What Is a RAT in Aircraft?
The Ram Air Turbine (RAT) is a critical emergency component found on many modern aircraft including the Boeing 787, Airbus A320, and A330. It is a small turbine deployed into the airstream to generate hydraulic or electrical power when the primary systems fail.
Primary Purpose and Function of the RAT
The primary function of the aircraft RAT is to act as an emergency backup by converting ram air (airflow due to the aircraft’s motion) into rotational energy. This powers either a hydraulic pump, electrical generator, or both, depending on the aircraft type.
When aircraft experience total engine failure, dual generator failure, or loss of both AC electrical buses, the RAT deploys automatically or manually to maintain power for essential flight systems:
- Primary flight controls
- Instrumentation
- Avionics
- Flight Management System (FMS)
- Emergency lighting
Types of Aircraft RAT Systems
Hydraulic RATs are often used in aircraft like the Airbus A320, while electro-hydraulic or electric RATs are found in more modern aircraft such as the Boeing 787 Dreamliner.
Examples:
- Airbus A320: Deploys a hydraulic RAT to maintain hydraulic pressure for flight control surfaces.
- Boeing 787: Uses an electrically driven RAT to supply emergency AC power to critical systems.
- Dassault Rafale (Military): Features a RAT designed for both power generation and cooling of avionics in combat conditions.
Uncommon Insights and Design Features of RAT
While many aviation professionals understand the basic role of RATs, here are some lesser-known details:
1. RAT Performance Is Speed-Dependent
- RATs require a minimum airspeed (typically above 100 knots) to generate sufficient power. Below this threshold, output can drop drastically.
- Some RATs are equipped with variable-pitch blades to optimize power generation across a wider speed envelope.
2. Self-Powered and Self-Regulating
- RATs operate independently of the aircraft battery or APU.
- Internal governors regulate output to avoid over-speed or over-voltage.
3. Material Selection and Durability
- RATs are typically constructed from titanium or advanced composites to balance strength, low weight, and resistance to high-speed airflow and icing.
4. Cold Weather & Icing Protection
- In some aircraft, RATs include internal heaters or anti-icing features, especially for polar routes or ETOPS-certified flights.
5. Deployment Mechanism Is Explosive or Pneumatic
- In high-speed aircraft (e.g., military jets), the RAT may be deployed using pyrotechnic cartridges or compressed gas for rapid deployment under extreme conditions.
Notable RAT Deployment Incidents
Air Transat Flight 236 (A330)
- Suffered complete engine flameout over the Atlantic.
- RAT deployment enabled continued control, leading to a successful emergency landing in the Azores.
US Airways Flight 1549 (A320)
- Both engines lost after bird strike.
- RAT powered the flight control systems during the famed “Miracle on the Hudson” landing.
Aircraft Models with RAT Systems
- Airbus A300 / A310 / A320 / A330 / A340 / A350 / A380
- Boeing 757 / 767 / 777 / 787
- McDonnell Douglas MD-11
- Military aircraft: Dassault Rafale, Eurofighter Typhoon
Maintenance and Inspection of RAT Units
Routine RAT inspections are covered under the aircraft’s Maintenance Planning Document (MPD) and include:
- Deployment test (usually via cockpit controls or external panel)
- Blade condition check for erosion or FOD
- Hydraulic or electric output test
- Lubricant inspection for gearbox-type RATs
RATs are non-primary systems but are life-critical during emergencies, and failures must be recorded in the aircraft’s Maintenance Control System (MCS).
Conclusion
The Ram Air Turbine (RAT) is a remarkable piece of emergency engineering that plays a vital role in the safety and redundancy systems of modern aircraft. Despite being seldom deployed, its presence is crucial in life-threatening situations where redundant power sources fail. Understanding how a RAT works, and appreciating its design intricacies, helps aviation professionals and enthusiasts respect the depth of aircraft engineering safety layers.
By Aeropeep Team
