Complex and High-Performance Airplane Systems

Module 3 · Complex and High-Performance Airplane Systems · Lesson 1 of 7

The Constant-Speed Propeller

The propeller control does not set blade angle. It sets an RPM, and a governor changes blade angle to hold it.

Complex, High-Performance or TAA?

The constant-speed propeller is one of the parts that make an airplane complex. Three terms decide which training and endorsements you need:

To act as pilot in command of a complex airplane you need ground and flight training from an authorized instructor and a one-time logbook endorsement that you are proficient in its systems and operation (§61.31(e)). A high-performance airplane needs the same, as a separate one-time endorsement (§61.31(f)). A Bonanza is both, so it needs both. Training in a complex airplane or a TAA also counts toward the 10 hours in §61.129(a)(3)(ii).

A fixed-pitch propeller is a compromise: its blade angle is right for one airspeed and power. A constant-speed propeller lets the blade angle change in flight, so the engine can turn at the RPM that gives the most useful power for each phase: high RPM and low pitch for takeoff and climb, lower RPM and higher pitch for cruise. You choose the RPM with the blue knob. The governor does the rest.

Inside the Governor

The governor sits on the engine and is driven by it, so its speed always follows engine RPM. Four parts do the work:

When RPM is exactly what you set, flyweight force equals spring force, the pilot valve is centered and nothing moves. That is on-speed. If something makes the engine speed up, such as adding throttle or lowering the nose, the flyweights tilt out, the valve opens and the blades take a bigger bite until RPM settles back. That is the overspeed correction. Reduce power or raise the nose and the reverse happens: underspeed, flyweights in, blades flatten.

When the Governor Cannot Govern

The governor can only hold RPM while the blades are between their stops. Pull the throttle back far enough, as in the flare or a power-off descent, and the blades flatten all the way to the low-pitch stop. Now RPM falls below what you set, and the propeller behaves like a fixed-pitch propeller. This is normal. It is also why moving the propeller control at idle changes nothing on the tachometer.

At the other end, a steep dive at high power can drive the blades to the high-pitch stop, after which RPM climbs with airspeed. Reduce power and airspeed.

Loss of Oil Pressure

On most single-engine airplanes, governor oil drives the blades toward high pitch, and the blade's centrifugal twisting moment, helped by a spring or air charge in some hubs, drives them toward low pitch. If oil pressure is lost, the blades go to low pitch. That gives full power for the engine-out landing you are now planning, but in cruise it can overspeed the engine. Reduce throttle and airspeed to keep RPM at or below redline. Multiengine propellers are built the other way, so a dead engine's propeller can feather; your POH says which design you have.

Run-Up and Preflight

• Cycle the propeller control during the run-up at the RPM the POH gives. Look for an RPM drop, a manifold pressure rise and an oil pressure dip, then a smooth return. It proves the governor works and moves warm oil into the hub. On a cold day, cycle it more than once.
• On the walk-around, look for oil streaks on the blades and hub. A seal leak can leave you with a governor that cannot hold RPM.
• Nicks in a constant-speed blade matter as much as on a fixed-pitch one. A crack can throw a blade, and the imbalance can tear the engine from its mounts.

Module 3 · Complex and High-Performance Airplane Systems · Lesson 2 of 7

Manifold Pressure, Power Settings and Turbocharging

Two gauges set the power, the order you move the levers protects the engine, and a turbocharger buys back the air that altitude takes away.

With a constant-speed propeller, the tachometer no longer tells you how much power the engine is making. Engine power depends on how much air and fuel each cylinder takes in (manifold pressure) and how often it fires (RPM). Every power setting in the POH is a pair: manifold pressure and RPM, with the mixture set as the POH says.

Reading the Manifold Pressure Gauge

• It reads absolute pressure in the intake manifold, in inches of mercury. With the engine stopped it shows the outside pressure, about 29.9 inches at sea level on a standard day. Check it before start: it should match field pressure.
• At idle it reads low, because the nearly closed throttle starves the manifold. Opening the throttle raises it toward outside pressure.
• A normally aspirated engine can never reach outside pressure at full throttle, and outside pressure falls about 1 inch per 1,000 feet. So full-throttle manifold pressure falls as you climb.

Changing Power in the Right Order

High manifold pressure at low RPM raises cylinder pressure and can push the engine toward detonation. So the rule, unless your POH says otherwise, keeps RPM ahead of manifold pressure:

"Oversquare" means manifold pressure, in inches, higher than RPM in hundreds (for example, 25 inches at 2,300 RPM). Many engines are approved to run oversquare, and the POH power tables show it. The real limit is whatever the POH and its tables allow, not the rule of thumb.

How a Turbocharger Works

A turbocharger uses exhaust gas that would otherwise be wasted. Exhaust spins a turbine; a shaft spins a compressor on the intake side; the compressor packs extra air into the intake. A wastegate in the exhaust controls how much exhaust reaches the turbine. Wastegate open, the exhaust bypasses the turbine and there is little boost. Wastegate closed, all exhaust goes through the turbine and boost is highest.

Operating a Turbocharged Engine

• Move the throttle slowly. The turbocharger takes a few seconds to spool up. Shoving the throttle forward, especially with cold, thick oil in the controller, can overshoot the limit. That is an overboost. A pressure relief valve protects most systems, but an overboost can damage the engine and may need a logbook entry and inspection.
• Watch turbine inlet temperature (TIT). It is the limit that matters for the turbocharger. Lean to the TIT the POH gives, not just by EGT.
• Expect heat. The exhaust and turbine run very hot. An exhaust leak near the turbocharger is a fire and carbon monoxide hazard.
• Cool it down. Hot oil left sitting in the turbocharger bearings after shutdown can coke. Follow the POH's cool-down time before shutting down.
• Turbocharger failure usually shows as manifold pressure dropping to what a normally aspirated engine would make at that altitude. Many systems then run rich, so adjust the mixture, descend if you need the power, and check the POH.

Module 3 · Complex and High-Performance Airplane Systems · Lesson 3 of 7

Retractable Landing Gear and Flaps

How the gear moves, what keeps it from moving on the ground, what warns you it is still up, and how to get it down when the normal system fails.

Retracting the gear cuts parasite drag, which is why complex airplanes cruise faster on the same power. The price is a system you have to manage. Gear-up landings are almost never caused by a gear failure. They are caused by a pilot who did not put the gear down.

Two Ways to Move the Gear

Safety Devices and Indications

• Squat (safety) switch: on a main gear strut. While the strut is compressed by the airplane's weight, it opens the gear-up circuit so the gear cannot retract on the ground. Some airplanes add a mechanical lock on the gear handle.
• Position lights: typically three green when all three gear are down and locked, and a red or amber light while the gear is in transit or unsafe. No lights usually means gear up and locked. Learn your airplane's exact scheme.
• Warning horn: sounds when the gear is not down and locked and the throttle is pulled back below a set position. On many airplanes it also sounds when the flaps go past a set position with the gear up.
• Gear speeds: V_LO is the fastest you may extend or retract the gear (some POHs list different speeds for each). V_LE is the fastest you may fly with the gear extended.

When the Gear Will Not Come Down

Fly the airplane first. You have time: climb to a safe altitude, away from the traffic pattern, and work through the POH checklist. A typical flow:

1. Check the Basics
   Master and alternator on, gear circuit breaker in, handle fully down.
   Electrical
2. Check the Lights
   Press to test, swap a bulb, and check whether the navigation lights have dimmed the gear lights.
   Indication
3. Slow Down
   Below V_LO, or the emergency extension speed in the POH.
   Speed
4. Extend by the Backup
   Free-fall valve, hand crank or hand pump, exactly as the POH says.
   Emergency
5. Confirm
   Three green, a gear mirror, or a low pass by the tower. Do not retract it again.
   Verify

Some older Piper Arrows had an automatic extension system that lowered the gear on its own at low airspeed and low power. Know whether yours has one, how to override it, and how it can surprise you during slow flight or a short-field climb.

Flaps in a Complex Airplane

Flaps raise both lift and drag, which lets you fly a steeper approach at a slower speed. The four basic types are plain, split, slotted and Fowler. A Fowler flap slides aft as well as down, adding wing area, so the first notch adds mostly lift and the last notches add mostly drag. Expect a pitch change with each notch, retract in steps on a go-around, and stay below V_FE for the setting you are using. If the airplane rolls as the flaps move, an asymmetric (split) flap condition may be starting: stop, return the switch to the last setting that was symmetric, and land with what you have.

Module 3 · Complex and High-Performance Airplane Systems · Lesson 4 of 7

Fuel, Oil and Hydraulic Systems

Fuel injection replaces the carburetor, fuel flow becomes a number you trust, and the oil gauges tell you how long the engine has left.

How Fuel Injection Works

Most complex and high-performance airplanes use fuel injection instead of a carburetor. Fuel is sprayed into each cylinder's intake port instead of being mixed in one place upstream.

The gains: no carburetor ice (though impact ice can still block the air filter, which is why there is an alternate air source), better fuel distribution, quicker throttle response and better economy. The costs: harder starts when the engine is hot, vapor lock in the lines on hot days, and nozzles small enough to clog.

The Fuel Flow Gauge Can Mislead You

Many fuel-injected engines, especially Continentals, show fuel flow with a gauge that actually measures fuel pressure at the manifold and is marked in gallons per hour. That works while every nozzle is clean. A clogged nozzle raises the pressure, so the gauge reads high while the engine is actually getting less fuel. Airplanes with a digital engine monitor usually use a flow transducer that measures real flow, but it can only count fuel that has passed it.

Tanks and Fuel Management

• Know which tanks feed the engine, which positions the selector has (Left, Right, Both, Off), and how much fuel in each tank is unusable. Unusable fuel is in the POH and counts in empty weight, not in your endurance.
• Many low-wing airplanes have no Both position. You switch tanks on a schedule to keep the airplane balanced, with the aux pump on during the change if the POH calls for it. Switch over an airport, not over water, the first time you use a tank.
• Hot-start procedures differ widely between engines. Use the one in your POH; it usually clears vapor from the lines before the engine is cranked.

Reading the Oil Gauges Together

Oil lubricates, cools, seals and cleans, and on your airplane it also moves the propeller blades. Oil pressure and oil temperature mean much more read together than either one alone. Pressure is the faster warning; temperature lags.

Hydraulic Systems

In a light single, hydraulics usually means the brakes and, on some airplanes, the gear power pack. Hydraulic fluid in these systems is commonly a red mineral-based fluid. Check the reservoir level where the POH says, look for red stains on the wheel pants and gear wells, and know the signs of trouble: a soft or fading brake, a gear that cycles slowly, or a pump that keeps running after the gear is up.

Module 3 · Complex and High-Performance Airplane Systems · Lesson 5 of 7

Electrical System, Avionics and Automation

In a technically advanced airplane the electrical system runs the instruments, the navigation and the autopilot. Losing it is a clock, not just an annoyance.

How the System Is Built

The alternator charges the battery and carries the electrical load while the engine runs. A voltage regulator holds the output at about 14 volts in a 12-volt system or 28 volts in a 24-volt system. Those numbers matter: they are higher than the battery's own voltage, so a bus reading at battery voltage tells you the alternator is not carrying the load.

A technically advanced airplane (TAA), as defined in 14 CFR 61.1, has a primary flight display, a multifunction display with a GPS moving map, and a two-axis autopilot integrated with the navigation and heading guidance. Commercial students may use one for the training that used to require a complex airplane.

Alternator Failure: How Long Do You Have?

When the alternator quits, the battery carries everything. Its endurance depends on how much you ask of it. Shedding loads early, before the voltage falls, is the difference between landing with avionics and landing with a dark panel.

Circuit Breakers

A popped breaker means something drew too much current. The general practice: let it cool, reset it once if you need that item for the flight, and leave it out if it pops again. Never reset a breaker if there is smoke or a burning smell; that circuit is the fire.

Automation: Anticipate, Act, Verify

The Risk Management Handbook gives three steps for every interaction with automation: anticipate what should happen before you press a button, act, then verify that the airplane did what you expected. The flight mode annunciator (FMA) is where you verify. On most systems, green means a mode is active and white means it is armed and waiting to capture.

One of the most common errors, the handbook says, is failing to move to a lower level of automation when things change. If the autopilot is doing something you do not understand, go to a simpler mode, such as heading and altitude, or fly by hand, and sort it out later.

Module 3 · Complex and High-Performance Airplane Systems · Lesson 6 of 7

Environmental and Ice Protection Systems

Cabin heat that can poison you, and ice protection equipment that may or may not make the airplane legal for icing.

Cabin Heat and Carbon Monoxide

Most piston singles heat the cabin with a shroud, often called a heater muff, around the exhaust muffler. Outside air passes over the hot muffler and into the cabin. A crack in the muffler lets exhaust, and its carbon monoxide, into that air. Carbon monoxide is colorless and odorless, and hemoglobin takes it up far more readily than oxygen, so even small amounts build up in the blood.

• Signs: headache, drowsiness, dizziness, blurred vision, or a smell of exhaust (the smell comes from other gases, not the CO itself). An electronic CO detector warns long before symptoms.
• Response: cabin heat off, all fresh-air vents open, supplemental oxygen if you have it, and land as soon as practical. Get checked: recovery takes hours.
• Prevention: a muffler inspection at every annual or 100-hour inspection, and a detector you trust. Turbocharged engines add an exhaust system that runs hotter and has more joints to leak.

Anti-Ice and Deice

Older guidance said to let ice build before cycling pneumatic boots to avoid "ice bridging." Current FAA guidance in AC 91-74B is to use them as soon as ice begins to form, unless the AFM says otherwise.

Equipment Is Not Approval

An airplane may carry heated pitot, a propeller deice system, even a weeping-wing system, and still be prohibited from flight into known icing. Only the AFM tells you. An airplane approved for flight into known icing (often called FIKI) has been tested and certificated with a complete set of systems. Systems installed without that approval, sometimes called "non-hazard" or inadvertent-encounter systems, are there to help you get out of ice you did not expect.

Module 3 · Complex and High-Performance Airplane Systems · Lesson 7 of 7

Recognizing and Managing Failures

Spot the failure early, name the system, fly the airplane, then use the checklist.

The examiner will not ask you to recite a checklist. They will describe what you see and ask what is wrong and what you would do. That takes three skills: noticing the change early (a scan that includes the engine and electrical gauges, not just the flight instruments), tracing the symptom to a system, and managing it in the right order.

Detect: Make the Scan Include the Systems

• Glance at the engine and electrical gauges at every level-off, every power change and at a regular interval in cruise. Most failures start as a trend, not a jump.
• Know your normal numbers: cruise manifold pressure, fuel flow, oil pressure and temperature, bus voltage. A failure is a change from normal, so you have to know normal.
• On a TAA, annunciations and engine monitor alerts are a gift. Acknowledge each one out loud, then find what it is telling you.

Diagnose: Symptom to System

Manage: The Order of Actions

Every failure is handled in the same order. Keep the airplane flying and pointed somewhere safe. Run the memory items the POH lists, if any. Then read the checklist, step by step. Then decide where to land and tell someone. The decision is part of the procedure: an alternator failure with 20 minutes of battery is a "land at the nearest suitable airport" problem, not a "continue to destination and see" problem.

Why Pilots Get This Wrong

The Risk Management Handbook's accident examples share a pattern: the pilot fixated on fixing the problem and stopped flying the airplane, or treated a failure as an inconvenience and pressed on. As a commercial pilot you will also feel pressure from the person who hired you. A client in the back seat does not change what a discharging ammeter means.

Module 3 · Complex and High-Performance Airplane Systems · Knowledge Check

Module 3 Knowledge Check

Fifteen questions in the style of the CAX test and the oral exam, each tagged with its ACS element. Pass mark: 80% (12 of 15).