diff --git a/server/bridge.js b/server/bridge.js
index 1855740..81427a2 100644
--- a/server/bridge.js
+++ b/server/bridge.js
@@ -180,6 +180,16 @@ function handleClientMessage(msg) {
     return;
   }
 
+  // Demo / no-sim: reflect dataref writes locally so cockpit controls (CDI,
+  // transponder, baro, AP bugs …) still respond, then stop — there's no sim to
+  // forward to. Must run BEFORE the live-socket guard below.
+  if (msg.type === 'setDataref' && (process.env.DEMO || !state.xpSocket)) {
+    const name = WRITABLE_DATAREFS[msg.name];
+    if (!name) return log(`! unknown writable dataref alias: ${msg.name}`);
+    state.values[msg.name] = Number(msg.value);
+    return broadcast({ type: 'values', data: { [msg.name]: Number(msg.value) } });
+  }
+
   // --- everything below talks to X-Plane; needs a live sim socket ---
   if (!state.xpSocket || state.xpSocket.readyState !== WsClient.OPEN) return;
 
@@ -196,8 +206,9 @@ function handleClientMessage(msg) {
     );
   } else if (msg.type === 'setDataref') {
     const name = WRITABLE_DATAREFS[msg.name];
-    const id = name && state.drefNameToId.get(name);
-    if (id == null) return log(`! unknown writable dataref alias: ${msg.name}`);
+    if (!name) return log(`! unknown writable dataref alias: ${msg.name}`);
+    const id = state.drefNameToId.get(name);
+    if (id == null) return log(`! writable dataref not resolved yet: ${msg.name}`);
     state.xpSocket.send(
       JSON.stringify({
         req_id: state.reqId++,
diff --git a/server/config.js b/server/config.js
index 4b1825e..7917248 100644
--- a/server/config.js
+++ b/server/config.js
@@ -134,6 +134,7 @@ export const WRITABLE_DATAREFS = {
   apSpdBug: 'sim/cockpit2/autopilot/airspeed_dial_kts_mach',
   xpdrMode: 'sim/cockpit2/radios/actuators/transponder_mode', // 0 off,1 stby,2 on,3 alt
   xpdrCode: 'sim/cockpit2/radios/actuators/transponder_code', // 4-digit squawk
+  cdiSrc:   'sim/cockpit2/radios/actuators/HSI_source_select_pilot', // 0 NAV1 · 1 NAV2 · 2 GPS (CDI softkey cycles it)
 };
 
 // Commands the frontend may TRIGGER (autopilot mode buttons etc.).
diff --git a/web/src/components/Bezel.jsx b/web/src/components/Bezel.jsx
index 5fef2ac..ad89dc4 100644
--- a/web/src/components/Bezel.jsx
+++ b/web/src/components/Bezel.jsx
@@ -93,6 +93,10 @@ export default function Bezel({ variant = 'pfd', xp, svt3d, onToggleSvt, inset,
       else if (label === 'NRST') onToggleNrst && onToggleNrst();
       else if (label === 'TMR/REF') onToggleTmr && onToggleTmr();
       else if (label === 'DME') onToggleDme && onToggleDme();
+      else if (label === 'CDI' && xp) {             // cycle the HSI/CDI nav source: GPS → NAV1 → NAV2
+        const cur = Math.round(num(xp.values?.cdiSrc, 2));
+        xp.setDataref('cdiSrc', (cur + 1) % 3);     // 2→0→1→2 = GPS→NAV1(VLOC1)→NAV2(VLOC2)
+      }
       else if (label === 'OBS') onObs && onObs();   // suspend / OBS mode (also fires the sim softkey above)
       else if (label === 'CAUTION') onToggleAlerts && onToggleAlerts();
       else if (label === 'XPDR') setPage('xpdr');