Understanding the 787 RAT – Ram Air Turbine Explained

What is a Ram Air Turbine (RAT)?

A Ram Air Turbine, commonly known by its acronym RAT, is a small turbine installed in an aircraft that serves as an emergency power source. Think of it as a miniature wind turbine that deploys from the fuselage or wing into the airstream. Its purpose is to generate power when all other primary and backup power sources have failed.

The operational principle of the RAT is straightforward. It uses the force of the air rushing past the aircraft due to its speed—a phenomenon known as ram air pressure.

Operation of the RAT on Boeing 787

On the Boeing 787, the Ram Air Turbine is more than a simple backup; it’s an intelligent and automated component of the aircraft’s layered safety systems. Its deployment is triggered automatically during a severe power failure that compromises both primary electrical and hydraulic sources. This immediate, autonomous action ensures the flight crew never loses access to essential power.

Once deployed, the variable-pitch turbine windmills in the airstream, generating power proportional to the aircraft’s speed. This energy is immediately channeled to the center hydraulic system and key electrical generators. While designed for automatic deployment, pilots can also activate the system manually if an emergency dictates. The RAT supplies power until the Auxiliary Power Unit (APU) can be started to restore full system functionality.

Hydraulic and Electrical Systems Powered by RAT

The RAT’s power is split between two essential functions:

• Hydraulic Power: Energizes the center hydraulic system to operate primary flight controls (ailerons, elevators, and rudder), enabling pilots to maintain control of the aircraft.

• Electrical Power: Drives a generator for essential systems, including key flight deck displays, navigation and communication equipment, and the fly-by-wire control systems.

Safety Concerns Related to the Boeing 787 RAT

Despite its critical safety role, the Boeing 787’s RAT has been subject to serious manufacturing flaws. A key concern involved forward fittings produced with a substandard titanium alloy. Instead of the required high-strength Grade 5 Ti-6Al-4V, these components were made from commercially pure Grade 1 or 2 titanium—a material with vastly inferior structural properties.

This material deficiency poses a serious risk. Using a weaker titanium alloy compromises the fitting’s strength, fatigue resistance, and damage tolerance. During an emergency, the RAT is subjected to immense aerodynamic forces. A substandard fitting could fail under this stress, potentially causing the RAT to malfunction or even detach from the aircraft entirely. Such a failure would cut off the emergency power the flight crew depends on to maintain control.

In response to these findings, the Federal Aviation Administration (FAA) issued a proposed airworthiness directive to address the risk. This directive mandated inspections of the RAT forward fittings on nine specific Boeing 787-9 and 787-10 aircraft identified as affected, ensuring any non-compliant parts are replaced to secure the integrity of this essential backup system.

Incidents Involving RAT Deployment

While the deployment of a Ram Air Turbine is a rare event, several real-world incidents have demonstrated its value as a last line of defense. Notable examples include emergencies on Air India and LATAM flights, where a significant loss of primary power triggered the RAT’s automatic deployment.

These successful deployments highlight the importance of stringent manufacturing standards and maintenance checks, as a material defect in such situations could have been catastrophic.

Case Study: LATAM Flight and RAT Deployment

On a LATAM flight that serves as a textbook example, the RAT deployed automatically after the aircraft lost primary electrical and hydraulic power. It successfully powered critical flight controls, allowing the crew to stabilize the aircraft, start the Auxiliary Power Unit (APU), and restore normal operations before landing safely.

Air India Flight 171: A Critical Incident

Similarly, on Air India Flight 171, a Boeing 787 experienced a dual loss of primary electrical and hydraulic power, triggering an immediate RAT deployment. The turbine provided the necessary power for the pilots to maintain control and navigate the complex systems’ failure, highlighting its role as a critical safety feature.

The Future of RAT Technology in Aviation

The technology behind the Ram Air Turbine continues to advance, with innovations focused on improving its reliability and performance. A key area of development is materials science, where engineers are creating stronger, lighter alloys.

Beyond stronger materials, the next generation of Rats is becoming more intelligent. Engineers are incorporating smarter deployment mechanisms to optimize power generation across a wide range of airspeeds. A future RAT could, for example, adjust its blade pitch in real-time.

Innovations in global manufacturing and supply chains are also shaping RAT technology. Modern production techniques are yielding higher-quality components and greater consistency, reinforcing the integrity of these critical systems.