What is the RAT on the Airbus A320, and when is it used?
The Airbus A320 RAT (ram air turbine) is a small emergency turbine that deploys into the airstream. It uses the aircraft’s forward speed to pressurise the blue hydraulic system, which can drive the emergency generator. It is used after a major power loss, not during normal flight.
In our Aviation & Real-World Flying coverage, the crucial distinction is that the RAT is an emergency energy source, not a spare engine or conventional generator. The energy path is airflow to hydraulic pressure and then, when required, emergency electrical power. Our guide to A320 electrical sources and bus logic explains how it fits into the wider system.
When does the A320 RAT deploy?
The RAT normally deploys automatically when both AC BUS 1 and AC BUS 2 lose power and the aircraft is moving fast enough, generally above about 100 knots.
- Automatic deployment: The trigger is loss of both main AC buses, not simply the number of failed engines. If the APU generator is supplying the buses, for example, the RAT should not deploy merely because both engine generators are unavailable.
- Manual deployment: The crew can command the RAT using guarded controls if an ECAM or checklist procedure requires it. The hydraulic RAT MAN ON control primarily commands physical deployment, while the emergency-electrical MAN ON function initiates the emergency electrical sequence subject to the required bus conditions.
Once deployed, the RAT cannot be retracted from the cockpit. Restoring an engine or APU generator may recover the normal electrical network, but the turbine remains extended until it is reset on the ground.
What does the Airbus A320 RAT power?
The RAT maintains the blue hydraulic system and enables the hydraulic emergency generator to feed a reduced essential electrical network.
- Airflow turns the turbine. Its output therefore depends on airspeed; it has little useful capability when the aircraft is stationary or moving slowly.
- The turbine drives a hydraulic pump. This restores pressure to the blue hydraulic system, supporting selected flight-control functions.
- Blue hydraulic pressure drives the emergency generator. The generator supplies the essential AC network and, through the appropriate conversion equipment, essential DC loads.
- Non-essential loads are shed. Normal cabin, galley and many redundant systems are not retained. The objective is controllability, essential instrumentation and communication rather than normal aircraft operation.
Batteries cover the interval while the RAT deploys and the emergency generator comes online. They also become increasingly important as airspeed falls and RAT output can no longer sustain emergency generation. Starting the APU, when available and permitted by the procedure, can provide a less restricted electrical source; we explain that role in our A320 APU operating overview.
How is the RAT different from the APU and batteries?
The RAT is the automatic last-resort source in flight, while the APU is an alternative generator and the batteries provide immediate but limited electrical support.
| Source | Energy source | Main emergency role |
|---|---|---|
| RAT | Aircraft airflow | Pressurises blue hydraulics and supports emergency generation |
| APU | Fuel-burning gas turbine | Can restore a more capable electrical source when available |
| Batteries | Stored electrical energy | Supply essential loads during transition and at low airspeed |
How can you test the RAT in an A320 simulator?
In a sufficiently detailed A320 simulation, remove both main AC sources while safely airborne and watch the electrical and hydraulic indications rather than relying only on the external animation.
- Establish a safe test condition. Use ample altitude, normal airspeed and a saved flight. This is a simulator exercise only, never a real-aircraft experiment.
- Remove both main AC sources. Ensure the APU generator and external power are not supplying the buses, then use the aircraft’s failure controls or switch off both engine generators.
- Monitor the systems. Use ECAM ELEC and HYD pages to look for blue hydraulic pressure, emergency-generator availability and electrical load shedding. Our guide to the relevant A320 controls and displays helps identify these indications.
- Restore a normal source. Bring an engine or APU generator back online. The normal buses should recover, although the deployed RAT should remain out.
A mistake we see constantly is attempting the test while the APU generator is still powering the aircraft. In that condition the automatic trigger has not occurred. Testing below the model’s airspeed threshold, testing on the ground, or expecting the emergency generator to appear with no deployment delay can cause similar confusion.
Simulation depth also matters. Some aircraft reproduce the bus logic, hydraulic pressure and load shedding; others provide only an animation or simplified ECAM message. For MSFS users, the detailed FlyByWire A32NX package is a practical reference, though system behaviour can still vary with the installed build and simulator platform.