Low rotor r.p.m. does not produce sufficient lift, and high r.p.m. may cause structural damage, therefore rotor r.p.m. limitations have minimum and maximum values. A green arc depicts the normal operating range with red lines showing the minimum and maximum limits. [Figure 6-3]

There are two different rotor r.p.m. 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. 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 rotorcraft’s engine including such items as r.p.m. range, power limitations, operating temperatures, and fuel and oil requirements. Most turbine engines and some reciprocating engines have a maximum power and a 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 6-4]

Like on a torque and turbine outlet temperature gauge, 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. A placard near the gauge lists the maximum readings for specific conditions. [Figure 6-5]

The Weight and Loading Distribution area contains the maximum certificated weights, as well as the center of gravity (CG) range. The location of the reference datum used in balance computations should also be included in this section. Weight and balance computations are not provided here, but rather in the Weight and Balance Section of the FAA-Approved Rotocraft Flight Manual.

This area lists any maneuvers which are prohibited, such as acrobatic flight or flight into known icing conditions. If the rotorcraft can only be flown in VFR conditions, it will be noted in this area. Also included are the minimum crew requirements, and the pilot seat location, if applicable, where solo flights must be conducted.

All rotorcraft generally have one or more placards displayed that have a direct and important bearing on the safe operation of the rotorcraft. These placards are located in a conspicuous place within the cabin and normally appear in the Limitations Section. Since V_NE changes with altitude, this placard can be found in all helicopters. [Figure 6-6]

Concise checklists describing the recommended procedures and airspeeds for coping with various types of emergencies or critical situations can be found in this section. Some of the emergencies covered include: engine failure in a hover and at altitude, tail rotor failures, fires, and systems failures. The procedures for restarting an engine and for ditching in the water might also be included.

Manufacturers may first show the emergencies checklists in an abbreviated form with the order of items reflecting the sequence of action. This is followed by amplified checklists providing additional information to help you understand the procedure. To be prepared for an abnormal or emergency situation, memorize the first steps of each checklist, if not all the steps. If time permits, you can then refer to the checklist to make sure all items have been covered. (For more information on emergencies, refer to Chapter 11—Helicopter Emergencies and Chapter 21—Gyroplane Emergencies.)