PT6A-140 Engine-Control Rigging
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.
PT6A-140 cambox, FCU deadband and reverse pickup
Follow the Grand Caravan EX linkage from its front baseline through fuel control unit (FCU) deadband, beta command and observed response. Ng means gas-generator speed. Deadband means a lever-travel region before a fuel/Ng increase. Position locates that region; width determines its span. Their adjustments and verification evidence have different jobs.
PT6A-140 control components and verification dependencies — select each component
Green outlines identify components named in the selected exercise record; they do not indicate a healthy component.
Named connections and what each arrow means
- Power cable and cambox → FCU arm, nut and indexed spacerTask sequence: Front rigging precedes forward-contact proof
- FCU arm, nut and indexed spacer → Deadband-width stop screwTask sequence: Forward position must pass before width
- Deadband-width stop screw → Low- and high-idle adjustmentsTask sequence: Changed width requires fresh idle work
- Power cable and cambox → Reversing cam, cable and beta valvePhysical relationship: Reversing-cam and cable command branch
- Reversing cam, cable and beta valve → Propeller speed, gas-generator speed and reverse torquePhysical relationship: Beta valve / oil / blade-angle response
- FCU arm, nut and indexed spacer → Propeller speed, gas-generator speed and reverse torqueInformation / signal: FCU input influences fuel/Ng response
Power cable and cambox
Transmits cockpit power-lever motion through the cambox to the FCU and beta/reverse linkage.
How it works with the rest
The cambox sends related commands toward FCU scheduling and the beta/reverse linkage. The front-linkage task first disconnects the aft beta terminal, power-cable terminal and FCU rod before cam work. It then secures the power cable and FCU rod while the aft beta terminal remains disconnected through the following dry paper-deadband checks. Correct cam action, cable engagement and permitted free movement must be proved; cockpit endpoints alone do not establish this baseline.
What the evidence must show
Check witness-hole engagement, the specified cam relationship and a free permitted sweep.
Selected: Power cable and cambox
Follow the change through the system.
Fictional record EX56-1: the PT6A-140 engine is stopped. Front-linkage condition, witness engagement and the permitted free sweep have passed. The power cable and FCU rod are secured; the aft beta terminal remains disconnected from the reversing cam for the dry paper checks. At the named mark 0.15 in forward of IDLE, the FCU stop screw does not contact the test paper. The supplied action uses the FCU-nut position branch first and repeats paper checks. No width-screw change is supplied.
Before the recorded change
Front baseline: current pass. Forward-mark paper contact: absent. Reverse paper-retention span: not yet accepted.
Next observation
Choose your prediction before revealing the supplied result.
Reference: Cessna D2078 Rev.42: 76-12-05 pp.501–503, Apr 1/2019 (PDF 3819–3821); 76-12-03 p.503, Jan 1/2024 (PDF 3813).
Course applicability and study references
Stated Cessna 208B/Grand Caravan EX PT6A-140 installation, aligned with TM-056 Rev G. This formative supplement uses original concept diagrams and fictional supplied work records. Diagram positions are not installed geometry, and supplied results are not calculated from adjustment turns. Earlier Caravan engines and King Air installations use different instructions. Current applicable aircraft and supplier instructions govern physical work.
- Front rigging and forward deadband
Supplied Cessna D2078 Rev.42, 76-12-05 pp.501–503, Apr 1/2019. Front-linkage priority, cable engagement, FCU-nut-first paper-contact correction and conditional marked spacer branch.
- Width, idle dependencies and reverse event order
Cessna 76-12-03 pp.501,503,506, Jan 1/2024. Forward position before width; verified width-screw direction; low before high; Np decrease before Ng increase and separate MAX REVERSE minimum. Cessna 71-00-05 pp.510–511, Apr 1/2019 supplies separate loaded proof context.
- Architecture and serviceability boundary
Supplied P&WC 3075742 Rev.23.0, Mar 3/2025: 72-00-00-900-801 pp.1–2 and 61-20-01-210-801 pp.7–8. The accepted TM-056 Rev G architecture distinguishes FCU scheduling, beta command and valve condition. A source-specific inspection disposition is not replaced by a setting change.
Original learning diagrams and supplied training records explain the stated relationships. Current aircraft-effective instructions and authorization govern actual maintenance.