The Automatic Flight Control System is EC 135's autopilot. The system is very complex and works in many different modes. The principle is similar to that of other airplanes' autopilots, but there are also many differences.

The AFCS is a two-axis autopilot. It only controls the pitch and roll axes. The power supply via the collective and the control around the vertical axis must be taken over by the pilot himself, even when operating with the AFCS.

When AFCS is installed and not activated, AUTOPILOT caution comes on while collective lever is raised more then about 30 %. This is only for information of pilot. Acknowledge the caution by pressing SELECT on CAD or CDS/AUDIO RESET on cyclic stick and ignore it.

Control Panel for AFCS is installed in the slant console or the center console, depending on other equipment.  

Engagement and Disengagement of AFCS

AFCS is engaged by pressing AP button. Amber indication light OFF will disappear. System is now active in A. TRIM mode. 

Pressing AP button again will disengage AFCS. Pressing SAS/AP CUT button at cyclic stick will also disengage AFCS and additionally all SAS functions. When AFCS is disengaged amber OFF in AP button is illuminated.

After disengaging AFCS warning light AP A.TRIM, caution AUTOPILOT and warning gong come on for 10 seconds.

Overriding AFCS

Pilot can override AFCS temporarily by pressing FTR button.

1. To change the reference attitude press FTR. 
2. AP is now overrides. Fly hands-on to the desired attitude while holding FTR pressed. 
3. When desired attitude is reached, release FTR button. 
4. Bring stick quickly back in it's neutral position. Autopilot will hold the new attitude (A. TRIM Mode) or reference airspeed or altitude (depending on engaged upper mode). 

Also BEEP TRIM overrides AFCS functions. Details depend on active mode and are described there. 

A. TRIM Mode

This is standard mode after activation of AFCS. While A. TRIM mode is active, amber indication OFF in A. TRIM button is off. AFCS's status lines in PFD are empty. In this mode autopilot will hold the helicopters flight attitude as it was when activating the system. 

At speeds below 30 KIAS, the autopilot automatically switches to a follow-up mode. The flight attitude then follows the movements of the stick. This allows the pilot to control the helicopter almost as if by hand when hovering or during takeoff and landing.

Disengage: Press A. TRIM button. OFF is illuminated. System goes to AFCS SAS mode. 

Override: BEEP TRIM buttons change the reference for desired flight attitude in pitch and roll. FTR Button can be used to set a new reference attitude as described above.

Upper Modes

In addition to A. TRIM Mode AFCS provides 10 Upper Modes. When an upper mode is armed an amber indication light A is illuminated in the respective button, when engaged a green C (coupled) or ON comes on. Activated HDG or ALT.A Mode is indicated by a green ▸ next to the caption. At PFD active modes are indicated by a green text, armed modes by a cyan text. 

Upper modes can only be activated if AFCS is on. Source for the upper modes is always the selected source on the pilot's side.

When an upper mode is disengaged caution DECOUPLE will come on for 10 s at CAD. Pressing A. TRIM button will disengage all upper modes an switch to AFCS SAS mode. 

ALT Mode

Holds altitude (vertical mode). 

Engage: Press ALT button. 

Disengage: Press ALT button oder select other vertical mode. 

Override: BEEP TRIM forwards and afterwards change reference altitude.

IAS Mode

Holds indicated airspeed (vertical mode). 

Engage: Press IAS button. 

Disengage: Press IAS button oder select other vertical mode. 

Override: BEEP TRIM forwards and afterwards change reference speed. 

VS Mode

Holds vertical speed (vertical mode). 

Engage: Press VS button. 

Disengage: Press VS button oder select other vertical mode. 

Override: BEEP TRIM forwards and afterwards change vertical speed. 

GS Mode

Follows glide path of an ILS (vertical mode). 

Engage: Press GS button. 

Disengage: Press GS button oder select other vertical mode. 

HDG Mode

Holds heading (lateral mode).  

Engage: Press HDG button. Set desired heading with HDG rheostat. (From V5.10)
Set desired heading with HDG rheostat. Press HDG button. (Up to V5.03)

Disengage: Press HDG button or select other lateral mode. 

Override: BEEP TRIM left or right and HDG rheostat change reference heading. 

APP Mode

Follows VOR or locator of an ILS (lateral mode). 

Engage: Tune in frequency of VOR or ILS. Press APP button. APP mode will be armed and automatically engaged when the nav source is captured. As long as APP mode is armed another active lateral mode stays engaged. 

Disengage: Press APP button or select other lateral mode. 

NAV Mode

Follows a course given by GPS/NMS, VOR or HSI (lateral mode).

Engage: Tune in frequency of VOR or programm GPS/NMS. Press NAV button. NAV mode will be armed and automatically engaged when the nav source is captured or GPS/NMS is selected. As long as NAV mode is armed another active lateral mode stays engaged.

Disengage: Press NAV button or select other lateral mode. 

ALT.A Mode

Holds a predefined altitude (vertical mode). 

Engage: Select target altitude by ALT.A rheostat. Press ALT.A button.

Disengage: Press ALT.A button or select other vertical mode. 

Override: BEEP TRIM forwards and afterwards change vertical speed.  

GA Mode

Go Around Mode is used to abort approach. It will hold a indicated airspeed of 75 kt.  

Engage: Press GA button at collective lever (assign the joystick command sim/autopilot/take_off_go_around to a button). 

Override: BEEP TRIM forwards and afterwards change reference speed. 

BC Mode

Back Course Mode is not supported. 

AFCS SAS Mode

Pressing the A.TRIM button when the AFCS is switched on activates the digital Stability Augmentation System. This is indicated by an amber OFF in the A.TRIM button. In this mode, the autopilot no longer controls the helicopter. Instead, it provides the same functions as the normal SAS, but with a slightly stronger function.

Limitations of the AFCS in the simulation

The autopilot in the real EC 135 carries out its control inputs in the same way as the pilot would. It moves the stick controlled by actuators.

In contrast, in the simulation the stick is usually in some fixed position, e.g. in its center. Therefore, control is carried out via a trim that the autopilot carries out in the background. This means that the position of the joystick and the trim are very far apart. The result is a severely limited control authority.

To minimize this effect, it is strongly recommended that any major attitude change be made using the FTR button. This is particularly important at the beginning of a landing approach and when making changes during the landing approach in order to maintain sufficient control authority. With a normal joystick with a centering spring, this procedure is usually sufficient.

If a joystick without centering is used, there are effects that can lead to a larger difference between trim and stick position without being noticed. To signal this to the pilot, the advisory PRESS FTR appears in the CAD if the deviation is too large. It is recommended that you press and hold FTR when this display appears. The internal trim is now slowly reset. Use the stick to compensate for the associated change in flight attitude. When the process is complete, release FTR. The stick is now in a position where the trim is only minimal.

For a non-centering joystick or a stick whose centering can be fixed in hardware with the FTR button, the corresponding configuration must be set as described at installation.