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Aircraft Systems
CHAPTER 01 AIRFRAME DESIGN AND MATERIALS
Introduction
Certification Standards
Design Concept
Loads and Stresses
Ultimate Load and Limit Load
Fatigue
Material Properties
Composites
Summary of Material Properties
Corrosion
Maintenance Methods
CHAPTER 02 MAJOR AIRFRAME COMPONENTS
The Major Air frame Components
Material Attachment Methods
Construction Principles
The Fuselage
The Pressure Hull The Wings
Torsional Stresses and Flutter
The Empennage
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CHAPTER 03 SUBSIDIARY AIRFRAME STRUCTURES
Introduction
The Floor
Doors and Hatches
Flight Deck Windows
Passenger Cabin Windows
CHAPTER 04 HYDRAULIC PRINCIPLES
Introduction
Hydraulic Principles Hydraulic Power
Hydraulic Fluid Requirements
Advantages and Disadvantages of Hydraulic Systems
A Elementary Hydraulic System
CHAPTER 05 HYDRAULIC SYSTEMS
Overview
Actuators
Basic System Components
Hydraulic Circuits
Light Aircraft Systems
Large Aircraft System Components
Large Aircraft Systems Emergency and Auxiliary Power Sources
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CHAPTER 06 THE LANDING GEAR
Types of Landing Gear
Retractable vs Fixed landing Gear
Light Aircraft Fixed Gear Systems
Landing Gear Configurations
Shock Absorption
Main Gear Components
Nose Gear Assemby
Retraction and Extension
Landing Gear Locks Control and Operation
Speed Limits
Emergency Extension
Nose Wheel Steering
Nose Wheel Shimmy
CHAPTER 07 WHEELS, TYRES AND BRAKES
Wheel Construction
Tyre Construction
Tyre Inspection
Aquaplaning
Tyre Overheat Protection
Wheel Brakes Light Aircraft Wheel Brakes
Large Aircraft Brake Systems
Heat Dissipation
Anti-skid Systems
Emergency Brakes
Parking Brake
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CHAPTER 08 PRIMARY FLIGHT CONTROLS
Overview
Manual Control System
Power Operated Controls
Partially Powered Controls
Fully Powered Controls
Trimming Systems
Rudder Limiter
Blow-back System
Fly-by-wire Control System Control Locks
CHAPTER 09 SECONDARY FLIGHT CONTROLS
The Principal Secondary Controls
Activation Methods - Light Aircraft
Activation Methods - Large Aircraft
Flap Load Relief
Flap Asymmetry Protection
Auto-slats
Flaps and Slats Alternate Operation
Speed Brakes and Spoilers
Mechanical Locking and Blow-back
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CHAPTER 10 PNEUMATICS AND AIR CONDITIONING
Introduction
Light Aircraft Pneumatic Sources
Gas Turbine Air Supplies
The Source of Bleed Air
The Bleed Tapping
Pneumatic System Architecture
Overheat Detection and Warning
Bleed Air Controls and Indictions
Duct Construction
CHAPTER 11 CABIN CONDITIONING AND PRESSURISATION
Introduction
Air Conditioning
Air Distribution
Cabin Pressurisation
Pressurisation Control
Pressurisation System Components
Pressurisation System Controls and Indicators
The Pressurisation Schedule
Cabin Decompression
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CHAPTER 12 ANTIICING, DEICING AND RAIN PROTECTION
Introduction
Countering the Effects of Icing
Aircraft Systems Requiring Ice Protection
Ice Detection Systems
Fluid Based Ice Protection System
Thermal Ice Protection Systems
Turbo-prop Ice Protection Systems
Windscreen Ice Protection
Rain Repellent and Rain Removal Systems
CHAPTER 13 FUEL SYSTEMS
Introduction
Fuel Tanks
Piston Engine Fuel
Light Aircraft Fuel Systems
Turbine Engine Fuel
Turbine Engine Fuel Systems
Fuel Heating
Fuel Contents Gauging
Manual Fuel Contents Checking
Fuel Flow Indicators
Fuel Jettison Refuelling
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CHAPTER 14 FIRE AND SMOKE PROTECTION AND DETECTION
Introduction
Smoke Detection
Fire Detection and Protection Systems
Fire Detection
Fire Warning Indicators
Fire Suppression
Engine Fire Extinguishers
Cargo Compartment Extinguishers
CHAPTER 15 OXYGEN SYSTEMS
Introduction
Crew Oxygen Supply
Flight Crew Oxygen Supply
Passenger Emergency Oxygen Systems
Portable Oxygen Systems
Personal Smoke Protection
Oxygen System Safety Precautions
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CHAPTER 7: WHEELS, TYRES AND BRAKES
Wheel Construction
Tyre Construction
Tyre Inspection
Aquaplaning
Tyre Overheat Protection
Wheel Brakes
Light Aircraft Wheel Brakes
Large Aircraft Brake Systems
Heat Dissipation
Anti-skid Systems
Emergency Brakes
Parking Brake
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Wheels, Tyres and Brakes
Introduction
The wheel and tyre assembly has to withstand the very large forcesgenerated on landing and support the weight of the aircraft. The
tyre absorbs some of the shock of landing and acts as the rst shock
absorbing system for all loads felt through the landing gear assembly
when manoeuvring on the ground. The integral braking system also has
to withstand the very high temperatures generated when bringing a
heavy aircraft to a halt on landing.
The tyres of heavy transport aircraft are inated to very high pressuresIf one were to fail the resulting explosion can impel pieces of the tyre a
very high speed into the aircraft structure causing signicant damage,
typically to the under wing surface and the aps.
Consequently it is vitally important that tyres are operated at the
correct pressure and the tyre assemblies are checked before every
ight for general wear and obvious signs of damage.
Well start this chapter by looking at the wheel assembly before going
on to look at tyres and braking systems.
Wheel Construction
Wheels are usually cast or forged from aluminium alloy or magnesium
alloy. There are 3 main types:
J Well based: usually tted to light aircraft with tubed tyres
J Detachable ange: to allow for easier tyre replacement.
J Split hub or divided. Allows the tyre to be mounted onto one half
of the wheel with the other half bolted to it, forming the complete
wheel assembly. This type is used on large aircraft.
07
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Modern large aircraft tyre assemblies run on tubeless tyres which allow
for a lighter wheel assembly and lower heat generation.
Tubeless tyres require sealing rings to ensure a gas tight seal and
prevent loss of nitrogen from the assembly.
The ination valve is incorporated into the wheel itself.
Figure 7.1
The split hub and detachable flange systems used on larger aircraft
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Tyre Construction
Aircraft tyres comprise a exible casingwhich is constructed of rubber
coated rayon, cotton or nylon ply cords. These arewrapped around
beadsat each edge of the tyre.
The core of the bead is a series of steel wires which reinforce the tyre
and hold its circular shape.
Tread
Sidewall
Casing Plies
Bead
Steel wire core
Figure 7.2
Tubed tyre construction
The casing plies make up the strength of the tyre and comprise the tyre
carcass. The rubber tread is then moulded to the carcass to form the
complete tyre.Tyres are normally inated with nitrogen which helps to absorb
shocks, support the weight of the aircraft, maintain the tyre shape and
determine the size of the surface contact area.
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The tyre is divided into the following four zones:
J The crown.This area holds the tread pattern and makes contact
with the surface.
J The shoulder.In this area the tyre thins out from crown to
sidewall.
J The sidewall. This is the weakest part of the tyre and is least able
to cope with any damage.
J The bead.This is the strong rim of the tyre which engages with the
rims on the wheel to form an airtight seal.
Figure 7.3
Regions of a tyre
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Types of Tyre
Tyres are classied according to the way they are built and the method
used to inate them. Some of the key dening characteristics are:
J Ply rating. The ply rating give an indication of the tyres strength.
The higher the ply rating, the greater the strength of the tyre.
J Tread.The tread is made from rubber and provides toughness,
durability and a good gripping surface. The tread pattern forms
exible channels which expel any water between the tyre and
the ground surface. The most common tread pattern for modern
transport aircraft is the ribbed tyre.
J Tubeless.Tubeless tyres, as the same implies, have no inner tubeto contain the gas. Instead an airtight lining is vulcanised to the
underside of the beads. This forms a gas tight seal against the
wheel rim. Having no inner tube reduces weight and allows the tyre
to run cooler.
J Bias (or cross-ply). On a cross-ply design the plies are laid in
pairs and set so that the adjacent cords of adjacent plies are at 90
to one another.
J Radial. On a radial design the plies are laid from bead to bead,
approximately perpendicular to the centreline of the tyre.
J Retread. Aircraft tyres can be remoulded several times with a new
crown when the tread pattern is worn to limits. This is done by heat
bonding new rubber to the carcass.
J Tube Tyres. Tube tyres use an inner tube much like a bicycle tyre.The inner tube has an ination valve attached to it which is fed out
through a hole in the wheel. This type of tyre is usually only tted
to older aircraft types and light aircraft. A major disadvantage of the
tubed tyre is that any movement of the tyre around the wheel (tyre
creep) can cause the ination valve to shear off the tube.
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Tyre Creep
The sudden acceleration of the tyre on landing can cause it to slip
around the wheel. This phenomenon is known as tyre creep.
Creep is greatest just after a new tyre has been tted, usually during
the rst ve landings. A certain amount of creep is acceptable but it has
to be monitored. Excessive creep could cause damage to the ination
valve.
The usual method is to paint a red bar across a portion of the tyre
sidewall and the wheel. This is known as a creep mark. Creep marks
should be:
J 1in wide for tyres of 24in or less in diameter
J 1.5in wide for tyres over 24in in diameter
Figure 7.4Creep
After each ight the creep mark is checked for movement. Provided
there is some overlap between the mark on the tyre and the mark on
the wheel the amount of creep is within limits. If the creep marks no
longer align the tyre must be re-set on the wheel.
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Tread Patterns
Commercial transport aircraft tend to use tyres with either a ribbed
or blockedtread pattern. The tread pattern clears surface water and
provides longitudinal stability and grip.
Figure 7.5
Different types of tread
Ribbedtread patterns are most common for commercial aircraft using
concrete or tarmac runways. Blocked treads are used for all-weather
tyres on rough runways or unmade runway strips.
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There are two other types of tyre design adapted for specic
purposes:
J Maarstrand tyre. The Maarstrand tyre is a single tyre used on
castoring nose wheels. It has two ridges to provide two areas of
contact with the ground. This reduces the risk of shimmying. The
tyre wear is within limits provided that there is no evidence of
surface contact in the centre section.
J Chined tyre. The chined tyre has a strip of rubber moulded onto
one or both sides of the tyre shoulder. The chine deects water
to the side of the tyre diverting it away from the centreline and
preventing excess water from being ingested by the engines.
Figure 7.6
Maarstrand tyre
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Tyre Speed Rating
Tyres are speed ratedto give a tyre limiting speed. The speed rating
must match or exceed the maximum anticipated ground rolling speed o
the aircraft. The correct rating must be used to guarantee that the tyre
can withstand the forces generated by takeoff and landing. Exceedingthe tyre limiting speed is likely to result in tyre failure.
Tyre Wear
Tyres must be inspected for signs of wear. The following limitations
must be strictly observed.
J Ribbed treads. The minimum tread depth is 2mm, measured from
bottom of the groove. The tyre may have a tyre wear marker bar.This is moulded into tyre between the treads and indicates 2mm
depth. The tyre is on its limit when the marker bar is at the same
height as the rib.
J Blocked treads. This type of tyre is within limits provided that the
block pattern is still visible.
Figure 7.7
Indications of tyre wear
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Tyre Inspection
It is extremely important that tyres are carefully inspected for damage
and that the tyre is operated at the correct pressure. Damage or
under-ination can lead to tyre failure or tread separation. Worse still
a tyre burst can result in serious damage to the aircrafts structure. In
extreme cases, as in the Concorde accident in Paris, it can result in loss
of the aircraft.
Figure 7.8
Tyre Inspection
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When inspecting tyres for damage look out for:
J Cuts.Any cuts to the cords or sidewall require the tyre to be
replaced.
J Bulges.Unusual bulges especially around sidewall areas are a sign
of impending tyre failure.
J Foreign object damage. Ensure no stones, fasteners, glass or
metal are embedded in the tyre.
J Contamination.Ensure no hydraulic oil or engine oil has been
spilled onto the tyre.
J Creep. Check that the creep marks are overlapping.
J Wear. If the tyre is worn beyond the acceptable limit it must be
replaced.
J Pressure. Over ination may lead to blow out and excess wear.
Under ination leads to tyre creep, excess wear and possible tyre
failure. Commercial aircraft tyres are normally inated with nitrogen.
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Aquaplaning
Aquaplaning is a phenomenon in which a wedge of water builds up
at the front of the tyre and, as speed increases, starts to lift the tyre
off the surface. A fully aquaplaning tyre will have no contact with the
surface and may even stop rotating altogether.
Aquaplaning may result in reduced or no braking ability, loss of
directional control and damage to the tyre from superheated steam
generated by the friction forces between water, tyre and surface.
Figure 7.9
Aquaplaning
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Aquaplaning only occurs above a certain speed, dictated by tyre
pressure. The formulae for calculating the minimumaquaplaning speed
are:
9P
where P is the tyre pressure in psi
and:
34P
where P is the tyre pressure in kg/cm2
The risk of aquaplaning can be minimised by:
J Ensuring tyre pressures and tread wear are correct.
J Using an anti-skid system.
J Avoiding ooded runways or large patches of standing water on a
runway.
Tyre Overheat Protection
If a wheel or tyre heats up excessively the heat is transferred to
the internal gas which then expands causing a dramatic rise in tyre
pressure. Eventually the pressure may rise to the point where the tyre
fails.
The primary cause of tyre overheating is braking. The very large
amounts of energy absorbed by the brake system on landing arereleased as heat. While some of this radiates away to atmosphere, a lot
of heat conducts through the brake assembly into the wheel and tyre.
A tyre burst from overheating can be very dangerous and possibly fatal
to any ground servicing staff who happen to be nearby. Consequently
each aircraft wheelis equipped with a fusible plugwhich is designed to
burst before the tyre fails.
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When the wheel assembly reaches a pre-determined temperature, the
fusible material in the plug melts allowing the pressurised air to escape
to atmosphere. Plugs come in various temperature settings and are
colour coded for identication.
Tubeless tyre
Plug
Split hub
Inflation valve
Fusible insert
Figure 7.10
Fusible plug
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Wheel Brakes
Wheel brakes produce friction at the wheel assembly to slow or stop the
rotation of the wheel. Light aircraft use a simple single disc type brake
but large transport aircraft require multiple discs to deal with the forces
generated. Most most modern transport aircraft use hydraulic power
to operate the brakes. However, the Boeing 787 uses an electrically
actuated system to reduce weight and increase braking efciency.
Light Aircraft Wheel Brakes
Simple braking systems comprise a steel disk xed to the wheel. A
brake unit or calliperis equipped with friction pads operated by an
hydraulic piston. When the brake pedals are pressed, hydraulic pressure
from foot pedal pressure transmits hydraulic pressure to the calliper
piston which squeezes the friction pads onto the disc.
Figure 7.11
Light aircraft disk brake
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Brake Wear Indication
The friction pads themselves are made from an ablatable material
which erodes with use. Eventually they wear down to the point where
they must be replaced. To check the amount of wear, some light aircraft
systems are equipped with brake wear indicators.
The brakes should be checked for wear after every ight, with the
brakes applied. A rule or special gauge may be needed measure the
gap between the disc and brake housing.
Figure 7.12
Measuring brake wear
On conventional steel disc brakes, excessive heat diminishes brakingefciency resulting in a condition known as brake fade. Brake fade
usually starts to occur at the end of a landing run. Despite standing
on the pedals the aircraft becomes very difcult to stop. Overheated
brakes may judder (chatter) when applied or make high pitched
squealing sounds. They may also cause the pads to stick to the discs
(draggingor binding) further increasing brake temperature.
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Large Aircraft Brake Systems
Large transport aircraft use multi disc and multi piston brakes to cope
with the much greater amounts of energy that must be absorbed.
On the multi disc system a series of pads are arranged concentricallyaround both sides of a stator assembly.
In between each pair of stators is a rotor segment. The rotor segment
is physically engaged with the wheel assembly via the torque tubeand
so rotates with the wheel.
A torque platecarries the operating pistons. When hydraulic pressure
is applied to the pistons they squeeze the entire assembly of rotors and
stators together between thepressure plateand the thrust plate.
Brake Assembly
Brake Pis
Brak
hous
Rotors and Stators
Pressure Plate
Thrust Plate
Figure 7.13
Boeing 737 brake units
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The discs are segmented and held together relatively loosely to allow
for thermal expansion. The rotors are constructed from steel alloy. The
brake pads are usually made from ceramic material.
Automatic Brake Adjuster
Automatic brake adjusters ensure correct clearance between the
rotating assemblies when the brakes are in the off position.
Figure 7.14
Automatic brake adjuster
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Brake Wear Indication
A wear indicator pin passes through brake housing. As the brake pads
wear down the pin starts to retract into the housing. A return spring
returns the indicator pin to the original position when the brakes are
selected off.
Brake wear is measured by the position of the pin. Usually the pads
must be replaced when end of the pin is ush with the adjuster
housing.
Figure 7.15
Brake wear indicator pin on a Boeing 737 showing plenty of brake pad remaining
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Carbon Braking Systems
The multi disc system is a very heavy bit of kit when built with
traditional materials so the latest generation of transport aircraft
tends to be equipped with carbon brakes. These have a number of
advantages:
J Weight. Carbon brakes are lighter, resulting in weight savings of
about 50% over steel brakes. On the Boeing 737 NG for example
the carbon brake system is 300kg lighter than the steel design.
J Performance. The carbon composite material retains its efciency
at all temperatures and at high or low speeds. It can absorb twice
as much heat as steel and so is much less prone to brake fade.
J Durability. Carbon brakes last longer; anything up to 4100
landings per overhaul. This is the number of landings each brake
can handle before the heat sinkstack of carbon disks has to be
refurbished. This represents a 30% to 175% improvement over the
service life of steel brakes.
J Economy. Although more expensive to t, carbon brakes are less
expensive than steel brakes over their service lifetime.
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Heat Dissipation
One of the biggest problems for any multi-disk system is getting rid of
the enormous amount of heat energy generated on landing.
A landing at normal speeds and weights, followed by a gentle taxito the stand with minimal braking will allow for a certain amount of
cooling, courtesy of the natural ow of air around the units and the
time available for cooling to take place. The brakes should then cool
further whilst the aircraft is on stand being prepared for ight.
The biggest problem however, comes from a high speed landing
at heavy weight followed by a short, brisk taxi to the stand. The
brakes will already be extremely hot after the landing roll and furtherapplications of brake during taxiing will add more heat energy. When
the aircraft stops on stand the lack of cooling air owing round the units
can lead to a progressive build up of heat and a brake re.
Furthermore, if the aircraft then departs the stand after a short
turnover it may begin its next take-off with the brakes already very hot
If the crew subsequently needs to reject the take-off the brakes may
become seriously overheated and fade or catch re.To deal with the heat problem large transport aircraft are often
equipped with brake fan units to articially ventilate the brake pack.
Clearly, it is very important that you monitor brake temperatures
carefully. Additionally manufacturers may specify a minimum brake
hold-over time to allow sufcient cooling between landing and the next
take-off.
ATC must be informed in the event of brake overheat. Consult the ops
manual before moving the aircraft. Avoid approaching hot brake units.
If you have to, make sure you approach either from the front or rear.
Do not allow refuelling until the brakes have cooled sufciently.
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Brake Temperature Indication
Brake temperature will be displayed either on the ECAM or EICAS
screens or on a dedicated display unit as shown below. The unit
defaults to display the hottest brake temperature. Pressing the caption
for each individual unit displays its temperature. A OVHT warning willshow if brake temperature is above the acceptable limit.
INNER
OVHT
INNER
OVHT
OUTER
OVHT
OUTER
OVHT
MAX
L MAX R
TEST
O
F
F
Figure 7.16
The brake temperature gauge by default displays the temperature of the hottest brake
Some indication systems use numbers to represent levels oftemperature. Higher numbers indicate higher temperature levels.
2 21 3
1 11 2
BRAKE TEMP
Figure 7.17
Brake temperature gauges
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Anti-Skid Systems
Maximum retardation from wheel braking is achieved when the
maximum braking force is applied to a rotating wheel without stopping
it. If the wheel locks the tyre will skid over the surface of the runway.
Skidding produces signicantly lessretardation than a properly braked
wheel.
The problem for the pilot is knowing how much pressure to apply to the
brakes. Too little pressure and he may not slow the aircraft adequately.
Too much pressure and he may lock the wheel. A locked wheel not only
produces less friction but the skid itself very quickly wears away the
tyre crown. At best this results in ruined tread requiring a new tyre.
But it might also cause the tyre to be weakened to the point where it
bursts.
The solution to this dilemma is the anti-skid system. An anti-skid
system works by monitoring wheel rotation. If a spinning wheel starts
to slow down quickly the system interprets this as an impending
skid. It then intervenes to release brake pressure and then quickly
reapply it. The process happens very quickly, several times a second,
but ultimately it ensures that, no matter how much brake force is
demanded by the pilot, the wheels never lock.
Anti-skid systems provide skid protection when braking on normal, dry
runways and on wet runways. They will also provide skid protection on
runways contaminated with snow and ice.
However, its important to understand the crucial difference between
skid protection and retardation. An anti-skid system prevents the tyrefrom skidding but it cant compensate for a general lack of friction
on the runway surface. In very slippery conditions the anti-skid will
operate continuously because every time brake pressure is reapplied
the wheel quickly slows down. The effect is very little braking action
and can end in an embarrassing encounter with the runway overrun
area.
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Mechanical Anti-Skid System
Mechanical anti-skid systems are nowadays only seen on older aircraft.
The most common is the DunlopMaxaretunit. The system comprises
an hydraulic valve regulated by a spring loaded, clutched ywheel. The
ywheel is mounted inside a drum which is tightly connected to theinside of the wheel hub. In normal operation the rotation of the wheel
causes the drum and ywheel to rotate at the same speed.
When the wheel starts to slow down, the natural inertia of the ywheel
causes it to overrun. When the position of the internal ywheel exceeds
60relative to the drum, the unit presses forward onto the hydraulic
valve which then opens to dump hydraulic pressure to the brake unit.
With brake pressure released the wheel (and the drum with it) then
speed up again. When drum and ywheel speeds once again match,
the hydraulic valve is released allowing brake pressure to be restored.
The unit becomes sensitive enough to be active above about 20kt. Once
active it is capable of operating at up to 10 times per second.
From brake control valve
Maxaret unit
To reservoir
Figure 7.18
Maxaret System
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Electronic Anti-Skid System
Electronic anti-skid control uses a small generator driven by the wheel
assembly. The electrical signal it produces varies with wheel speed. This
signal is sent to the anti-skid controller which cross-references it with
the signals being received from the other wheel units.
The controller estimates the speed of the aircraft based on the
measured wheel speed and then predicts the slip ratio based on the
measured wheel speed and estimated aircraft speed. The controller
signals the pressure control valve to momentarily release pressure to
the brake when the difference between the predicted slip ratio and the
desired slip ratio reaches a pre-determined value.
PARK BRAKE
PARKING BRK OFF
PULL & TURN
Anti
skid
control
Anti
skid
control
Anti
skid
control
Anti
skid
controlTacho Tacho Tacho Tacho
Brake
unit
Brake
unit
Brake
unit
Brake
unit
Skidcontrolvalve
Skidcontrolvalve
Skidcontrolvalve
Skidcontrolvalve
Brakecontrolvalve
Brakecontrolvalve
Inertial reference
Left
outer
wheel
Left
inner
wheel
Right
inner
wheel
Right
outer
wheel
Independent anti skid control
for all wheels
Parking
brake
valve
Anti skid
returnBrake
hydraulic
supply
Captains pedals First officers pedals
Left Right Left Right
Parking Brake:
Applies pressure to all brakes
Closes parking brake valve
Figure 7.19
Electronic anti-skid protection
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Pressure is then reapplied at a lower pressure depending on the time
interval of the skid. Brake pressure then rises steadily in search of the
maximum braking force before the next skid begins to develop.
Changeover circuits couple the valves of all brake units so that the loss
of a speed signal from one unit doesnt affect system operation.
Touchdown and Bounce Protection
Modern anti-skid systems usually incorporate touchdown and bounce
protectionfeatures.
This system prevents brake pressure being applied at the wheel before
touchdown even if the pilot inadvertently applies pressure to the brake
pedals.
If the aircraft bounces after initial touchdown the system releases any
brake pressure, allowing the wheel to spin up again before the second
touchdown.
Automatic Braking
Sophisticated anti-skid systems have automatic braking or auto-brake.
This brings the aircraft to a halt after landing, or after a rejected take-
off, with no intervention from the pilot.
A two-position three-way solenoid valve is energised after the wheels
spin-up. The valve feeds hydraulic pressure to the adaptive pressure
control valves which adjusts the amount of pressure fed to the brake
units.
The amount of pressure fed by the control units is determined by a
setting on the ight deck. The settings are either numbered or labelled.
For example 1 or MIN sets the lowest level of retardation; 3 or
MAX guarantees to have the passengers pinned against their lap
straps!
The system is automatically overridden if the pilot manually applies the
brakes or sets the power levers to TOGA (take-off or go-around).
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AGK - Systems Wheels, Tyres and Brake
The system requires a number of prerequisites before it can be armed
(meaning that the system is ready to operate):
J Auto-brake must be selected ON and a deceleration level selected.
J The anti-skid system must be on and serviceable.
J The power levers must be set below a certain value.
J The hydraulic system must be functional.
J The brake pedals must not be depressed.
1
2
3
MAXOFF
RTO
AUTO BRAKE
ANTI-SKID
ANTI SKID
INOP
ANTI BRAKE
DISARM
Figure 7.20
Boeing 737 Auto Brake
The system operates when the aircraft is on the ground and the wheels
have spun-up.
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AGK - Systems Wheels, Tyres and Brake
Anti-Skid Inoperative
Anti-skid braking systems greatly enhance overall braking performance
so much so that if the system is lost the required landing distance can
double, particularly on contaminated runways.
An amber warning caption illuminates if a fault is detected in the
anti-skid system. Faulty anti-skid carries a number of operational
considerations including the type and length of runway that you are
permitted to land on.
HYD BRAKE
PRESS
3
2
1
0
4
PSI X 1000
SPEEDBRAKE
12
10
8
6
4
2
012
10
8
6
4
2
0
12
10
8
6
4
2
012
10
8
6
4
2
0
MAN SET
FF/FUx 1000
% RPM
N2
EGTC
% RPMN1
PULLTO
SETN1
PULLTO
SETN1
PPH
PUSHLB FUELUSED
RESET
100
500
100
500
100200
0
100200
0
02
34
5
1 02
34
5
1
43
21
0
43
21
0
TAT C
ENGOIL
PRESS
OILTEMP
OIL QTY
VIB
HYDPRESS
QTY
PSI
C
% FULL
PSIx 1000
% FULL
RF 88%
A B
1
2 3
10
15
25
3040
UP
FLAPS
RL
YAW DAMPER
1
2
3
MAXOFF
RTO
AUTO BRAKE
ON
OFF
ANTI-SKID
ANTI SKIDINOP
ANTI BRAKE
DISARM
1 2
1 2
LANDING GEAR
LIMIT (IAS)
FLAPS LIMIT (IAS)
OPERATING
EXTEND 270K-82MRETRACT 235KEXTEND 320K-82M
1-230K2-230K5-225K10-210K
15-195K25-190K30-185K40-158K
230K ALT FLAP EXT
L
A
N
D
I
NG
G
E
A
R
UP
OFF
DN
LE FLAPS
TRANSIT
LE FLAPS
EXT
REVERSER
UNLOCKED
REVERSER
UNLOCKEDA/T LIM
STARTVALVE OPEN
LOW OIL
PRESSURE
OIL FILTER
BYPASS
STARTVALVE OPEN
LOW OIL
PRESSURE
OIL FILTER
BYPASS NOSE
GEAR
NOSE
GEAR
LEFT
GEAR
RIGHT
GEAR
LEFT
GEAR
RIGHT
GEAR
Autobrake and Anti-sk
Controls
Gear and Flap
Limits Placard
Gear Selector
Brake
Pressure
Gauge
Figure 7.21
Location of gear and brake controls on a Boeing 737
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AGK - Systems Wheels, Tyres and Brake
Auto-Retract or Flight Brake
Some aircraft, are equipped with an auto-braking system for the main
wheels. On retraction the wheels are automatically braked to a halt
before they enter the wheel wells.
Emergency Braking Systems
Commercial transport aircraft will always be equipped with an alternate
hydraulic source for braking. The example system shown here provides
separate hydraulic supplies to the brakes from the Yellow and Green
systems.
EDPeng 1
EDPeng 1
Elecpump
Elecpump
Handpump
EDPeng 1 RAT
Elecpump
EDPeng 2
PTUpump
PTUmotor
PTUmotor
PTUpump
Brakes
Landinggear
Cargodoors
High lift devices
Flying controls
P
P
P
P
BlueReservoir
GreenReservoir
YellowReservoir
PTU PTU
RAT
EDP
PTU
= Ram Air Turbine
= Engine Driven Pump
= Power Transfer Unit
= Non return valve
= Priority valve
= Control valve
Figure 7.22
Duplicated hydraulic supplies to the braking system
As a last resort a brake accumulator provides up to six applications of
brake should all hydraulic pressure be lost.
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AGK - Systems Wheels, Tyres and Brake
The Parking Brake
The parking brake allows brake pressure to the wheel brakes to be
applied and held applied.
The parking brake is usually set using a lever. On some systems theparking brake lever must be applied simultaneously with the toe brakes
to engage the system.
When the parking brake is set to on it overrides all other braking
systems including anti-skid and touch-down protection. For this reason
you must neverset the parking brake on in ight.
Furthermore, the parking brake should not be set on if your brakes are
excessively hot (more than 500C on the Boeing 737). Applying parkingbrake in these circumstances increase the risk of the rotors welding to
the stators.
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AGK - Systems Wheels, Tyres and Brake
0
5
10
15
APL
NOSEUP
STAB
TRIMAPL
NOSE
DOWN
T
AKE-OFF
0
5
10
15APL
NOSE
UP
STAB
TRIM
APL
NOSE
DOWN
TAKE-OF
F
STAB TRIM
NORMALMAIN
ELEC
AUTO
PILOT
CUT
OUT
PARKING
BRAKE
PULL
FLAP
SPEEDBRAKE
FLIGHT
DETENT
UP
ARMED
DOWN
FLAP
UP
0
1
2
5
15
10
25
30
40
HORN
CUTOUT
FLAP
DOWN
Parking Brake
Lever
Parking Brake
Warning LightLanding Gear
Warning Horn
Cutout Switch
Figure 7.23
Location of parking brake lever
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