Tail Rotor Authority and Loss of Tail Rotor Effectiveness on Approach
You are flying a light single-engine helicopter on a photographic task at 500 ft above ground level, at 45 KIAS, in a light and variable wind reported as 5 kt. The task requires you to turn slowly to the right while maintaining a low groundspeed so the photographer can frame a subject. As you begin the right turn, the nose yaws sharply to the right despite left pedal input, and the yaw rate increases. You are at 500 ft, over open farmland, with no obstacles within a kilometre. The helicopter has a conventional tail rotor on the left side, and the flight manual warns against prolonged flight in the 30–60 KIAS band with a left crosswind. The photographer is unstrapped from the shoulder harness to move a camera.
1. Identify the phenomenon and explain why the right turn at low speed with a light wind triggered it.
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The symptoms describe loss of tail rotor effectiveness: an uncommanded right yaw that does not respond normally to left pedal, occurring at low speed in a configuration where the tail rotor is producing less thrust than required. Several mechanisms combine. At 45 KIAS the main rotor wake is being drawn through the tail rotor, and in a right turn the tail rotor moves toward the wake, reducing its efficiency. A light wind from the left rear quadrant can cause the tail rotor to operate in the main rotor vortex ring state or to suffer from weathercocking effects, and the yaw rate can increase as the aircraft turns. The flight manual's warning band of 30–60 KIAS with a left crosswind matches your situation. The key point is that the yaw is not a rigging fault: it is an aerodynamic condition in which tail rotor thrust is degraded and the aircraft's yaw stability is lost.
2. State the recovery technique and the immediate priorities.
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The recovery is: reduce collective pitch to lower main rotor torque and therefore the tail rotor thrust required, apply full opposite (left) pedal, and simultaneously lower the nose to gain airspeed and translational lift, which restores airflow over the tail and improves tail rotor effectiveness. Do not pull collective to arrest a descent until yaw control is regained, because more power demands more anti-torque thrust. Maintain a safe altitude if possible; at 500 ft you have little margin, so be prepared to accept a descent over open farmland rather than lose control. Once yaw is controlled, accelerate out of the 30–60 KIAS band and away from the triggering wind direction. The priority order is: control yaw, gain airspeed, then recover altitude. If the yaw cannot be controlled, enter an autorotation and land into wind or into the least damaging area.
3. What should you have done differently before starting the task, and what does the unstrapped photographer add to the risk?
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Before the task you should have briefed and flown the manoeuvre to avoid the low-speed, high-power, left-crosswind corner of the envelope: plan the orbit so that turns are made with adequate airspeed, avoid prolonged hovering turns, and choose an orbit direction and altitude that keep the tail rotor out of the wake. You should also have set a minimum altitude for task work and a go-around trigger. The unstrapped photographer is a serious hazard: without the shoulder harness, an abrupt yaw or a recovery manoeuvre can throw the person against the cabin or out of the seat, and the pilot's attention is divided. The correct action is to suspend the task, ensure the photographer is strapped in, and re-brief before continuing. The judgement tested is that task pressure must not override the flight manual's warning and the basic rule that everyone is secured before flight.