diff --git a/libraries/GCS_MAVLink/GCS_Common.cpp b/libraries/GCS_MAVLink/GCS_Common.cpp
index c1f07fea17c828..7908d64ea92b00 100644
--- a/libraries/GCS_MAVLink/GCS_Common.cpp
+++ b/libraries/GCS_MAVLink/GCS_Common.cpp
@@ -172,7 +172,7 @@ bool GCS_MAVLINK::init(uint8_t instance)
     }
     // since tcdrain() and TCSADRAIN may not be implemented...
     hal.scheduler->delay(1);
-    
+
     _port->set_flow_control(old_flow_control);
 
     // now change back to desired baudrate
@@ -328,7 +328,7 @@ void GCS_MAVLINK::send_battery_status(const uint8_t instance) const
 
     float current, consumed_mah, consumed_wh;
     const int8_t percentage = battery_remaining_pct(instance);
-    
+
     if (battery.current_amps(current, instance)) {
          current = constrain_float(current * 100,-INT16_MAX,INT16_MAX);
     } else {
@@ -1787,7 +1787,7 @@ GCS_MAVLINK::update_receive(uint32_t max_time_us)
     {
         const uint8_t c = (uint8_t)_port->read();
         const uint32_t protocol_timeout = 4000;
-        
+
         if (alternative.handler &&
             now_ms - alternative.last_mavlink_ms > protocol_timeout) {
             /*
@@ -1799,7 +1799,7 @@ GCS_MAVLINK::update_receive(uint32_t max_time_us)
                 alternative.last_alternate_ms = now_ms;
                 gcs_alternative_active[chan] = true;
             }
-            
+
             /*
               we may also try parsing as MAVLink if we haven't had a
               successful parse on the alternative protocol for 4s
@@ -2600,19 +2600,7 @@ void GCS_MAVLINK::handle_set_mode(const mavlink_message_t &msg)
     const MAV_MODE _base_mode = (MAV_MODE)packet.base_mode;
     const uint32_t _custom_mode = packet.custom_mode;
 
-    const MAV_RESULT result = _set_mode_common(_base_mode, _custom_mode);
-
-    // send ACK or NAK.  Note that this is extraodinarily improper -
-    // we are sending a command-ack for a message which is not a
-    // command.  The command we are acking (ID=11) doesn't actually
-    // exist, but if it did we'd probably be acking something
-    // completely unrelated to setting modes.
-    if (HAVE_PAYLOAD_SPACE(chan, COMMAND_ACK)) {
-        mavlink_msg_command_ack_send(chan, MAVLINK_MSG_ID_SET_MODE, result,
-                                     0, 0,
-                                     msg.sysid,
-                                     msg.compid);
-    }
+    _set_mode_common(_base_mode, _custom_mode);
 }
 
 /*
@@ -3150,7 +3138,7 @@ float GCS_MAVLINK::vfr_hud_climbrate() const
 {
 #if AP_AHRS_ENABLED
     Vector3f velned;
-    if (AP::ahrs().get_velocity_NED(velned) || 
+    if (AP::ahrs().get_velocity_NED(velned) ||
         AP::ahrs().get_vert_pos_rate_D(velned.z)) {
         return -velned.z;
     }
@@ -3183,7 +3171,7 @@ void GCS_MAVLINK::send_vfr_hud()
 }
 
 /*
-  handle a MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN command 
+  handle a MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN command
 
   Optionally disable PX4IO overrides. This is done for quadplanes to
   prevent the mixer running while rebooting which can start the VTOL
@@ -3731,7 +3719,7 @@ void GCS_MAVLINK::handle_att_pos_mocap(const mavlink_message_t &msg)
 
     // correct offboard timestamp to be in local ms since boot
     uint32_t timestamp_ms = correct_offboard_timestamp_usec_to_ms(m.time_usec, PAYLOAD_SIZE(chan, ATT_POS_MOCAP));
-   
+
     AP_VisualOdom *visual_odom = AP::visualodom();
     if (visual_odom == nullptr) {
         return;
@@ -4120,7 +4108,7 @@ void GCS_MAVLINK::handle_message(const mavlink_message_t &msg)
 #endif
 
     case MAVLINK_MSG_ID_REQUEST_DATA_STREAM:
-        // only pass if override is not selected 
+        // only pass if override is not selected
         if (!(_port->get_options() & _port->OPTION_NOSTREAMOVERRIDE)) {
             handle_request_data_stream(msg);
         }
@@ -4128,7 +4116,7 @@ void GCS_MAVLINK::handle_message(const mavlink_message_t &msg)
 
     case MAVLINK_MSG_ID_DATA96:
         handle_data_packet(msg);
-        break;        
+        break;
 
 #if HAL_VISUALODOM_ENABLED
     case MAVLINK_MSG_ID_VISION_POSITION_DELTA:
@@ -4514,7 +4502,7 @@ MAV_RESULT GCS_MAVLINK::_handle_command_preflight_calibration(const mavlink_comm
         AP::compass().force_save_calibration();
         ret = MAV_RESULT_ACCEPTED;
     }
-    
+
     return ret;
 }
 
@@ -5645,7 +5633,7 @@ void GCS_MAVLINK::send_water_depth() const
 
     if (rangefinder == nullptr || !rangefinder->has_orientation(ROTATION_PITCH_270)){
         return;
-    } 
+    }
 
     // get position
     const AP_AHRS &ahrs = AP::ahrs();
@@ -5654,7 +5642,7 @@ void GCS_MAVLINK::send_water_depth() const
 
     for (uint8_t i=0; i<rangefinder->num_sensors(); i++) {
         const AP_RangeFinder_Backend *s = rangefinder->get_backend(i);
-        
+
         if (s == nullptr || s->orientation() != ROTATION_PITCH_270 || !s->has_data()) {
             continue;
         }
@@ -6709,7 +6697,7 @@ uint64_t GCS_MAVLINK::capabilities() const
     if (!AP_BoardConfig::ftp_disabled()){  //if ftp disable board option is not set
         ret |= MAV_PROTOCOL_CAPABILITY_FTP;
     }
- 
+
     return ret;
 }
 
@@ -6829,7 +6817,7 @@ void GCS_MAVLINK::send_high_latency2() const
 
     //send_text(MAV_SEVERITY_INFO, "Yaw: %u", (((uint16_t)ahrs.yaw_sensor / 100) % 360));
 
-    mavlink_msg_high_latency2_send(chan, 
+    mavlink_msg_high_latency2_send(chan,
         AP_HAL::millis(), //[ms] Timestamp (milliseconds since boot or Unix epoch)
         gcs().frame_type(), // Type of the MAV (quadrotor, helicopter, etc.)
         MAV_AUTOPILOT_ARDUPILOTMEGA, // Autopilot type / class. Use MAV_AUTOPILOT_INVALID for components that are not flight controllers.
@@ -6879,7 +6867,7 @@ int8_t GCS_MAVLINK::high_latency_air_temperature() const
 }
 
 /*
-  handle a MAV_CMD_CONTROL_HIGH_LATENCY command 
+  handle a MAV_CMD_CONTROL_HIGH_LATENCY command
 
   Enable or disable any marked (via SERIALn_PROTOCOL) high latency connections
  */