Airspeed-knots 0 to 130 Knots (0 to 150 MPH) continuous operation 130 Knots (150 MPH) maximum 100 Knots (115 MPH) maximum for autorotation 150 120 100 20 80 60 40 0 KNOTS 4 6 8 10 12 14 17 AIRSPEED MPH x 10 RPM X100 ROTOR ENGINE 2 3 4 5 1 0 25 30 5 10 40 20 15 35 R T Figure 5-3.  Markings on a typical dual-needle tachometer in a  reciprocating-engine helicopter. The outer band shows the limits  of the superimposed needles when the engine is turning the rotor.  The inner band indicates the power-off limits.  Figure 5-2.  Typical airspeed indicator limitations and markings. Altitude Limitations Rotor Limitations Powerplant Limitations 40 50 60 70 80 90 100 110 120 0 10 20 30 TORQUE PERCENT TURB OUT TEMP °C x 100 1 2 3 4 5 6 7 8 9 Figure 5-4.  Torque and turbine outlet temperature (TOT) gauges  are commonly used with turbine-powered aircraft. 5-3 If the rotorcraft has a maximum operating density altitude  (see page 7-2), it is indicated in this section of the flight  manual. Sometimes the maximum altitude varies based on  different gross weights. maximum continuous power rating. The “maximum power” rating is the maximum power the engine can generate and  is usually limited by time. The maximum power range is  depicted by a yellow arc on the engine power instruments,  with a red line indicating the maximum power that must not be exceeded. “Maximum continuous power” is the maximum  power the engine can generate continually and is depicted  by a green arc.  [Figure 5-4] Low rpm does not produce sufficient lift, and high rpm may  cause structural damage, therefore rotor rpm limitations have  minimum and maximum values. A green arc depicts the  normal operating range with red lines showing the minimum  and maximum limits.  [Figure 5-3] Manifold pressure is a measure of vacuum at the intake  manifold. It is the difference between the air pressure  (or vacuum) inside the intake manifold and the relative  atmospheric pressure of the air around the engine. The  red line on a manifold pressure gauge indicates the  maximum amount of power. A yellow arc on the gauge  warns of pressures approaching the limit of rated power.  There are two different rotor rpm limitations: power-on and  power-off. Power-on limitations apply anytime the engine  is turning the rotor and is depicted by a fairly narrow green  band. A yellow arc may be included to show a transition  range, which means that operation within this range is limited  due to the possibility of increased vibrations or harmonics.  This range may be associated with tailboom dynamic modes.  Power-off limitations apply anytime the engine is not turning  the rotor, such as when in an autorotation. In this case, the  green arc is wider than the power-on arc, indicating a larger  operating range. The powerplant limitations area describes operating  limitations on the helicopter’s engine including such items  as rpm range, power limitations, operating temperatures,  and fuel and oil requirements. Most turbine engines and  some reciprocating engines have a maximum power and a