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README-web.md

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+# Pilot's Toolkit — Web
+
+A collection of aviation utilities for flight crews, built with React and Vite. Single-page application designed for browser-based cockpit use and future Docker deployment.
+
+**Not for operational use — verify all calculations independently.**
+
+---
+
+## Modules
+
+- **Fuel Order Calculator** — Fuel quantity in US/imperial gallons and liters with ASTM D1250 Table 6B density correction and ambient temperature adjustment.
+- **Pavement Strength / ESWL** — ACN/ACR calculation with PCN/PCR comparison, rigid/flexible pavement types, four subgrade categories. Reverse-solves maximum allowable weight when pavement is exceeded.
+- **Crosswind Calculator** — Headwind, tailwind, and crosswind components from wind direction/speed and runway heading. Auto-formats five-digit wind input on blur.
+- **Fuel Buckets** — Stage length vs. fuel burn schedule with slider interpolation. Supports operator-specific CSV and JSON profile import.
+- **HF Frequencies** — Active ARINC HF assignments for Atlantic and Pacific with staleness indicator.
+- **Passdown** — Crew changeover form with local storage, autocomplete, history, batch .ptz export, email compose via `mailto:`, and stale-record detection on send.
+- **Flight Level ↔ Meters** — ICAO meters-to-feet conversion table and China RVSM FLAS with directional filtering.
+- **Crew Rest** — Augmented operations rest calculator for 3–4 pilots. Equal-division sequential rest rotation with lock toggle to prevent accidental edits mid-flight.
+
+## Project Structure
+
+```
+pilot-toolkit-web/
+  package.json                        ← Dependencies and scripts
+  vite.config.js                      ← Vite + React plugin
+  index.html                          ← Entry HTML
+  src/
+    main.jsx                          ← React root mount
+    toolkit.jsx                       ← All eight modules (~3,600 lines)
+    data/
+      reference.json                  ← Flight levels, subgrade labels
+      aircraft/
+        G450.json                     ← Per-airframe data
+        G500.json
+        G650.json
+        G700.json
+```
+
+## Data Architecture
+
+All aircraft and reference data lives in JSON files under `src/data/`. Vite imports these statically at build time — they are tree-shaken into the production bundle.
+
+- **`reference.json`** — Airframe-agnostic: meters-to-feet table (107 entries), China FLAS (50 entries), RVSM direction sets, pavement subgrade labels.
+- **`aircraft/*.json`** — One file per airframe: weight limits, ESWL config (formula or thresholds), PCN/PCR linear regression coefficients, fuel bucket schedules. Each file is imported individually in `toolkit.jsx` and wrapped in a `loadAircraft()` call with error handling.
+
+Each aircraft file loads independently. A parse failure is caught and logged to `dataLoadErrors` — it does not crash the app or affect other airframes.
+
+**Adding a new airframe** requires adding an import line and a `loadAircraft()` call in `toolkit.jsx` (Vite does not support dynamic JSON imports at build time).
+
+## Storage
+
+- **`localStorage`** — Dark mode, default aircraft, volume unit, passdown retention period, fuel profiles (per aircraft).
+- **IndexedDB** — Passdown records and autocomplete lookups. Accessed via async helper functions.
+
+All data is local to the browser. No backend, no accounts, no external APIs (except ARINC HF frequency pages).
+
+## Exchange Formats
+
+- **`.ptz`** — Gzipped JSON array of passdown objects. Exported via browser `CompressionStream`, imported via `DecompressionStream`. Open format.
+- **Fuel profile JSON** — Validated on import by `format: "pilot-toolkit-fuel-profile"` field.
+- **Fuel profile CSV** — Two columns (stage length, fuel burn), optional header row.
+
+## Dependencies
+
+Production: `react`, `react-dom` (2 packages). No other runtime dependencies.
+
+Dev: `vite`, `@vitejs/plugin-react`.
+
+Compression uses the browser-native `CompressionStream` / `DecompressionStream` APIs — no external gzip library.
+
+## Build
+
+```
+npm install
+npm run dev        # Development server
+npm run build      # Production build → dist/
+npm run preview    # Preview production build
+```
+
+Production build produces a single HTML file and a single JS bundle (~250 KB, ~72 KB gzipped).
+
+## Deployment
+
+Currently runs as a local dev server. Docker deployment (Phase II) is planned — the production build output (`dist/`) can be served by any static file server (nginx, Caddy, etc.) with no backend required.