diff --git a/docs/CURRENT-STATE.md b/docs/CURRENT-STATE.md
index 5c2e52c58..4fa9edd5b 100644
--- a/docs/CURRENT-STATE.md
+++ b/docs/CURRENT-STATE.md
@@ -4257,8 +4257,11 @@ down | auth-failed` (plus the unchanged `missing-key`/`unsupported`) with
 >   advances dead reckoning from the host frame.
 > - **Scheduled route plausibility:** Aircraft route labels and selected-route
 >   context reject the distant backwards, forwards and antipodal extensions of
->   an airport pair's great circle. The existing 130 km endpoint admission and
->   200 km cross-track tolerance remain; a projected fix outside the finite
+>   an airport pair's great circle. The existing 130 km endpoint admission
+>   remains; the cross-track tolerance is 200 km or 15% of the route's length,
+>   whichever is larger (JFK–SFO allows 623 km, as airways and winds take a
+>   coast-to-coast flight several hundred kilometres off the great circle); a
+>   projected fix outside the finite
 >   origin-to-destination minor arc also has a generous 200 km extension at
 >   either end. Missing coordinates and coincident or antipodal endpoint pairs
 >   retain their loose, unjudgeable behavior; vertical-trend checks are unchanged.
diff --git a/src/data/routePlausible.js b/src/data/routePlausible.js
index d52b44ef8..7b2cffc06 100644
--- a/src/data/routePlausible.js
+++ b/src/data/routePlausible.js
@@ -46,7 +46,13 @@ function alongTrackKm(position, origin, destination) {
 }
 
 const NEAR_ENDPOINT_KM = 130;
+/** Least allowed distance off the great circle, and how far past either
+ *  endpoint the plane may be along it. */
 const CROSS_TRACK_KM = 200;
+/** On a long route the allowed distance off the great circle grows to this
+ *  share of its length: airways and winds take a coast-to-coast flight several
+ *  hundred kilometres off it (JFK–SFO: 623 km). */
+const CROSS_TRACK_ROUTE_FRACTION = 0.15;
 const LOW_ALT_M = 3700; // ~12 000 ft
 const VERT_TREND_MPS = 2; // ~400 fpm
 const LOCAL_AIRPORT_KM = 150;
@@ -90,6 +96,9 @@ export function routePlausible({
     // existing loose check when the segment cannot be judged reliably.
     const segmentKnown =
       routeKm > 0.001 && routeKm < Math.PI * EARTH_RADIUS_KM - 0.001;
+    const corridorKm = segmentKnown
+      ? Math.max(CROSS_TRACK_KM, CROSS_TRACK_ROUTE_FRACTION * routeKm)
+      : CROSS_TRACK_KM;
     geomOk =
       Math.abs(
         crossTrackKm(
@@ -100,7 +109,7 @@ export function routePlausible({
           destination.lat,
           destination.lon,
         ),
-      ) < CROSS_TRACK_KM &&
+      ) < corridorKm &&
       (!segmentKnown ||
         (segmentAlongKm >= -CROSS_TRACK_KM &&
           segmentAlongKm <= routeKm + CROSS_TRACK_KM));
diff --git a/src/data/routePlausible.test.mjs b/src/data/routePlausible.test.mjs
index aa59a0c18..f4ca0c573 100644
--- a/src/data/routePlausible.test.mjs
+++ b/src/data/routePlausible.test.mjs
@@ -27,6 +27,24 @@ test('plane in London with an SFO→LAX route: implausible', () => {
   }), false);
 });
 
+test('a long route allows a wider corridor; a short one does not', () => {
+  // JFK→SFO over Kansas, 384 km south of the great circle.
+  assert.equal(routePlausible({
+    latDeg: 38.21, lonDeg: -99.69, altitudeM: 10370, verticalRateMps: 0,
+    origin: JFK, destination: SFO,
+  }), true);
+  // 516 km off the 543 km SFO→LAX route is still the wrong route.
+  assert.equal(routePlausible({
+    latDeg: 37.9, lonDeg: -115.0, altitudeM: 10000, verticalRateMps: 0,
+    origin: SFO, destination: LAX,
+  }), false);
+  // 960 km off, past 15 % of the 4,152 km JFK→SFO route, is still wrong.
+  assert.equal(routePlausible({
+    latDeg: 33.0, lonDeg: -99.69, altitudeM: 10000, verticalRateMps: 0,
+    origin: JFK, destination: SFO,
+  }), false);
+});
+
 test('vertical trend: low climbing plane near SFO — origin must be local', () => {
   const nearSfo = { latDeg: 37.7, lonDeg: -122.4, altitudeM: 2500 };
   // JFK→SFO passes geometry (near destination), but a CLIMBING plane here just