# Autothrottle

{% hint style="info" %}
The autothrottle is an option and can be enabled/disabled via the clipboard options.
{% endhint %}

The autothrottle system automatically moves all three throttles in response to preselected airspeed bug, causing the airplane to acquire and maintain the selected airspeed.

The autothrottle is independent of the autopilot. It will retard the throttles on a signal from the radio altimeter as the airplane descends through the final 30 ft of the flare maneuver. The autothrottle will disconnect two seconds after touchdown.

{% hint style="warning" %}
The autothrottle is only certified for manuevring and approach and can't put the throttles into full thrust/go around power but uses a fixed maximum thrust lever angle.
{% endhint %}

{% hint style="warning" %}
The EPR (Press Ratio) Limit is not linked to any system but a visual reference for the pilots only. Autothrottle will not take EPR limit into account in our version. There were some retrofitted aircrafts with an automatic power rate calculator that was linked to the autothrottle. However only a hand full of aircrafts used it so we didn't recreate that.
{% endhint %}

### ENGAGEMENT AND CONTROL

The autothrottle system is engaged by a switch on the glareshield panel which also selects the captain's airspeed indicator inner bug for the selected airspeed.

With the autothrottle engaged, pressing either No. 1 or 3 throttle finger switch will cause the autothrottle to go to go-around thrust.

### FAST-SLOW INDICATOR

A fast-slow indicator is located on each ADI and provides overspeed and underspeed indications. The amount of needle deflection from the zero position is proportional to the airspeed error. Maximum deflection at approach speeds is about +- 10 kt, and about +- 25 kt at crusie speed.

### DISENGAGEMENT

The system will be disengaged by:

* Positioning the autothrottle engage switch to OFF.
* Pressing either No. 1 or No. 3 autothrottle disengage switch.
* Two seconds after touchdown.

### GO AROUND

The throttle unit has two GA push buttons (thumb) which set the autothrottle to go around when one of them is pressed.


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