January 3, 2014

Did You Know? Dynon Autopilot: Safety Features

In any aircraft equipped with an autopilot, it is critical for a pilot to be familiar with all the ways in which the autopilot may be disengaged or overridden. Dynon’s integrated autopilot system is designed with multiple failsafe features to ensure the autopilot can be disengaged, disabled, and even mechanically disconnected from the aircraft’s primary controls in the event of electronic or mechanical failure.
The first method to disengage the autopilot is to press the dedicated menu button for each autopilot mode.  These buttons are located both on the EFIS display itself or on an optional autopilot control panel, for example the AP74 used in our first-generation EFIS D10/D100/D180 systems.  The SkyView system also has a dedicated OFF button on the AUTOPILOT menu when using the Simplified control scheme.

A second method of disengaging the autopilot in all Dynon systems is to momentarily press the mandatory autopilot disconnect switch, commonly located on the control stick/control wheel but sometimes mounted on the instrument panel.  This disconnect switch will disengage any autopilot mode currently active.

Next, Dynon autopilot servos are also designed so that a pilot can manually overpower them without damage to the servos or the aircraft, and without the need for a failure-prone mechanical clutch in the system.  In this way a pilot can quickly command the aircraft primary controls without the need to reach for or even think about any of the various buttons and menus. The need for prompt evasive action in the event of spotting conflicting traffic is a good example of when a pilot might physically overpower the servos. Next, a pilot can also completely disengage the autopilot subsystem by removing electrical power from the autopilot servos in their aircraft, for example via a dedicated power switch or a pullable circuit breaker. Finally, in the unlikely event of an internal mechanical failure of the servo, moderate but firm force on the control/stick yoke would physically decouple the servo’s drive mechanism from its mechanical link to the aircraft’s primary controls. This action breaks a specially-designed shear screw which is engineered to yield in this scenario to preserve the pilot’s direct control of the aircraft.
The shearable screw is a simple yet elegant solution to a “worst case” failure in which a servo might become mechanically bound. In fact, we engineered our servos with this feature precisely because we judged it is less susceptible to mechanical failures than, for example, servos relying on a clutch mechanism to transfer their force to the aircraft controls.  Clutch-driven servos are typically much more complex with many more moving parts and rely on mechanical or electrical actuation to decouple the servo from the aircraft’s primary controls. Kirk Kleinholz, CFII
Sales Manager, Dynon Avionics