POWER INDEX INDICATOR (CONT'D)
The Power Index indicator (displayed on PFD and when a DU is in
Composite format) is a single scale instrument that provides the pilot with an
overall indication of engine performance by displaying a composite of the
three primary engine parameters (Ng, ITT, Tq) over a scale that is the same
as the TQ indicator in Pwr Plant page of the MFD.
PI is an expression of “equivalent torque”; to achieve this, Ng and ITT values
are re-scaled to percent of torque.
PI displays the power available at any instant and the parameter that is
closest to reaching its operational limit.
The limiting parameter is forced to TQ when PI value is between 0 and 10%.
The PI indicator is automatically rescaled according to the power plant
status: AEO, OEI, Power off. PI scale always reflects the TQ indicator scale
when TQ is the limiting parameters.
The actual parameter values are always available in the Power Plant page
on MFD.
PI indication for each engine is computed independently from each other.
The following figure shows a possible scenario as an example:
• the legend ITT is displayed on the left side of the PI scale meaning that
engine 1 is closest to reaching the temperature limit;
• the legend NG is displayed on the right side of the PI scale meaning
that engine 2 is closest to reaching the NG limit;
• primary engine data on MFD show the actual values, in particular
actual torque is 90% for both engines.