Understanding Aircraft Performance Limits and Rudder Overstresses

When discussing the performance of aircraft, one cannot leave out the important consideration of limits and design parameters. Whether it’s a Boeing airliner or an Airbus, these planes are designed with certain performance limits to ensure the safety of passengers and crew. However, there have been instances where these limits have been surpassed, leading to significant issues. One such incident involving a radical use of rudder forces occurred during an American Airlines flight on an Airbus A310, which departed from JFK airport. In a later incident, a Boeing 777 encountered similar problems, underscoring the importance of design and operational procedures.

Design Flaws and the Incident with the Airbus A310

The accident you referred to was an Airbus A310 departing from JFK airport. An earlier incident involving an Airbus A300 in New York further highlighted the potential for rudder overstresses. The aircraft in question was flying into the wake turbulence of a departing 747 when the first officer made several rapid deflections of the rudder. This rapid movement overstressed the vertical stabilizer (empennage), causing it to separate from the aircraft. This incident was a design flaw that should not allow the rudder to exceed its design parameters, as rudder limiters are supposed to prevent such overstraining.

According to industry experts, rudder limiters are crucial components designed to keep rudder movements within safe boundaries. In the case of the Airbus A310, the rudder breakout force was too low, which made it easy for the first officer to overstress the stabilizer by rapidly deflecting the rudder to the stops and then reversing movement. This rapid and extreme application of force on the rudder led to the separation of the vertical stabilizer. While newer Airbuses might have a higher breakout force, rapid and full-scale rudder movements can still lead to airframe damage if the pilot is experiencing pilot-induced oscillation (PIO).

Empennage Breakaway and Structural Integrity

It is almost impossible for an airplane to exceed its performance limits during normal flight. However, in extreme and uncommon situations, it can happen. The rudder, which is a crucial component for directional control of the aircraft, is subject to wear and tear due to repeated stress. Just as bending a wire will eventually cause it to break, the repeated use of rudder forces can cause the bearings to heat up and ultimately seize, leading to the failure of the rudder mechanism.

On all aircraft, including those manufactured by Boeing and Airbus, the risk of exceeding design limits exists. Pilots are trained to understand and respect these limits, but sometimes, they may find themselves in unusual situations that necessitate exceeding these limits. For instance, a pilot may use the rudder at maximum left and right repeatedly, which can force the rudder to detach from the airplane’s empennage. This can happen in cases of pilot-induced oscillation, where the pilot’s maneuvers can lead to extreme forces on the aircraft’s control surfaces.

Best Practices for Safe Flying

The incident involving the Airbus A300 and the Boeing 777 underscores the importance of robust design and operational procedures. All airplanes have their maximum limits, and pilots must be aware of these to ensure safe flight operations. The recommended practice is to avoid rapid and full-scale rudder movements unless absolutely necessary. Pilots should also be trained to recognize and mitigate the risks of pilot-induced oscillation and take appropriate measures to avoid causing excessive stress on the aircraft’s structure.

For instance, my client’s private B737-700 operated by a Business Jet (BBJ) had a pilot operating handbook (POH) that clearly outlined the risks and proper procedures for handling such situations. Understanding and adhering to these guidelines are crucial for preventing rudder overstresses and maintaining the structural integrity of the aircraft.

By educating pilots on the importance of respecting performance limits, airlines can significantly reduce the risks associated with rudder overstresses and ensure a safer flying environment for all.