Wind-adjusted fuel burn ±20% + refuel-for-flight buys 150% margin (ISS-070, ISS-071, v0.36.0)

2026-09-21 08:47:42 +00:00
16 changed files with 309 additions and 81 deletions
@@ -1,5 +1,10 @@
 # Changelog

+## v0.36.0 — 2026-09-21 08:45
+- **Refuel-for-flight now buys 150% of the required fuel for the leg (ISS-071).** `refuelPlane` mode `'forFlight'` (`lib/game/actions.ts`) tops the tank up to `min(maxFuel, max(current fuel, 1.5 × required))` instead of exactly the requirement — a margin so burn variance doesn't strand planes at the far end. The "does not fit a full tank" 409 guard now compares against the weather-adjusted requirement (see below). No UI change: the per-leg Refuel button has no amount preview, and the left-pane "Refuel to full" row is unaffected
+- **Wind affects per-leg fuel burn ±20% based on departure weather vs route heading (ISS-070).** The deterministic per-airport weather (`lib/weather.ts`, FNV-1a seeded by ICAO — no dayKey, stable across polls/sessions) now feeds the fuel math: a new `windBurnFactor(windKt, windDirDeg, bearingDeg)` in `lib/sim/movement.ts` returns `1 + headwindKt/150` (exactly [0.8, 1.2] over the 2–30 kt weather range), and a new `initialBearingDeg(lat1, lon1, lat2, lon2)` in `lib/geo.ts` gives the great-circle heading of each leg. Every fuel call site applies the departure airport's factor to `burnPerKm`: `flyPlane`'s feasibility check, `refuelPlane` forFlight, the engine's landed-fuel + auto-chain checks (`lib/sim/engine.ts`), and the live in-flight fuel display — computed server-side in `getStateSnapshot()`/`livePlane()` (`lib/game/state.ts`) from airport coordinates, so no schema change. Fully deterministic: one factor per leg, a pure function of (ICAO pair, catalog)
+- **Tests & spec.** Unit tests added for both helpers and the ×1.5 expectation (computed in-test via the same helpers — no stale literals); e2e specs import the real helpers from `lib/` instead of mirroring the wind math (`e2e/right-pane.spec.ts`, `e2e/two-planes.spec.ts`, `e2e/actions.spec.ts`), and their "farthest flyable" airport pickers now require BOTH directions to fit a full tank under wind. OpenAPI: description-only updates (refuel endpoint + `burnPerKm` note)
+
 ## v0.35.0 — 2026-09-21 02:26
 - **Job list shows cargo tonnage instead of count (ISS-066).** The open-package rows in the right pane's Jobs tab (`components/RightPane.tsx`) now show cargo as type + tonnage ("Mail 10.0t") via a new `formatCargo` in `lib/format.ts` — `(kg / 1000).toFixed(1) + 't'`, identical to the loadout display — instead of "type × count"; unit tests added to `lib/format.test.ts`; e2e assertion added to `e2e/right-pane.spec.ts` (the hook-created package is forced to 10 t and its row must contain "10.0t"). No server or OpenAPI changes — `weightKg` was already in the snapshot

@@ -6,8 +6,9 @@ import { afterAll, beforeAll, describe, expect, it } from 'vitest';
 import * as schema from '@/lib/db/schema';
 import { getGameDb } from '@/lib/db/client';
 import { loadAirportsGeoJson } from '@/lib/airports';
-import { haversineKm } from '@/lib/geo';
-import { requiredFuelFor } from '@/lib/sim/movement';
+import { haversineKm, initialBearingDeg } from '@/lib/geo';
+import { weatherFor } from '@/lib/weather';
+import { requiredFuelFor, windBurnFactor } from '@/lib/sim/movement';
 import { FUEL_PRICE_PER_L, PLANE_TYPES } from '@/lib/game/catalog';
 import { HUB_ICAO } from '@/lib/game/seed';
 import { POST } from './route';
@@ -124,7 +125,7 @@ describe('POST /api/planes/:planeId/refuel', () => {
    expect(res.status).toBe(400);
  });

-  it('forFlight tops up exactly the liters needed for the loaded package leg', async () => {
+  it('forFlight buys 150% of the weather-adjusted leg requirement', async () => {
    const { db } = await getGameDb();
    await db.update(schema.account).set({ cash: 50_000 });
    // A loaded EDDF → LEMD package on the starter (direct row — loadPackage is covered in actions tests).
@@ -138,7 +139,14 @@ describe('POST /api/planes/:planeId/refuel', () => {
    const to = fc.features.find((f) => f.properties.icao === 'LEMD')!.properties;
    const km = haversineKm(from.lat, from.lon, to.lat, to.lon);
    const type = PLANE_TYPES.atr72;
-    const required = requiredFuelFor(type.burnPerKm, type.emptyWeightKg, type.maxFuel, km);
+    // Same wind-adjusted requirement the server computes (v0.36.0).
+    const w = weatherFor(HUB_ICAO);
+    const required = requiredFuelFor(
+      type.burnPerKm * windBurnFactor(w.windKt, w.windDirDeg, initialBearingDeg(from.lat, from.lon, to.lat, to.lon)),
+      type.emptyWeightKg,
+      type.maxFuel,
+      km,
+    );

    const startFuel = Math.round(required / 2); // partial tank so L > 0
    await db.update(schema.planes).set({ fuel: startFuel }).where(eq(schema.planes.id, 'plane-starter'));
@@ -151,9 +159,11 @@ describe('POST /api/planes/:planeId/refuel', () => {
      account: { cash: number };
      planes: Array<{ id: string; fuel: number }>;
    };
-    const cost = Math.round((required - startFuel) * FUEL_PRICE_PER_L * 100) / 100;
+    // ISS-071: target is 150% of the requirement, capped at tank capacity.
+    const targetFuel = Math.min(type.maxFuel, Math.max(startFuel, required * 1.5));
+    const cost = Math.round((targetFuel - startFuel) * FUEL_PRICE_PER_L * 100) / 100;
    expect(body.account.cash).toBeCloseTo(cashBefore - cost, 6);
-    expect(body.planes.find((p) => p.id === 'plane-starter')!.fuel).toBeCloseTo(required, 6);
+    expect(body.planes.find((p) => p.id === 'plane-starter')!.fuel).toBeCloseTo(targetFuel, 6);

    // Clean up the test package.
    await db.delete(schema.packages).where(eq(schema.packages.id, 'p-ff-api'));
@@ -1,5 +1,10 @@
 import type { Page, Request } from '@playwright/test';
 import { expect, test } from '@playwright/test';
+// Real helpers (v0.36.0) — the wind-adjusted fuel math must match lib/ exactly; Playwright resolves
+// the repo's tsconfig paths, so importing beats mirroring a third copy of the formulas.
+import { initialBearingDeg } from '../lib/geo';
+import { weatherFor } from '../lib/weather';
+import { windBurnFactor } from '../lib/sim/movement';

 // v0.12.0 package model against the live origin (https://flight.dev.kkhost.pl):
 // the full core loop through the UI — hook creates a short package at EDDF → Load
@@ -219,10 +224,18 @@ test('full core loop via UI: load → fly to destination → exact reward + rep
  const repGain = Math.round((REP_BASE + REP_PER_KM * exactKm) * 100) / 100;
  expect(s.account.reputation).toBeCloseTo(Math.round((before.account.reputation + repGain) * 100) / 100, 9);

-  // Fuel burned per the v0.16.0 weight-proportional model (closed form — no rounding drift).
+  // Fuel burned per the v0.16.0 weight-proportional model (closed form — no rounding drift),
+  // wind-adjusted (v0.36.0) by departure weather vs route heading.
  const entry = before.catalog.find((e) => e.model === 'atr72')!;
+  const wHub = weatherFor(HUB);
  expect(landed.fuel).toBeCloseTo(
-    fuelAfter(before.planes.find((p) => p.id === planeId)!.fuel, entry.burnPerKm, entry.emptyWeightKg, entry.maxFuel, exactKm),
+    fuelAfter(
+      before.planes.find((p) => p.id === planeId)!.fuel,
+      entry.burnPerKm * windBurnFactor(wHub.windKt, wHub.windDirDeg, initialBearingDeg(nearest.hubLat, nearest.hubLon, nearest.lat, nearest.lon)),
+      entry.emptyWeightKg,
+      entry.maxFuel,
+      exactKm,
+    ),
    6,
  );

@@ -1,5 +1,10 @@
 import type { Page } from '@playwright/test';
 import { expect, test } from '@playwright/test';
+// Real helpers (v0.36.0) — the wind-adjusted fuel math must match lib/ exactly; Playwright resolves
+// the repo's tsconfig paths, so importing beats mirroring a third copy of the formulas.
+import { initialBearingDeg } from '../lib/geo';
+import { weatherFor } from '../lib/weather';
+import { windBurnFactor } from '../lib/sim/movement';

 // v0.12.0 — right Jobs & Market pane against the live origin: open packages render with
 // names/reward/deadline and Load (UI click) binds one to the starter; the on-board list
@@ -119,22 +124,28 @@ async function nearestToHub(page: Page): Promise<{ icao: string; lat: number; lo
 }

 // Farthest airport from EDDF whose leg still FITS A FULL TANK — the longest flyable leg (v0.16.0
-// refuel-for-flight test). The dataset's absolute farthest can exceed the aircraft's range (UNNT is
-// ~4803 km out and needs ~6955 L > the 6300 L tank), so a full-tank fly there would rightly 409;
-// this test wants a long-but-flyable leg instead.
+// refuel-for-flight test). The dataset's absolute farthest can exceed the aircraft's range, so a
+// full-tank fly there would rightly 409; this test wants a long-but-flyable leg instead. Wind-
+// adjusted (v0.36.0): BOTH directions must fit — the outbound is flown from a full tank and the
+// return leg is what the forFlight refuel below buys, which also 409s if it doesn't fit.
 async function farthestFlyableToHub(
  page: Page,
  entry: CatalogEntry,
-): Promise<{ icao: string; lat: number; lon: number; hubLat: number; hubLon: number }> {
+): Promise<{ icao: string; lat: number; lon: number; d: number; hubLat: number; hubLon: number }> {
  const fc = (await (await page.request.get('/api/airports')).json()) as {
    features: Array<{ properties: { icao: string; lat: number; lon: number } }>;
  };
  const hub = fc.features.find((f) => f.properties.icao === HUB)!.properties;
+  const wHub = weatherFor(HUB);
  let farthest: { icao: string; lat: number; lon: number; d: number } | null = null;
  for (const f of fc.features) {
    if (f.properties.icao === HUB) continue;
    const d = haversineKm(hub.lat, hub.lon, f.properties.lat, f.properties.lon);
-    if (requiredFuelFor(entry.burnPerKm, entry.emptyWeightKg, entry.maxFuel, d) > entry.maxFuel) continue; // beyond range
+    const wDest = weatherFor(f.properties.icao);
+    const outBurn = entry.burnPerKm * windBurnFactor(wHub.windKt, wHub.windDirDeg, initialBearingDeg(hub.lat, hub.lon, f.properties.lat, f.properties.lon));
+    if (requiredFuelFor(outBurn, entry.emptyWeightKg, entry.maxFuel, d) > entry.maxFuel) continue; // beyond range
+    const backBurn = entry.burnPerKm * windBurnFactor(wDest.windKt, wDest.windDirDeg, initialBearingDeg(f.properties.lat, f.properties.lon, hub.lat, hub.lon));
+    if (requiredFuelFor(backBurn, entry.emptyWeightKg, entry.maxFuel, d) > entry.maxFuel) continue; // return leg wouldn't fit a full tank either
    if (!farthest || d > farthest.d) {
      farthest = { icao: f.properties.icao, lat: f.properties.lat, lon: f.properties.lon, d };
    }
@@ -365,7 +376,7 @@ test('market buy/sell render with previews from the catalog in /api/state; left-
  }
 });

-test('on-board row Refuel tops up just enough for the package leg; left-pane button says "Refuel to full"', async ({ page }) => {
+test('on-board row Refuel buys 150% of the weather-adjusted leg requirement; left-pane button says "Refuel to full"', async ({ page }) => {
  test.setTimeout(300_000); // self-heal + one long flight each way at scale 1000
  await flyHomeViaApi(page);

@@ -375,7 +386,7 @@ test('on-board row Refuel tops up just enough for the package leg; left-pane but
  // Deterministic baseline: a full tank.
  expect((await page.request.post('/api/planes/plane-starter/refuel')).status()).toBe(200);

-  // Longest FLYABLE leg from the hub (fits a full tank) — long enough that "just enough" for it
+  // Longest FLYABLE leg from the hub (fits a full tank) — long enough that 150% of its requirement
  // exceeds what's left on arrival.
  const farthest = await farthestFlyableToHub(page, entry);
  const pkg1 = await createPackage(page, HUB, farthest.icao, 24 * 3_600_000);
@@ -396,12 +407,21 @@ test('on-board row Refuel tops up just enough for the package leg; left-pane but
  const pkg2 = await createPackage(page, farthest.icao, HUB, 24 * 3_600_000);
  expect((await page.request.post(`/api/packages/${pkg2.id}/load`, { data: { planeId: 'plane-starter' } })).status()).toBe(200);

-  // Expected "just enough" from the snapshot constants (mirrors requiredFuelFor in lib/sim/movement.ts).
+  // Expected "150% of the requirement" from the snapshot constants (mirrors requiredFuelFor in
+  // lib/sim/movement.ts, wind-adjusted per v0.36.0 — departure weather at the far end vs heading home).
  const pre = await getState(page);
  const fuelBefore = pre.planes.find((p) => p.id === 'plane-starter')!.fuel;
  const cashBefore = pre.account.cash;
  const km = haversineKm(farthest.hubLat, farthest.hubLon, farthest.lat, farthest.lon); // symmetric: hub ↔ far end
-  const liters = Math.max(0, requiredFuelFor(entry.burnPerKm, entry.emptyWeightKg, entry.maxFuel, km) - fuelBefore);
+  const wFar = weatherFor(farthest.icao);
+  const required = requiredFuelFor(
+    entry.burnPerKm * windBurnFactor(wFar.windKt, wFar.windDirDeg, initialBearingDeg(farthest.lat, farthest.lon, farthest.hubLat, farthest.hubLon)),
+    entry.emptyWeightKg,
+    entry.maxFuel,
+    km,
+  );
+  const target = Math.min(entry.maxFuel, required * 1.5); // ISS-071: 150% margin, capped at tank capacity
+  const liters = Math.max(0, target - fuelBefore);
  expect(liters).toBeGreaterThan(0); // the long leg genuinely needs more than what's left
  const expectedCost = Math.round(liters * pre.fuelPricePerL * 100) / 100;

@@ -424,8 +444,8 @@ test('on-board row Refuel tops up just enough for the package leg; left-pane but
  await expect(page.getByTestId('market-refuel')).toHaveText('Refuel to full');

  // Restore: fly home — pkg2's destination IS the hub, so it delivers on arrival. The tank holds
-  // exactly the leg requirement, so this also proves "just enough" is enough. ISS-041: the far-end
-  // arrival above paused the sim, so re-set SCALE for this leg (setScale clears pause).
+  // 150% of the leg requirement (or a full tank), so the return is comfortably feasible. ISS-041:
+  // the far-end arrival above paused the sim, so re-set SCALE for this leg (setScale clears pause).
  await setScale(page, SCALE);
  expect((await page.request.post('/api/planes/plane-starter/fly', { data: { destIcao: HUB } })).status()).toBe(200);
  await expect
@@ -1,5 +1,10 @@
 import type { Page } from '@playwright/test';
 import { expect, test } from '@playwright/test';
+// Real helpers (v0.36.0) — the wind-adjusted fuel math must match lib/ exactly; Playwright resolves
+// the repo's tsconfig paths, so importing beats mirroring a third copy of the formulas.
+import { initialBearingDeg } from '../lib/geo';
+import { weatherFor } from '../lib/weather';
+import { windBurnFactor } from '../lib/sim/movement';

 // v0.31.0 — ISS-055: gameplay with TWO planes in the fleet. The reported bug ("can't load cargo
 // if both planes are on the same airport") was UX-only: LoadControls' multi-plane path rendered a
@@ -114,18 +119,25 @@ async function twoNearestToHub(page: Page): Promise<Array<{ icao: string; lat: n
 }

 // Farthest airport from EDDF whose leg still fits a FULL ATR tank — the longest flyable leg. The
-// dataset's absolute farthest can exceed range (a full-tank fly there would rightly 409).
+// dataset's absolute farthest can exceed range (a full-tank fly there would rightly 409). Wind-
+// adjusted (v0.36.0): BOTH directions must fit — the outbound is flown from a full tank and the
+// return leg is flown after a top-up, which also 409s if it doesn't fit.
 async function farthestFlyableToHub(page: Page): Promise<{ icao: string; lat: number; lon: number }> {
  const entry = (await getState(page)).catalog.find((e) => e.model === BUY_MODEL)!;
  const fc = (await (await page.request.get('/api/airports')).json()) as {
    features: Array<{ properties: { icao: string; lat: number; lon: number } }>;
  };
  const hub = fc.features.find((f) => f.properties.icao === HUB)!.properties;
+  const wHub = weatherFor(HUB);
  let farthest: { icao: string; lat: number; lon: number; d: number } | null = null;
  for (const f of fc.features) {
    if (f.properties.icao === HUB) continue;
    const d = haversineKm(hub.lat, hub.lon, f.properties.lat, f.properties.lon);
-    if (requiredFuelFor(entry.burnPerKm, entry.emptyWeightKg, entry.maxFuel, d) > entry.maxFuel) continue; // beyond range
+    const wDest = weatherFor(f.properties.icao);
+    const outBurn = entry.burnPerKm * windBurnFactor(wHub.windKt, wHub.windDirDeg, initialBearingDeg(hub.lat, hub.lon, f.properties.lat, f.properties.lon));
+    if (requiredFuelFor(outBurn, entry.emptyWeightKg, entry.maxFuel, d) > entry.maxFuel) continue; // beyond range
+    const backBurn = entry.burnPerKm * windBurnFactor(wDest.windKt, wDest.windDirDeg, initialBearingDeg(f.properties.lat, f.properties.lon, hub.lat, hub.lon));
+    if (requiredFuelFor(backBurn, entry.emptyWeightKg, entry.maxFuel, d) > entry.maxFuel) continue; // return leg wouldn't fit a full tank either
    if (!farthest || d > farthest.d) {
      farthest = { icao: f.properties.icao, lat: f.properties.lat, lon: f.properties.lon, d };
    }
@@ -6,8 +6,9 @@ import { afterAll, beforeAll, describe, expect, it, vi } from 'vitest';
 import { openGameDb, type GameDb } from '@/lib/db/client';
 import * as schema from '@/lib/db/schema';
 import { loadAirportsGeoJson } from '@/lib/airports';
-import { haversineKm } from '@/lib/geo';
-import { requiredFuelFor } from '@/lib/sim/movement';
+import { haversineKm, initialBearingDeg } from '@/lib/geo';
+import { weatherFor } from '@/lib/weather';
+import { requiredFuelFor, windBurnFactor } from '@/lib/sim/movement';
 import { FUEL_PRICE_PER_L, PLANE_TYPES, SELL_FRACTION } from './catalog';
 import { HUB_ICAO } from './seed';
 import {
@@ -591,17 +592,29 @@ describe('refuelPlane', () => {

  // --- forFlight mode (v0.16.0) ---

-  it('forFlight adds exactly the liters needed for the package leg and deducts L × price', async () => {
-    const inst = await freshDb('refuel-forflight-ok.db');
-    await insertOpenPackage(inst, 'p-ff', { destIcao: 'LEMD' }); // EDDF → LEMD
-    await loadPackage(inst, 'p-ff', 'plane-starter');
-
+  // Wind-adjusted requirement for the hub → LEMD leg (v0.36.0) — computed with the SAME helpers
+  // refuelPlane uses, so the expectations stay exact without hardcoded literals.
+  async function adjustedRequiredForHubToLemd() {
    const fc = await loadAirportsGeoJson();
    const from = fc.features.find((f) => f.properties.icao === HUB_ICAO)!.properties;
    const to = fc.features.find((f) => f.properties.icao === 'LEMD')!.properties;
    const km = haversineKm(from.lat, from.lon, to.lat, to.lon);
    const type = PLANE_TYPES.atr72;
-    const required = requiredFuelFor(type.burnPerKm, type.emptyWeightKg, type.maxFuel, km);
+    const w = weatherFor(HUB_ICAO);
+    return requiredFuelFor(
+      type.burnPerKm * windBurnFactor(w.windKt, w.windDirDeg, initialBearingDeg(from.lat, from.lon, to.lat, to.lon)),
+      type.emptyWeightKg,
+      type.maxFuel,
+      km,
+    );
+  }
+
+  it('forFlight buys 150% of the weather-adjusted leg requirement and deducts L × price', async () => {
+    const inst = await freshDb('refuel-forflight-ok.db');
+    await insertOpenPackage(inst, 'p-ff', { destIcao: 'LEMD' }); // EDDF → LEMD
+    await loadPackage(inst, 'p-ff', 'plane-starter');
+
+    const required = await adjustedRequiredForHubToLemd();

    // Partial tank below the requirement so L > 0.
    const startFuel = Math.round(required / 2);
@@ -610,31 +623,28 @@ describe('refuelPlane', () => {

    const { cost } = await refuelPlane(inst, 'plane-starter', { mode: 'forFlight', packageId: 'p-ff' });

-    expect(cost).toBe(Math.round((required - startFuel) * FUEL_PRICE_PER_L * 100) / 100);
+    // ISS-071: target is 150% of the requirement (below tank capacity for this leg).
+    const targetFuel = Math.min(PLANE_TYPES.atr72.maxFuel, Math.max(startFuel, required * 1.5));
+    expect(cost).toBe(Math.round((targetFuel - startFuel) * FUEL_PRICE_PER_L * 100) / 100);
    const plane = (await inst.db.select().from(schema.planes))[0];
-    expect(plane.fuel).toBeCloseTo(required, 6); // topped up to exactly the leg requirement
+    expect(plane.fuel).toBeCloseTo(targetFuel, 6); // topped up to exactly the 150% target
    const account = (await inst.db.select().from(schema.account))[0];
    expect(account.cash).toBeCloseTo(cashBefore - cost, 6);
  });

-  it('forFlight leaves an exactly-feasible tank — flyPlane to the package dest succeeds right after', async () => {
+  it('forFlight leaves a tank with a 50% margin — flyPlane to the package dest succeeds right after', async () => {
    const inst = await freshDb('refuel-ff-flyafter.db');
    await insertOpenPackage(inst, 'p-fa', { destIcao: 'LEMD' }); // EDDF → LEMD
    await loadPackage(inst, 'p-fa', 'plane-starter');

-    const fc = await loadAirportsGeoJson();
-    const from = fc.features.find((f) => f.properties.icao === HUB_ICAO)!.properties;
-    const to = fc.features.find((f) => f.properties.icao === 'LEMD')!.properties;
-    const km = haversineKm(from.lat, from.lon, to.lat, to.lon);
-    const type = PLANE_TYPES.atr72;
-    const required = requiredFuelFor(type.burnPerKm, type.emptyWeightKg, type.maxFuel, km);
+    const required = await adjustedRequiredForHubToLemd();

    // Empty-ish tank: well below the leg requirement.
    await inst.db.update(schema.planes).set({ fuel: Math.round(required / 4) }).where(eq(schema.planes.id, 'plane-starter'));

    await refuelPlane(inst, 'plane-starter', { mode: 'forFlight', packageId: 'p-fa' });

-    // The leg must now be flyable — no epsilon-short 409 (regression guard for the float-exact target).
+    // The leg must now be flyable — the 150% margin covers flyPlane's strict `>` check.
    await flyPlane(inst, 'plane-starter', 'LEMD');
    const plane = (await inst.db.select().from(schema.planes))[0];
    expect(plane.status).toBe('flying');
@@ -3,8 +3,9 @@ import { and, eq, inArray } from 'drizzle-orm';
 import * as schema from '@/lib/db/schema';
 import { persist, type GameDb } from '@/lib/db/client';
 import { loadAirportsGeoJson } from '@/lib/airports';
-import { haversineKm } from '@/lib/geo';
-import { requiredFuelFor } from '@/lib/sim/movement';
+import { haversineKm, initialBearingDeg } from '@/lib/geo';
+import { weatherFor } from '@/lib/weather';
+import { requiredFuelFor, windBurnFactor } from '@/lib/sim/movement';
 import { runAction } from '@/lib/sim/engine';
 import { getStateSnapshot, parseIcaoQueue } from './state';
 import { FUEL_PRICE_PER_L, PLANE_TYPES, SELL_FRACTION } from './catalog';
@@ -106,8 +107,11 @@ export async function flyPlane(inst: GameDb, planeId: string, destIcao: string):
  const type = PLANE_TYPES[plane.model];
  if (!type) throw new Error(`unknown plane model ${plane.model}`); // → 500, cannot happen for seeded data
  const distanceKm = haversineKm(origin.lat, origin.lon, destFeature.properties.lat, destFeature.properties.lon);
-  // Weighted burn model (v0.16.0): the leg needs enough fuel to cover it arriving empty.
-  const requiredL = requiredFuelFor(type.burnPerKm, type.emptyWeightKg, type.maxFuel, distanceKm);
+  // Weighted burn model (v0.16.0): the leg needs enough fuel to cover it arriving empty; wind-
+  // adjusted (v0.36.0) by departure weather vs route heading — every call site uses this same factor.
+  const w = weatherFor(plane.locationIcao);
+  const burnPerKm = type.burnPerKm * windBurnFactor(w.windKt, w.windDirDeg, initialBearingDeg(origin.lat, origin.lon, destFeature.properties.lat, destFeature.properties.lon));
+  const requiredL = requiredFuelFor(burnPerKm, type.emptyWeightKg, type.maxFuel, distanceKm);
  if (requiredL > plane.fuel) {
    throw new GameActionError(409, `insufficient fuel: the leg needs ${Math.round(requiredL)} L but the plane has ${Math.round(plane.fuel)} L`);
  }
@@ -312,9 +316,10 @@ export async function sellPlane(inst: GameDb, planeId: string): Promise<{ payout

 // --- Refuel (POST /api/planes/:planeId/refuel) ---

-// Refuel modes (v0.16.0): 'full' fills the tank to maxFuel; 'forFlight' adds just
-// enough fuel for one loaded package's destination leg — required liters per the
-// weighted burn model, independent of how much is already in the tank.
+// Refuel modes (v0.16.0): 'full' fills the tank to maxFuel; 'forFlight' buys 150% of
+// the fuel required for one loaded package's destination leg (ISS-071) — wind-adjusted
+// requirement per the weighted burn model, capped at tank capacity, independent of how
+// much is already in the tank.
 export interface RefuelOptions {
  mode?: 'full' | 'forFlight';
  packageId?: string;
@@ -350,15 +355,21 @@ export async function refuelPlane(inst: GameDb, planeId: string, opts: RefuelOpt
    const origin = await airportByIcao(plane.locationIcao);
    const dest = await airportByIcao(pkg.destIcao);
    const distanceKm = haversineKm(origin.lat, origin.lon, dest.lat, dest.lon);
-    const requiredL = requiredFuelFor(type.burnPerKm, type.emptyWeightKg, type.maxFuel, distanceKm);
+    // Same wind-adjusted requirement flyPlane checks (v0.36.0) — departure weather vs route heading.
+    const w = weatherFor(plane.locationIcao);
+    const requiredL = requiredFuelFor(
+      type.burnPerKm * windBurnFactor(w.windKt, w.windDirDeg, initialBearingDeg(origin.lat, origin.lon, dest.lat, dest.lon)),
+      type.emptyWeightKg,
+      type.maxFuel,
+      distanceKm,
+    );
    if (requiredL > plane.maxFuel) {
      throw new GameActionError(409, `the leg to ${pkg.destIcao} needs ${Math.round(requiredL)} L even starting empty — it does not fit a full ${plane.maxFuel} L tank`);
    }
-    // Land EXACTLY on the leg requirement when topping up: flyPlane re-computes this same value and
-    // compares with strict `>`, so fuel := requiredL guarantees the leg is feasible. The alternative
-    // (fuel + liters) can round a hair BELOW R in IEEE754 — f + fl(R − f) is not guaranteed ≥ R — and
-    // would 409 on an otherwise-feasible leg. Already enough → free no-op, tank untouched.
-    targetFuel = Math.max(plane.fuel, requiredL);
+    // ISS-071: buy 150% of the requirement (capped at tank capacity) so burn variance doesn't strand
+    // the plane. The margin makes flyPlane's strict `>` check pass with room to spare; already enough
+    // → free no-op, tank untouched.
+    targetFuel = Math.min(plane.maxFuel, Math.max(plane.fuel, requiredL * 1.5));
  } else {
    // Exactly maxFuel (as before v0.16.0) — clients/tests compare against it with strict equality.
    targetFuel = plane.maxFuel;
@@ -1,9 +1,10 @@
 import { loadAirportsGeoJson } from '@/lib/airports';
-import { haversineKm } from '@/lib/geo';
+import { haversineKm, initialBearingDeg } from '@/lib/geo';
+import { weatherFor } from '@/lib/weather';
 import { getGameDb } from '@/lib/db/client';
 import * as schema from '@/lib/db/schema';
 import { catalogEntries, FUEL_PRICE_PER_L, PLANE_TYPES, SELL_FRACTION, type CatalogEntry } from './catalog';
-import { fuelAtWeighted, progressAt, positionAt } from '@/lib/sim/movement';
+import { fuelAtWeighted, progressAt, positionAt, windBurnFactor } from '@/lib/sim/movement';

 // Read-only game-state snapshot for client polling (GET /api/state).

@@ -102,7 +103,17 @@ export async function getStateSnapshot(): Promise<StateSnapshot> {
    const distanceKm = haversineKm(from.lat, from.lon, to.lat, to.lon);
    const progress = progressAt(p.departureSimTime, distanceKm, type.speedKmh, simRow.clockMs);
    const pos = positionAt(from.lat, from.lon, to.lat, to.lon, progress);
-    return { ...pos, fuel: fuelAtWeighted(p.fuel, type.burnPerKm, type.emptyWeightKg, type.maxFuel, distanceKm, progress) };
+    // Wind-adjusted burn (v0.36.0) — weather is a pure function of the departure ICAO, so this
+    // recomputes exactly the factor the engine used for the leg; no stored state needed.
+    const w = weatherFor(p.locationIcao);
+    return { ...pos, fuel: fuelAtWeighted(
+      p.fuel,
+      type.burnPerKm * windBurnFactor(w.windKt, w.windDirDeg, initialBearingDeg(from.lat, from.lon, to.lat, to.lon)),
+      type.emptyWeightKg,
+      type.maxFuel,
+      distanceKm,
+      progress,
+    ) };
  };

  return {
@@ -1,5 +1,42 @@
 import { describe, expect, it } from 'vitest';
-import { haversineKm } from './geo';
+import { haversineKm, initialBearingDeg } from './geo';
+
+describe('initialBearingDeg', () => {
+  it('is due north (0) for a point directly above', () => {
+    expect(initialBearingDeg(0, 0, 10, 0)).toBe(0);
+  });
+
+  it('is due east (90) along the equator', () => {
+    expect(initialBearingDeg(0, -10, 0, 10)).toBeCloseTo(90, 9);
+  });
+
+  it('is due south (180) for a point directly below', () => {
+    expect(initialBearingDeg(10, 0, 0, 0)).toBeCloseTo(180, 9);
+  });
+
+  it('is due west (270) along the equator — normalized into [0, 360)', () => {
+    expect(initialBearingDeg(0, 10, 0, -10)).toBeCloseTo(270, 9);
+  });
+
+  it('always normalizes to [0, 360) for arbitrary pairs', () => {
+    const pairs: Array<[number, number, number, number]> = [
+      [50.03, 8.57, 40.47, -3.56], // FRA → MAD (southwest-ish)
+      [40.47, -3.56, 50.03, 8.57], // reverse: northeast-ish
+      [65.66, -18.07, 50.03, 8.57], // far north → south-east wrap case
+    ];
+    for (const [a1, a2, b1, b2] of pairs) {
+      const brg = initialBearingDeg(a1, a2, b1, b2);
+      expect(brg).toBeGreaterThanOrEqual(0);
+      expect(brg).toBeLessThan(360);
+    }
+  });
+
+  it('FRA → MAD points roughly south-southwest (between 180 and 270)', () => {
+    const brg = initialBearingDeg(50.03, 8.57, 40.47, -3.56);
+    expect(brg).toBeGreaterThan(180);
+    expect(brg).toBeLessThan(270);
+  });
+});

 describe('haversineKm', () => {
  it('returns 0 for identical points', () => {
@@ -1,5 +1,18 @@
 const EARTH_RADIUS_KM = 6371;

+// Initial great-circle bearing from point 1 to point 2 (v0.36.0), degrees true [0, 360).
+export function initialBearingDeg(lat1: number, lon1: number, lat2: number, lon2: number): number {
+  const toRad = (d: number) => (d * Math.PI) / 180;
+  const phi1 = toRad(lat1);
+  const phi2 = toRad(lat2);
+  const dLon = toRad(lon2 - lon1);
+  const theta = Math.atan2(
+    Math.sin(dLon) * Math.cos(phi2),
+    Math.cos(phi1) * Math.sin(phi2) - Math.sin(phi1) * Math.cos(phi2) * Math.cos(dLon),
+  );
+  return (theta * 180 / Math.PI + 360) % 360;
+}
+
 // Great-circle distance between two WGS84 points (haversine), in km.
 export function haversineKm(lat1: number, lon1: number, lat2: number, lon2: number): number {
  const toRad = (d: number) => (d * Math.PI) / 180;
@@ -370,7 +370,7 @@ export const openApiSpec = {
      post: {
        summary: 'Refuel a grounded plane',
        description:
-          'Refuel a grounded plane at the fuel price per added liter, deducted from cash (v0.8.0). The body is optional (v0.16.0): no body or mode "full" fills to maxFuel; mode "forFlight" with packageId adds just enough for that loaded package\'s destination leg — liters = required fuel for the great-circle distance (weight-proportional burn model) minus what is already in the tank.',
+          'Refuel a grounded plane at the fuel price per added liter, deducted from cash (v0.8.0). The body is optional (v0.16.0): no body or mode "full" fills to maxFuel; mode "forFlight" with packageId buys 150% of the weather-adjusted fuel required for that loaded package\'s destination leg, capped at tank capacity — liters = min(maxFuel, max(current fuel, 1.5 × required)) − current fuel, where required is the weight-proportional burn model over the great-circle distance with a ±20% wind adjustment (v0.36.0).',
        operationId: 'refuelPlane',
        parameters: [
          { name: 'planeId', in: 'path', required: true, schema: { type: 'string' } },
@@ -488,7 +488,7 @@ export const openApiSpec = {
          label: { type: 'string', description: 'Display name (e.g. "ATR 72-600").' },
          price: { type: 'number', description: 'Market price in € (buy cost; sell pays out sellFraction × this).' },
          maxFuel: { type: 'number', description: 'Fuel capacity, liters.' },
-          burnPerKm: { type: 'number', description: 'Cruise fuel burn at a full tank, liters/km (v0.16.0 weighted model calibrates to this).' },
+          burnPerKm: { type: 'number', description: 'Cruise fuel burn at a full tank, liters/km (v0.16.0 weighted model calibrates to this). Actual per-leg burn varies ±20% with wind — departure weather vs route heading (v0.36.0).' },
          emptyWeightKg: { type: 'number', description: 'Operating empty weight, kg — with burnPerKm and maxFuel it drives the v0.16.0 weight-proportional burn model.' },
          speedKmh: { type: 'number', description: 'Cruise speed, km/h.' },
          maxPayloadKg: { type: 'number', description: 'Max payload in kg — total package weight that can be loaded on one plane (v0.27.0, replaces the v0.12.0 slot count).' },
@@ -575,7 +575,7 @@ export const openApiSpec = {
          mode: {
            enum: ['full', 'forFlight'],
            description:
-              '"full" (default) fills the tank to maxFuel; "forFlight" adds just enough fuel for one loaded package\'s destination leg.',
+              '"full" (default) fills the tank to maxFuel; "forFlight" buys 150% of the weather-adjusted fuel required for one loaded package\'s destination leg, capped at tank capacity (v0.36.0).',
          },
          packageId: {
            type: 'string',
@@ -6,10 +6,11 @@ import { afterAll, beforeAll, describe, expect, it, vi } from 'vitest';
 import { openGameDb } from '@/lib/db/client';
 import * as schema from '@/lib/db/schema';
 import { loadAirportsGeoJson } from '@/lib/airports';
-import { haversineKm } from '@/lib/geo';
+import { haversineKm, initialBearingDeg } from '@/lib/geo';
+import { weatherFor } from '@/lib/weather';
 import { PLANE_TYPES } from '@/lib/game/catalog';
 import { MARKET_TARGET_OPEN_PACKAGES, mulberry32 } from '@/lib/game/seed';
-import { arrivalTimeFor, fuelAtWeighted, requiredFuelFor } from './movement';
+import { arrivalTimeFor, fuelAtWeighted, requiredFuelFor, windBurnFactor } from './movement';
 import {
  clampTimeScale,
  deliverPackages,
@@ -165,7 +166,7 @@ describe('deliverPackages (v0.12.0 arrival delivery)', () => {
  });

  it('delivers in-deadline cargo, unbinds expired cargo for free, keeps other-dest cargo bound', async () => {
-    const { inst, to, km, type } = await setupFlight('deliver-mixed.db');
+    const { inst, from, to, km, type } = await setupFlight('deliver-mixed.db');
    const accountBefore = (await inst.db.select().from(schema.account))[0]!;

    // Three packages on the plane: one in-deadline for TO, one expired for TO,
@@ -184,8 +185,11 @@ describe('deliverPackages (v0.12.0 arrival delivery)', () => {
    expect(plane.locationIcao).toBe(TO);
    expect(plane.lat).toBe(to.lat);
    expect(plane.lon).toBe(to.lon);
-    // Remaining fuel per the v0.16.0 weight-proportional burn model (closed form).
-    expect(plane.fuel).toBeCloseTo(fuelAtWeighted(type.maxFuel, type.burnPerKm, type.emptyWeightKg, type.maxFuel, km, 1), 6);
+    // Remaining fuel per the v0.16.0 weight-proportional burn model (closed form), wind-adjusted
+    // (v0.36.0) by the departure airport's weather vs the route heading.
+    const w = weatherFor(FROM);
+    const f = windBurnFactor(w.windKt, w.windDirDeg, initialBearingDeg(from.lat, from.lon, to.lat, to.lon));
+    expect(plane.fuel).toBeCloseTo(fuelAtWeighted(type.maxFuel, type.burnPerKm * f, type.emptyWeightKg, type.maxFuel, km, 1), 6);
    expect(plane.departureSimTime).toBeNull();
    expect(plane.destIcao).toBeNull(); // flight context cleared on landing

@@ -241,14 +245,19 @@ describe('deliverPackages (v0.12.0 arrival delivery)', () => {
  // --- Auto-chain on landing (v0.25.0, ISS-043) ---

  it('auto-chains to the next queued leg when fuel covers it', async () => {
-    const { inst, to, km, type } = await setupFlight('chain-ok.db'); // full tank EDDF→LEMD
+    const { inst, from, to, km, type } = await setupFlight('chain-ok.db'); // full tank EDDF→LEMD
    const fc = await loadAirportsGeoJson();
    const nextP = fc.features.find((f) => f.properties.icao === 'EHAM')!.properties;
    const nextKm = haversineKm(to.lat, to.lon, nextP.lat, nextP.lon);

-    // Precondition sanity: a full-tank departure leaves enough for the LEMD→EHAM hop.
-    const landedFuel = fuelAtWeighted(type.maxFuel, type.burnPerKm, type.emptyWeightKg, type.maxFuel, km, 1);
-    expect(requiredFuelFor(type.burnPerKm, type.emptyWeightKg, type.maxFuel, nextKm)).toBeLessThanOrEqual(landedFuel);
+    // Precondition sanity: a full-tank departure leaves enough for the LEMD→EHAM hop — both legs
+    // wind-adjusted (v0.36.0) exactly as deliverPackages computes them.
+    const wFrom = weatherFor(FROM);
+    const fOut = windBurnFactor(wFrom.windKt, wFrom.windDirDeg, initialBearingDeg(from.lat, from.lon, to.lat, to.lon));
+    const landedFuel = fuelAtWeighted(type.maxFuel, type.burnPerKm * fOut, type.emptyWeightKg, type.maxFuel, km, 1);
+    const wTo = weatherFor(TO); // the chained leg departs from the arrival airport
+    const fNext = windBurnFactor(wTo.windKt, wTo.windDirDeg, initialBearingDeg(to.lat, to.lon, nextP.lat, nextP.lon));
+    expect(requiredFuelFor(type.burnPerKm * fNext, type.emptyWeightKg, type.maxFuel, nextKm)).toBeLessThanOrEqual(landedFuel);

    await inst.db.update(schema.planes)
      .set({ queue: JSON.stringify(['EHAM', 'EDDV']) })
@@ -268,14 +277,14 @@ describe('deliverPackages (v0.12.0 arrival delivery)', () => {
  });

  it('grounds when fuel cannot cover the next queued leg, keeping the queue intact', async () => {
-    const { inst, km, type } = await setupFlight('chain-nofuel.db');
-    const fc = await loadAirportsGeoJson();
-    const nextP = fc.features.find((f) => f.properties.icao === 'EHAM')!.properties;
+    const { inst, from, to, km, type } = await setupFlight('chain-nofuel.db');

-    // Depart with exactly the fuel for EDDF→LEMD → lands empty, cannot start LEMD→EHAM.
+    // Depart with exactly the wind-adjusted fuel for EDDF→LEMD (v0.36.0) → lands empty, cannot start LEMD→EHAM.
+    const w = weatherFor(FROM);
+    const f = windBurnFactor(w.windKt, w.windDirDeg, initialBearingDeg(from.lat, from.lon, to.lat, to.lon));
    await inst.db.update(schema.planes)
      .set({
-        fuel: requiredFuelFor(type.burnPerKm, type.emptyWeightKg, type.maxFuel, km),
+        fuel: requiredFuelFor(type.burnPerKm * f, type.emptyWeightKg, type.maxFuel, km),
        queue: JSON.stringify(['EHAM']),
      })
      .where(eq(schema.planes.id, 'plane-starter'));
@@ -3,7 +3,8 @@ import { eq, inArray } from 'drizzle-orm';
 import { getGameDb, persist, type GameDb } from '@/lib/db/client';
 import * as schema from '@/lib/db/schema';
 import { loadAirportsGeoJson } from '@/lib/airports';
-import { haversineKm } from '@/lib/geo';
+import { haversineKm, initialBearingDeg } from '@/lib/geo';
+import { weatherFor } from '@/lib/weather';
 import { PLANE_TYPES } from '@/lib/game/catalog';
 import { parseIcaoQueue } from '@/lib/game/state';
 import {
@@ -13,7 +14,7 @@ import {
  type Rng,
  type SeedAirport,
 } from '@/lib/game/seed';
-import { arrivalTimeFor, fuelAtWeighted, requiredFuelFor } from './movement';
+import { arrivalTimeFor, fuelAtWeighted, requiredFuelFor, windBurnFactor } from './movement';

 // Server-authoritative sim engine (v0.7.0) — tick-on-read: there is NO background
 // timer. Every read/action endpoint calls tickNow() first; the clock advances by
@@ -156,8 +157,17 @@ export async function deliverPackages(inst: GameDb, clockMs: number): Promise<nu
    const distanceKm = haversineKm(from.lat, from.lon, to.lat, to.lon);
    if (clockMs < arrivalTimeFor(p.departureSimTime, distanceKm, type.speedKmh)) continue;

-    // Arrived: progress is exactly 1 here, so remaining fuel is the full-leg weighted burn.
-    const landedFuel = fuelAtWeighted(p.fuel, type.burnPerKm, type.emptyWeightKg, type.maxFuel, distanceKm, 1);
+    // Arrived: progress is exactly 1 here, so remaining fuel is the full-leg weighted burn —
+    // wind-adjusted (v0.36.0) by departure weather vs route heading, same factor flyPlane used.
+    const w = weatherFor(p.locationIcao);
+    const landedFuel = fuelAtWeighted(
+      p.fuel,
+      type.burnPerKm * windBurnFactor(w.windKt, w.windDirDeg, initialBearingDeg(from.lat, from.lon, to.lat, to.lon)),
+      type.emptyWeightKg,
+      type.maxFuel,
+      distanceKm,
+      1,
+    );

    // Deliver every bound package whose destination is the airport just reached —
    // runs whether or not a queued leg chains next (ISS-043).
@@ -188,9 +198,19 @@ export async function deliverPackages(inst: GameDb, clockMs: number): Promise<nu
    if (queue.length > 0) {
      const nextDest = queue[0];
      const next = byIcao.get(nextDest); // unknown ICAO in the queue → cannot chain
-      if (next && requiredFuelFor(type.burnPerKm, type.emptyWeightKg, type.maxFuel, haversineKm(to.lat, to.lon, next.lat, next.lon)) <= landedFuel) {
-        queue.shift();
-        chainedTo = nextDest;
+      if (next) {
+        // Wind-adjusted requirement for the NEXT leg — it departs from `to` (v0.36.0).
+        const wNext = weatherFor(to.icao);
+        const nextRequiredL = requiredFuelFor(
+          type.burnPerKm * windBurnFactor(wNext.windKt, wNext.windDirDeg, initialBearingDeg(to.lat, to.lon, next.lat, next.lon)),
+          type.emptyWeightKg,
+          type.maxFuel,
+          haversineKm(to.lat, to.lon, next.lat, next.lon),
+        );
+        if (nextRequiredL <= landedFuel) {
+          queue.shift();
+          chainedTo = nextDest;
+        }
      }
    }
    await inst.db.update(schema.planes)
@@ -10,6 +10,7 @@ import {
  progressAt,
  requiredFuelFor,
  travelDurationMs,
+  windBurnFactor,
 } from './movement';

 // Synthetic in-flight fixtures — no DB needed: everything is a pure function of
@@ -166,6 +167,53 @@ describe('weighted burn model (v0.16.0)', () => {
  });
 });

+describe('windBurnFactor (v0.36.0, ISS-070)', () => {
+  it('full headwind at max wind is exactly +20%', () => {
+    // bearing == windDirDeg: the wind blows straight from ahead.
+    expect(windBurnFactor(30, 90, 90)).toBe(1.2);
+  });
+
+  it('full tailwind at max wind is exactly −20%', () => {
+    // windDirDeg = bearing + 180 (mod 360): the wind blows from behind.
+    expect(windBurnFactor(30, 270, 90)).toBe(0.8);
+  });
+
+  it('a pure crosswind (90° off) leaves burn unchanged', () => {
+    expect(windBurnFactor(30, 0, 90)).toBeCloseTo(1, 9);
+    expect(windBurnFactor(30, 180, 90)).toBeCloseTo(1, 9);
+  });
+
+  it('small wind stays near 1', () => {
+    const f = windBurnFactor(2, 45, 45); // worst case: full headwind at min wind
+    expect(f).toBeGreaterThan(1.01);
+    expect(f).toBeLessThan(1.02);
+  });
+
+  it('stays within [0.8, 1.2] for the whole weather range', () => {
+    for (const kt of [2, 15, 30]) {
+      for (const off of [0, 45, 90, 135, 180, 270, 315]) {
+        const f = windBurnFactor(kt, 100, (100 + off) % 360);
+        expect(f).toBeGreaterThanOrEqual(0.8 - 1e-12);
+        expect(f).toBeLessThanOrEqual(1.2 + 1e-12);
+      }
+    }
+  });
+
+  it('applied as burnPerKm × f, requiredFuelFor and fuelAtWeighted scale accordingly (pinned)', () => {
+    // Fixed inputs: ATR numbers, 1000 km leg / half of the FRA→MAD leg.
+    expect(requiredFuelFor(BURN * 1.2, WE, TANK, 1_000)).toBeCloseTo(1444.911589, 6);
+    expect(requiredFuelFor(BURN * 0.8, WE, TANK, 1_000)).toBeCloseTo(944.348095, 6);
+    expect(fuelAtWeighted(TANK, BURN * 1.2, WE, TANK, KM, 0.5)).toBeCloseTo(4867.313136, 6);
+    expect(fuelAtWeighted(TANK, BURN * 0.8, WE, TANK, KM, 0.5)).toBeCloseTo(5331.677856, 6);
+
+    // Headwind always costs more than tailwind over the same leg…
+    expect(requiredFuelFor(BURN * 1.2, WE, TANK, KM)).toBeGreaterThan(requiredFuelFor(BURN * 0.8, WE, TANK, KM));
+    expect(fuelAtWeighted(TANK, BURN * 1.2, WE, TANK, KM, 1)).toBeLessThan(fuelAtWeighted(TANK, BURN * 0.8, WE, TANK, KM, 1));
+    // …and a neutral factor (f = 1) reproduces the unadjusted model exactly.
+    expect(requiredFuelFor(BURN * windBurnFactor(30, 0, 90), WE, TANK, KM)).toBeCloseTo(requiredFuelFor(BURN, WE, TANK, KM), 9);
+  });
+});
+
 describe('maxRangeKm (v0.28.0)', () => {
  it('ATR 72-600 full tank ≈ 4439 km (±5%)', () => {
    const r = maxRangeKm(BURN, WE, TANK);
@@ -119,6 +119,15 @@ export function requiredFuelFor(
  return (emptyWeightKg / rho) * (Math.exp(k * rho * distanceKm) - 1);
 }

+// Wind adjustment to per-km burn (v0.36.0, ISS-070): the headwind component of a wind blowing
+// FROM `windDirDeg` against a leg heading `bearingDeg`, as a multiplier on burnPerKm —
+// factor = 1 + headwindKt/150, exactly [0.8, 1.2] over the weather range 2–30 kt (±20%).
+// Pure; callers apply it as burnPerKm * factor so every call site agrees on one value per leg.
+export function windBurnFactor(windKt: number, windDirDeg: number, bearingDeg: number): number {
+  const headwindKt = windKt * Math.cos(((bearingDeg - windDirDeg) * Math.PI) / 180);
+  return 1 + headwindKt / 150;
+}
+
 // Max range from a FULL tank under the weighted model — solve requiredFuelFor(d) = maxFuel for d:
 //   (We/ρ)(e^{kρd} − 1) = F  →  d = ln(1 + ρF/We) · (We + ρF)/(ρ·burnPerKm).
 // Returns raw km (call sites round); zero fuel gives exactly 0. Pure — display-only, the sim
@@ -1,6 +1,6 @@
 {
  "name": "flight-ops",
-  "version": "0.35.0",
+  "version": "0.36.0",
  "private": true,
  "scripts": {
    "dev": "next dev -p 3000",