The Critical Engine in the ATR72: An Essential Aspect of Flight Safety

The ATR72 is a widely used twin-engine turboprop regional airliner. Like all twin-engine aircraft, it has a "critical engine." But what exactly does this mean, and why is it so important?

What is the Critical Engine?

In a twin-engine aircraft, the critical engine is the one whose failure has the most adverse effect on the aircraft's performance. In propeller-driven aircraft, the "P-factor" effect is also significant. In other words, the critical engine is the engine that, if it were to stop functioning, would make it most difficult for the pilot to maintain control of the aircraft.

Why Does the ATR72 Have a Critical Engine?

The ATR72, like many twin-engine aircraft, has propellers that rotate clockwise. This rotation creates an airflow that exerts a force on the aircraft, called the "P-factor." The P-factor tends to yaw the aircraft towards the failed engine.

What is the Critical Engine of the ATR72?

In the ATR72, the critical engine is the left engine. This is because, with the clockwise rotation of the propellers, the loss of the left engine creates a stronger yawing moment than the loss of the right engine.

What Happens If the Critical Engine Fails?

If the critical engine of the ATR72 flames out, the pilot must apply greater rudder input to counteract the yaw and maintain control of the aircraft. This can be particularly challenging during takeoff and initial climb, when the aircraft is flying at low speed and has less control. Additionally, the greater the angle of attack, the greater the P-factor will be.

How Are Pilots Trained to Handle a Critical Engine Failure?

ATR72 pilots are thoroughly trained to handle a critical engine failure. Training includes both theory and flight simulator practice. Pilots learn to recognize the signs of a critical engine failure and to apply the correct procedures to maintain control of the aircraft. One technique in the ATR cockpit to recognize the critical engine is the slightly wider throttle lever no. 1 (although the reason why it is wider is more due to an "ergonomic" issue).

The Importance of the Critical Engine for Flight Safety

Understanding the critical engine and the ability to manage its failure are fundamental to flight safety on the ATR72. Pilots must be aware of the critical engine and trained to handle its failure safely and effectively. In this case, it is always advisable to make right turns to the side of the operating engine.

The critical engine is an important element to consider in the design and operation of twin-engine aircraft. Understanding the critical engine and its implications is essential to ensure flight safety.

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