King Air Propeller Control, Autofeather & Synchrophasing
Explore the named components, make a prediction, then connect the supplied result to the system. This workshop adds coached practice alongside the course handbook and assessed lab.
Follow governing, autofeather and synchrophaser commands
The King Air's governor changes oil flow so the servo changes blade pitch. Autofeather can release that oil on the affected engine while disarming the opposite system. Synchrophasing compares both propellers' timing pulses and trims the governors through electromagnets. Follow the actual input, control action and physical response for each function. Revolutions per minute (RPM) describe rotational speed; phase describes the relative timing of the two propellers' blades.
Three control paths sharing the propeller mechanism — simplified signal and oil relationships
Recorded state: before the supplied change
Green outlines identify components named in the selected exercise record; they do not indicate a healthy component.
Named connections and what each arrow means
- ARM/TEST inputs and armed indications → Torque switches and opposite-side interlockInformation / signal: ARM through lever switches; TEST bypasses those switches
- Torque switches and opposite-side interlock → ARM/TEST inputs and armed indicationsInformation / signal: Affected high-switch transition drops opposite armed relay
- Torque switches and opposite-side interlock → Affected-side autofeather dump valveInformation / signal: Affected low-switch/relay command energizes dump valve
- Affected-side autofeather dump valve → Servo, blade links, spring and counterweightsElectrical power: Oil release permits spring/counterweight feathering
- Targets, pickups and synchrophaser controller → Primary governor and trim electromagnetInformation / signal: Constant voltage + variable ground change electromagnet current
- Primary governor and trim electromagnet → Servo, blade links, spring and counterweightsElectrical power: Metered servo oil changes blade pitch
- Servo, blade links, spring and counterweights → Primary governor and trim electromagnetPhysical relationship: Changed shaft speed changes governor flyweight force
ARM/TEST inputs and armed indications
Select the autofeather feed and display the applicable armed state.
Supplied record: Not observed
How it works with the rest
Normal ARM uses the power-lever-switch paths as well as the pressure-switch/relay conditions. TEST bypasses the power-lever switches for its defined comparison. The green armed indication belongs to its actual installed presentation; selecting ARM alone does not establish the complete armed state. In the normal ARM power-lever-switch check, retarding either lever through its switch range extinguishes both armed lights.
What the evidence must show
Read TEST versus normal ARM before interpreting either a staged or a simultaneous light change.
Selected: ARM/TEST inputs and armed indications
Follow the change through the system.
Fictional B300/B300C record KP71-1 identifies the stated propeller and primary governor. Synchrophasing is OFF and no autofeather dump is commanded. The propeller is initially on speed in normal governing, away from angle stops and operating restrictions. Engine power and external conditions remain steady; oil, an open return, healthy spring/counterweights and free blade motion are supplied. The recorded action lowers the propeller-lever speed selection.
Before the recorded change
Actual speed initially agrees with the former setting. The displayed record has not yet applied the lower selection; ordinary hydraulic/mechanical governing is available.
Next observation
Choose your prediction before revealing the supplied result.
Reference: B300/B300C MM 61-20-00 p.1, Apr 1/2018; 61-10-01 p.1, Apr 1/2018. Qualitative normal governing with all stated prerequisites.
Course applicability and study references
Supplemental practice for the HC-B4-MP-3 B300/B300C installation described in supplied Maintenance Manual 130-590031-11, Chapter 61 LEP Nov 1/2025. Actual propeller, switch, pickup, serial and noise-reduction modifications select the applicable tasks. Autofeather indication locations vary with the installation. Fictional supplied records and original concept diagrams do not calculate geometry, dynamics, calibration limits or a safe engine-run sequence. Existing graded work and saved records remain separate.
- Hydraulic governing and mechanical feathering
Supplied B300/B300C MM 130-590031-11, Chapter 61 LEP Nov 1/2025: 61-10-01 p.1 and 61-20-00 pp.1–2, Apr 1/2018. Normal governing, servo-oil direction, opposing mechanical forces and distinct beta feedback. The source's complete tasks control actual operation.
- Autofeather selection and side-specific sequence
61-21-00 pp.1–2, Apr 1/2018, and Task 61-21-00-7100 pp.602–603, Nov 1/2025. TEST bypasses power-lever switches and reveals the high/low-pressure sequence; normal ARM separately checks each lever-switch path. Matching switch identities and complete applicable setup are supplied, with no new numerical switch threshold.
- Timing control and accepted course
61-23-00 p.1 and 61-20-00 p.1, Apr 1/2018. Pulse phasing, constant voltage/variable ground, electromagnet/governor trim, selected-speed floor and capture/low-pitch constraints. The TM-071 handbook and lab provide the underlying connected-system teaching and complete diagnostic cases for this supplement.
Original learning diagrams and supplied training records explain the stated relationships. Current aircraft-effective instructions and authorization govern actual maintenance.