Autopilot All Weather Operation

🧩 Key Terms (CS-AWO: All Weather Operations)

1. Fail-Passive Autoland System

• If a failure happens → autopilot disconnects smoothly, no big flight path change.
• But the autoland stops — the pilot must take over and land manually.
• ✅ Aircraft remains stable
• ❌ Autoland cannot continue
• Example: Single autopilot autoland system.

2. Fail-Operational Autoland System

• If one part fails → the remaining autopilots continue the approach and landing.
• The system can still complete the landing automatically.
• ✅ Autoland continues safely
• ❌ System is now degraded to fail-passive
• Example: Triple autopilot system (three channels, two still working after a failure).

3. Fail-Operational Hybrid Landing System

• Combines fail-passive autoland with manual or head-up display (HUD) guidance.
• If the automatic system fails, the pilot uses visual cues or HUD to finish the landing manually.
• ✅ Safe manual completion possible
• Used on some modern aircraft as a backup concept.

4. Alert Height (AH)

• A specific radio height (usually around 200 ft AGL) used in fail-operational systems.
• Based on how the aircraft behaves and its system design.

Meaning:

• Above Alert Height → If a failure occurs, you must go around (too high to accept degraded capability).
• Below Alert Height → If a failure occurs, you continue landing (too low to react safely; system alerts are inhibited).

✈️ Pilot Actions (LO 022.06.05.01.06)

⚙️ Example Scenario (from your question)

• System: Fail-Operational autoland
• Event: One autopilot fails at 400 ft
• Alert Height: ≈200 ft

Explanation:

• 400 ft is above the alert height
• Failure → system annunciates the problem
• System now reverts to fail-passive → new (higher) minima required
• Not enough time to set new DH/RVR or brief crew
• ✅ Correct action: Go Around

Summary Table

✅ You’ve almost got it perfectly right — just a couple of small clarifications to make it 100% accurate:

FAIL-OPERATIONAL system

• If one autopilot fails, the system can still complete the landing automatically (it becomes fail-passive).
• What you do depends on when the failure happens:

✅ So your summary for fail-operational is correct — just note that the “1000 ft” is a typical example for stable approach criteria, not a regulatory rule; the key legal threshold is the Alert Height (AH).

FAIL-PASSIVE system

• If one autopilot fails, the system cannot complete the autoland.
• Aircraft stays stable, but autopilot disconnects, and pilot must take control.

✅ Your summary (“NO AUTOLAND – take over manually or go around”) is exactly correct.

💡 Quick visual summary