Installation manual

Avidyne | DFC90, 100 FAQs (Last updated: 26 June 2012)

(DFC100) Can you explain more about the Underspeed protection that comes with

Envelope Protection (EP) in the DFC100? Like the DFC90, Underspeed protection is

designed to prevent autopilot-induced stall conditions. If, between a combination of

power settings or commanded climb conditions result in a decaying airspeed to be

approximately 1.2 Vstall, the autopilot will: provide an annunciation on the PFD that

UNDERSPEED is active; provide an aural alert in your headset that speed protection

mode is active; flash the engaged (green) lateral and vertical mode annunciators; and will

adjust the aircraft pitch angle and/or bank angle as required to maintain 1.2 Vstall. The

system will stay in this state until there is sufficient energy/airspeed to provide the

original commanded state through a pilot-commanded action such as adding power or

changing the commanded condition (e.g. lowering the requested climb rate, increasing

the requested IAS value, etc). The autopilot needs to be engaged in some mode for this

protection to be active. Another change from the initial release of DFC90 is that the

DFC100 EP takes flap position into account, thereby generating a more accurate value for

true Vs. Envelope protection is not functional in Flight Director only operations.

(DFC90, 100) Can you explain more about the Overspeed protection that comes with

Envelope Protection? Overspeed protection is designed to prevent autopilot-induced

overspeed conditions. For Vne aircraft, this protection kicks in right at Vne. As the

aircraft reaches Vne, the autopilot will: provide an annunciation on the PFD that

OVERSPEED is active; provide an aural alert in your headset that speed protection mode

is active; flash the engaged (green) lateral and vertical mode annunciators; and will adjust

the aircraft flight path angle as required to maintain Vne. The system will stay in this

state until a pilot-commanded action such as reducing power or changing commanded

pitch is made. The autopilot needs to be engaged in some mode for this protection to be

active. (updated 10 Oct 2011)

(DFC90, 100) What is the Full-time Envelope Alerting (EA) capability in the

DFC90,100 all about? EA takes EP a step further and provides speed-based and

attitude-based envelope alerting whenever the autopilot is not engaged (servos not

coupled). EA is provided during flight director operations (servos not coupled) and is

also provided even when the autopilot and flight director are off and the autopilot is in the

standby position as noted by the AP READY mode annunciator on the top strip of the

PFD pages. Full-time Envelope Alerting is triggered when the DFC90, 100 recognizes

an underspeed, overspeed or excessive bank angle condition and will alert the pilot via

text alerts on the PFD pages and aural alerts in the headset. One common scenario this is

intended to alert the pilot to is a traffic pattern stall. If/when the DFC90, 100 detects a

traffic pattern stall situation developing, the system will issue a “Caution, Underspeed”

aural alert and the PFD/IFD will display an accompanying “UNDERSPEED” text alert.

(updated 10 Oct 2011)

(DFC90, 100) Will the existing servos wear out with the DFC autopilot like they are in

S-TEC systems? No, no more so than pre-DFC installation. While the flight controls are

still actuated frequently in a DFC system, the magnitude of motor actuator movements

are substantially smaller. Think of it this way – the entire time you are hand-flying the