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Commercial Pilot — Airplane
Commercial Oral Exam Questions: Complex Aircraft & Systems
Commercial applicants are expected to talk about machinery at a different depth than private pilots: not just 'the prop lever controls RPM' but how the governor does it, what fails, and what you'd see. The ACS systems task plus the training requirement that brought you here (training in a complex, turbine, or technically advanced airplane) make constant-speed props, retractable gear, and modern avionics fair game — and turbocharging appears whenever the training airplane has one.
Answer at the level of: component, normal operation, failure modes, and pilot response. The POH for your specific airplane is the controlling document — quote its numbers (gear speeds, prop limits, manifold pressure limits) and the examiner will follow your lead.
Constant-speed propellers and the governor
A constant-speed prop maintains the RPM you select by automatically varying blade pitch. The governor does the work: engine-driven flyweights balance against a speeder spring set by the prop lever; when RPM rises above the setting (overspeed), the flyweights fly out and the governor ports oil to change pitch toward coarse (bigger bite, more load, RPM back down); when RPM sags (underspeed), the reverse. In most singles, governor oil pressure drives the blades toward high pitch/low RPM, and counterweights/springs drive toward low pitch — so losing oil pressure typically sends the prop to high RPM/fine pitch (a noisy overspeed at full throttle); many twins are opposite, feathering on oil loss with accumulators/locks involved. State your airplane's failure direction from the POH.
Operational knowledge that gets asked: why 'prop full forward' before landing (go-around readiness — fine pitch gives maximum power availability); the manifold-pressure/RPM relationship and the old 'over-square' myth (operate per the POH power tables, which frequently approve MP above RPM/100); cycling the prop on runup (exchanges cold oil, verifies governor response); and what a surging or stuck-RPM prop tells you (governor or oil-system trouble — reduce power, land).
Gear, turbocharging, and TAA
Retractable gear: know your system's type (electro-hydraulic power pack is common), the gear-speed trio (VLO extend / VLO retract — often different — and VLE), squat switches and what they prevent, automatic extension systems if installed, the emergency extension method (free-fall, hand pump, or CO2 — and why you slow down and follow the POH exactly), and indications (three green, in-transit, warning horn triggers like low MP with gear up or flaps beyond a setting). Gear-up-landing decision content: if it won't extend, fly the checklist, burn fuel, and land on the longest suitable runway — the airplane is replaceable.
Turbocharging: exhaust gas spins a turbine driving a compressor that raises induction air density; the wastegate (fixed, manual, or automatic via controller) bypasses exhaust to limit boost. Vocabulary the examiner expects: critical altitude (highest altitude maintaining rated MP), overboost (exceeding MP limits — possible with abrupt throttle on manual/fixed systems), bootstrapping (small power oscillation when the wastegate is closed at high altitude), and operational care: smooth throttle movements, observe cool-down practice per POH (turbo bearings live on oil flow), lean per POH with TIT limits in mind. TAA: for the avionics, know your PFD/AHRS architecture, what fails together (AHRS vs ADC failures and their flags), backup instruments and batteries, GPS/WAAS approach annunciations (LPV vs LNAV), and automation discipline — modes verified, and a stated policy for when to click it all off and hand-fly.
Practice questions with answers & rationales
Q1. Explain how the propeller governor maintains the RPM you set.
Answer: The prop lever compresses a speeder spring against engine-driven flyweights. At the selected RPM the forces balance. RPM rising (overspeed) flings the flyweights outward, repositioning a pilot valve that directs governor-boosted oil to change blade pitch toward coarse, increasing the prop's load and pulling RPM back to the setting; underspeed reverses the porting toward fine pitch. The result: torque and airspeed changes are absorbed as pitch changes while RPM holds — which is why MP, not RPM, moves when you change throttle alone.
Q2. You lose engine oil pressure in your single. What happens to the prop, and why does it matter?
Answer: In a typical single, governor oil pressure drives the blades toward coarse pitch, with springs/counterweight forces toward fine — so losing oil sends the prop to fine pitch/high RPM. You'd hear an overspeed tendency and must reduce power to keep RPM in limits; meanwhile the engine is about to fail from oil starvation, so plan a precautionary landing immediately. In many twins it's the opposite by design (oil loss drives toward feather) — knowing your airplane's direction from the POH is the actual test.
Q3. Why do we push the prop control full forward before landing?
Answer: So a go-around delivers maximum available power instantly: fine pitch/high RPM is the takeoff setting, and the governor can't add power that the blade angle won't absorb quickly. Doing it on final (at low MP) keeps it quiet and smooth. The linked habit: throttle movements gentle, and on go-around the order is power up against an already-fine prop — not fumbling levers at 50 ft.
Q4. Define critical altitude, overboost, and bootstrapping on a turbocharged engine.
Answer: Critical altitude: the highest altitude at which the turbo system can maintain rated manifold pressure — above it, MP falls off like a (better) normally aspirated engine. Overboost: exceeding the MP limit, typically by aggressive throttle with a cold/manual/fixed wastegate — can damage cylinders; respond per POH and log/report it. Bootstrapping: at high altitude with the wastegate fully closed, small disturbances loop through the turbine-compressor system causing MP/RPM oscillations — annoying, not damaging, managed with smooth small adjustments.
Q5. The gear handle is down but you have two green lights and one dark. Walk me through it.
Answer: First interrogate the indication: swap or press-to-test the bulb, check the dimmer/nav-light interlock (a classic), and cycle the gear if the POH allows. If the leg truly isn't locked: fly the emergency extension checklist exactly (slow below the POH speed, free-fall/hand-pump/blow-down per system), consider a tower fly-by for a visual, yaw/G techniques only if the POH endorses them. If it won't lock: plan the landing per POH — longest runway, consider fuel burn-off, brief the rollout. The graded behavior is methodical checklist use, not improvisation.
Q6. What's the difference between VLO and VLE, and why are they different numbers?
Answer: VLO is the maximum speed to operate (extend/retract) the landing gear — limited by the mechanism and doors moving through the airstream, and sometimes split into different extend vs retract values. VLE is the maximum speed with gear extended — usually higher, because a locked-down gear is structurally happier than one in transit. Practical use: VLE generosity makes the gear a great drag device for slowing down or going downhill without overspeeding.
Q7. In your TAA, the AHRS fails in IMC. What do you lose, what do you keep, and what's your plan?
Answer: AHRS failure takes attitude and heading on the PFD (red-X), while the air-data computer keeps airspeed/altitude/VS; GPS position remains. Plan: revert to the standby attitude indicator and magnetic compass, declare the equipment problem to ATC, reduce workload (autopilot may be unusable depending on architecture — know yours), and fly to VMC or an approach compatible with what's left. The bigger point for the examiner: you know your specific airplane's failure groupings (AHRS vs ADC vs display vs GPS) and the standby instruments' battery endurance.
Common mistakes to avoid
- Explaining the governor with 'it just holds the RPM' — flyweights, speeder spring, and oil porting are the expected vocabulary.
- Not knowing which way your prop fails with oil loss (and that singles and twins commonly differ).
- Repeating the 'never over-square' myth instead of citing the POH power tables.
- Forgetting the gear-light dimmer/bulb checks and jumping straight to an emergency extension.
- Treating turbo questions casually — critical altitude, wastegate type, and overboost response are standard commercial fare.
- Demonstrating TAA button mastery but no failure-mode knowledge. Examiners fail screens, not GPS units.