The autopilot is installed under an Approved Model List (AML) STC that lists this airframe — a by-the-book approved installation. The autopilot manufacturer's own maintenance-training guidance, however, holds that STC modifications altering the flight envelope effectively disqualify an otherwise AML-listed aircraft from installation approval, because the autopilot's gain schedule, speed protection, and servo authority are validated against the baseline aircraft.
This airframe carries a separate high-performance engine-conversion STC that materially changed the flight envelope the autopilot must control. The autopilot's control laws were validated against the left column below; the aircraft is operating in the right column.
| Parameter | Stock (baseline) | Modified (conversion STC) | Change |
|---|---|---|---|
| Engine | 210 hp | 305 hp | +45.2% |
| Rate of climb | 1,080 fpm | 1,550 fpm | +43.5% |
| Cruise speed | 188 kts | 230 kts | +22.3% |
| Max level speed | 198 kts | 240 kts | +21.2% |
| Max gross weight | 2,900 lbs | 3,200 lbs | +10.3% |
| Empty weight | 1,860 lbs | 2,068 lbs | +11.2% |
| Wing loading | 16.6 lbs/ft² | 19.15 lbs/ft² | +15.4% |
| VNO | 174 KCAS (flat) | 174/170/166 KCAS (weight-scheduled) | Envelope changed |
| CG range | Baseline | +208 lb empty wt; CG shifts fwd; battery relocated ~54 in aft; gross expanded to 3,200 lb | Envelope modified |
| Propeller | 2-blade | 3-blade, full-feathering | Config change |
| Electrical | Single battery | Dual batteries (relocated aft for CG balance) | Config change |
The autopilot's gain addendum, speed protection, and servo authority were validated against the left column. The aircraft is operating in the right column.
An autopilot operating outside its STC approval renders the aircraft not airworthy. If this is identified now — before release — it is corrected on the ground at no exposure. If it is discovered after release, on a ramp check, an insurance claim, or an accident investigation, the exposure shifts to liability and potential certificate action. Acting ahead of the release is the lowest-cost position available.
| Risk | If addressed now | If found after release | Regulatory basis |
|---|---|---|---|
| Tort liability (accident) | None — corrected before release | Near-certain if autopilot is a factor; seven-figure exposure, no cap | State tort law; negligence / strict liability |
| Insurance denial | N/A | High — policy may void for work outside approved data | Policy terms; 14 CFR §43.13 |
| FAA certificate action | Very low — compliance philosophy favors self-correction | High — suspension 30–120 days; revocation possible | 49 USC §44709; FAA Order 2150.3C |
| Civil penalty | Low — voluntary disclosure mitigates | Up to statutory maximum per violation, stackable | 49 USC §46301 |
1 · Autopilot manufacturer. Request a Letter of No Technical Objection for the modified configuration on this specific airframe, establishing that the manufacturer has no technical objection to operation of the autopilot in the converted envelope.
2 · FSDO / DER. Engage the local FSDO to discuss a DER evaluation and approval of the combined STC configuration on this airframe, producing approved data for the installed configuration.