The term “retard” in aviation, particularly within the context of flight technology, refers to a specific control input designed to reduce the aircraft’s thrust or power output. This action is crucial for managing speed, controlling descent, and ensuring safe operation during various flight phases, most notably during landing. While the word itself might carry connotations in general language, its aviation meaning is precise and technical, directly linked to the systems that govern engine performance.
Understanding Thrust Management
At its core, aviation relies on a delicate balance of forces: lift, weight, thrust, and drag. Thrust, generated by the aircraft’s engines, propels it forward, counteracting drag and enabling flight. The pilot’s ability to precisely control this thrust is paramount. This control is typically exercised through a throttle or thrust lever, which, when moved towards the “retard” position, signals the engines to decrease their power output.
The Throttle Lever and Its Functions
The throttle lever is one of the primary controls for the pilot. Its movement translates directly into changes in engine power. In most propeller-driven aircraft, moving the throttle forward increases propeller pitch and/or engine RPM, thereby increasing thrust. Conversely, moving the throttle backward reduces propeller pitch and/or engine RPM, decreasing thrust.
In jet aircraft, the throttle lever controls the amount of fuel injected into the engines, which in turn dictates the exhaust gas velocity and thus the thrust produced. Moving the throttle forward increases fuel flow and thrust, while moving it backward decreases fuel flow and thrust. The “retard” position represents the extreme backward movement of this lever, signifying the lowest possible thrust setting for normal operation.
Engine Control Systems
Modern aircraft are equipped with sophisticated engine control systems. For propeller-driven aircraft, this can range from simple mechanical linkages to more complex systems like Constant Speed Propellers (CSP) and, in turboprops and jets, Full Authority Digital Engine Control (FADEC). FADEC systems, in particular, precisely manage engine parameters like fuel flow, blade angle, and bleed air to optimize performance and respond to pilot inputs. The “retard” command, when initiated by the pilot, is interpreted by these systems to reduce the engine’s power output to its minimum, idle setting.
Idle Thrust and Its Significance
The “retard” position typically corresponds to the engine’s idle thrust. Idle thrust is the minimum thrust a jet engine can produce while running. It’s not zero thrust, but a low level of thrust sufficient to keep the engines running smoothly and ready to accelerate. For propeller-driven aircraft, idle thrust means the propeller is set to its minimum pitch, generating minimal forward force.
Idle thrust is critical during approach and landing. It allows the aircraft to maintain a stable airspeed and descent rate without excessive speed, while also providing a buffer for potential engine adjustments if needed. If an aircraft were to shut down its engines entirely during landing, it would lose all aerodynamic control and be subject to a rapid and uncontrollable descent. Therefore, maintaining idle thrust is a safety imperative.
The Role of “Retard” in Landing Procedures
The application of “retard” is most prominently associated with the landing phase of flight. It’s a deliberate action taken by the pilot to manage the aircraft’s energy as it approaches the runway.
Approach and Speed Control
During the approach to landing, pilots aim to establish a stable airspeed and descent rate. The thrust setting is a key component in achieving this stability. As the aircraft approaches the runway threshold, the pilot will typically bring the throttles back to the “retard” position. This reduces the forward thrust, allowing drag (both aerodynamic drag and the drag generated by the propellers or wings) to slow the aircraft down to the desired landing speed.
Maintaining the correct approach speed is vital. Too fast, and the aircraft may float over the runway, requiring a longer landing roll or even an overshoot. Too slow, and the aircraft may stall, leading to a loss of control and a potentially catastrophic event. The “retard” command, by reducing thrust, helps the pilot precisely manage this deceleration.
Flare and Touchdown
The “flare” is the maneuver where the pilot raises the aircraft’s nose just before touchdown to reduce the descent rate and decelerate the aircraft gently onto the runway. During the flare, the throttles are typically already at or near the “retard” position. The primary control during the flare is the elevator, which controls pitch. However, the reduced thrust from the “retard” setting ensures that the aircraft doesn’t balloon (climb unexpectedly) due to excessive thrust during this critical phase.
Once the aircraft is firmly on the ground, the pilot may advance the throttles slightly from the absolute idle position to maintain directional control on the runway, especially in crosswinds or on slippery surfaces. However, the initial command to significantly reduce thrust during the approach and flare is the “retard” function.
Go-Around Procedure
The “retard” command is also implicitly linked to the go-around procedure, which is initiated when a safe landing cannot be assured. If a pilot decides to abort a landing, the first action is to apply full power. This involves moving the throttles forward from the “retard” position to their maximum setting. The immediate increase in thrust allows the aircraft to climb away from the runway and re-enter the traffic pattern for another attempt. The transition from “retard” (idle thrust) to full power is a critical, rapid maneuver during a go-around.
Beyond Landing: Other Applications of Thrust Reduction
While landing is the most common scenario for utilizing the “retard” function, there are other situations in flight technology where controlled reduction of thrust is important.
Descending and Speed Management
During a descent, especially if a steep descent is required or if the aircraft is above its optimal descent speed, pilots will reduce thrust to manage their rate of descent and airspeed. While not always explicitly referred to as “retard” in every descent scenario, the principle of reducing thrust to slow down or control descent rate is the same. In some aircraft, specific descent modes within the autothrottle system might command a reduction in thrust that is analogous to the “retard” function.
Holding Patterns and Speed Restrictions
In holding patterns, aircraft are required to maintain specific speeds and altitudes. If an aircraft enters a holding pattern at a speed that is too high, the pilot will reduce thrust to decelerate to the mandated holding speed. This reduction in thrust can involve moving the throttles to a lower setting, effectively “retarding” the engines to achieve the desired speed profile.
Approach to Stalls
Understanding engine response is crucial for stall prevention. If an aircraft is approaching a stall condition, a common recovery procedure involves simultaneously lowering the nose and applying maximum power. The ability to quickly advance the throttles from a reduced thrust setting (potentially near “retard” if a speed reduction was being managed) to full power is key to regaining airspeed and avoiding a stall.
The Evolution of Thrust Control
The concept of “retard” has evolved with the advancement of flight technology. Early aircraft often had direct mechanical linkages for throttle control, requiring more manual effort and precision from the pilot. Modern aircraft, especially those with glass cockpits and advanced flight management systems, incorporate sophisticated autothrottle and autothrust systems.
Autothrottle and Autothrust Systems
Autothrottle (A/T) systems automatically adjust engine thrust to maintain a selected airspeed or thrust setting. In these systems, the “retard” function is often programmed to automatically move the throttles to the idle position at a predetermined point during the approach, usually at a specific altitude or distance from the runway. This automation reduces pilot workload and can enhance precision during the critical landing phase. The pilot can typically override the autothrottle at any time by manually moving the throttles.
FADEC and Engine Management
As mentioned earlier, FADEC systems play a significant role in how the “retard” command is executed. FADEC continuously monitors engine parameters and pilot inputs, ensuring that the engine responds precisely to the command to reduce thrust to idle. This digital control offers greater accuracy and responsiveness compared to older mechanical systems.
Crew Resource Management (CRM) and Communication
Clear communication between pilots is essential, especially during critical phases of flight like landing. The term “retard” is part of the standard aviation lexicon, and its use in communication during landing is well-defined. For example, one pilot might call out “retard” as they move the throttles, confirming the action to the other pilot. This standard terminology ensures that both crew members are aware of the aircraft’s thrust setting and flight profile.
In conclusion, the term “retard” in aviation, within the realm of flight technology, is a technical command that signifies the reduction of engine thrust, typically to idle. It is a fundamental control input that enables pilots to manage airspeed, control descent, and execute safe landings. Its application is deeply integrated into the physics of flight and the sophisticated control systems of modern aircraft, underscoring its importance in maintaining flight safety and precision.