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Engine and Systems

Engine and Systems

Welcome to the Engine and System section. All questions and answers are again unverified regarding correctness. Please report any errors in our Pilot Forum.

  • What is a reverse annular combustion chamber?
  • What is Flat rating?
  • In which axis does a rate gyro [measures rate of turn] spin?
  • In which axis does a stand-by attitude indicator spin?
  • What type of thrust reversers are fitted to jet aircraft?
  • Why are thrust reversers more effective at high speed?
  • What features make the B777 unique from other jet transports?
  • What are your actions following a Pitot static blockage and an attitude indicator failure?
  • Why are bleed valves fitted to jet engines?
  • What is the error of an altimeter at 10 000’ PH at ISA -34ï‚°?
  • What aircraft damage might come about from a lightning strike?
  • What do you know about TCAS?
  • What colours make up the colour spectrum?
  • From the cockpit engine indications how could you tell the difference between the 747-400 and the A340-300?
  • Describe the construction of an AC generator.
  • Describe the construction of a DC generator.
  • What is a safety cell battery?
  • What is the combustion cycle of a jet engine?
  • What is a fuel dipper?
  • Why do engines have auto-ignition?
  • What must you check before paralleling a generator?
  • What do Constant Speed Drives [CSDs] do?
  • What is the purpose of engine re-light boundaries?
  • On a wet runway initially what is the most effective way of braking?
  • When do you turn on engine anti-icing?
  • Fly by wire
  • Mixed Fleet Flying
  • Cross Crew Qualification
  • Airbus commonality
  • What are the advantages of the 747-400 over the 747 classic?
  • What uses does bleed-air have?
  • What are the advantages of a centrifugal compressor?
  • Explain truck tilt.
  • How does a fire wire work?
  • What are balanced hydraulic actuators and what are their main advantage?
  • What is the fuel saving on the 747-400 compared to the classic?
  • What is by-pass ratio?
  • What is the difference between a Turbojet, Turbofan and a Turboprop?
  • How do bleed valves assist during engine start and acceleration?
  • What kind of power supplies an EGT gauge?
  • What are the formulas for calculating approximate hydroplaning speeds?
  • What are the three types of hydroplaning?
  • How does a blown main tyre affect ASD?
  • Prior to take-off, what do tyre temperatures depend on?
  • On a double wheeled bogie, which brake gets the hottest?
  • What reduces braking efficiency?
  • What are the disadvantages of carbon brakes?
  • What are the advantages of carbon brakes?
  • How does a turbine engine work?
  • Explain the operation of an Air cycle machine.
  • Why are bleed valves fitted to jet engines?
  • When might we use continuos ignition?
  • What is TSFC?
  • What are the advantages of a Fan engine?
  • What are the advantages and disadvantages of pod mounted engines?
  • What is the fundamental difference between the CFM engines and the Rolls Royce engines?
  • What spool is the accessory gearbox driven off on the RB211-524?
  • How do you start the RB211-524?
  • What can you tell me about the RB211-524?
  • How much thrust is produced by a Cathay Pacific 747-400’s engine?
  • Why do jets use reduced thrust take offs?
  • What is assumed temperature used for?
  • What are the advantages of a wide chord fan engine?
  • What is the difference between N1 and EPR?
  • If EPR increases with constant power on descent, what does this indicate?
  • Why do we usually set take off EPR prior to 80kts?
  • What happens to EPR on the take off roll?
  • What are the advantages of a High-bypass fan?
  • How does a High-Bypass Turbofan work?
  • Why do we (CX) use EPR instead of N1?
  • Do we still need to know how fast the fan is spinning if we set EPR?
  • How do we set thrust on the B747?
  • What is Integrated EPR?
  • What is N1?
  • What is EPR?
  • How does Doppler radar work?
  • How does Iso-Contour radar work?
  • How does anti-skid braking work?
  • What would happen if it failed?
  • Why shouldn’t you use reverse thrust at low airspeeds?
  • Thrust reversers, when do we use them?
  • When are they most effective?
  • Describe fuel management in the A340-600.
  • Describe fuel management in the A330/A340-300.
  • Describe fuel management in the B747-400.
  • Why does the 747-400 have stabilizer fuel tanks?
  • Where do we keep fuel in the B747?

What is a reverse annular combustion chamber?

  • Single annular shaped combustion chamber [single flame tube]
  • Compressed air flows past [outside] the combustion chamber before entering it [does a 180º turn]
  • Allows better cooling and is a shorter unit
  • Results in a slight loss of efficiency due to the 180º turn

What is Flat rating?

The rating of a jet engine is the thrust performance that is guaranteed by the manufacturer for a new engine under specific operating conditions such as, take off, maximum continuous, climb, cruise.

The temperature and density of the ambient air vary inversely. Lower temperature = > Higher Density Higher Temperature = >Lower Density

The amount of airflow [lbs/sec] through the engine is a function of compressor speed and air density. It is greater when the compressor speed and density are high.

The compressor speed is a function of the energy available to the compressors turbine. That energy comes from the combustion or air and fuel, so the turbine turns faster when the fuel flow rate is greater. The compressor speed is also a function of the airflow through the compressor. Higher rates of airflow reduce the speed of the compressor.

The compressors rotational speed and the amount of airflow through the compressor are independent they affect each other though. The turbine inlet temperature is proportional to the energy available to turn the turbine. The exhaust temperature is proportional to the turbine inlet temperature. So a higher EGT corresponds to a larger amount of energy to the turbine so it can turn the compressor faster. When EGT is held constant, or lowered the result is a prolonged hot section life and at the same time provides the thrust to meet the certification requirements.

In which axis does a rate gyro [measures rate of turn] spin?

The horizontal axis.

In which axis does a stand-by attitude indicator spin?

The vertical axis.

What type of thrust reversers are fitted to jet aircraft?

Clamshell [hot stream]:

Large metal plates are hydraulically deflected into the jet efflux, changing its direction by about 135º [to 45º backwards]. Material need to be heat resistant due to the operating environment.

Commonly used on turbo-jet and low by-pass turbofan engines [also many rear engine mounted aircraft].

Cascade [cold stream]:

Incorporate a system of blocker doors, which hydraulically deflect into the fan [N1 by-pass] airflow. It then escapes through rearward facing cascade vanes, exposed by a translating sleeve moving rearwards

Commonly used on high-pass turbofan engines

Why are thrust reversers more effective at high speed?

  • The net amount of reverse thrust increases with speed because the acceleration imposed on the [constant] mass flow is greater because the aircraft forward speed is additional when in reverse thrust as opposed to subtractional when in forward thrust.
  • The kinetic energy of the aircraft is being destroyed at a higher rate at the higher speed

What features make the B777 unique from other jet transports?

Wing Design

The 777 wing is the most aerodynamically efficient airfoil ever developed for subsonic commercial aviation. In a further refinement of designs introduced on the Boeing 757 and 767, the 777 wing features a long span with increased thickness. This advanced wing enhances the airplane’s ability to achieve higher cruise speeds, climb quickly and cruise at higher altitudes than competing airplanes. It also allows the airplane to carry full passenger payloads out of many high-elevation, high-temperature airfields.

Fuel volume requirements for the 777 are accommodated entirely within the wing and its structural centre section.

Airlines helping to design the 777 encouraged Boeing to commit to the performance capabilities of an optimum wing, which has a span of 199 feet 11 inches (60.9 m).

Raked 6.5-foot wingtips are being added to the 777-200LR and 777-300ER to improve the overall aerodynamic efficiency of the wing. The raked wingtips help reduce takeoff field length, increase climb performance and reduce fuel burn.

Propulsion

The three engine manufacturers developed more efficient and quieter turbofans to power the 777, and 777 customers have selected all three. Engine selection for the 777 is split at roughly one-third for each of the engine manufacturers. Pratt & Whitney offers the PW4000 series of engines, General Electric offers its GE90 series, and Rolls Royce offers the Trent 800 series of engines.

All three engines offer excellent fuel efficiency, while allowing the 777 to be as quiet as a 767, even though the 777 engines provide 40 percent more power. Key factors in this performance are new, larger-diameter fans with wide-chord fan blade designs and bypass ratios ranging from six-to-one to as high as nine-to-one. This compares to the typical five-to-one ratio for the engines of previous twin-aisle jets.

Materials

New, lightweight, cost-effective structural materials are used in several 777 applications. For example, an improved aluminium alloy is used in the upper wing skin and stringers. Known as 7055, this alloy offers greater compression strength than previous alloys, enabling designers to save weight and also improve corrosion and fatigue resistance.

Progress in the development and fabrication of weight-saving advanced composite materials is evident in the 777. Carbon fibres embedded in recently available toughened resins are found in the vertical and horizontal tails. The floor beams of the passenger cabin also are made of these advanced composite materials.

Other composite applications include those on secondary structures such as aerodynamic fairings. Composites, including resins and adhesives, account for nine percent of the 777’s structural weight, compared to about three percent on other Boeing jets.

Flight Deck and Airplane Systems

In response to airline preference, the layout of the 777 flight deck is in a horizontal format similar to that of the 747-400. Principal flight, navigation and engine information is presented on six large display screens.

Although these displays resemble conventional cathode ray tube (CRT) screens, they incorporate advanced liquid-crystal display technology. The depth of the new “flat panel displays” are about half that of CRTs. In addition to saving space, the new displays weigh less and require less power. They also generate less heat, which contributes to greater reliability and a longer service life. As another benefit, the displays do not require the heavy, complex air conditioning apparatus needed to cool equipment on previous flight decks. Pilots appreciate that flat panel displays remain clearly visible in all conditions, even direct sunlight.

Three multipurpose control display units (CDU), installed in the centre aisle stand, provide data display and entry capabilities for flight management functions. These units are the primary interface with an integrated Airplane Information Management System (AIMS). The CDUs have colour displays, again in response to market preferences. Adding colour allows pilots to assimilate the information more quickly.

AIMS provides flight and maintenance crews all pertinent information concerning the overall condition of the airplane, its maintenance requirements and its key operating functions, including flight, thrust and communications management.

The flight crew transmits control and manoeuvring commands through electrical wires, augmented by computers, directly to hydraulic actuators for the elevators, rudder, ailerons and other control surfaces. This three-axis “fly-by-wire” flight control system saves weight, simplifies factory assembly compared to conventional mechanical systems relying on steel cables, and requires fewer spares and less maintenance in airline service.

A key part of the 777 systems is a Boeing-patented two-way digital data bus, which has been adopted as a new industry standard: ARINC 629. It permits airplane systems and associated computers to communicate with one another through a common wire path (a twisted pair of wires) instead of through separate one-way wire connections. This further simplifies assembly and saves weight, while increasing reliability through a reduction in the amount of wires and connectors. There are 11 of these ARINC 629 pathways in the 777.

The 777 was the first Boeing model to be equipped with the Enhanced Ground Proximity Warning System (EGPWS) as standard equipment. The EGPWS displays potentially threatening terrain and gives an audible alert up to a minute in advance of possible terrain conflict, compared with 10 to 15 seconds for previous systems. It incorporates a proprietary digital terrain map, which it continuously compares to aircraft position data from the navigation system.

One new feature in the 777-300 flight deck is the addition of a Ground Manoeuvre Camera System (GMCS), designed to assist the pilot in ground manoeuvring of the 777-300 with camera views of the nose gear and main gear areas. The cameras are on the leading edge of the left and right horizontal stabilizers and the underside of the fuselage and are used during ground manoeuvring. The images are displayed at the Multi-Functional Display positions in the flight deck in a three-way split format.

Landing Gear

The main landing gear for the 777 is in a standard two-post arrangement but features six-wheel trucks, instead of the conventional four-wheel units. This provides the main landing gear with a total of 12 wheels for better weight distribution on runways and taxi areas, and avoids the need for a supplemental two-wheel gear under the centre of the fuselage. The 777’s landing gear is the largest ever incorporated into a commercial airplane.

The 777 and the 767-400ER share the same wheels, tires and brakes. The Longer-range 777s share a new and improved gear. Because of its longer length, the 777-300ER uses a new semi-levered gear, which allows it to take off fields with a limited runway length.

High Reliability and Quality

New design and testing initiatives helped ensure the highest possible levels of reliability on the very first 777, compared to what had been possible on previous jetliner introductions. Today’s 777 operators enjoy a 99 percent dispatch reliability rate, which is unmatched in the industry.

Design/build teams, which bring together representatives of the diverse disciplines involved in airplane development, as well as suppliers and representatives of airline customers, allowed team members to work concurrently on the 777-structural and systems designs.

Continuing the “market-driven” approach, four 777 customers had on-site representatives working side by side with Boeing designers to ensure that the new airplane filled their needs. United Airlines, All Nippon Airways, British Airways, and Japan Airlines had teams of two to four engineers’ onsite who were actively involved in developing the 777.

For the first time, Boeing engineers were able to design and electronically pre-assemble the entire airplane on computers, which increased accuracy and improved quality. New laboratory facilities enabled the various airplane systems to be tested together as a single integrated entity in simulated flight conditions — before the first jetliner took to the air. This allowed a smoother transition to flight testing and service introduction.

Among other initiatives, standard certification flight tests were supplemented with 1,000 flight cycles on each airframe/engine combination for the initial 777-200 model to demonstrate reliability in simulated airline operating environments. The Boeing/United Airlines 1,000-cycle flight tests for the Pratt & Whitney engine were completed on May 22, 1995. In addition, engine makers and the many parts suppliers for the airplane intensified their own development and testing efforts to ensure that their products met airline requirements.

On May 30, 1995, the 777 became the first airplane in aviation history to earn U.S. Federal Aviation Administration (FAA) approval to fly 180-minute extended range twin-engine operations (ETOPS) at service entry. On May 4, 1998, the 777-300 achieved another historic milestone by becoming the first commercial airplane to receive type certification and 180-minute ETOPS approval on the same day.

What are your actions following a Pitot static blockage and an attitude indicator failure?

Pitot static blockage:
Pitot heat on
Use alternate static source

Attitude indicator:
Refer to stand-by AI

Why are bleed valves fitted to jet engines?

Several reasons:

Pressurisation
Air conditioning
Anti-icing
Engine start

What is the error of an altimeter at 10 000’ PH at ISA -34?

Over reads by 14%.

What aircraft damage might come about from a lightning strike?

Electrical system damage [current limiter, bus and circuit breakers]
Structural damage [exit hole]
Damage to bearings and compressor/turbine blades

What do you know about TCAS?

The Traffic Alert and Collision Avoidance System (TCAS) alerts the crew to traffic that may present a collision threat, and provides the crew with a vertical avoidance manoeuvre. TCAS is independent of, but does not replace, the ground based ATC system.

TCAS equipment uses the Mode S transponder to interrogate the transponders of other aircraft in the vicinity to determine their range, bearing and altitude. TCAS generates a Traffic Advisory (TA) when another aircraft becomes a potential threat and is approximately 40 seconds from the closest point of approach. No manoeuvres are required for a TA. If the intruder continues to close and becomes an imminent threat, a Resolution Advisory (RA) is generated when the other aircraft is approximately 25 seconds from the closest point of approach. The RA provides a vertical restriction or manoeuvre to maintain or increase separation from the traffic.

Non-transponder equipped aircraft are invisible to TCAS, and no RA is generated for aircraft operating in Mode A only, or without serviceable Mode C (altitude reporting). TCAS has the ability to resolve multiple aircraft encounters.

TCAS displays

Annunciations associated with TCAS are displayed either in the middle of a flat panel improved VSI (IVSI), or on the ADI and HSI, according to the aircraft fit.

A TA is indicated by the aural “TRAFFIC, TRAFFIC” which sounds once, and is then reset until the next TA occurs. On aircraft with the EFIS fit, the TRAFFIC message appears on the HSI, and pressing the TFC switch on the HSI range selector displays the range and relative bearing of the other aircraft. Intruder aircraft are automatically displayed on aircraft with the IVSI fit. If the other aircraft’s transponder is operating in Mode C or S, altitude information and vertical motion, if applicable, are also displayed.

Resolution advisory

RAs are indicated by one or more of the aurals shown in the table below:

Aural meaning

“MONITOR VERTICAL SPEED, MONITOR VERTICAL SPEED” Avoid deviations from the current vertical speed.

“CLIMB, CLIMB, CLIMB” Climb at the pitch required.

“DESCEND, DESCEND, DESCEND” Descend at the pitch required.

“REDUCE CLIMB, REDUCE CLIMB” Reduce climb pitch as required.

“REDUCE DESCENT, REDUCE DESCENT” Reduce descent pitch as required.

“CLIMB, CROSSING CLIMB, CLIMB, CROSSING CLIMB” Directs a climb and informs the pilot that safe vertical separation will result in climbing through the intruder’s altitude.

“DESCEND, CROSSING DESCEND, DESCEND, CROSSING DESCEND” Directs a descent and informs the pilot that safe vertical separation will result in descending through the intruders altitude.

“INCREASE CLIMB, INCREASE CLIMB” Increase climb rate after an initial “CLIMB” RA is received.

“INCREASE DESCENT, INCREASE DESCENT” Increase descent rate after an initial “DESCEND” RA is received.

“CLIMB – CLIMB NOW, CLIMB – CLIMB NOW” Reversal manoeuvre after an initial “DESCEND” RA is received.

“DESCEND – DESCEND NOW, DESCEND – DESCEND NOW” Reversal manoeuvre after an initial “CLIMB” RA is received.

“CLEAR OF CONFLICT” The RA encounter is terminated.

The TRAFFIC message appears as before, and pressing the TFC switch on the HSI range selector displays the other aircraft’s range, relative bearing and altitude on the HSI. An RA pitch indication or manoeuvre appears on the ADI. A manoeuvre is required if any portion of the aircraft symbol is within the red region on the ADI. On those aircraft with the IVSI fit, red and green arcs appear around the outside of the IVSI scale, and manoeuvring is required to position the vertical speed pointer out of the red region and into the green.

An OFFSCALE message appears during a TA or RA if the traffic’s position is outside the selected Traffic Display’s range.

A TA or RA message followed by the traffic’s range, altitude and (if applicable) vertical motion arrow appear on the display if TCAS cannot determine the other aircraft’s bearing.

TCAS inhibits

TCAS alerts are inhibited by GPWS, and Windshear warnings, and at low altitudes where the Traffic Avoidance Manoeuvre would be inappropriate.

If an inhibit occurs during an RA, the RA aural is silenced, and the traffic symbol reverts to a TA symbol. If an inhibit occurs during a TA, only the TA aural is silenced.

Mode control

The TCAS operating mode is controlled from the transponder panel. TCAS is normally operated in the TA/RA (TA and RA) mode. Sometimes it may be necessary to operate in the TA Only mode to prevent undesired RAs.

The TA Only mode is used during engine out operation to prevent RAs when inadequate thrust is available to follow the RA commands. Also, it may be used when intentionally operating near other aircraft that may cause RAs, such as during parallel approaches and VFR operations.

What colours make up the colour spectrum?

Red, yellow and green.

From the cockpit engine indications how could you tell the difference between the 747-400 and the A340-300?

A340-300 N1, N2, EGT
B747-400 EPR, N1, EGT

Describe the construction of an AC generator.

Consists of a rotor, which is an electromagnet

3 coils of stationary windings form the stator

Individually single phase AC is induced in each coil and the resultant output of the generator is 3-phase AC

 

Magnitude of voltage and current depends on:

  • Magnetic field strength

  • Number of windings in the coil

  • Rotation speed

Describe the construction of a DC generator.

Consists of a fixed stator [commutator] and a moving rotor The stator contains 4 electromagnets [older permanent magnets] The rotor is an arrangement of conductors which when rotated cuts the flux lines of the electromagnets in the stator and induces a current. The current is then transferred from the shaft of the rotor by carbon brushes and exits the generator as DC current.

What is a safety cell battery?

A wet battery where the electrolyte is in a gel form.

What is the combustion cycle of a jet engine?

Known as the Brayton cycle of continuous combustion

Characterised by a constant total pressure during the cycle

Intake

Pressure, Temperature and volume remain same

Compression

Pressure, Temperature increase

Volume decrease

Combustion

Temperature and Volume increase

Pressure remains same

What is a fuel dipper?

Essentially a fuel bypass system If disrupted inlet airflow causes a high TGT damage could occur Dippers sense the TGT rise and by-pass fuel, preventing an over-temp situation

Why do engines have auto-ignition?

Prevent flame out by automatically switching on engine igniters if flame propagation is disturbed by disrupted inlet airflow.

What must you check before paralleling a generator?

That the phase, frequency and voltage are the same.

What do Constant Speed Drives [CSDs] do?

They drive accessory generators from variable RPM, providing constant DC generator frequency output.

Each CSD is self-contained [oil supply, temperature indication, disconnect device]. Can be disconnected in flight buy only reconnected on the ground.

What are the basic parameters of an aircraft electrical system? Large aircraft utilise more AC power than DC power for onboard systems and avionics [run at a constant frequency], therefore they have AC generators.

What is the purpose of engine re-light boundaries?

To ensue correct N1 prior to ignition [so no over-temp]
Usually 10-25% N1 depending on TAS

On a wet runway initially what is the most effective way of braking?

Reverse thrust.

When do you turn on engine anti-icing?

In visible moisture with an OAT of +10ºc or less.

Fly by wire

Fly-by-wire is an electronically managed flight control system, which uses computers to make aircraft easier to handle while further enhancing safety. First introduced on a commercial jetliner on the Airbus A320 in 1988, it has become an industry standard.

Pilots manoeuvre their aircraft by controlling the moveable parts, known as flight control surfaces, on the aircraft’s wings and tail plane. Fly-by-wire replaces the mechanical linkage between the pilot’s cockpit controls and the moving surfaces by lighter electrical wires – hence its name. At the heart of the system are computers that convert the pilot’s commands into electrical impulses delivered to the control surfaces.

When this technology, already used extensively on fighter aircraft, was first used on the A320, it was a major achievement for several reasons. Firstly it reduced the weight of aircraft – and therefore the amount of fuel consumed. This in turn lowered operating costs for airlines and benefited the environment by reducing exhaust gas Fly-by-wire technology also provided a considerable safety enhancement with the introduction of hard protection. Indeed, the pilot’s commands to the control surfaces are monitored to ensure the aircraft is kept within a safety margin, called the ‘flight protection envelope’. Thus, the pilot can always get the maximum out of the aircraft in an emergency without running the risk of exceeding the flight envelope or over-stressing the aircraft.

Finally, fly-by-wire technology has also made it possible for Airbus to develop a true family of aircraft, from the 107-seat A318 to the 555-seat A380, with near identical cockpit designs and handling characteristics. This makes crew training and conversion shorter, simpler and highly cost-effective for airlines and allows pilots to remain current on more than one type simultaneously.

Mixed Fleet Flying

Building on Airbus’ operational commonality, a growing number of airlines are implementing Mixed Fleet Flying (MFF). With MFF, a pilot can be current on more than one fly-by-wire aircraft type simultaneously and can regularly switch from short and medium-haul operations on the A320 Family to very long-haul flights on the A340, for example.

Everyone benefits from the MFF concept. The long-haul pilot, switching to short-haul gets more take-off and landing opportunities, which eliminates the need for currency training, and is less subject to sleep-cycle disruption. Short-haul crews switching to long-haul are subject to less fatigue from intense traffic high-cycle operations. For airlines, the increase in revenue hours flown by pilots for the same duty hours due to less standby and “dead time” means a significant improvement in productivity.

MFF also enables airlines to interchange differently sized aircraft at short notice without crew-scheduling difficulties, allowing them to better match aircraft capacity to passenger demand.

Total CCQ and MFF improvements can lead to a saving of up to $1,000,000 annually, for each new Airbus aircraft added to the fleet, a significant advantage in today’s economic environment.

Cross Crew Qualification

Cross Crew Qualification (or CCQ) is a unique concept developed by Airbus, which gives pilots the possibility of transitioning from one Airbus fly-by-wire family type to another via differences training instead of full transition training. The Federal Aviation Administration approved the CCQ concept in 1991. For example, pilots transitioning from an A320 Family aircraft to the larger A330 or A340 need only eight working days for CCQ instead of 25 working days for a full type rating training course. Pilots transitioning from the A330 to the A340 require only three days, and to move from the A340 to the A330, one day only.

These time savings lead to lower training costs for airlines and considerably increase crew productivity. The annual savings in payroll cost, through improved productivity only from the reduced transition time can be $300,000 annually for each new Airbus aircraft added to the fleet. It is also more economical for an airline to recruit new pilots who are already Airbus-qualified. For pilots, this benefit provides greater mobility and better prospects for employment.

Airbus commonality

Commonality is a unique feature of Airbus’ new generation of jetliners, developed thanks to the introduction of fly-by-wire. Offering airlines increased flexibility and cost-efficiency; it has become one of the keys of Airbus’ success.

Airbus developed full design and operational commonality with the introduction of digital fly-by-wire technology on civil aircraft in the late 1980s. As a result, ten aircraft models, ranging from the 100-seat A318 through to the world’s largest aircraft, the 555-seat A380, feature very similar flight decks and similar handling characteristics. In many cases, such as the entire single-aisle A320 Family, the aircraft in fact share the same pilot type rating, which enables pilots to fly any of them with a single licence endorsement. The benefits of commonality for operators include a much shorter training time for pilots and engineers to transition from one type to another. It also leads to significant savings through streamlined maintenance procedures and reduced spare parts holdings, with common parts accounting for as much as 95 per cent within the single-aisle family for example.

Commonality also offers schedule planners an unparalleled level of flexibility as aircraft of different sizes, such as the A320 and the A330, can be operated and maintained by the same teams, as a single aircraft fleet. It also offers pilots the possibility of flying a wide range of routes – from short-haul to ultra-long-haul. Commonality has proved to be a major economic and commercial advantage for Airbus operators.

What are the advantages of the 747-400 over the 747 classic?

Better fuel economy and lower DOCs [8-11% more fuel efficient]

Increased range [1150nm]

Internally

2 pilot flight deck [no Flight engineer]

Glass cockpit [1/3 the buttons/switches and checklists]

CAT 3B Autopilot

Improved cockpit sound proofing

Increased use of fire resistance materials

11000kg BEW saving with use of alloys and composite materials

BRW increased from 377 850kg to 396 900kg

Crew rest facilities

Stabiliser tank [increased range/aft C of G]

Higher power APU

Externally

Increased wingspan [12′]

Winglets [drag reduction]

Newer, more efficient engines [H wide chord fan, T Trent hot section]

Winglets [drag reduction]

Carbon brakes

Ability to use speed brakes and flaps simultaneously

What uses does bleed-air have?

Engine starting
Air-conditioning and pressurisation
Anti-icing

What are the advantages of a centrifugal compressor?

Lightweight
Rugged and FOD resistance
Simple [for maintenance]
Low cost
High compression ratio [number of stages are limited]

Explain truck tilt.

Designed to fit landing gear in the wheel well Numerous systems operate off truck tilt ground logic [spoilers, pressurisation etc.]

How does a fire wire work?

Fire wire consists of 2 conductive wires surrounded by a substance, which becomes conductive when heated, and then the whole component is shrouded. When enough heat is applied, a circuit is completed and the fire warning will sound. Evan if the wire is broken it can still operate normally, though depending on the instillation it may not test normally.

What are balanced hydraulic actuators and what are their main advantage?

It is one with fluid pressure on both sides. It is used to provide control feel.

What is the fuel saving on the 747-400 compared to the classic?

10-11%

What is by-pass ratio?

The ratio of fan [N1] airflow to engine [exhaust] airflow
CFM56-5C: 6.6 to 1
RB211-524GH/T 5.1 to 1

What is the difference between a Turbojet, Turbofan and a Turboprop?

Turbojet: All thrust from exhaust
Turbofan: Thrust a mixture of exhaust and by-pass air
Turboprop: Nearly all thrust produced by the propeller [sometimes a small amount may be produced by the exhaust depending on the design]

How do bleed valves assist during engine start and acceleration?

They open to dump pressure allowing easier compressor acceleration.

What kind of power supplies an EGT gauge?

None, they are thermocouples.

What are the formulas for calculating approximate hydroplaning speeds?

Wheels locked 7.7 x √ tyre pressure [psi]
Wheels spinning 9 x √ tyre pressure [psi]

What are the three types of hydroplaning?

Dynamic:

Standing water on runway

Tyre is completely lifted off the runway and supported by the water

Viscous:

Surface is damp and there exists a very thin film of fluid, which cannot be penetrated by the tyre, occurs and persists down to much lower speeds than dynamic.

Surface is usually smooth, such as the touch down area.

Reverted rubber:

The heat from friction between the runway and the tyre causes the rubber to become tacky, the water boils, which forms a seal and delays water dispersal.

How does a blown main tyre affect ASD?

Increases ASD due to reduced braking effectiveness

Prior to take-off, what do tyre temperatures depend on?

Aircraft weight
Taxi length/time
Brake usage
Turn around length or time since RTO
Tyre-flex [cornering speed]

On a double wheeled bogie, which brake gets the hottest?

Rear wheels suffer reduced braking efficiency as they receive less airflow and what airflow they receive is heated from the brakes in front.

What reduces braking efficiency?

Brakes require maximum heat dissipation for maximum efficiency [the cooler the brakes, the better]. A thin brake pad also reduces efficiency.

What are the disadvantages of carbon brakes?

More expensive
Don’t give much feel

What are the advantages of carbon brakes?

  • 40% lighter [300-800kg weight saving, depending on the aircraft]
  • Higher thermal efficiency means they maintain effectiveness at higher temperatures.
  • Last longer 2500-3000 landings as opposed to 2000 landings
  • Absorb more heat [up to 3000ºF]
  • Don’t lose their strength as they heat up
  • Can be re-used by fitting 2 worn pads together

How does a turbine engine work?

Air is compressed
Fuel is then added
Ignition takes place
The gasses expand and pass over a turbine/turbines
Gasses are then exhausted providing thrust

Explain the operation of an Air cycle machine.

Air to air heat exchanger, cooling turbine [30-60ºF cooler than OAT]

Why are bleed valves fitted to jet engines?

Pressurization/air-conditioning Anti-ice/De-ice Engine starts

When might we use continuos ignition?

Take-offs in strong crosswind
Take-offs and landings whenever the runway is wet
Flight near thunderstorms
Flight through heavy rain
Before selecting engine anti-ice

What is TSFC?

Thrust Specific Fuel Consumption, the amount of fuel required to produce 1 pound of thrust for one hour

What are the advantages of a Fan engine?

↑ Propulsive efficiency

↓ Fuel burn

↑Thrust to weight ratio

↓Noise levels [bypass air mixing with exhaust]

What are the advantages and disadvantages of pod mounted engines?

Advantages:

  • Depending on geometry and design cruise Mach number, interference drag is minimised
  • Intake efficiency is rarely compromised [pods are in clear air]
  • Engines provide bending relief reducing wing structure weight
  • The wing profile is not compromised
  • At high angles of incidence the pylons tend to act as fences, reducing span-wise flow
  • Less acoustic damage to the airframe
  • Thrust reverser design is comparatively uninhibited
  • Good engine accessibility
  • Less overall damage in the event of a gear-up landing

Disadvantages:

  • Greater asymmetric yawing moment
  • Roll freedom near to ground is reduced
  • Low thrust line can have adverse effects on longitudinal control [nose down pitching moment with thrust reduction and vv]
  • Swept wing 4 engined aircraft may suffer disturbed inlet airflow during reverse thrust application
  • Low mounted engines are more susceptible to FOD ingestion

What is the fundamental difference between the CFM engines and the Rolls Royce engines?

The Rolls Royce engines are triple spooled where as the CFM engines are two spooled.

What spool is the accessory gearbox driven off on the RB211-524?

N2

How do you start the RB211-524?

  • Pulling the Start switch out [held out by a solenoid], opens
    the start and engine bleed air valves
  • The Start light illuminates
  • At 25% N3 or maximum motoring, the Fuel Control switch is moved to RUN
  • The spar, fuel metering, and engine fuel valves open and the selected igniter energizes
  • One igniter is normally selected for ground start while two igniters are selected for in-flight start
  • Starter cut-out occurs at 50% N3 RPM
  • At starter cut-out, the Start switch is released to the in position, the start and bleed air valves close, the Start light extinguishes, and ignition discontinues
  • The start must be monitored until the engine stabilizes at idle

What can you tell me about the RB211-524?

Triple spooled engine

Physically smaller than other similar engines [3 spools]

Less shaft-flex and distortion [longer life]

3 sections mean each section works closer to its optimum

N1 100% = 3900rpm
N2 100% = 7000rpm
N3 100% = 10611rpm

Easier to start as only 1 shaft needs to be turned

Better thrust to weight ratio than competitors

Better propulsive efficiency

Lower fuel consumption

Reduced noise

Slightly heavier due to the extra spool

86.3″ fan diameter [75% of thrust]

Modular construction [easier to build and maintain]

Seven-stage IP compressor

Six-stage HP compressor

Single annular combustor with 24 fuel burners on the G/H-T

Single-stage HP turbine, single-stage IP turbine and a three-stage LP turbine

How much thrust is produced by a Cathay Pacific 747-400’s engine?

They are rated to 60600lbs [RB211-524 G/HT]

Why do jets use reduced thrust take offs?

Thrust reduction or de-rate, lowers EGT, and extends engine life. Also may be applicable for noise abatement. Will reduce Vmca due to less thrust produced

What is assumed temperature used for?

It is used to ‘trick’ the FMC into thinking the ambient conditions are hotter than actual, enabling take-offs to be performed using less than full rated thrust.

What are the advantages of a wide chord fan engine?

  • Better aerodynamic efficiency
  • ↑ Thrust
  • ↓ Noise Better
  • FOD resistance

What is the difference between N1 and EPR?

EPR is the Engine pressure ratio where N1 is the speed of the fan of low-pressure shaft. N1 may be used to assess engine thrust, but it doesn’t give an absolute indication of the thrust being produced because inlet temperature and pressure conditions affect the thrust at a given engine speed.

If EPR increases with constant power on descent, what does this indicate?

An EPR malfunction, probably a blocked/iced up PT2 probe

Why do we usually set take off EPR prior to 80kts?

Because of the ram-rise effect you need to accurately set the EPR to ensure correct thrust setting on take-off.

What happens to EPR on the take off roll?

It increases due to the ram-rise effect. The air entering the intake effectively has more energy due to the airspeed increasing.

What are the advantages of a High-bypass fan?

Increased mass airflow, reduced exhaust velocity reduces noise, lower specific fuel consumption.

How does a High-Bypass Turbofan work?

The large front-mounted fan of a high-bypass turbofan draws in huge volumes of air, on the order of 2400 pounds/second. Of the total volume of air that is drawn in by the fan, as little as 10% of it will actually pass through the engine’s core [compressor, combustor, turbine]. In the compressor, the air’s pressure will increase by up to 40 times and the temperature will greatly increase.

The hot, pressurized air from the compressor is mixed with a steady stream of fuel and then ignited in the combustor to create a flame. The shape and perforations of the combustor allow the pressurized air to then expand, slowing it down enough to sustain the flame continuously [as long as fuel is supplied]. A number of turbines are driven by the gases from the combustor. The high-pressure turbine, located just behind the combustor, uses the energy of the exhaust gases to power the compressor. The low-pressure turbine located after the high-pressure unit powers the front-mounted fan as speeds of 5,000 rpm for large fans. Generally, the smaller the fan, the faster it moves.

Up to 90% of the air pulled in by the fan is channelled around the major components of the engine, bypassing the compressor, combustor and turbine. This bypass air flows into the narrow part of the nacelle [the engine casing] and then through the nozzle, where it meets up with the hot exhaust created during combustion.

The exhaust and the bypass air will exit the engine through another nozzle – the core nozzle. The net difference between the speed of the air entering the engine at the fan and the speed at which it leaves at the nozzle is thrust.

Large commercial airliners use a turbofan jet engine. Turbofans use the same compressor, combustor and turbine common to all turbojet engines. The difference is the addition of a large fan mounted to the front of the engine. These fans, some as large as 10′ in diameter, draw air into the engine. Some of the air is sent to the compressor and the combustor, while the rest bypasses these components through ducts on the outside of the engine.

Most turbofans in use today are designated as high-bypass turbofans, where the ratio of bypass air to the air directed into the compressor is 5:1 or greater. At subsonic speed, high-bypass turbofans are more fuel efficient and quieter than other types of jet engines, making them ideally suited for commercial aircraft. It is the fan, and the high volume of air it pulls in which creates most of the engine’s thrust at takeoff. [General Electric]

Why do we (CX) use EPR instead of N1?

Rolls Royce engines use EPR calculations to set thrust. All Cathay Pacific’s 744s have Rolls Royce engines. GE use %N1 to set thrust.

Do we still need to know how fast the fan is spinning if we set EPR?

Yes. You need to know it’s within engine rpm limits.

How do we set thrust on the B747?

Set the calculated EPR.

What is Integrated EPR?

Integrated EPR applies to Rolls Royce engines such as the RB211 where the exhaust gas and the by-pass air from the fan are integrated in the jet pipe as exhaust.

What is N1?

N1 refers to the speed of the low-pressure shaft [fan]. It is expressed as a percentage of the maximum N1 rpm.

What is EPR?

Turbine engine output on a High by-pass fan engine may be measured in a number of ways. Engine Pressure Ration [EPR] is the ratio of engine jet pipe pressure to the compressor inlet pressure. An EPR of 1.0 means the engine is producing no thrust. [Rolls Royce]
RB211 5:1

Trent 800 6-9:1

How does Doppler radar work?

A Doppler radar is used to detect wind shear It uses the principle of Doppler shift

How does Iso-Contour radar work?

Iso-contour radar is a type of primary radar used for weather detection. Pulses of radio waves are transmitted ahead of the aircraft in a sweeping motion and returns are received from reflection of the radio waves off precipitation. Range is a function of elapsed time between TX and RX, The steeper the contour gradient [on the display] the greater the presence of precipitation including rain, wet hail and possible associated turbulence and micro burst activity. [Hooks, scallops, fingers Etc.]

How does anti-skid braking work?

  • Prevents a locked wheel situation, maintaining aircraft control
  • A control unit receives input from wheel speed transducers which sense a wheel locked situation or an excessive slow down
  • A control valve then releases hydraulic pressure allowing the wheel to regain traction and spin up
  • Anti-skid illuminated denotes a system failure [dark cockpit]
  • Auto-brake failure doesn’t mean anti-skid failure

What would happen if it failed?

Anti-skid fail warning would illuminate [dark cockpit]

I would think about:
You would need to plan for a landing on the most appropriate runway [the longest]
Careful application of braking would be required depending on the landing surface conditions [dry/wet]

Why shouldn’t you use reverse thrust at low airspeeds?

To avoid FOD ingestion
To avoid compressor stall

Thrust reversers, when do we use them?

During landing and carrying out a rejected take-off.

When are they most effective?

At higher speeds.

Describe fuel management in the A340-600.

Automatic tank usage is sequenced in the following, priority order:

  1. Centre
  2. Trim
  3. Outer wings
  4. Inner wings
  5. Collector cells

Describe fuel management in the A330/A340-300.

Automatic tank usage is sequenced in the following, priority order:

  1. Centre [not on A330]
  2. Inner wings [to a prescribed level]
  3. Trim
  4. Outer wings
  5. Inner wings
  6. Collector cells

On departure after passing FL255, Fuel Control and Monitoring Computers [FCMCs] have a built-in C of G control band which is approximately 2% MAC forward of the certified aft limit. The calculated C of G is compared to the target and an appropriate amount of fuel is transferred to the trim tank. The process is fully automated. In a max fuel case, no aft transfer is possible. From this point and because of continuing tank depletion, the C of G will move aft [initial depletion of the inner wing tanks is the exception]. If the aft C of G is reached, there will be forward transfers equivalent to 0.5% MAC. The process will continue until 75 minutes before destination, when any remaining fuel in the trim tank will be transferred forward. [Airbus]

Describe fuel management in the B747-400.

1.Centre tank
2.Stab tank [flows into centre tank]
3.Inboard tanks [down to a prescribed level]
4.Tank to engine [inner/outer mains 1-4]

Why does the 747-400 have stabilizer fuel tanks?

More fuel equals more range and weight in the tail of the aircraft will mean a more rearward C of G which will reduce the stabilizer aerodynamic down force required and consequently reduce total drag and fuel burn.

Where do we keep fuel in the B747?

  • Horizontal stabilizer
  • Centre tank [fuselage]
  • Wing tanks [inner/outer]