Operation of Systems
Private Pilot ACS · Area I · Task G · 14 CFR 61, 14 CFR 91, FAA-H-8083-25
Everything you need to know about Operation of Systems for your private pilot checkride. Aligned to FAA-S-ACS-6C Task I-G, covering pitot-static system, engine systems, compass errors & vacuum system.
Pitot-Static System PHAK Ch.8 §
Blockage Scenarios Matrix §
| What's Blocked | ASI | Altimeter | VSI |
|---|---|---|---|
| Pitot tube only (drain open) | Reads zero | Normal | Normal |
| Pitot tube + drain hole | Acts like altimeter ↑climb ↓descend | Normal | Normal |
| Static port only | Inaccurate | Freezes | Reads zero |
| Alternate static used | Slightly high | Slightly high | Momentary spike down then corrects |
Pitot heat: Electrically heated element melts ice forming on the pitot tube. Use whenever visible moisture is present AND temperature is near/below freezing. Also pre-emptively in icing-risk conditions.
Pitot cover: Remove before every flight. Insects (especially mud dauber wasps) build nests inside the pitot tube during overnight storage.
PHAK Ch.8; AFH Ch.17
Gyroscopic Instruments §
Rigidity in space: A spinning gyro resists changes to its axis. Used in the AI and HI.
Precession: Force on spinning gyro causes movement 90° later in the direction of rotation. Used in the turn coordinator.
Attitude Indicator (AI): Vacuum-powered (or electric). Shows pitch and bank. Erection limits: typically ±60° pitch, ±100° bank before tumbling. Can take 5 min to erect after tumbling.
Heading Indicator (HI/DI): Vacuum-powered. Precesses 3–5°/15 min — realign with compass every 10–15 min during straight, unaccelerated flight.
Turn Coordinator: Electrically powered — survives vacuum failure. Standard rate = 3°/sec = 360° in 2 min. Bank angle approximation: TAS ÷ 10 + 5. Ball = slip/skid — step on the ball to coordinate.
Precession: Force on spinning gyro causes movement 90° later in the direction of rotation. Used in the turn coordinator.
Attitude Indicator (AI): Vacuum-powered (or electric). Shows pitch and bank. Erection limits: typically ±60° pitch, ±100° bank before tumbling. Can take 5 min to erect after tumbling.
Heading Indicator (HI/DI): Vacuum-powered. Precesses 3–5°/15 min — realign with compass every 10–15 min during straight, unaccelerated flight.
Turn Coordinator: Electrically powered — survives vacuum failure. Standard rate = 3°/sec = 360° in 2 min. Bank angle approximation: TAS ÷ 10 + 5. Ball = slip/skid — step on the ball to coordinate.
PHAK Ch.8
Engine Systems PHAK Ch.7 §
Fuel System §
Fuel colors: 100LL = blue. 100 (no lead) = green. Jet-A = colorless/straw. Never use Jet-A in a piston engine — catastrophic failure.
Sumping: Drain fuel from each sump, gascolator, and main tank drain. Water is heavier than avgas and collects at the bottom. Water in a sump sample = clear globules at the bottom. Keep draining until sample is pure blue with no globules or sediment.
Blocked fuel vent: Creates vacuum above fuel as fuel burns. Engine eventually starves as fuel cannot flow out of tank. Fuel gauge shows fuel remaining but engine stops.
Carbureted engines: Carburetor ice can form between 20–70°F with humidity. Apply full carb heat — expect brief RPM drop (normal), then rise as ice melts.
Sumping: Drain fuel from each sump, gascolator, and main tank drain. Water is heavier than avgas and collects at the bottom. Water in a sump sample = clear globules at the bottom. Keep draining until sample is pure blue with no globules or sediment.
Blocked fuel vent: Creates vacuum above fuel as fuel burns. Engine eventually starves as fuel cannot flow out of tank. Fuel gauge shows fuel remaining but engine stops.
Carbureted engines: Carburetor ice can form between 20–70°F with humidity. Apply full carb heat — expect brief RPM drop (normal), then rise as ice melts.
PHAK Ch.7
Magneto System §
Two magnetos (L and R) operate independently of the aircraft electrical system. Each fires one plug per cylinder. The aircraft continues to operate on one magneto if the other fails.
Runup mag check: From BOTH → L → BOTH → R → BOTH.
• Acceptable max drop per magneto: 125 RPM
• Acceptable max differential: 50 RPM between mags
Large drop (150+ RPM): Fouled spark plug or failing magneto. Do not depart.
No RPM drop: Magneto may not be properly grounded — also unsafe (magneto would be "live" even when OFF). Do not depart.
Magnetos are p-lead grounded to turn off. A broken p-lead = HOT magneto even with mags switched off. Always treat the propeller as live.
Runup mag check: From BOTH → L → BOTH → R → BOTH.
• Acceptable max drop per magneto: 125 RPM
• Acceptable max differential: 50 RPM between mags
Large drop (150+ RPM): Fouled spark plug or failing magneto. Do not depart.
No RPM drop: Magneto may not be properly grounded — also unsafe (magneto would be "live" even when OFF). Do not depart.
Magnetos are p-lead grounded to turn off. A broken p-lead = HOT magneto even with mags switched off. Always treat the propeller as live.
PHAK Ch.7
Electrical System §
Alternator: Engine-driven generator. Provides power to electrical system and keeps battery charged during flight.
Battery: Provides power for engine start and backup if alternator fails. Typically 20–30 min of endurance at full load.
Ammeter (charge/discharge type): Positive deflection = charging (alternator working). Negative deflection = discharging (alternator failed, battery providing power).
Loadmeter type: Shows electrical load in percent of maximum. High reading = alternator working normally. Sudden drop to zero = alternator failure.
Alternator failure procedure: Check CB, check alternator switch. If cannot restore: shed all non-essential electrical load, navigate with partial panel, land as soon as practicable.
Battery: Provides power for engine start and backup if alternator fails. Typically 20–30 min of endurance at full load.
Ammeter (charge/discharge type): Positive deflection = charging (alternator working). Negative deflection = discharging (alternator failed, battery providing power).
Loadmeter type: Shows electrical load in percent of maximum. High reading = alternator working normally. Sudden drop to zero = alternator failure.
Alternator failure procedure: Check CB, check alternator switch. If cannot restore: shed all non-essential electrical load, navigate with partial panel, land as soon as practicable.
PHAK Ch.7
Left-Turning Tendencies — All Four §
P-factor: At high AoA, the descending prop blade (right side) has greater AoA → more thrust → yaws left. Most pronounced at high power, high AoA (takeoff, climb).
Torque: Reaction to clockwise prop rotation → aircraft rolls/yaws left. Newton's 3rd law.
Spiraling slipstream: Prop wash spirals around the fuselage and strikes the left side of the vertical stabilizer → yaws nose left.
Gyroscopic precession: Mainly tailwheel aircraft during rotation on takeoff — pushing the tail down causes the gyroscopic gyro (prop) to precess → yaw left.
Correction: Right rudder. All four are most pronounced at full power + high AoA (takeoff, go-around, power-on stalls).
Torque: Reaction to clockwise prop rotation → aircraft rolls/yaws left. Newton's 3rd law.
Spiraling slipstream: Prop wash spirals around the fuselage and strikes the left side of the vertical stabilizer → yaws nose left.
Gyroscopic precession: Mainly tailwheel aircraft during rotation on takeoff — pushing the tail down causes the gyroscopic gyro (prop) to precess → yaw left.
Correction: Right rudder. All four are most pronounced at full power + high AoA (takeoff, go-around, power-on stalls).
PHAK Ch.5
Compass Errors & Vacuum System PHAK Ch.8 §
Magnetic Compass Errors — ANDS / OSUN §
ANDS (Acceleration/Deceleration errors on E/W headings):
• Accelerate → apparent turn toward North
• Decelerate → apparent turn toward South
Mnemonic: ANDS = Accelerate North, Decelerate South
OSUN (Turning errors, northern hemisphere):
• Turning to a northerly heading: compass overshoots — start rollout early
• Turning to a southerly heading: compass undershoots — hold bank slightly past heading
• Lead/lag approximation ≈ local latitude in degrees
These errors only occur during turns and acceleration/deceleration — not in steady, straight, unaccelerated flight.
• Accelerate → apparent turn toward North
• Decelerate → apparent turn toward South
Mnemonic: ANDS = Accelerate North, Decelerate South
OSUN (Turning errors, northern hemisphere):
• Turning to a northerly heading: compass overshoots — start rollout early
• Turning to a southerly heading: compass undershoots — hold bank slightly past heading
• Lead/lag approximation ≈ local latitude in degrees
These errors only occur during turns and acceleration/deceleration — not in steady, straight, unaccelerated flight.
PHAK Ch.8
Vacuum System Failure §
Normal suction: 4.5–5.4 in Hg. Check suction gauge during taxi and periodically in flight.
Signs of vacuum failure:
• Suction gauge drops below green arc
• AI shows erroneous or tumbling attitude
• HI begins precessing rapidly then freezes
Action:
1. Cover AI and HI — do not attempt to use them
2. Transition to partial panel: turn coordinator (electric), altimeter, ASI, VSI, magnetic compass
3. Communicate with ATC — request radar vectors
4. Declare emergency if in or approaching IMC
5. Land as soon as practicable
Note: Turn coordinator is typically electric — it survives vacuum failure.
Signs of vacuum failure:
• Suction gauge drops below green arc
• AI shows erroneous or tumbling attitude
• HI begins precessing rapidly then freezes
Action:
1. Cover AI and HI — do not attempt to use them
2. Transition to partial panel: turn coordinator (electric), altimeter, ASI, VSI, magnetic compass
3. Communicate with ATC — request radar vectors
4. Declare emergency if in or approaching IMC
5. Land as soon as practicable
Note: Turn coordinator is typically electric — it survives vacuum failure.
PHAK Ch.8