EASA Part-66 Module12 helicopter systems foundations key terms

Unequal aerodynamic loading associated with different relative airflow on advancing and retreating rotor sides in the stated condition, if uncompensated.

Blade motion above and below the defined rotor reference, accommodated by the actual hub design and distinguished from pitch change and lead-lag.

Blade movement in the rotor plane relative to its reference position, distinguished from vertical flapping or rotation about the feathering axis.

The upward rotor-blade geometry resulting from the balance of aerodynamic and centrifugal effects in the actual condition, not an arbitrary rigging angle.

Rotor operation driven by the relevant airflow rather than engine torque, requiring the actual aircraft procedure for any real maneuver.

The control function changing main-rotor blade pitch together in the defined system, distinguished from azimuth-dependent cyclic variation.

Variation of blade pitch with rotor azimuth to control rotor behavior, interpreted through the actual phase and control architecture.

An overrun mechanism permitting the rotor and relevant engine input to rotate at different speeds as designed rather than rigidly locking them together.

The rotating/nonrotating interface transmitting the defined collective and cyclic control inputs through the actual links to rotor blade pitch mechanisms.

A mechanism combining defined control commands to manage their interactions, not an independent guarantee of correct trim or control margin.

An energy-storage component in a fluid system, whose remaining pressure and safe servicing state must be established through applicable procedures.

The specified prevention, detection or response to heat-related conditions, whose equipment capability and required action depend on the actual installation.

The ambient-pressure reference used by relevant air-data instruments, distinguished from pitot total pressure and the aircraft's true geometric height.

A system permitting the specified alternate fuel-supply path, not proof that every tank can feed every engine or automatically transfer fuel for balance.

Additional capability provided by the actual architecture, assessed against common sources and the particular failure rather than merely counting displays or pumps.

Comparing blade-tip paths with a specified reference and tolerance, distinct from determining all mass moments or rotating vibration sources.

A defined angular or timing reference used to relate a measured vibration to rotor position, requiring the actual measurement convention.

Health and Usage Monitoring System, combining appropriate condition and usage information to support trending rather than guarantee every failure will be predicted.

A device responding to relevant metallic debris in its specified location, whose clean indication cannot rule out all materials or failure modes.

A component with an applicable retirement limit based on the defined usage measure, requiring traceable status independently of surface appearance.