Autopilot

ATA Chapter 22 — N720AK Systems Reference

Overview

N720AK uses the Dynon 3-axis autopilot integrated with the Skyview HDX EFIS. The system provides roll (aileron), pitch (elevator), and yaw damper servo control. The autopilot is controlled via the Dynon autopilot panel on the instrument panel and can be disconnected instantly via the red button on the Tosten CS Military stick grip.

Components

How It Works

Known Quirk: Silent TRK Reversion on Localizer Signal Loss

Community-reported on SkyView HDX + GTN installations: a temporary localizer signal loss while coupled drops the autopilot from NAV to TRK mode with no alert, and it does not recapture when the signal returns — NAV must be re-armed manually. If the top bar shows TRK on a coupled localizer, guidance has been lost.

Control Wheel Steering (CWS)

The Dynon autopilot supports Control Wheel Steering mode. Press and hold the autopilot disconnect button on the stick grip to temporarily override the autopilot, manually fly the aircraft to a new attitude/heading, then release the button. The autopilot will hold the new state. This allows quick course corrections without fully disconnecting and re-engaging the autopilot.

Disconnect Logic

The autopilot disconnects when:

• The red disconnect button on either stick grip is pressed
• Manual force is applied to the controls (servo clutch slip)

Dynon TSB 080219 — SV42T servo pulley (COMPLIED 2026-10-02)

N720AK’s pitch servo is affected. The pulley reads as the unidirectional “wood-grain” texture (Sam), which the bulletin defines as an affected pulley regardless of whether a crack is present. Dynon Technical Support was contacted 2026-09-22 and is sending the LA pulley assembly and a shear screw replacement kit — see the repair procedure below.

Outcome, 2026-10-02 (tach 182.6): the removed pulley was not just wood-grain — it was cracked from the shear-screw bore clean through to the rim, the exact failure the bulletin describes. Replaced with the crosshatch pulley assembly; the original shear screw was left in place.

Why it matters: “This can cause poor autopilot performance and presents a risk of interfering with the flight controls.” This is a flight-controls hazard, not an autopilot-availability one — disconnecting the autopilot does not address it, because the linkage stays coupled to the elevator either way. That is why Dynon’s wording is before further flight.

Applicability. The bulletin (2019-08-02) covers the pulley on the Dynon linear actuator found on “Some Dynon Avionics SV42T Autopilot Servos (P/N 101008-003 / 101058-003)” and on some SV32/SV42 servos retrofitted with the linear actuator, received after 2011-12-13. This airplane’s pitch servo is an SV42T, P/N 101008-003, S/N 50220 — the part number is listed, and the airframe postdates the cutoff by over a decade. The bulletin is “in effect indefinitely or until superseded by a future bulletin.”

Dynon’s compliance wording: “Due to the nature of the issue, we recommend complying with this service bulletin before further flight. However, it is up to the owner/operator to determine the airworthiness of the aircraft for flight.”

Inspection procedure

1. Crack check — look for a crack running from the centre of the pulley out through the shear-screw bore. “It may be necessary to engage the autopilot on the ground and apply force to the control surface in order to load the pulley to make the crack visible.” An unloaded look can miss it. A crack alone condemns the pulley.
2. Texture read, with a magnifier. Both bulletin figures are loupe shots; the distinction is not reliable with the naked eye.

If affected — removal

Dynon allows either removal path:

• the entire servo assembly, or
• the linear actuator sub-assembly alone, per Dynon’s “Servo Arm / Capstan Removal and Replacement Instructions.”

Two safety steps apply either way:

• “ensure that any remaining linkages are secured and do not interfere with flight controls.”
• If removing only the linear actuator, “disable the servo circuit electrically to prevent misleading autopilot behavior” — disconnect the servo wiring and/or pull its fuse or open its breaker. This touches the SERVOS circuit in plans/electrical-mods-2026-annual.md.

Contact Dynon Technical Support on 425-402-0433 or support@dynonavionics.com. The bulletin says to contact Dynon, not to ship the unit blind.

The repair — LA pulley assembly + shear screw kit

Done 2026-10-02: pulley assembly replaced (crosshatch confirmed), castle nut 4 in-lb, new cotter pin. The shear screw kit was not needed — the original screw stays in place. AP SERVO CALIBRATION completed successfully the same day.

Dynon’s disposition (2026-09-22): they are sending the linear actuator pulley assembly and a shear screw replacement kit, not a replacement servo. So S/N 50220 stays in the airplane, and this is a field repair rather than a swap — no SkyView Network reconfiguration, since it is the same device on the bus.

Two Dynon documents govern it:

⚠ The two documents disagree on castle nut torque. 101156-001 Rev B says “DO NOT EXCEED 4.5 in-lb (72 in-oz)”; 103000-000 Rev C says “beyond 4 in-lbs. of torque may prevent the capstan from separating from the servo output shaft if the controls become jammed.” Use 4 in-lb — it is the lower figure and the newer document (2025 vs 2019). Over-torquing defeats the shear screw’s entire purpose, so err low.

Tools: needle-nose pliers, torque driver reading to 4 in-lb, 1/2“ SAE socket, side cutters, 5/64“ hex wrench (supplied in the kit).

Consumables: cotter pin MS24665-210 — “cotter pins should never be reused.” Castle nut is AN310-5. The kit supplies its own cotter pin, shear screw, 5/64“ hex wrench and a red Loctite 271 capsule.

Stack order, output shaft outward: pulley → nylon washer → wavy washer → castle nut (AN310-5) → new cotter pin. Finger-tighten the nut, then torque only until a slot lines up with the cotter pin hole. Servo rotation must be smooth afterwards, with no movement between the actuating component and the attachment disc.

On the shear screw. 101156-001 is explicit that for a plain pulley change the screw stays put: “DO NOT REMOVE the socket head safety shear screw… The autopilot safety shear screw should NEVER be removed or adjusted during this procedure.” The pulley has a hole that fits over the screw head. The kit is therefore a contingency for a screw found broken or damaged on teardown.

If the screw does need replacing (103000-000 Rev C):

• The attachment disc has three threaded holes, so a servo accepts at most two field shear-screw replacements before it must go back to Dynon.
• The broken screw’s threaded shaft stays in the disc. Check it for burrs and file smooth. If that shaft is loose and rotating in the threads it must come out — “If the loose shear screw shaft vibrates out of the servo attachment disc, it may jam the flight controls.” If it will not come out, the servo goes back to Dynon.
• Only a Dynon shear screw. Any other fastener “will void the servo’s warranty and can cause the aircraft to be unsafe for flight.”
• Light strip of red Loctite 271 on one side of the lower half of the threads; fit into an unused hole; 5/64“ hex, hand strength only, head fully seated against the disc. Under-seating or over-tightening both cause premature failure.
• Cure: 15 minutes before refitting the pulley, and a minimum of one hour before flight.

Finally, recalibrate. 103000-000 Rev C closes with “Perform servo calibration procedure provided in the appropriate installation manual.” On SkyView that is SETUP > HARDWARE CALIBRATION > AP SERVO CALIBRATION > CALIBRATION. Autopilot status will not return to the top bar until it completes. Follow with a flight test and fine-tune per the tuning guide.

Check the new pulley before fitting it — crosshatch weave, plastic-like smooth finish, under a loupe. The bulletin covers only some servos by receipt date, and it is worth thirty seconds to confirm the replacement is not itself the affected design.

Roll and yaw servos. SV32/SV42 are on the bulletin’s unaffected list unless retrofitted with the Dynon linear actuator. N720AK’s roll servo installs per doc 101046-003, the capstan/pushrod kit — almost certainly out of scope. Read the label to close it out.

Compliance is tracked in ad-sb-compliance.tsv. Full bulletin: Dynon TSB 080219 — SV42T Servo Pulley.

Servo Installation

Inspection & Maintenance

References

• Actuator Component Removal and Replacement Instructions (101156-001, Rev B) — removing and refitting the LA pulley; castle nut AN310-5, cotter pin MS24665-210.
• Servo Shear Screw Replacement Kit Installation Guide (103000-000, Rev C) — kit P/N 102991-000; three disc holes, two field replacements maximum.
• Dynon TSB 080219 — SV42T Servo Pulley (2019-08-02) — the pulley cracking bulletin; N720AK’s pitch servo is affected.
• Dynon SkyView Autopilot In-Flight Tuning Guide (Rev F)
• Dynon SkyView System Installation Guide (Rev AX)
• Dynon AP Roll Servo for RV-10 Right Wing (Doc 101046-003, Rev H) — Kit P/Ns: 100870-001 Right Roll Bracket, 100872-001 Right Support Bracket, 100966-008 Aluminum Pushrod 3.0“, 100836-000 Large Male Rod End. Hardware: AN3H-3A, AN3H-10A, AN3H-17A, AN970-3, AN365-1032A.
• Dynon AP Pitch Servo for RV-10 Linear Actuator (Doc 101046-007, Rev E) — Kit P/Ns: 100973-002, 100836-000, 100982-001.
• Dynon AP Yaw Tiller Arm/Bow Kit for RV-10/14 (Doc 102710-000, Rev A) — Kit P/Ns: 102701-000, 102702-000, 100904-001, 100905-000, 101877-000.