Autopilot Pitch Power Relationship
Pitch–Power Relationship, also called Energy Management, which defines how pitch and power (thrust) work together in different flight phases — climb, cruise, descent, and level flight.
🧭 1️⃣ The Core Idea
Aircraft performance is always a balance between:
- Pitch (attitude) → controls aircraft’s flight path angle (and therefore altitude or rate of climb/descent).
- Power (thrust) → controls energy available, mainly influencing airspeed.
But which one controls which changes depending on what you’re trying to maintain — speed or altitude.
✈️ 2️⃣ Basic Pitch–Power Relationships
| Flight Condition | Primary Control for | Secondary Control for | Typical Autopilot / Autothrust Relationship |
|---|---|---|---|
| Climb | Pitch → Speed | Power → Rate of Climb | Pitch holds target speed, thrust set to climb power (THR CLB) |
| Descent | Pitch → Speed | Power → Rate of Descent | Pitch maintains descent speed/path, thrust reduces (IDLE/SPEED) |
| Level Flight (Cruise) | Power → Speed | Pitch → Altitude | Thrust maintains speed, pitch holds altitude |
| Acceleration (in level flight) | Power → Speed Increase | Pitch → Altitude Hold | Increase thrust, maintain altitude |
| Deceleration (in level flight) | Power → Speed Decrease | Pitch → Altitude Hold | Reduce thrust, maintain altitude |
⚙️ 3️⃣ Rule of Thumb — “Primary vs Secondary Effect”
| Flight Type | Primary Effect of Pitch | Primary Effect of Power |
|---|---|---|
| Level Flight | Altitude | Speed |
| Climb / Descent | Airspeed | Rate of climb / descent |
So:
- In level flight, pitch keeps you level, and power controls your speed.
- In climb/descent, power sets climb rate, and pitch maintains speed.
🧩 4️⃣ Visualizing It (Mental Picture)
Imagine a simple see-saw of energy:
↑ Pitch Up → Kinetic → Potential Energy
↓ Pitch Down → Potential → Kinetic Energy
- Pitch up → aircraft slows, climbs (converts speed into altitude)
- Pitch down → aircraft speeds up, descends (converts altitude into speed)
- Power → adds or removes total energy (affects both altitude and speed)
✈️ 5️⃣ In Autopilot / Autothrust Terms
| Flight Mode | Who Controls Speed? | Who Controls Flight Path? |
|---|---|---|
| THR / THR CLB (fixed thrust) | Pitch controls speed | Thrust constant |
| SPEED mode (A/THR active) | Autothrust controls speed | Pitch controls altitude or path |
| ALT / ALT HOLD | Autothrust maintains speed | Pitch holds altitude |
| VNAV / DES | Autothrust maintains speed | Pitch maintains path (idle thrust descent) |
✈️ 6️⃣ Example Summary
| Flight Phase | Pitch Action | Power Action | Primary Control |
|---|---|---|---|
| Climb | Adjusts for speed | Set climb power | Pitch for speed |
| Cruise / Level | Maintain altitude | Adjust for speed | Power for speed |
| Descent | Adjusts for speed | Set idle/descent power | Pitch for speed |
| Approach | Maintain glide path | Adjust for target speed | Both coordinated |
💬 7️⃣ Quick Pilot Mnemonics
🛫 Climb / Descent: “Pitch for speed, power for performance.” ✈️ Level flight: “Pitch for altitude, power for speed.”