Operation of Systems

The pilot controls engine rpm indirectly through a propeller control connected to the governor, which adjusts blade angle to hold the selected rpm.

• Pull the prop control back → higher blade pitch → more air resistance on the blades → more load on the engine → rpm decreases until forces balance.
• Push it forward → lower blade pitch → less resistance → rpm increases until forces balance.

The governor is geared to the crankshaft so it can sense rpm, and it uses engine oil pressure (usually boosted by a pump integrated with the governor) to move the blades. Nose up into a climb and the engine tends to slow; the governor decreases blade angle just enough to hold rpm. Nose down and it increases blade angle. The result is an infinite number of power settings from any combination of manifold pressure and rpm (AFH ch. 12).

A fixed-pitch propeller is designed for best efficiency at one rpm and one airspeed, and efficiency suffers considerably outside that narrow band. A constant-speed prop keeps blade angle adjusted for maximum efficiency across most flight conditions (AFH ch. 12).

Concretely:

• Takeoff — low pitch / high rpm keeps blade angle of attack small and efficient at low speed, keeps propeller load light so the engine develops maximum power, and maximizes thrust at brake release.
• Climb — reduce manifold pressure, then increase blade angle to lower rpm; the prop handles a greater mass of air per second at lower slipstream velocity, and increased propeller efficiency offsets the power reduction.
• Cruise — higher airspeed and higher blade angle put the propeller at or near maximum efficiency.

Increasing power: propeller control forward first (rpm up), then throttle forward (manifold pressure up).

Decreasing power: throttle back first (manifold pressure down), then propeller control back (rpm down).

The rule of thumb: the last lever you move is the one that leaves the engine under-stressed — never a high manifold pressure against a low rpm. Whatever the memory aid, the POH's published power settings are the actual authority; some engines are approved for combinations the rule of thumb would forbid.

Blade angle range for constant-speed propellers runs roughly 11.5° to 40°, and the higher the airplane's speed the greater the range (AFH ch. 12).

As long as the blades operate between the high and low pitch stops, constant rpm is maintained. Once the blades reach a pitch-stop limit, the propeller is effectively fixed-pitch — engine rpm then increases or decreases with airspeed, exactly as a fixed-pitch airplane does. Seeing rpm wander with airspeed is your cue that you are against a stop.

A loss of governor oil pressure sends the propeller toward whichever pitch its design defaults to — typically low pitch / high rpm (an overspeed risk) on a single-engine airplane; feathering propellers on twins fail toward feather (AFH ch. 12).

Why it varies by design:

• Some props use the blades' inherent centrifugal twisting moment to flatten toward low pitch, with oil pressure driving them toward high pitch — losing oil pressure sends these toward low pitch (high rpm).
• Others use counterweights on the blade shanks: governor oil pressure and the twisting moment drive toward low pitch, and centrifugal force on the counterweights drives toward high pitch — losing oil pressure sends these toward high pitch (low rpm).

Know which yours is before you need to know — check your POH.

A turbocharger is an exhaust-driven device that raises the pressure and density of the induction air. Two components on a common shaft: a compressor between the ambient air intake and the induction manifold, and a turbine in the exhaust system driving it. It takes no horsepower from the engine to operate (AFH ch. 12).

Altitude turbocharging (or "normalizing") maintains maximum allowable sea-level manifold pressure — normally 29 to 30 inches Hg — up to the critical altitude, the manufacturer-specified altitude above which manifold pressure decreases as you climb.

Ground boosting uses more than the standard 29 inches in flight; some airplanes take off at manifold pressures as high as 45 inches Hg (AFH ch. 12).

• Power-control movements stay slow and smooth — aggressive or abrupt throttle movement increases the possibility of over-boosting.
• Manifold pressure behaves backwards above critical altitude: with the waste gate open the engine acts like a normally aspirated one — increase rpm, manifold pressure drops slightly; with the waste gate closed, increasing rpm increases manifold pressure, and decreasing rpm decreases it.
• Airspeed changes move manifold pressure above critical altitude: ram-air rise is magnified by the compressor, raising manifold pressure, which raises mass flow, which raises turbine speed, which raises manifold pressure further.
• Vapor lock. At high altitude avgas tends to vaporize before reaching the cylinder; a boost pump provides positive pressure to push the fuel and reduce vaporization.
• Heat is everything. Compressor turbine speeds reach 80,000 to 100,000 rpm; turbocharged engines are especially heat-sensitive, and continuous monitoring of pressures and temperatures is the operating discipline (AFH ch. 12).

Over-boost — an excessive rise in manifold pressure during normal throttle advancement, possibly from faulty waste gate operation:

• Immediately retard the throttle smoothly to bring manifold pressure below the maximum for the rpm and mixture setting
• Operate the engine so as to avoid a further over-boost

Low manifold pressure — may be minor, but quite possibly a serious exhaust leak, which is a hazardous condition:

• Shut down the engine per the recommended engine-failure procedures, unless a greater emergency warrants continued operation
• If you must keep running it, use the lowest power setting the situation demands and land as soon as practicable

Either way, corrective maintenance before further flight.

Why: increased climb performance and higher cruise speeds from the drag reduction after retraction.

How: hydraulic, electric, or a combination.

• Electric — a motor drives shafts, gears, an actuator screw, and a torque tube to the drag-strut linkages; the motor runs until an up or down limit switch on the gearbox trips.
• Hydraulic — fluid is directed to the gear-up or gear-down line through sequenced valves and downlocks to the actuating cylinders. The pump may be engine-driven or electric (an electrohydraulic system). Each gear has two limit switches — one for extension, one for retraction — that de-energize the pump when the cycle completes, with a backup pressure relief valve if a limit switch fails.

Indications: typically three green lights for down and locked; some systems use one green (down) and one amber (up); others add a red or amber light for in transit or unsafe. Many are press-to-test with interchangeable bulbs. Integrated electronic displays may show gear position without dedicated lights. Tab-type indicators show "UP," red-and-white diagonal stripes for unlocked, or a gear silhouette when locked down.

Most retractable-gear airplanes have a gear warning horn that sounds when the airplane is configured for landing with the gear not down and locked — normally linked to throttle position, flap position, and/or the airspeed indicator (AFH ch. 12).

Systems for emergency extension are always provided, and the mechanism differs by airplane: a hand pump, a free-fall release with gravity and airloads doing the work, or a CO₂ blowdown bottle. The procedure is in the POH and it is memory-item territory for a commercial pilot.

The oral answer that earns credit: verify it is a gear problem and not an indication problem (check the circuit breaker, cycle the switch, press to test / swap bulbs, get a visual confirmation from the tower or another aircraft), then run the emergency extension checklist, then plan the landing — including that most emergency extensions are one-way: once blown down, the gear may not retract again.

Anti-ice prevents ice from forming; deice removes ice already formed. Turn anti-ice on before entering conditions; use deice after an accumulation.

• Inflatable deicing boots — rubber sheet bonded to the leading edge, inflated by an engine-driven pneumatic pump or by diverted engine bleed air, cracking the ice off. Operated by a flight deck switch, single cycle or automatic timed intervals. Many use the instrument suction gauge plus a pneumatic pressure gauge to verify operation.
• Thermal anti-ice — hot compressor bleed air directed to leading edges on high-performance turbine aircraft; ThermaWing uses electrically heated graphite foil laminate with a continuously heated leading-edge zone and a cycled aft zone.
• Weeping wing (TKS) — antifreeze pumped through small holes in the leading edge; prevents formation and can also deice by chemically breaking the ice-to-airframe bond.
• Windscreen — alcohol flow, or embedded electrical heating elements.
• Propeller — electrically heated boots embedded with wires, monitored on a prop anti-ice ammeter.
• Electrically heated pitot and static ports, fuel vents, and stall-warning sensors.

No, and PHAK says so directly: anti-icing and deicing equipment "are not intended to sustain long-term flight in icing conditions" (PHAK ch. 7).

Most light aircraft have only a heated pitot tube and are not certified for flight in icing — such aircraft "must exit icing conditions immediately." Encounters with structural ice require immediate action regardless of equipment.

One correction worth carrying: the old "ice bridging" warning is obsolete. Bridging does not occur with modern boots; cycle them as soon as an accumulation is observed rather than waiting for a thickness to build (PHAK ch. 7).

• Continuous-flow — usually for passengers; the mask has a reservoir bag that collects oxygen during exhalation, allowing a higher flow rate on inhalation and reducing dilution. Ambient air is added once the bag is depleted.
• Diluter-demand — supplies oxygen only when the user inhales. An automix lever mixes cabin air and oxygen automatically or supplies 100 percent, by altitude. The tight-sealing demand mask is safe to 40,000 ft.
• Pressure-demand — like diluter-demand, but supplies oxygen under pressure above 34,000 ft cabin altitude, pressurizing the user's lungs. Safe above 40,000 ft.
• Electrical pulse-demand — portable; detects inhalation effort and delivers oxygen during the initial portion of the inhalation, avoiding waste.
• Cannula — plastic tubing under the nose; more comfortable but may not deliver adequate flow reliably at higher altitudes. Aircraft with oxygen systems certified for operations above 18,000 ft must be equipped with masks rather than cannulas. Check the green flow detector as part of your scan.

Beards and mustaches must be trimmed so they do not interfere with the mask seal — check the fit on the ground.

• Cabin pressure altitude above 12,500 ft up to and including 14,000 ft MSL — the required minimum flight crew must use supplemental oxygen for that part of the flight more than 30 minutes in duration
• Above 14,000 ft MSL — the required minimum flight crew must use it the entire time at those altitudes
• Above 15,000 ft MSL — each occupant must be provided with supplemental oxygen

Pressurized aircraft (91.211(b)): above FL250, at least a 10-minute supply for each occupant in addition to (a); above FL350, one pilot at the controls must wear and use a secured, sealed oxygen mask — unless there are two pilots at the controls, each with a quick-donning mask placeable with one hand from the ready position within 5 seconds, in which case the mask need not be worn at or below FL410. If one pilot leaves the controls above FL350, the remaining pilot puts the mask on until the other returns.

By 61.129(j): an electronic PFD (airspeed, turn coordinator, attitude, heading, altimeter, VSI), an electronic MFD with a GPS moving map showing aircraft position, a two-axis autopilot integrated with the navigation and heading guidance system, and those displays continuously visible.

Managing it:

• Know what mode the autopilot is in and what it will do next — mode confusion, not mode failure, is the usual accident chain.
• Verify what you programmed against the chart and the plan, not against what you expected to see.
• Have a level of automation you deliberately drop to: full coupled, heading-and-altitude hold, flight director only, hand-flown. Pick one for the situation rather than defaulting to maximum.
• Know the disconnect — the button, the breaker, and what happens to trim when you press it.
• Know the reversion — what the PFD does when the AHRS or air data computer fails, and where the standby instruments are.

1. Fly the airplane. Nothing is diagnosed while the airplane is not under control.
2. Confirm the failure is real. A single indication is a hypothesis. Cross-check a second source — a different instrument, a different gauge, a circuit breaker, the sound and feel of the engine.
3. Memory items, if the POH has them, then the checklist.
4. Contain it. Reduce the demand on the failed system: lower power for a rough engine, shed electrical load for an alternator failure, descend out of ice.
5. Decide. Land as soon as possible, as soon as practicable, or continue — and say which, and why.
6. Tell someone. Declare an emergency if you need priority. The reluctance to declare is a hazardous-attitude problem, not a paperwork one.

Ram air can no longer enter, so the trapped pressure bleeds out the drain and the ASI drops toward zero. If instead the drain hole is also blocked, pressure is trapped in the line and the ASI stops behaving like an airspeed indicator and starts behaving like an altimeter:

• Climb → static pressure falls, the diaphragm expands → ASI reads higher than actual
• Descent → static pressure rises → ASI reads lower than actual

Cause is usually visible moisture. The prevention is pitot heat per the AFM/POH — and the commercial habit is turning it on before entering the moisture, not after the needle misbehaves. Altimeter and VSI are unaffected by a pitot blockage; they are static-only instruments.

With static blocked and the pitot clear, the altimeter freezes at the blockage altitude and the VSI freezes at zero. The ASI keeps operating but is inaccurate: above the blockage altitude it reads lower than actual (trapped static is higher than normal for that altitude), and below it reads faster than actual.

The fix is the alternate static source, normally inside the flight deck. Because the venturi effect of air flowing around the fuselage makes cabin pressure lower than exterior pressure, expect (PHAK ch. 8):

1. Altimeter indicates a slightly higher altitude than actual
2. ASI indicates an airspeed greater than actual
3. VSI shows a momentary climb, then stabilizes if altitude is held constant

Consult the AFM/POH for the actual error values. With no alternate source installed, the last resort is breaking the VSI glass — the VSI is the least critical of the three and doing so vents the static line to the cabin, giving the same indications with reversed VSI sense.

Three surfaces, three axes:

• Ailerons — roll about the longitudinal axis. Outboard trailing edge of each wing, moving opposite each other. Wheel right raises the right aileron (less camber, less lift) and lowers the left (more camber, more lift), rolling right.
• Elevator or stabilator — pitch about the lateral axis.
• Rudder — yaw about the vertical axis.

Control feel is the part worth saying out loud: at low airspeeds the controls feel soft and sluggish and the airplane responds slowly; at higher airspeeds they become increasingly firm and response is more rapid. That is the same dynamic pressure story behind V_A in Task I.F.

Design limits — control-stop mechanisms in the linkages, or limits on control column and rudder pedal travel — exist to keep the pilot from inadvertently overcontrolling and overstressing the airplane during normal maneuvers (PHAK ch. 6).

The downward-deflected aileron produces more lift, and therefore more drag, which slows that wing. The airplane yaws toward the rising wing — from the pilot's seat, yaw opposite the direction of bank. It is a result of differential drag plus the slight velocity difference between the wings, and it becomes more pronounced at low airspeeds — exactly where you are during commercial maneuvers.

The design fixes:

• Differential ailerons — one aileron is raised a greater distance than the other is lowered, producing extra drag on the descending wing to offset the yaw.
• Frise-type ailerons — the raised aileron pivots so its leading edge projects into the airflow below the wing, creating drag on the descending wing. These may also be designed to function differentially.

Neither eliminates it. Coordinated rudder is still the pilot's fix, and it is graded on every chandelle and lazy eight.

Flaps work primarily by changing the camber of the airfoil, which increases the wing's lift coefficient; some designs also increase wing area. Flap deflection does not increase the critical angle of attack — in some cases it actually decreases it (AFH ch. 12).

The threshold to remember: deflection up to 15° primarily produces lift with minimal drag increase. Deflection beyond 15° produces a large increase in drag — parasite drag, proportional to the square of the speed. Beyond 15° also produces a significant nose-up pitching moment in most high-wing airplanes because the changed downwash alters flow over the horizontal tail.

Whether the airplane pitches up, down, or barely at all with flaps depends on flap type, wing position, downwash behavior, and horizontal tail location — it is a design characteristic, not a rule.

On a turbocharged engine this is the AFH's "low manifold pressure" case, and the concern is not the gauge — it is a serious exhaust leak in a system running at high temperature and pressure, which is a fire risk (AFH ch. 12).

The published guidance is aggressive for a reason: shut the engine down per the engine-failure procedures unless a greater emergency warrants keeping it running; if you must continue, use the lowest power setting the situation demands and land as soon as practicable.

On a normally aspirated engine, the differential diagnosis runs to a gradual power loss: carburetor or induction icing (apply carb heat and watch for the drop-then-rise), a partially blocked induction filter (alternate air), or a throttle linkage problem. Note that the reasoning is the same either way — cross-check a second indication (EGT, fuel flow, rpm, sound), then act on the most dangerous plausible cause.

Not because they forgot the gear exists — because a normal flow was interrupted. The pattern is almost always a distraction inside the approach: a traffic call, a runway change, a passenger question, an unstabilized approach that consumed attention.

What prevents it:

• A gear extension point that is a fixed geographic or configuration trigger, flown identically every time — abeam the numbers, glideslope intercept, entering the pattern.
• A verification separate from the action. "Gear down" is the action; "three green" is the verification, and it is spoken.
• A final check that survives interruption — a short GUMPS-style flow on final, run again after any interruption, on the theory that any interruption invalidates everything before it.
• The warning horn treated as a real warning, not as a nuisance that means the throttle is back.
• Not accepting a rushed approach. Go around. Every gear-up landing had a stabilized-approach decision available earlier.