0° 30° 60° 90° 120° 150° 180° 210° 240° 270° 300° 330° R e g i o n o f r o u g h n e s s d u e  to t a i l r o t o r v o r t e x r $_{i}$n g $_{ }$s $_{t}$a t e 1 0 k n o t s 360° 5 k n o t s 1 5 k n o t s 1 7 k n o t s Wind Figure 11-11.  Tail rotor vortex ring state.  Main Rotor Disk Interference (285–315°) Weathercock Stability (120–240°) necessary to maintain rotor rpm, and reducing the collective  (thus reducing the high-power demand on the tail rotor), is the  key to a safe recovery. Pilots should always set themselves  up when conducting any maneuver to have enough height  and space available to recover in the event they encounter  an aerodynamic situation such as LTE.  Understanding the aerodynamic phenomenon of LTE is by  far the most important factor in preventing an LTE-related  accident, and maintaining the ability and option either to go  around if making an approach or pull out of a maneuver safely  and re-plan, is always the safest option. Having the ability to  fly away from a situation and re-think the possible options  should always be part of a pilot's planning process in all phases  of flight. Unfortunately, there have been many pilots who  have idled a good engine and fully functioning tail rotor disk  and autorotated a perfectly airworthy helicopter to the crash  site because they misunderstood or misperceived both the  limitations of the helicopter and the aerodynamic situation.  Unfortunately, the aerodynamic conditions that a helicopter  is susceptible to are not explainable in black and white terms.  LTE is no exception. There are a number of contributing  factors, but what is more important in preventing LTE is to  note them, and then to associate them with situations that  should be avoided. Whenever possible, pilots should learn  to avoid the following combinations: Refer to  Figure 11-9.  Winds at velocities of 10–30 knots from  the left front cause the main rotor vortex to be blown into the  tail rotor by the relative wind. This main rotor disk vortex  causes the tail rotor to operate in an extremely turbulent  environment. During a right turn, the tail rotor experiences a  reduction of thrust as it comes into the area of the main rotor  disk vortex. The reduction in tail rotor thrust comes from the  airflow changes experienced at the tail rotor as the main rotor  disk vortex moves across the tail rotor disk.  The effect of the main rotor disk vortex initially increases the  AOA of the tail rotor blades, thus increasing tail rotor thrust.  The increase in the AOA requires that right pedal pressure  be added to reduce tail rotor thrust in order to maintain the  same rate of turn. As the main rotor vortex passes the tail  rotor, the tail rotor AOA is reduced. The reduction in the  AOA causes a reduction in thrust and right yaw acceleration  begins. This acceleration can be surprising, since previously  adding right pedal to maintain the right turn rate. This thrust  reduction occurs suddenly, and if uncorrected, develops  into an uncontrollable rapid rotation about the mast. When  operating within this region, be aware that the reduction in  tail rotor thrust can happen quite suddenly, and be prepared  to react quickly to counter this reduction with additional left  pedal input. Pilots who put themselves in situations where the combinations  above occur should know that they are likely to encounter  LTE. The key is not to put the helicopter in a compromising  condition, while at the same time being educated enough  to recognize the onset of LTE and being prepared to react  quickly to it before the helicopter cannot be controlled.  In this region, the helicopter attempts to weathervane,  or weathercock, its nose into the relative wind.  [Figure 11-10]  Unless a resisting pedal input is made, the  helicopter starts a slow, uncommanded turn either to the right  Early detection of LTE, followed by the immediate flight  control application of corrective action, applying forward  cyclic to regain airspeed, applying right pedal not left as  11-20 1.  Low and slow flight outside of ground effect. 2.  Winds from ±15º of the 10 o’clock position and  probably on around to 5 o’clock position  [Figure 11-9] 3.  Tailwinds that may alter the onset of translational lift  and translational thrust, and hence induce high power  demands and demand more anti-torque (left pedal)  than the tail rotor can produce.  4.  Low speed downwind turns. 5.  Large changes of power at low airspeeds. 6.  Low speed flight in the proximity of physical  obstructions that may alter a smooth airflow to both  the main rotor and tail rotor. 