Grand Caravan EX Engine Fuel Metering & Diagnostic Testing
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 fuel metering, control air and indication
Follow the liquid-fuel stream and its separate mechanical and pneumatic controls. Then use three supplied records to explain a demand change, a governor influence and a disagreement between actual flow and its report.
Trace the fuel/oil heat exchanger → engine-driven fuel pump → fuel control unit → flow transmitter → flow divider; then add power command, gas-generator speed (Ng) feedback, P3 compressor air and the Py governing influence.
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
- Fuel/oil heat exchanger → Engine-driven fuel pumpPhysical relationship: Conditioned liquid fuel to the pump inlet
- Engine-driven fuel pump → Fuel control unit (FCU) and Po returnPhysical relationship: P1 pump delivery through the outlet filter
- Fuel control unit (FCU) and Po return → Engine-driven fuel pumpPhysical relationship: Po normal regulating return toward the pump inlet
- Power command and Ng feedback → Fuel control unit (FCU) and Po returnPhysical relationship: Power setting and mechanical Ng feedback influence metering
- P3 compressor-air input → Fuel control unit (FCU) and Po returnInformation / signal: Filtered P3 air influences the acceleration schedule
- Nf governor and Py air path → Fuel control unit (FCU) and Po returnInformation / signal: Py air bleed influences fuel reduction
- Fuel control unit (FCU) and Po return → Inline fuel-flow transmitterPhysical relationship: Metered fuel through the FCU outlet toward the engine
- Inline fuel-flow transmitter → Flow divider and fourteen duplex nozzlesPhysical relationship: Metered fuel to the primary/secondary distribution assembly
- Inline fuel-flow transmitter → GEA engine/airframe unit and G1000 fuel-flow indicationInformation / signal: Electrical flow signal, distinct from physical fuel delivery
Fuel/oil heat exchanger
Warm incoming fuel with engine oil before the engine-driven fuel pump.
Supplied record: Not evaluated by this record.
How it works with the rest
The temperature-sensitive valve changes the oil route through or around the heater core. It does not select engine fuel flow. Fuel then passes to the pump inlet screen. A thermal complaint and a metering complaint therefore involve different functions even though both affect the same fuel stream.
What the evidence must show
Identify whether the evidence concerns fuel temperature, oil routing, inlet delivery or metered output. A fuel-temperature finding alone does not establish FCU metering.
Selected: Fuel/oil heat exchanger
Follow the change through the system.
A PT6A-140 functional trainer represents steady operation. The pump delivers more fuel than the engine requires. Its inlet screen and outlet filter remain in their normal, unrestricted paths. Only the FCU demand is reduced. The trainer records the identified Po return and the pressure difference P1 minus P2; no aircraft test limit is assigned.
Before the recorded change
The metering opening is steady. P1-minus-P2 is stable, metered output is steady and the identified Po return is flowing. Filter restriction has not been introduced.
Next observation
Choose your prediction before revealing the supplied result.
Reference: P&WC3075742 Rev23,73-00-00 pp5,20–23.
Course applicability and study references
Formative supplement for the Grand Caravan EX PT6A-140 using the supplied P&WC3075742 Revision23 (March3,2025) and Cessna D2078 Revision42 compilation (June1,2024). These source editions are identified, not asserted current for every airplane. Original functional trainer records teach relationships; they do not set aircraft test limits or provide engine operating, calibration or release instructions. PT6A-114/-114A hardware and procedures remain separate.
- P&WC PT6A-140 Maintenance Manual3075742
Supplied Revision23,March3,2025;73-00-00 description and operation pp1–23, including Figures2 and5. Supports physical path, pressure identities, normal FCU return, Ng feedback and P3/Py functions.
- Cessna Model208 Maintenance Manual D2078
Supplied Revision42 compilation,June1,2024;73-10-00 p1 (July1,2016),73-30-05 p401 (March1,2017),73-00-00 pp101–102 (May1,2024). Separates PT6A-140 duplex installation and transmitter reporting; event2536 retains its listed serial/software applicability.
Original learning diagrams and supplied training records explain the stated relationships. Current aircraft-effective instructions and authorization govern actual maintenance.