Aircraft Systems

Module 3 · Aircraft Systems · Lesson 1 of 8

The Reciprocating Engine

Your engine turns the chemical energy in fuel into the rotation of a crankshaft. Four strokes of a piston do the work.

An aircraft engine, or powerplant, produces thrust. Reciprocating and turboprop engines work with a propeller to do it. Every powerplant also drives the systems that support the airplane's operation. PHAK 7-1

Most small aircraft have reciprocating engines, named for the back-and-forth movement of the pistons. They convert chemical energy (fuel) into mechanical energy through combustion inside the cylinders. PHAK 7-2

How Engines Are Classified

Both designs can be classified by cylinder arrangement around the crankshaft, by operating cycle (two- or four-stroke), and by cooling method (liquid or air). PHAK 7-2

A two-stroke engine completes intake, compression, power, and exhaust in two strokes, so it has a power stroke every revolution and typically a higher power-to-weight ratio. Early designs were inefficient and dirty, which limited them in aviation. PHAK 7-3 Spark ignition four-stroke engines remain the most common design in general aviation. PHAK 7-3

Main Parts

The main parts are the cylinders, the crankcase, and the accessory housing. The intake and exhaust valves, spark plugs, and pistons are in the cylinders. The crankshaft and connecting rods are in the crankcase. The magnetos are normally on the accessory housing. PHAK 7-3

The Four-Stroke Cycle

1. Intake
   The piston starts down, the intake valve opens, and the fuel-air mixture is drawn into the cylinder.
   PHAK 7-3
2. Compression
   The intake valve closes and the piston moves back up, compressing the charge for much greater power once it is ignited.
   PHAK 7-3
3. Power
   The mixture is ignited. Pressure rises sharply and forces the piston down, turning the crankshaft.
   PHAK 7-3
4. Exhaust
   The exhaust valve opens and the piston moves up again, purging the burned gases.
   PHAK 7-4

Even at fairly low engine speed the cycle happens several hundred times a minute. In a four-cylinder engine each cylinder is on a different stroke, and precise timing of the power strokes keeps the crankshaft turning. The engine also depends on its induction, ignition, fuel, oil, cooling, and exhaust systems all working at once. PHAK 7-4

Diesel and Jet-Fueled Piston Engines

Compression ignition engines, often called jet fuel piston engines, burn readily available, lower-cost diesel or jet fuel. PHAK 7-2 Thielert Aircraft Engines certified a Jet-A-burning diesel cycle engine in 2001. These engines are found on the Diamond DA40 and DA42, and an STC allows re-engining Cessna 172 and Piper PA-28 models. A FADEC is standard on these installations. PHAK 7-4

Module 3 · Aircraft Systems · Lesson 2 of 8

Propellers and Power Instruments

The propeller is a rotating wing. How you set its pitch, or let a governor set it, decides which gauge tells you your power.

The propeller is a rotating airfoil, subject to induced drag, stalls, and the other aerodynamic principles of any airfoil. It makes thrust much as a wing makes lift. The thrust depends on the airfoil shape, the blade's angle of attack, and the engine rpm. PHAK 7-4

Why the Blade Is Twisted

The blade angle is greatest at the hub and smallest at the tip. The tip travels a greater distance in the same time, so it moves faster. Twisting the blade to match gives uniform lift from hub to tip. PHAK 7-4 In PHAK Figure 7-7, at 2,500 rpm, the blade on the 20-inch circle moves about 129 knots, on the 40-inch circle about 259 knots, and on the 60-inch circle about 389 knots. PHAK 7-5

A blade with the same angle all the way out would be inefficient, because no single blade angle suits every section: at high airspeed the slow hub section would have a negative angle of attack, and at low airspeed and high rpm the fast tip section would stall. PHAK 7-5

Fixed-Pitch Propellers

A fixed-pitch propeller's blade angle is set by the manufacturer. It is most efficient at only one combination of airspeed and rpm, so it is ideal for neither climb nor cruise. It is used where low weight, simplicity, and low cost matter. PHAK 7-5

With a fixed-pitch propeller, the tachometer is your power indicator. It is calibrated in hundreds of rpm, and the green arc marks the maximum continuous operating range. The throttle sets the rpm. PHAK 7-5 Power output depends on air density, so 2,300 rpm at 5,000 feet makes less horsepower than 2,300 rpm at sea level, and as you climb you must open the throttle further to hold the same rpm. PHAK 7-5 to 7-6

Adjustable-Pitch and Constant-Speed Propellers

A ground-adjustable propeller's pitch can be changed only on the ground with the engine stopped. A constant-speed propeller is a controllable-pitch propeller whose blade angle is varied in flight by a governor to hold a constant rpm. It converts a high percentage of brake horsepower into thrust horsepower over a wide range of rpm and airspeed. PHAK 7-6

It has two controls. The throttle controls power output, shown on the manifold pressure gauge. The propeller control regulates rpm, shown on the tachometer. Speed up or unload the propeller and the governor increases blade angle to hold rpm; slow down or load it and the blade angle decreases. PHAK 7-6

The high and low pitch stops bound the constant-speed range. Slow down far enough that the blades reach the low pitch stop, and further slowing reduces rpm just as with a fixed-pitch propeller. Accelerate until the blades reach the high pitch stop, and rpm rises. PHAK 7-6

Changing Power in the Right Order

For any rpm there is a manifold pressure you should not exceed; too much stresses the cylinders and, repeated often enough, can lead to engine failure. PHAK 7-7

• Decreasing power: reduce manifold pressure first, then rpm. Reduce rpm first and the manifold pressure rises on its own, possibly past the manufacturer's limit. PHAK 7-7
• Increasing power: increase rpm first, then manifold pressure. PHAK 7-7

Propeller Overspeed

FAA Special Airworthiness Information Bulletin CE-10-21 describes a single-engine airplane whose pitch-change mechanism failed to the low pitch stop at 7,000 feet. Throttle gave an overspeed with little thrust. Gliding at the published best glide speed, the pilot could not reach an airport. A performance evaluation found that a speed below best glide would have given enough thrust to hold altitude. PHAK 7-7 Follow the emergency procedure, and know that with an overspeed the airspeed for level flight may differ from engine-out best glide; work that out only at a safe altitude. PHAK 7-7

Module 3 · Aircraft Systems · Lesson 3 of 8

Induction, Carburetor Ice, and Mixture

Ice can form inside a carburetor on a warm day in clear air. Knowing why it forms tells you when to look for it and how to clear it.

The induction system brings in outside air, mixes it with fuel, and delivers the mixture to the cylinders. Air enters through an intake on the front of the cowling, usually through a filter. Because the filter can clog, there is an alternate air source, usually from inside the cowling; some work automatically and some are manual. PHAK 7-7

Small engines use one of two induction systems. A carburetor mixes fuel and air before the mixture enters the intake manifold. Fuel injection mixes them just before each cylinder or injects fuel directly into each cylinder. PHAK 7-8

The Float-Type Carburetor

Filtered air flows through a venturi, a narrow throat in the carburetor. The venturi creates low pressure that draws fuel through the main jet into the airstream. A float in the float chamber works a needle valve that meters fuel in. The throttle valve, worked by the throttle in the flight deck, controls how much mixture flows to the cylinders. PHAK 7-8

Float-type carburetors work poorly in abrupt maneuvers and vaporize fuel incompletely, but their chief disadvantage is icing. PHAK 7-8 A pressure-type carburetor sprays fuel under pressure on the engine side of the throttle valve, where engine heat offsets the cooling, so vaporization icing is practically eliminated. They are usually not found on small aircraft. PHAK 7-8 to 7-9

Why Carburetor Ice Forms

Fuel vaporization and the pressure drop in the venturi sharply cool the air in the carburetor. If water vapor condenses with the carburetor at or below freezing, ice forms on internal surfaces, generally near the throttle valve and in the venturi throat. It restricts the mixture and reduces power, and enough of it can stop the engine. PHAK 7-9

Recognizing Carburetor Ice

• Fixed-pitch propeller: the first sign is a drop in rpm, which may be followed by roughness. PHAK 7-10
• Constant-speed propeller: manifold pressure drops but rpm does not, because the governor flattens the blades to hold rpm. PHAK 7-10
• It can form in any phase of flight, but it is especially dangerous at reduced power in a descent, where it can build unnoticed until you add power. PHAK 7-10

Using Carburetor Heat

Carburetor heat is an anti-icing system: it preheats the air to keep the mixture above freezing. It can melt ice that has formed if there is not too much, but using it as prevention is the better option. It also serves as alternate air if the intake filter clogs. Check it during the runup. PHAK 7-10

• If you detect ice, apply full heat at once and leave it on until all the ice is gone. Partial heat or heat removed too soon can make it worse. PHAK 7-10
• Expect power to drop further and the engine to run rough as melted ice passes through, for 30 seconds to several minutes. Resist the temptation to reduce the heat; leave it full hot until normal power returns. PHAK 7-10
• Expecting closed-throttle operation in icing conditions, apply full heat before closing the throttle and open the throttle smoothly for a few seconds now and then to keep the engine warm. PHAK 7-10
• Heated air is less dense, so power drops, sometimes by up to 15 percent, and the mixture richens. Do not use it when you need full power, as on takeoff, or in normal operation except to check for or remove ice. PHAK 7-10 to 7-11

A carburetor air temperature gauge, where installed, usually has a yellow arc from −15 °C to +5 °C where icing may occur. In icing conditions, use carburetor heat to keep the needle out of the yellow arc. PHAK 7-11 The outside air temperature gauge also helps you spot icing conditions and gives the temperature for computing true airspeed. PHAK 7-11

Mixture Control

Carburetors are calibrated at sea level with the mixture full rich. As altitude increases the air gets less dense but the fuel does not, so the mixture becomes progressively richer. That causes roughness, mostly from spark plug fouling, and an appreciable loss of power. It can happen during a runup at a high-elevation airport and in climbs or cruise at altitude. Leaning reduces fuel flow to match the thinner air. PHAK 7-9

Descending, enrich the mixture or it may become too lean. An overly lean mixture causes detonation, which can bring roughness, overheating, and a loss of power. Monitor engine temperature, use the EGT gauge where installed, and follow the POH leaning procedure. PHAK 7-9

Module 3 · Aircraft Systems · Lesson 4 of 8

Fuel Injection, Turbocharging, and Combustion

Some engines meter fuel without a carburetor, some pump extra air in, and every engine can hurt itself if the charge burns the wrong way.

Fuel Injection

Fuel is injected directly into the cylinders or just ahead of the intake valve. The alternate air source inside the cowling usually works automatically, with a manual backup. PHAK 7-11

A typical system has six parts: an engine-driven fuel pump, a fuel-air control unit, a fuel manifold (distributor), discharge nozzles, an auxiliary fuel pump, and fuel pressure or flow indicators. The auxiliary pump supplies pressure for starting and emergencies; after start the engine-driven pump takes over. The fuel-air control unit, which essentially replaces the carburetor, meters fuel by the mixture setting and sends it on at a rate set by the throttle. Nozzles in each cylinder head inject it into each intake port. PHAK 7-11 to 7-12

Fuel injection is less susceptible to icing than a carburetor, but impact icing, ice on the outside blocking the air intake, can affect either system. PHAK 7-12

Superchargers and Turbochargers

Both compress the intake air to raise its density. A supercharger is driven by the engine; a turbocharger is driven by exhaust gas spinning a turbine that turns the compressor. Both airplanes have a manifold pressure gauge. PHAK 7-12

Atmospheric pressure drops about 1 "Hg per 1,000 feet, so on a standard day at a 5,000-foot airport the engine-off manifold pressure reads about 24.92 "Hg. A normally aspirated airplane eventually climbs to where manifold pressure is too low for a normal climb, which limits its service ceiling (the altitude where the maximum rate of climb falls to 100 fpm). Boosting the intake raises it. PHAK 7-12 At 8,000 feet, a typical normally aspirated engine makes about 75 percent of its sea level power and about 22 "Hg; supercharged, it could still make 25 "Hg. PHAK 7-12

The turbocharger is the most efficient way to add horsepower because it uses exhaust energy that would otherwise be lost. It can hold rated sea level horsepower up to the engine's critical altitude, the maximum altitude at which it can produce rated horsepower. Above that, power falls off like a normally aspirated engine's. PHAK 7-13

The waste gate, an adjustable butterfly valve in the exhaust, varies how much exhaust goes through the turbine. Closed, most exhaust drives the turbine; open, it bypasses the turbine. Compression heats the intake air, so many engines add an intercooler to lower the risk of detonation. PHAK 7-13

Operating a Turbocharged Engine

• Most modern systems position the waste gate automatically with engine oil pressure; you simply set the throttle for the desired manifold pressure. PHAK 7-14
• With a manual waste gate left closed after a descent from altitude, manifold pressure can exceed the engine's limit. That overboost can cause severe detonation. PHAK 7-14
• Even an automatic system can overboost if takeoff power is applied with cold oil that cannot leave the actuator quickly. Advance the throttle cautiously. PHAK 7-14
• The turbine can exceed 80,000 rpm at very high temperature. Get oil temperature into the normal range before high power, and let the turbo cool before shutdown so the oil in the bearings doesn't boil and coke. PHAK 7-14
• If manifold pressure starts to drop before the specified critical altitude, have the system inspected. PHAK 7-15

Normal Combustion, Detonation, and Preignition

In normal combustion the mixture starts burning at the spark plugs and burns away from them smoothly, giving the piston maximum force at the right moment of the power stroke. PHAK 7-18 to 7-19 Detonation is an uncontrolled, explosive ignition of the mixture. It causes excessive temperatures and pressures that can quickly ruin a piston, cylinder, or valve; milder cases cause overheating, roughness, or power loss. It is marked by high cylinder head temperature and is most likely at high power. PHAK 7-19

Detonation and preignition often occur together, and one can cause the other. Both raise engine temperature and cut performance, so they are hard to tell apart. The right fuel grade and operation within temperature, pressure, and rpm limits reduce the chance of either. PHAK 7-20

FADEC

Full authority digital engine control uses sensors and a computer to control the engine and propeller, setting each injector pulse and the ignition timing. It eliminates magnetos, carburetor heat, mixture controls, and priming; you move a single lever to a detent such as start, idle, cruise, or max power. PHAK 7-20 Because a FADEC failure could mean a complete loss of thrust, it needs a backup power source and has two identical channels, each able to run the engine alone. PHAK 7-20

Module 3 · Aircraft Systems · Lesson 5 of 8

Ignition, Oil, Cooling, and Exhaust

Two magnetos light the fire, oil keeps the parts apart, and air carries the heat away. The gauges tell you which one is in trouble.

The Ignition System

The ignition system is made up of magnetos, spark plugs, high-tension leads, and an ignition switch. A magneto uses a permanent magnet to generate current completely independent of the airplane's electrical system. It starts firing when the starter turns the crankshaft and keeps firing whenever the crankshaft turns. PHAK 7-15

Most certificated aircraft have dual ignition: two magnetos, separate wires, and two plugs per cylinder, each magneto firing one plug. Two plugs burn the mixture more completely and give slightly more power. If one magneto or one plug fails, the engine keeps running with a slight loss of power. PHAK 7-15

The ignition switch has five positions: OFF, R, L, BOTH, and START. On R or L only that magneto works. PHAK 7-15

The Magneto Check

During the pretakeoff check, move the switch from BOTH to RIGHT, back to BOTH, then to LEFT, watching the rpm drop each time. A small drop is normal; the permissible drop is in the AFM or POH. PHAK 7-15

• If the engine stops on one magneto or the drop exceeds the limit, do not fly until it is fixed. Causes include fouled plugs, broken or shorted wires, or improper timing. PHAK 7-15 to 7-16
• "No drop" is not normal either. Do not fly. PHAK 7-16

The Oil System

Engine oil lubricates moving parts, cools by reducing friction, removes heat from the cylinders, seals between the cylinder walls and pistons, and carries away contaminants. PHAK 7-16 In a wet-sump system the oil sits in a sump that is part of the engine; in a dry-sump system it is in a separate tank and circulated by pumps. PHAK 7-16

Check the oil level with the dipstick during preflight. The AFM or POH and placards near the access panel give the correct type, weight, and minimum and maximum quantity. PHAK 7-17

Engine Cooling

Most small engines are air cooled. Air enters behind the propeller hub, baffles route it over the cylinder fins, and it leaves through openings at the bottom rear of the cowling. PHAK 7-17 Air cooling works worst on the ground, on takeoff, in go-arounds, and in any high-power, low-airspeed condition. High-speed descents can shock cool the engine with abrupt temperature changes. PHAK 7-17

Running hot causes loss of power, high oil consumption, and detonation, and can do permanent damage: scored cylinder walls, damaged pistons and rings, and burned or warped valves. PHAK 7-17

The oil temperature gauge gives an indirect and delayed sign of rising engine temperature. The cylinder head temperature gauge gives a direct and immediate one. PHAK 7-18

Exhaust and Cabin Heat

The exhaust system vents burned gases overboard and heats the cabin and windscreen. Outside air flows through a shroud around the muffler, picks up heat, and is ducted to the cabin. PHAK 7-18 Exhaust gas carries large amounts of carbon monoxide, which is odorless, colorless, deadly, and virtually impossible to detect, so the exhaust system must be free of cracks. PHAK 7-18 A defective exhaust heating system risks carbon monoxide poisoning, lost engine performance, and fire. PHAK 7-29

An EGT probe measures exhaust gas temperature at the exhaust manifold. EGT varies with the fuel-air ratio, so it is a highly accurate guide for leaning; follow the manufacturer's procedure. PHAK 7-18

Starting the Engine

Most small aircraft have a direct-cranking electric starter powered by the battery or an external power receptacle. With the battery switch on, power reaches the main bus through the battery solenoid; the starter runs only when the starter switch energizes the starting solenoid. A clutch keeps the running engine from driving the starter. PHAK 7-18 Before you start, make sure no one is near the propeller, chock the wheels, set the brakes, and avoid gravel or dust the propeller could throw. PHAK 7-18

Module 3 · Aircraft Systems · Lesson 6 of 8

The Fuel System

Clean fuel of the right grade has to reach the engine in every attitude you fly. Your preflight sample is the last check before it does.

The fuel system provides an uninterrupted flow of clean fuel from the tanks to the engine at all power settings, altitudes, attitudes, and approved maneuvers. PHAK 7-25

Tanks, Gauges, and Selectors

Tanks are vented to keep atmospheric pressure inside, through the filler cap or a tube, and have an overflow drain; fuel coming from it after filling on a hot day is not unusual. PHAK 7-26 Certification rules require fuel gauges to be accurate only when they read empty. Visually check the fuel in each tank during preflight and compare it with the gauges. PHAK 7-26

A common selector has LEFT, RIGHT, BOTH, and OFF. LEFT or RIGHT can balance the fuel. Placards show limits such as "level flight only" or "both" for takeoff and landing. Running a tank dry stops the engine, unbalances the fuel load, and can let air into the system and cause vapor lock, making a restart difficult. PHAK 7-26

Strainers, Sumps, and Drains

Fuel passes through a strainer that removes water and sediment, which are heavier than fuel and settle in a sump, the system's low point. Drain the strainer before each flight and check the samples visually for water and contaminants. PHAK 7-27 Water can freeze and block fuel lines in cold weather, or reach the carburetor and stop the engine in warm weather. If you find water in the sump, expect more in the tanks and drain until none remains. Never take off until all water and contaminants are removed. PHAK 7-27

Drain enough from the strainer to be sure you are getting fuel from the tank, not just the lines, and keep draining until a sample shows no trace. Water can remain in the tanks after the strainer runs clean; only the tank sump drains remove it. PHAK 7-27 to 7-28 Water shows as cloudy fuel or as a clear layer separated from the colored fuel. PHAK 7-28

Fuel Grades and Colors

From PHAK Figure 7-32 and PHAK 7-27.

The grade is an antiknock rating: the higher the grade, the more pressure the fuel withstands without detonating. If the proper grade is not available, use the next higher grade; never use a lower one, which can push cylinder head and oil temperatures past their limits and cause detonation. Automobile gasoline may be used only with an FAA STC. PHAK 7-27 AVGAS equipment is marked with white letters on red; turbine fuel with white letters on black. PHAK 7-27

Contamination, Icing, and Refueling

• Fuel contamination accidents have been traced to poor preflights, improperly filtered fuel from small tanks or drums, storing aircraft with partly filled tanks, and poor maintenance. PHAK 7-27
• Fill the tanks after the last flight of the day to prevent condensation, and avoid refueling from cans and drums. A chamois does not reliably filter water. PHAK 7-28
• Water suspended in fuel can freeze into crystals that block screens and filters. Anti-icing additives, where approved, are not a substitute for carburetor heat. PHAK 7-28
• Static from fuel flow can ignite fumes. Ground the aircraft before removing the cap and bond the nozzle to the aircraft for the whole fueling. From drums: drum to ground, ground to aircraft, then drum or nozzle to aircraft before the cap comes off; reverse to disconnect. PHAK 7-29

Module 3 · Aircraft Systems · Lesson 7 of 8

Electrical, Hydraulic, and Landing Gear Systems

An alternator failure does not stop the engine, but it starts a clock on your battery. The ammeter is how you notice.

The Electrical System

Most aircraft have a 14- or 28-volt direct current system: an alternator or generator, battery, master or battery switch, alternator or generator switch, bus bar with fuses and circuit breakers, voltage regulator, ammeter or loadmeter, and wiring. PHAK 7-30

The engine-driven alternator or generator powers the system and keeps the battery charged. The battery starts the engine and gives a limited supply of power if the alternator or generator fails. PHAK 7-30 Most generators make too little current at low rpm, so the battery carries the load and can run down. Alternators produce enough current even at low engine speed, and their output is more constant. PHAK 7-30

The master switch powers all electrical circuits except the ignition: lights, radios, turn indicator, fuel gauges, electric fuel pump, stall warning, pitot heat, and the starter. PHAK 7-30 to 7-31 With a split master switch, turning off the alternator half puts the whole load on the battery, so turn off all nonessential equipment. PHAK 7-31

Ammeter and Loadmeter

A center-zero ammeter shows whether the alternator is keeping up and whether the battery is charging. Plus is the battery charging rate; minus means more current is leaving the battery than is being replaced. A full-scale minus deflection points to an alternator or generator malfunction; full-scale plus points to the regulator. Some airplanes use a warning light instead. PHAK 7-31 A loadmeter starts at zero and shows the load on the alternator as a percentage of its capacity. PHAK 7-31

Hydraulic Systems

On small airplanes hydraulics often work the wheel brakes, retractable landing gear, and some constant-speed propellers. A basic system has a reservoir, a pump (hand, electric, or engine-driven), a filter, a selector valve to control the direction of flow, a relief valve for excess pressure, and an actuator. PHAK 7-31 The actuator, or servo, is a cylinder and piston that turns fluid power into work; it may be single- or double-acting. PHAK 7-32 Mineral-based fluid is most common in small aircraft; it is dyed for identification, and you must service with the type the manufacturer specifies. PHAK 7-33

Landing Gear and Brakes

A tricycle gear airplane has a nosewheel; a conventional (tailwheel) airplane has its third wheel at the rear. PHAK 7-33 Tricycle gear allows harder braking without nosing over, gives better forward visibility, and resists ground looping because the CG is ahead of the main wheels. PHAK 7-33 Nosewheels are steerable (linked to the rudder pedals) or castering (free to swivel, often needing differential braking). PHAK 7-33

On a tailwheel airplane the CG is behind the main gear, which makes ground directional control harder: let it swerve at low speed and the CG tries to get ahead of the mains, which can cause a ground loop. Forward visibility is also reduced, so specific training is required. PHAK 7-34 Fixed gear is simple and low-maintenance; retractable gear streamlines the airplane in cruise. Brakes on the main wheels are worked by hand or toe/heel pedals, and independent pedals give differential braking. PHAK 7-34

Module 3 · Aircraft Systems · Lesson 8 of 8

Cabin Environment, Oxygen, and Ice Protection

Up high, pressurization or oxygen keeps you conscious. In cloud near freezing, most trainers have no protection beyond pitot heat.

Cabin Heat

Exhaust heating systems are the simplest and are used on most light aircraft. PHAK 7-29 Some aircraft use fuel-fired heaters, whose byproducts include some carbon monoxide; a poorly maintained one can be dangerous. PHAK 7-29 Larger aircraft may use combustion heaters, which have an overheat switch that shuts off fuel; turbine aircraft use compressor bleed air. PHAK 7-29 to 7-30

Pressurization

Aircraft fly high because they burn less fuel for a given airspeed and can climb above weather and turbulence. To fly there, the aircraft must be pressurized or carry supplemental oxygen for each occupant. PHAK 7-34 The cabin is sealed to hold air above outside pressure. Turbine engines supply bleed air; piston engines may use turbocharger air through a sonic venturi. An outflow valve releases air to regulate pressure. PHAK 7-34 to 7-35

A typical system holds a cabin altitude of about 8,000 feet at the airplane's maximum designed cruising altitude. At or below 8,000 feet cabin altitude, oxygen equipment is not required. PHAK 7-35

The cabin pressure safety valve combines pressure relief, vacuum relief, and a dump valve. The cabin differential pressure gauge, cabin altimeter, and cabin rate-of-climb indicator monitor the system. PHAK 7-36

Decompression is the inability to hold the designed differential. Explosive decompression happens faster than the lungs can decompress, generally in less than 0.5 seconds; rapid decompression is slower than the lungs. PHAK 7-36 Rapid decompression cuts your effective performance time to one-third to one-fourth of normal. The primary danger is hypoxia; evolved-gas decompression sickness and being blown toward an opening are others. Descend rapidly. PHAK 7-36 to 7-37

Supplemental Oxygen

• Flight crews must have and use supplemental oxygen after 30 minutes at cabin pressure altitudes between 12,500 and 14,000 feet. PHAK 7-37
• Above 14,000 feet cabin altitude, the crew must use it immediately. PHAK 7-37
• Above 15,000 feet cabin altitude, every occupant must be provided supplemental oxygen. PHAK 7-37
• For best protection, pilots are encouraged to use oxygen above 10,000 feet cabin altitude by day and above 5,000 feet at night. PHAK 7-37

Oxygen is usually stored at 1,800 to 2,200 psi. Cylinder pressure drops when it gets cold, so a lower reading in an unheated compartment may not mean oxygen was used. Use aviator's breathing oxygen meeting SAE AS8010. PHAK 7-37 Oxygen makes nearly fireproof materials burnable, and oils and greases can ignite: no smoking, clean hands, and a full preflight of the mask, tubing, regulator, quantity, gauges, and connections, with the mask donned and tested. PHAK 7-37

Anti-Ice and Deice Systems

Anti-icing equipment prevents ice from forming; deicing equipment removes it after it forms. PHAK 7-40 Most light aircraft have only a heated pitot tube and are not certified for flight in icing; an airplane not certificated for icing must exit icing conditions immediately. PHAK 7-40

Check anti-icing and deicing systems before you encounter icing. Structural ice requires immediate action, and the equipment is not intended for long-term flight in icing. PHAK 7-41

Module 3 · Aircraft Systems · Module Exam

Module 3 Exam

Twenty questions drawn from all eight lessons, in the three-option format of the FAA knowledge test. Pass mark: 80 percent.

Module 3 · Aircraft Systems · Oral Scenario

Oral Scenario: A Damp Morning in a Rental Trainer

The examiner starts from a planned flight and follows your answers. Say each answer out loud before you open it.

"It's 7 a.m., 50 °F, and it rained overnight. The airplane sat outside with half-full tanks. It has a carbureted engine and a fixed-pitch propeller. You're planning a 9,500-foot cruise to an airport 90 miles away. Take me through the systems side of this flight."