diff --git a/app/page.tsx b/app/page.tsx
index 40cccb6..77457db 100644
--- a/app/page.tsx
+++ b/app/page.tsx
@@ -10,6 +10,7 @@ import AircraftForm from "../components/AircraftForm";
 import LegalDisclaimerModal from "../components/LegalDisclaimerModal";
 import LandingPage from "../components/LandingPage"; 
 import { isPointInPolygon, getCGLimitsAtWeight } from "../utils/calculations";
+import { validateSavedFleet } from "../utils/validation";
 
 export interface CustomStation {
   id: string;
@@ -48,7 +49,14 @@ export default function Home() {
   useEffect(() => {
     const loadedFleet = localStorage.getItem("wb_saved_fleet");
     if (loadedFleet) {
-      try { setSavedPlanes(JSON.parse(loadedFleet)); } catch (e) { console.error(e); }
+      try {
+        const parsed = JSON.parse(loadedFleet);
+        const validated = validateSavedFleet(parsed);
+        setSavedPlanes(validated);
+      } catch (e) {
+        console.error("Failed to load saved fleet:", e);
+        // Optionally clear invalid data or just warn
+      }
     }
     const savedTheme = localStorage.getItem("wb_theme");
     if (savedTheme === "dark") {
@@ -100,16 +108,17 @@ export default function Home() {
     reader.onload = (event) => {
       try {
         const json = JSON.parse(event.target?.result as string);
-        if (Array.isArray(json)) {
-          setSavedPlanes(json);
-          localStorage.setItem("wb_saved_fleet", JSON.stringify(json));
+        try {
+          const validated = validateSavedFleet(json);
+          setSavedPlanes(validated);
+          localStorage.setItem("wb_saved_fleet", JSON.stringify(validated));
           alert("Fleet imported successfully!");
           setShowSettings(false);
-        } else {
-          alert("Invalid file format.");
+        } catch (validationErr) {
+          alert(`Import Failed: ${(validationErr as Error).message}`);
         }
       } catch (err) {
-        alert("Error parsing file.");
+        alert("Import Failed: The file could not be read. Please ensure it is a valid JSON file.");
       }
     };
     reader.readAsText(file);
diff --git a/public/sw.js b/public/sw.js
index d7b0292..b03a253 100644
--- a/public/sw.js
+++ b/public/sw.js
@@ -1 +1 @@
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+if(!self.define){let e,s={};const a=(a,n)=>(a=new URL(a+".js",n).href,s[a]||new Promise(s=>{if("document"in self){const e=document.createElement("script");e.src=a,e.onload=s,document.head.appendChild(e)}else e=a,importScripts(a),s()}).then(()=>{let e=s[a];if(!e)throw new Error(`Module ${a} didn’t register its module`);return e}));self.define=(n,i)=>{const t=e||("document"in self?document.currentScript.src:"")||location.href;if(s[t])return;let c={};const r=e=>a(e,t),d={module:{uri:t},exports:c,require:r};s[t]=Promise.all(n.map(e=>d[e]||r(e))).then(e=>(i(...e),c))}}define(["./workbox-f1770938"],function(e){"use 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diff --git a/utils/validation.ts b/utils/validation.ts
new file mode 100644
index 0000000..13aa2ce
--- /dev/null
+++ b/utils/validation.ts
@@ -0,0 +1,104 @@
+import { SavedAircraft, Station, EnvelopePoint } from "../data/aircraft";
+
+/**
+ * Validates that the input data matches the Station interface
+ */
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+function validateStation(data: any): data is Station {
+  if (typeof data !== 'object' || data === null) return false;
+
+  if (typeof data.id !== 'string') return false;
+  if (typeof data.name !== 'string') return false;
+  if (typeof data.arm !== 'number') return false;
+  if (typeof data.maxWeight !== 'number') return false;
+
+  return true;
+}
+
+/**
+ * Validates that the input data matches the EnvelopePoint interface
+ */
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+function validateEnvelopePoint(data: any): data is EnvelopePoint {
+  if (typeof data !== 'object' || data === null) return false;
+
+  if (typeof data.cg !== 'number') return false;
+  if (typeof data.weight !== 'number') return false;
+
+  return true;
+}
+
+/**
+ * Validates that the input data matches the SavedAircraft interface
+ */
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+function validateSavedAircraft(data: any): data is SavedAircraft {
+  if (typeof data !== 'object' || data === null) return false;
+
+  // Check required string fields
+  const stringFields = ['id', 'make', 'model', 'registration'];
+  for (const field of stringFields) {
+    if (typeof data[field] !== 'string') return false;
+  }
+
+  // Check required number fields
+  const numberFields = ['emptyWeight', 'emptyArm'];
+  for (const field of numberFields) {
+    if (typeof data[field] !== 'number') return false;
+  }
+
+  // Check isCustomPlane flag (must be true for SavedAircraft)
+  if (data.isCustomPlane !== true) return false;
+
+  // Check arrays
+  if (!Array.isArray(data.stations)) return false;
+  if (!Array.isArray(data.envelope)) return false;
+
+  // Optional: utilityEnvelope
+  if (data.utilityEnvelope !== undefined && !Array.isArray(data.utilityEnvelope)) return false;
+
+  // Validate stations
+  for (const s of data.stations) {
+    if (!validateStation(s)) return false;
+  }
+
+  // Validate envelope
+  for (const pt of data.envelope) {
+    if (!validateEnvelopePoint(pt)) return false;
+  }
+
+  // Validate utilityEnvelope if present
+  if (data.utilityEnvelope) {
+    for (const pt of data.utilityEnvelope) {
+      if (!validateEnvelopePoint(pt)) return false;
+    }
+  }
+
+  // Validate savedArmOverrides if present
+  if (data.savedArmOverrides !== undefined) {
+    if (typeof data.savedArmOverrides !== 'object' || data.savedArmOverrides === null) return false;
+    for (const key in data.savedArmOverrides) {
+      if (typeof data.savedArmOverrides[key] !== 'number') return false;
+    }
+  }
+
+  return true;
+}
+
+/**
+ * Validates and casts the input data to SavedAircraft[]
+ * Throws an error if validation fails
+ */
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+export function validateSavedFleet(data: any): SavedAircraft[] {
+  if (!Array.isArray(data)) {
+    throw new Error("The file format is incorrect (expected a list of aircraft).");
+  }
+
+  return data.map((item, index) => {
+    if (!validateSavedAircraft(item)) {
+      throw new Error(`Aircraft #${index + 1} (${item?.registration || 'Unknown Registration'}) is missing required data or has invalid values.`);
+    }
+    return item;
+  });
+}