diff --git a/routes/adsb.py b/routes/adsb.py
index c718415..338a32a 100644
--- a/routes/adsb.py
+++ b/routes/adsb.py
@@ -893,6 +893,36 @@ def start_adsb():
                 'message': full_msg
             })
 
+        # dump1090 is still running but SBS port never came up — device may be
+        # held by a stale process from a previous mode.  Kill it so the USB
+        # device is released and report a clear error to the frontend.
+        if not dump1090_ready:
+            logger.warning("dump1090 running but SBS port not available after %.1fs — killing", DUMP1090_START_WAIT)
+            try:
+                pgid = os.getpgid(app_module.adsb_process.pid)
+                os.killpg(pgid, 15)
+                app_module.adsb_process.wait(timeout=ADSB_TERMINATE_TIMEOUT)
+            except (subprocess.TimeoutExpired, ProcessLookupError, OSError):
+                try:
+                    pgid = os.getpgid(app_module.adsb_process.pid)
+                    os.killpg(pgid, 9)
+                except (ProcessLookupError, OSError):
+                    pass
+            app_module.adsb_process = None
+            clear_dump1090_pid()
+            app_module.release_sdr_device(device_int, sdr_type_str)
+            adsb_active_device = None
+            adsb_active_sdr_type = None
+            return jsonify({
+                'status': 'error',
+                'error_type': 'DEVICE_BUSY',
+                'message': (
+                    'SDR device did not become ready in time. '
+                    'Another mode may still be releasing the device. '
+                    'Please wait a moment and try again.'
+                ),
+            })
+
         adsb_using_service = True
         thread = threading.Thread(target=parse_sbs_stream, args=(f'localhost:{ADSB_SBS_PORT}',), daemon=True)
         thread.start()
diff --git a/templates/adsb_dashboard.html b/templates/adsb_dashboard.html
index 4a4d3c8..a7fa318 100644
--- a/templates/adsb_dashboard.html
+++ b/templates/adsb_dashboard.html
@@ -2172,6 +2172,58 @@ sudo make install</code>
                 const [adsbSdrType, adsbDeviceIdx] = adsbSelectVal.includes(':') ? adsbSelectVal.split(':') : ['rtlsdr', adsbSelectVal];
                 const adsbDevice = parseInt(adsbDeviceIdx) || 0;
 
+                // Pre-flight: check if another mode is using this device and auto-stop it
+                if (!useAgent) {
+                    try {
+                        const devResp = await fetch('/devices/status');
+                        if (devResp.ok) {
+                            const devices = await devResp.json();
+                            const target = devices.find(d => d.sdr_type === adsbSdrType && d.index === adsbDevice);
+                            if (target && target.in_use && target.used_by && target.used_by !== 'adsb') {
+                                const stopEndpoints = {
+                                    pager: '/stop',
+                                    sensor: '/stop_sensor',
+                                    morse: '/morse/stop',
+                                    adsb: '/adsb/stop',
+                                    acars: '/acars/stop',
+                                    vdl2: '/vdl2/stop',
+                                    ais: '/ais/stop',
+                                    dsc: '/dsc/stop',
+                                    weathersat: '/weather-sat/stop',
+                                    sstv: '/sstv/stop',
+                                    radiosonde: '/radiosonde/stop',
+                                    rtlamr: '/rtlamr/stop_rtlamr',
+                                    aprs: '/aprs/stop',
+                                    tscm: '/tscm/sweep/stop',
+                                    wefax: '/wefax/stop',
+                                    sstv_general: '/sstv-general/stop',
+                                };
+                                const mode = target.used_by;
+                                const stopUrl = stopEndpoints[mode];
+                                if (stopUrl) {
+                                    console.log(`Device ${adsbSdrType}:${adsbDevice} in use by ${mode}, stopping...`);
+                                    btn.textContent = `Stopping ${mode}...`;
+                                    btn.disabled = true;
+                                    try {
+                                        await fetch(stopUrl, { method: 'POST',
+                                            headers: { 'Content-Type': 'application/json' },
+                                            body: JSON.stringify({ source: 'adsb_conflict' })
+                                        });
+                                    } catch (e) {
+                                        console.warn(`Failed to stop ${mode}:`, e);
+                                    }
+                                    // Wait for USB device to be released
+                                    await new Promise(resolve => setTimeout(resolve, 1500));
+                                    btn.textContent = 'Starting...';
+                                    btn.disabled = false;
+                                }
+                            }
+                        }
+                    } catch (e) {
+                        console.warn('Device conflict check failed:', e);
+                    }
+                }
+
                 const requestBody = {
                     device: adsbDevice,
                     sdr_type: adsbSdrType,