAircraftSpeed_knots <= 0) {
-        // not set or unknown. no bits set
-    } else if (_frontend.out_state.cfg.maxAircraftSpeed_knots <= 75) {
-        encoded_null |= 0x01;
-    } else if (_frontend.out_state.cfg.maxAircraftSpeed_knots <= 150) {
-        encoded_null |= 0x02;
-    } else if (_frontend.out_state.cfg.maxAircraftSpeed_knots <= 300) {
-        encoded_null |= 0x03;
-    } else if (_frontend.out_state.cfg.maxAircraftSpeed_knots <= 600) {
-        encoded_null |= 0x04;
-    } else if (_frontend.out_state.cfg.maxAircraftSpeed_knots <= 1200) {
-        encoded_null |= 0x05;
-    } else {
-        encoded_null |= 0x06;
-    }
-
+    encoded_null = AP_ADSB::convert_maxknots_to_enum(_frontend.out_state.cfg.maxAircraftSpeed_knots);
 
     if (_frontend.out_state.cfg.rf_capable & ADSB_BITBASK_RF_CAPABILITIES_1090ES_IN) {
         encoded_null |= 0x10;
diff --git a/libraries/AP_ADSB/AP_ADSB_uAvionix_UCP.cpp b/libraries/AP_ADSB/AP_ADSB_uAvionix_UCP.cpp
index 0f92293c519f24..7f426985135e01 100644
--- a/libraries/AP_ADSB/AP_ADSB_uAvionix_UCP.cpp
+++ b/libraries/AP_ADSB/AP_ADSB_uAvionix_UCP.cpp
@@ -411,8 +411,8 @@ void AP_ADSB_uAvionix_UCP::send_Transponder_Control()
     _frontend.out_state.ctrl.identActive = false; // only send identButtonActive once per request
     msg.modeAEnabled = _frontend.out_state.ctrl.modeAEnabled;
     msg.modeCEnabled = _frontend.out_state.ctrl.modeCEnabled;
-    msg.modeSEnabled = _frontend.out_state.ctrl.modeSEnabled;
-    msg.es1090TxEnabled = _frontend.out_state.ctrl.es1090TxEnabled;
+    msg.modeSEnabled = _frontend.out_state.cfg.mode3AC_only ? 0 : _frontend.out_state.ctrl.modeSEnabled;
+    msg.es1090TxEnabled = _frontend.out_state.cfg.mode3AC_only ? 0 : _frontend.out_state.ctrl.es1090TxEnabled;
 
     // if enabled via param ADSB_OPTIONS, use squawk 7400 while in any Loss-Comms related failsafe
     // https://www.faa.gov/documentLibrary/media/Notice/N_JO_7110.724_5-2-9_UAS_Lost_Link_2.pdf