GUIDE: Correct use of PC-12 Autopilot (KMC321/KAC297)

[~Craig~ 10]

Correct / typical use of the PC-12's KMC321/KAS297 autopilot

 

 

 

 

I thought it might be useful to outline the typical operating procedure for the PC-12's Autopilot. I spent  a week flying with a PC-12 four years ago, while on a student exchange programme in Idaho. I won't pretend I did any flying, or even controlled so much as a flaps lever J ..... but as an aviation enthusiast I did make many notes of the operating procedures of this outstanding turbine aircraft.

 

IMPORTANT NOTE:  These procedures can only be followed if you have installed the autopilot modifications for this aircraft, by Bert Pieke.  The stock autopilot has many errors and inaccuracies and these procedures cannot be adopted using it.    Send Bert Pieke a PM with your email address to receive the modified autopilot gauges, which are now 95% accurate.

Even the SP1 for the PC-12 does not have the correct autopilot function:    Bert's mod really is vital.

 

Preparation

 

This was completed after the 'Engine Starting Checklist' as part of the 'Radios/Avionics' scan, and prior to the Before Taxi Checklist.

 

• Press the Flight Director (FD) Button, on the main KMC321 autopilot panel.
• Select  a lateral mode (this will almost always be HDG mode, but it is possible to use NAV button, where NAV is slaved to the GPS, flying a loaded departure procedure).
• Dial the initial cleared altitude into the KAS297 Preselector.
• Press 'ARM' on the Preselector (this is Altitude Arming Mode).  Do not confuse this with the ALT mode on the main Autopilot Panel which is only a 'current altitude hold' mode.
• Press the centre of the Altitude Dial on the KAS297 Preselector.   This accesses Vertical Speed (VS) mode;  dial in a Vertical Speed of ^2000 FPM.
• Press the centre of the altitude dial once again, to return to altitude selected mode.
• DO NOT PRESS THE 'VS' (ENG) MODE ON THE PRESELECTOR!  (This mode is almost never used).

 

Engagement

 

The following take-off procedures are used, prior to AP engagement;-

 

- After rotation, press both brake pedals momentarily, to cease wheel spin.

- Gear Up, at positive rate.

- Flaps up, at 100kts.

- Yaw Damper (YD) button on, on main KMC321 autopilot panel.

- At 1500 AGL (or within 5 mins of take-off), set climb power of 36.9lb/in2, on the Torque Gauge.

 

Now, back to the AP procedures...........

 

• Fly the Flight Director bars, and once stable on lateral and vertical speed indications, engage AP Master on the main KMC321 autopilot panel.
• If airspeed is not in the range of 130-180*kts, press the centre of the altitude dial on the KAS297 preselector, and adjust Vertical Speed until a forward airspeed of 130-180*kts is achieved.  Press the centre of the dial again once achieved, to return to the altitude display.
• Engage IAS mode on the main KMC321 autopilot panel.
• Carenado Bug:  at this point the real aircraft would instantaneously hold the correct pitch to maintain a forward airspeed of 130-180kts.   The Carenado PC12 however has a bug whereby when IAS mode is selected, the vertical speed will always momentarily go down to 500 FPM, after which it will then set to the correct pitch to maintain the IAS.
• Allow the aircraft to climb at the IAS that it is holding.
• To increase or decrease the IAS that the aircraft is flying at, press the 'UP' or 'DN' buttons on the main KMC321 autopilot panel. ' UP' relates to the aircraft nose rising up (eg. a reduction in speed), and 'DN' relates to the aircraft nose being lowered (eg... an increase in airspeed). Note: this behaviour will only work correctly with Bert's mod applied.
• On reaching the preselected altitude, the IAS mode will disengage within 500' of the preselected altitude, and on reaching the precise preselected altitude, 'ARM' mode will disengage, and ALT mode will automatically engage on the main KMC321 autopilot panel, to hold altitude.

* 150kts is optimum IAS for climb.

 

En-route Climbs

 

• For further en-route climbs;  Dial the new altitude in to the preselector and press 'ARM'.
• Press the centre of the altitude dial.
• Select an appropriate vertical speed for climbing (between 500-1200 FPM).
• DO NOT PRESS VS (ENG) !
• The aircraft will begin climbing and will once again level off automatically and engage ALT mode, when the new altitude is reached.

 

Descent

 

• Select lower altitude in to the KAS297 preselector and press 'ARM'
• Press the centre of the altitude dial.
• Select an appropriate vertical speed for descent.
• DO NOT PRESS VS (ENG) !
• Reduce power to avoid an overspeed.
• Autopilot will level out when selected altitude is reached, and will automatically revert to ALT on the main autopilot panel.

 

NOTES: 

 

When climbing in vertical speed mode, there is no annunciation of 'VS' on the main autopilot panel, or on the preselector.  This is because the autopilot treats VS as the default mode for altitude changing.  

 

When IAS is used for climbing (it is not recommended for descent), an indication of IAS is shown on the main autopilot.

 

You should never use the VS (Eng) mode on the Preselector.   It overrides the 'ARM' and preselection functions, and the aircraft will fly at a Vertical Speed but will not automatically level out.

 

Generally speaking, IAS mode is used for climbing and VS is used for further en-route climbing, or for descent.
 

[RobdeVries 28]

Thanks Craig. That confirmed my initial thoughts

Thanks Bert for the mods!

[Shousa 0]

Just awesome Craig - without you, Bert & Nick this would have been......well I don't want to say...just thanks!