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Tail Rotor Malfunctions

By Vertical Mag

By Andy Roe | July 26, 2013

Published on: July 26, 2013
Estimated reading time 5 minutes, 42 seconds.

Tail Rotor Malfunctions

Tail Rotor Malfunctions

By Vertical Mag | July 26, 2013

Estimated reading time 5 minutes, 42 seconds.

Among the many emergency situations pilots need to be ready to manage are those involving tail rotor problems. As well as rotating, the tail rotor blades also change pitch angle; this is needed when increasing and deceasing main rotor pitch to eliminate airframe torque with anti-torque tail rotor thrust. The tail rotor can fail if the rotor stops turning or the pitch change mechanism stops functioning.

The loss of tail rotor drive is an emergency which might require the lowering of the collective to maintain control.  With a pitch change malfunction, if flight control can be maintained, the yaw can be managed to a landing. However, you can’t group all the possible tail thrust malfunction combinations and a complete loss of thrust into one recovery procedure.

A few years ago, a serious accident took place when a pilot experienced a loss of drive at altitude and did not immediately consider autorotation. The pilot had practiced simulated pitch change malfunction emergency landings many times. Did he confuse a pitch change malfunction with a total loss of drive?

If the tail rotor driveshaft fails at altitude from a seized gearbox, the resulting emergency situation is controllable if you lower collective and manage the existing yaw with airframe airflow keel effect which will probably require increased speed.

At the end of the approach the aft application of cyclic to flare and the use of collective at touchdown must be positive to spot land without forward movement. If the helicopter is rotating about the mast on landing and does roll on its side, the rotor RPM at that point will be very low and the chance of injury minimized from the well flown procedure. If the surface permits, a run-on landing can also be considered.

If the tail rotor pitch change mechanism jams in one position the emergency can be less severe compared with a complete loss of thrust. Myriad theories, techniques and opinions abound about how to cope with a jammed pedal as it is often called.

Let’s start with what might cause the pedals to jam, rendering the pitch change mechanism inoperable. I remember hearing about  someone’s long line once coming up like a bungee cord through the open area surrounding the cargo hook in a medium helicopter, from an improperly jettisoned external load.  The pitch change mechanism jammed at a tail rotor pitch angle close to the thrust needed to hover, and the pilot landed at a nearby airport. A faulty bearing sleeve on the push/pull tube which controlled tail rotor pitch used to seize and jam the pedals on some early mediums until design modifications were made.

At the hover, a jammed pedal situation can be managed with combined movements of the collective pitch lever and the throttle. If your main rotor blades rotate counter-clockwise, an uncontrollable rotation to the right can be stopped with a reduction in throttle as you pull collective to land smoothly. A rotation to the left can be stopped with the application of collective pitch. Increasing pitch angle will raise the helicopter further off the ground, which is not useful, so reducing throttle carefully (but not excessively) while raising collective will slow the turn and keep the helicopter close to the ground as you continue to work with pitch to land. If your ship torques left, the inverse procedures apply.

If the pitch failure occurs at altitude, descend to land, and at an air taxi close to the ground you will be back facing the same recovery procedures as at the hover. Control the tendency of the nose to rotate left or right with speed — on the way down you can anticipate whether the nose will go to the left or right prior to landing by using the collective to put the airframe in trim at a low but manageable speed.

If the power setting in trim relative to the anticipated power to land is lower, you can expect the nose to rotate to the right. If the power setting is more than landing power, you might be able to hover or plan to manage a rotation left on landing. No matter which direction the nose wants to rotate prior to touchdown, you have a procedure to manage it.

Most tail rotor incidents are in the form of strikes from objects behind the helicopter, and if the strike is close to the ground, the landing will be imminent. This might not be a bad thing, but if you are working at the top of a 100-foot tower and your risk appetite is low, keep the tail rotor out of harm’s way — because if you do lose the tail rotor drive, you will be in a serious situation.

Remember to keep your tail rotor obstacle free, and even though a mechanical malfunction of the tail rotor is not likely, we all need to have a workable procedure ready to implement just in case Murphy is on board.

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1 Comment

  1. could the A2-380 crash been diverted because of this I think not because the crash was caused by a tail rotor shaft failure so what is a tail rotor shaft failure

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