AE2252 AIRCRAFT SYSTEMS AND INSTRUMENTS Two Marks Questions With Answers 2014

Anna University, Chennai




1. What is fly by wire system?

Unit I

For a fly by wire system all the inputs are converted corresponding electrical signals and transmitted to the actuators through electrical wires. Some of advantage of fly by wire system

Weight saving

Improved handling

Fuel saving

Reduced maintenance

2. What is meant by ILS?

An instrument landing system (ILS) is a ground-based instrument approach system that provides precision guidance to an aircraftapproaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument meteorological conditions (IMC), such as low ceilings or reduced visibility due to fog, rain, or blowing snow.

3. What are the advantages of fly by wire system?

Weight saving

Improved handling

Fuel saving

Reduced maintenance

4. What do you understand by push pull rod system?

A stiff rod or hollow tube in an aircraft control system that moves a control surface by either pushing it or pulling it.

5. List out the components of instruments landing system. Localizer, Marker beacons (Inner, Middle & Outer), Glide scope

6. In what way the instrument landing system differ from ground controlled approach?

In aviation a ground-controlled approach (GCA), is a type of service provided by air- traffic controllers whereby they guide aircraft to a safe landing in adverse weather conditions based on radar images.

An instrument landing system (ILS) is a ground-based instrument approach system that provides precision guidance to an aircraftapproaching and landing on a runway,

7. What are the purposes of SELCAL and INTERPHONE systems?

The selective calling (SELCAL) system operates in conjunction with the VHF andHF systems, and provides a visual and aural indication when the airplane is beingcalled. SELCAL enables ground facilities to selectively call an individualairplane.

The service interphone system allows communication between the various serviceand maintenance areas, the cockpit, and the cabin attendant stations.Telephone-type handsets in the cockpit and at the forward, mid and aft attendantpanels are used for both the service interphone system and the PA system.

8. List down the uses of the communication system in a modern airliner.

HF (High Frequency) communication for long range

VHF (Very High Frequency) communication for short range

Sat Com (Satellite Communication)


To communicate between aircraft to aircraft, aircraft to airport, aircraft to ATC

9. Name any four modern control systems?

- Fly by wire (computer):- May be Analog computer or digital computer

- Fly by optics (light):-

- Power by size (user electro-hydraulic actuators

- Intelligent flight control system

10. What do you mean by active control technology? Give at least three examples?

Activate control technology helps to improve the handling of aircraft and to reduce the time lag or control delays by increasing the no. of computers, etc., in the aircraft (i.e. redundancy). This advance concept in applicable to following e.g.

- Fly by wire

- Control configured vehicles

- Automatic flight control system.

Unit II

1. How do you classify the airbrakes for an aircraft?

Air brakes or speed brakes are a type of flight control surface used on an aircraft to increase drag or increase the angle of approach during landing.

2. What are the advantages of pneumatic system over hydraulic system?

Simplicity of design and control—Machines are easily designed using standard cylinders and other components,

Reliability—Pneumatic systems generally have long operating lives and requires little maintenance.

Gas absorbs excessive force, whereas fluid in hydraulics directly transfers force.

Compressed gas can be stored, so machines still run for a while if electrical power is lost.

Safety—there is a very low chance of fire compared to hydraulic oil.

3. What is the need of moisture control in aircraft pneumatic system?

The aircraft pneumatic system need to be moisture control because it affects the pressure of the gases and reduces the system performance.

4. Distinguish between hydraulic and pneumatic system

Pneumatic systems use compressed gas such as air or nitrogen to perform work processes.

Pneumatic systems are open systems, exhausting the compressed air to atmosphere after use.

Hydraulic systems use liquids such as oil and water to perform work processes.

Hydraulic systems are closed systems, recirculation the oil or water after use.

One of the main differences between the two systems is that in pneumatics, air is compressible. In hydraulics, liquids are not.

5. List out the different types of selector valves in hydraulic systems.

Selector valves are used in a hydraulic system todirect the flow of fluid.Three general types of selector valves are

(a) poppet,(b) slide,and (c) solenoid-operated valves

6. Differentiate between the check valve and non return valve.

A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid (liquid or gas) to flow through it in only one direction.

7. Differentiate between springs oleo struts and air oleo struts?

In spring oleo struts, the spring supports the A/C weight on the ground and during taxiing and oleo strut aborts the shock of landing.

In air oleo struts, the air supports the A/C weight on the ground and abserts shocks during taxiing and oleo strut aborts the shock of landing.

8. Differentiate between single disk brake and multiple disk breaks?

Single disk brakes are used in smaller aircraft single disk may be conducted with a many separate pistons and linings as needed for the airplane. Each piston in equipped with separate sets of linings, which bear against the brake disk when the brake see applied multiple disk brakes are used in large aircraft. Braking action is produced by hydraulic pressures forcing the pistons against the pressures plate, which, in turn, forces the disk together and create friction between the retracting and stationary disks.

9. Differentiate between expander – shoe brake and expands – tube brake?

Expander shoe brake: Relation of break drum adds braking energy to the break shoes and makes them operate more effectively & with Len effort by the pilot. They are also known as serve brakes.

Expander tube break: The pressure of hydraulic fluid in the tube forces the blocks radically outward against the break drum.

Unit III

1. How do you select the ignition system for an aircraft?

The ignition system for an aircraft must be capable of delivering a high voltage spark to each cylinder under all condition

The spark must be created and delivered at the correct moment during the operating cycle

The ignition system must have high degree of reliability.

2. What are the advantages of air turbine starters?

Self-contained starts possible for large engines

Very high torque-to-weight ratio

Quick starts possible for military

3. Why mineral base fluids are preferable in small aircrafts hydraulic systems?

It is petroleum based hydraulic fluids

It do not mix with vegetable base

Cost is less

4. List out the aircraft engine lubrication oil requirements.

The oil should highly viscous

The oil must able to withstand the high temperatures

It should be in light color

5. Give main requirements of hydraulic fuels.

Low compressibility (high bulk modulus)

Fast air release

Low foaming tendency

Low volatility

6. Distinguish between fuel system of piston and jet engine

Piston engine fuel system

Jet engine fuel system

To feed fuel for combustion process

To feed fuel for combustion process

Eg: gravity feed system, pressure

feed system

Engine driven pump system

7. List out the main requirements of a typical starting system of a gas turbine engine.

The starting system must capable of producing initial torque.

It must senses the speed and disengage the unit after starting

The starting system should be light weight

8. List down lubricants used in the aircraft lubrication systems.

Vegetable based hydraulic fluid,

Mineral based hydraulic fluid,

Phosphate ester based hydraulic fluid,

synthetic based hydraulic fluid

9. What are the main functions of engine oil in the oil system?

There are at least five main functions of engine oil:

Cool--absorbs heat as it is circulated, cooling the engine.

Lubricate--creates a viscous barrier between moving parts that reduces friction, which means less heat and longer life for those parts.

Clean--small particles of dirt or other contaminants are suspended in oil and carried away to be filtered out.

Seal--helps to seal the space between the pistons and the cylinder walls so that compression is more effective and power is not lost during combustion.

Protect--coats parts to provide a layer of protection against corrosion/rust.

10. Differentiate between nigh tension ignition system & low tension ignition system?

- Magneto Ignition system operate on the principles of electro magnetic induction. They can be high tension & low tension ignition system.

- High tension magnetic Ignition system High voltages are induced either by rotating the transformer windings between poles of permanent magnet or by rotating the magnet between fixed transformer windings car by rotating soft iron bass between fixed permanent magnets and transformers winding.

- Low tension magnate Ignition system then system were developed far engineer having large no of better then high tension. In this, the low voltage impulses from the magneto primary are directly supplied to the distributor. The low tension magnet are suited on and off similar to the high tension magneto.

Unit IV

1. What is meant by anti icing and deicing?

De-icing means removing ice that has already farmed.

Thermal anti-icing heated air flowing through passages in the leading edge of wings, Stabilizers and engine cowlings tee pre unit the formation of ice

2. List out the types of over heat detectors used in fire protection system.

Thermal switch system

Fenwal spot detector

Thermocouple system

3. What are the methods available to provide heated air to the thermal anti-icing system?

Anti icing using combustion heater

Anti icing using exhaust heater

Anti icing using engine bleed air

4. Distinguish between air cycle cooling and vapour cycle cooling.

Air cycle machine:- The turbine, compressor unit by which air is cooled is called air cycle machine(ACM) The ACM user compression and expansion of air to lower the temperature of cabin air.

Vapor cycle machine: - User refrigerant instead of air the vapor cycle machine in a closed system usury the evaporation and condensation of Freon to remove heat from the cabin interior.

5. What is the need for pressurizing the aircraft cabin?

Cabin pressurization is the pumping of compressed air into an aircraft cabin to maintain a safe and comfortable environment for crew and passengers when flying at altitude. Pressurization becomes necessary at altitudes beyond 10,000 feet (3,000 m) above sea level to protect crew and passengers from the risk of a number of physiological problems caused by the low outside air pressure above that altitude


Altitude sickness.

Decompression sickness.


6. How is cabin pressure dumped?

All exhaust air is dumped to atmosphere via an outflow valve, usually at the rear of the fuselage. This valve controls the cabin pressure and also acts as a safety relief valve, in addition to other safety relief valves.

7. Differentiate between the anti-icing and de-icing method used in aircrafts.

De-icing is defined as removal of snow, ice or frost from a surface.

Anti-icing prevent adhesion of ice to make mechanical removal easier.

8. What do you mean by purging the system?

In vapor cycle refrigeration system, purging means releasing the refrigerant. In fuel system, purging means draining the fuel from tank by introducing inert gas as co2 or N2 to the tank. In oxygen system, purging means releasing oxygen from the system.

9. What is shirt sleeve environment?

In order to make the cabin environment comfortable for the air craft occupants, the cabin must normally be pressurized to maintain the cabin air pressure at the level reahed at no higher than 800 it. This enables the crew and passengers to function without the uses of supplemental oxygen and, with adjustments of the cabin air temperature, allows them to be in a shirt sleeve” environment.

10. Differentiate between super changer and turbo charger?

A supercharger is an engine drive air pump; mechanically drive for engine, which compresses air for use by the engine in the combustion process.

A turbocharger is used in a similar manner as a system charger except that the turbo charger is driven by exhaust gases from the engine, which driver an air

compressed to supply an air charge to the engine.

1. What is principle involved in ADF?

Unit V

ADF (Automatic direction finder) are radio receiver equipped with the directional antennas which are used to determine the direction from which signal are received.

2. Distinguish between engine instruments and navigation instruments.

Engine instrument - are designed to measure the quantity and pressure of liquids (fuel and oils), r.p.m, and temperature

Navigation instruments - provides information that enables the pilot to guide the aircraft accurately along the definite courses

3. What is the principle involved in air speed indicator?

The airspeed indicator or airspeed gauge is an instrument used in an aircraft to display the aircraft's airspeed, typically in knots, to thepilot. Airspeed indicators work by measuring the difference between static pressure, captured through one or more static ports; and stagnation pressure due to "ram air", captured through a pitot tube.

4. What are the different types of aircraft pressure gauge?

oil pressure gauge

manifold pressure gauge

air pressure gauges

5. Mention the aircraft pressure gauges.

oil pressure gauge

manifold pressure gauge

air pressure gauges

6. What are TAS and EAS?

The true airspeed (TAS; also KTAS, for knots true airspeed) of an aircraft is the speed of the aircraft relative to the air mass in which it is flying. The true airspeed is important information for accurate navigation of an aircraft.

Equivalent airspeed (EAS) is the airspeed at sea level in the International Standard Atmosphere at which the dynamic pressure is the same as the dynamic pressure at the true airspeed (TAS) and altitude at which the aircraft is flying. In low-speed flight, it is the speed which would be shown by an airspeed indicator with zero error.

7. What is the principle involved in accelerometer.

An accelerometer is a device that measures proper acceleration. The proper acceleration measured by an accelerometer is not necessarily the coordinate acceleration (rate of change of velocity).

8. Discuss the principle in which the temperature gauges functions.

Thermometers filled with either a liquid such as mercury or an evaporating fluid as used in refrigerators in both cases the inside of the sensor head and the connecting tube are completely full any rise in temperature produces expansion or evaporation of the liquid so the sensor becomes pressurised. the pressure is related to the temperature and it may be indicated on a simple pressure gauge.

9. How is cabin pressure dumped?

All exhaust air is dumped to atmosphere via an outflow valve, usually at the rear of the fuselage. This valve controls the cabin pressure and also acts as a safety relief valve, in addition to other safety relief valves.

10. What are the navigation instruments?

VHF Direction Finder (VDF)

NDB non- directional beacon

ADF Automatic direction finder

GPS global positioning system

11. How can use measure RPM of engine?

- By Electronic Tachometer

- By electrical Tachometer

- By Magnetic Tachometer