General Systems

Why large aircrafts generally use Hydraulic Powered Actuation Systems?. Additional typical factors are good response time, efficiency, reliability and robustness of hydromechanical systems when compared with another systems. Water hammer is negligible in hydraulic system pipe installation. Hydraulic Pumps generally used in aircraft hydraulic systems are gear type and capable to provide roughly same pressure at any flow demand (if below specified max flow demand). Hydraulic Pumps generally used in aircraft hydraulic systems are variable displacement piston-type and capable to provide roughly same pressure at any flow demand (if below specified max flow demand). High hydro-mechanical stiffness and associated high frequency response is relevant for flight control actuation.

Generally, with regards to the number of hydraulic systems used in a civil type certified large aircraft under Part 25 - EASA Airworthiness Regulations: There is no any aircraft using two hydraulic systems. If any primary flight control is required to be hydraulically powered, definitively three hydraulic systems are required. Large aircrafts with two engines and three hydraulic systems normally requires a PTU (Power Transfer Unit) to transfer hydraulic power between the hydraulic systems in determined failure cases or for ground taxing with one engine shut down. If the aircraft's hydraulic system supplies all the primary (PFC) and secondary (SFC) flight controls and there is no manual reversion, then usually a minimum of three hydraulic systems will be required. If hydraulic system supplies no primary flying controls, then usually only a single main hydraulic system is required.

Aerodynamic heating is given, basically, by the total temperature of the air computed as follows Ttot = Tambient (1+ 0.2 * Mach2). Given an ISA atmosphere, the heating is maximum in one of the following conditions: 40 kft, Mach=0.8. Sea Level (SL), Mach=0.4.

Select the correct response(s): Water hammer is negligible in hydraulic system pipe installation. Hydraulic Pumps generally used in aircraft hydraulic systems are gear type and capable to provide roughly same pressure at any flow demand (if below specified max flow demand). Relief valves are used to relieve excessive pressure in a blocked line condition. Relief valves do not react rapidly enough to prevent water hammer excessive pressure spikes. Use of check valves in return lines generally avoids effects of back pressure.

If the aircraft hydraulic system supply the services that control the direction of the aircraft on the ground (e.g. nosewheel steering and differential braking): The emergency braking system must have differential control. The nosewheel steering and normal brakes are supplied by different hydraulic systems. The nosewheel steering usually has differential control.

Common use Aerospace Hydraulic Pumps: Either Engine Driven or Electrical Motor Driven, are normally located in Engine Nacelle. Engine Driven Pump EDP (Variable displacement Pump) usually used as the main power source for hydraulic systems. Electric Motor driven pump can be used for normal backup, emergency and ground servicing operation of hydraulic systems. (DC allows use on ground). Manually operated pumps: backup pump (only for small aircraft), for ground maintenance, to recharge a parking brake accumulator, to refill hydraulic systems.

Which one of the cooling methods will provide the best performances in terms of thermal conductance (watt/degK): Water. Air. Fluorochemical Liquids. Fluorochemical Vapor. Silicone oil.

Common use Hydraulic Reservoirs: Do not need pressurization. Vented type reservoir is sufficient whenever located above the pump. There shall be no hydraulic reservoirs located in a designated fire zone. The interior pressure must be enough to avoid pump cavitation at Pcrit. All are pressurized (bootstrap) type. Generally are bootstrap type and air pressurized, but not limited to. Hydraulic pressurized reservoirs utilize system pressure acting on a different piston to achieve the required tank pressure.

Minimum standard ventilation to maintain CO2 levels in enclosed spaces is (at SL, 15 ºC) according to ASHRAE. 1.5 kg/min of air. 15 kg/min of air. 1 kg/min of air. 0,5 kg/min of air. 7,21 L/sec of air. 15,28 ft^3/min of air.

The RAT (Ram Air Turbine) is a device that, when deployed, acting as ram air generator. In case of Total Engine Flame Out (TEFO), can provide hydraulic and or electrical power to the essential systems to ensure the aircraft control during its descent until landing. It can provide power to re-start the engines in flight. RAT requires a minimum airspeed. RAT size shall be defined to supply emergency loads in the emergency configuration.

Redundancy in cabin pressurization outflow valves is requested. Always. Never. In some cases.

Select the correct response(s) regarding the hydraulic systems' protection devices: The “Priority Valve” is a device typically used to isolate the power supply to general services (utility subsystems) when it is required to preserve the supply to critical services (generally, primary flight controls). Fuse (two types: quantity and flow fuses): This component typically senses the flow rate and/or fluid volume through it so that if the rated value is exceeded, the fuse will close. Shutoff valves are electrically operated (e.g. signaled by the hydraulic reservoir quantity sensor through computer monitoring system).

CFG main advantages compared with VFG are: Better reliability. Mechanic simplicity. Constant frequency output not dependent on engine speed. Less weight. Lower probability of overvoltage. Cheaper. Less volume and weight for the same power delivered.

The emergency system shall power the services necessary to complete a flight and make a safe landing. The services to be powered must include: Those required for descent, approach and landing. Continued controlled flight. Immediate safety. Those required to ensure passenger comfort during the emergency landing.

A deicing system is basically sized to limit quantity of ice accreted. What is the worst flying condition in terms of design: Low Speed, high outside ambient temperature. Low Speed, Low outside ambient temperature. High Speed, high outside ambient temperature. High Speed, Low outside ambient temperature.

New high voltage levels (270 Vdc and 230 Vac) are applicable to civil and military electrical systems since they permit to: Reduce electrical power demand. Increase hydraulic Systems. Increase generated power for a defined size of generator. Decrease losses in feeders and distribution wiring. Reduce current level. Reduce cross section of wire (save weight -> fuel saving). Reduce voltage drop in lines.

Which two of the conditions below are equivalent in terms of water catch: 0.1 grm/m2 @ 20m/sec and 0.5 grm/m3 @ 50 m/sec. 0.5 grm/m3 @ 20m/sec and 0.1 grm/m3 @ 50m/sec.

Electrical power quality is determined by: The electrical power generation equipment. The electrical consumers. The interactions of all the electrical generation and supplied equipment. Some characteristics such as: voltage level, frequency margins, transient response, total harmonic distortion...

Li-Ion battery technology main advantages compared with Ni-Cd ones are: Maintenance free and higher service life. High Power capability. Lower weight. Better control of the SoC (State of Charge).

Which are the key features of the Solid State Power Controller?. Maintenance free and higher service life. Less susceptible to abuse conditions. Less weight for the same power delivered. Better control of the SOC. Lower Cost. Storage of batteries shall not be monitored.

LED technology main advantages compared with HID one are: Higher maximum operating temperature. Better performance. Higher reliability. Higher heat dissipation. Lower power consumption. Higher effective illumination power. Lower cost.

What of the following exterior lights have their illumination performances covered by the EASA Part 25 requirements?. Taxi lights. Navigation lights. Anti-collision lights. Landing lights. Wing/Engine lights.

Which of the following are functions of the APU systems used in AIRBUS Aircrafts?. To supply full hydraulic power to the aircraft systems up to 42000 ft. On Ground Electrical & Pneumatic demands from the A/C systems. To provide enough energy without any external means on ground during 12 hours. In flight Electrical & Pneumatic demands from the A/C systems, relieving or supplementing the main engines. To assist the Main Engines re-start in windmilling.

The biggest problem in humans associated to exposure at high altitudes is: Reduction in temperature. Reduction in pressure that causes a reduction in the air’s O2 concentration and might result in hypoxia. Reduction in pressure that causes a reduction in the solubility of the N3 diluted in the blood stream and might result in embolism.

What is the type of hypoxia due to exposure at high altitude: Hypemic. Hypoxic. Stagnant. Hystotoxic.

Being one of the most efficient cooling systems, why liquid cooling is not so used: Weight. Limited temperature range not adequate for worldwide operation. Too low maximum operating temperatures. Complexity. Cost.

Which of the following is an A350 APU requirement?. The APU in its installed configuration shall have an adequate in-flight start reliability (not less than 91%) throughout the flight envelope taking account of all approved fuel types and temperatures. The A350 shall be capable to start any engines - regardless of engine starting sequence or engine type ( RR or GE ) - on ground using battery power supply. The A350 shall be able to take-off and land in manual operation with steady crosswind 35 kts gusting to 40 kts. The A350 shall be capable of transporting maximum passengers from Bangkok to Heathrow using IATA 1 and 2 ( Alternatives to L888 airway ). The APU shall be operative without permanent presence of operator. The APU shall be capable to pressurize up to 22500 ft. The APU shall be capable to pressurize up to 22500 ft taking into account one engine inoperative.

What will be the minimum differential pressure in an aircraft designed with a ceiling at 25 kft: 5 psi. 34.5 KPa. 40 KPa.

Which of these are aircraft key operational cases that are normally considered for the sizing of the APU. APU Bleed air supply for aircraft cabin pressurization & for adequate cabin environment up to 42500 ft. Main engine Start in flight at 30 kft. On Ground Electrical power demands only. On ground Electrical and pneumatic power demands from the A/C systems. Main engines start in flight at 22 kft. In flight electrical power demands (for twin engine A/C).

In a wing profile section, ice accretion impingement limits will be most extended in the following case: Thin profile, high speed, big droplets. Thick profile, high speed, big droplets. Thin profile, low speed, big droplets. Thick proofile, low speed, big droplets.

The A380 APU model PW980A is steadily operating on Max ECS supply condition on ground. Due to an incorrect tightening of the clamp that couples the APU Bleed Valve and the ATA36 pneumatic duct, a small air leak takes place in fuselage section 19.1. Which of these statements are correct at that instant with a normally running APU?. The Surge Control Valve (SCV) will be commanded to ‘close’ since the L/C operating condition reaches the cracking line. The APU Inlet door position regulated by the ECB will be further opened to increase the airflow through the APU Load Compressor. The APU lubrication system heat exchanger will remain air cooled by airflow pumped by the APU exhaust eductor or a gearbox driven fan. The L/C IGVs control logic will command the closing of the SCV to further increase the flow towards the ECS.

The APU model PW980 in the AIRBUS A380 is steadily supplying bleed air for the aircraft pneumatic systems (ECS) on ground. In a matter of a couple of seconds, such demand signal from the ECS is significantly reduced . Which of these will be a normal reaction of the APU Ctrl system under such situation: To keep fully open the Bleed Shut-off Valve while correspondingly closing the Load Compressor IGVs. To automatically shut down the APU in case an oil system over temperature is sensed by the APU ECB. To correspondingly close the Load Compressor IGVs to reduce the bleed flow, while keeping constant the fuel flow to maintain a constant L/C speed. To keep the Surge Valve fully closed while progressively reducing the fuel flow to avoid an APU over speed condition potentially leading to a rotor burst.

What is the worst flying condition in terms of design of an evaporative thermal anti-ice system: Low speed, low Outside Ambient Temperature. Low speed, high Outside Ambient Temperature.

The APU model PW980 in the AIRBUS A380 is steadily supplying bleed air for the aircraft pneumatic systems (MES or ECS) on ground. In a matter of a couple of seconds, such demand is significantly reduced. What would be the expected immediate reaction from the APU control system?. To keep fully open the Bleed Shut-off Valve while opening the Load Compressor IGVs (Inlet Guide Vanes) to maximum open position, to alleviate excess pressure at the Load Compressor outlet. The ECB commands the Bleed Valve to close and the APU electrical generator to absorb more shaft power in order to avoid a Load Compressor over speed. To command the opening of the Anti-surge Valve and the closure of the Inlet guide Vanes, to alleviate the bleed pressure raise and reduce the bleed airflow supply. The command to the aircraft’s fuel system to shut off completely the fuel supply to the APU and stop it to prevent the burst of the aircraft’s bleeding piping.

For the start of the APU engine on large civil aircrafts for passenger transport, the most commonly used system consists on: An electrical 12VDC Starter/Generator. An air turbine starter. An electrical 28VDC Starter/Generator. An electrical 115VAC Starter/Generator.

What is the purpose of the compensation valve in the oxygen mask. Holds the pressure in the mask cavity when the pressure at which breathing gas is provided by the supply system is increased. Ensure unidirectional gas flow through the ports of the mask. Facilitate breathing to the user.

Which of the following statements is/are not correct?. Same as in a propulsive power plant, the APU shall be installed in a Fire Compartment. The APU engine shall be mounted on the A/C structure with a Suspension System designed to withstand the corresponding inertial loads. Cooling inlet function is to convey necessary atmospheric air flow into APU for Power Unit and Load Compressor. Exhaust Muffler outlet at the rear end point of fuselage is the most favourable location for in flight APU starts pressure effect.

A pressure demand oxygen pressure regulator will be more appropriate: To provide low breathing resistance. Pressure demand: gas is delivered pressurized for use at altitudes above 35 Kft.

The installation of the APU in the fuselage tailcone section on large civil aircrafts for passenger transport, presents as a significant drawback: The noise projection on the ground. In-flight aerodynamic conditions. Accessibility for ground maintenance. The impacts on the aircraft in case of rotor burst.

The installation of the APU in the fuselage section 19.1 on AIRBUS’s large civil aircrafts for passenger transport, presents a main advantage (when compared to an APU installed in the wing root or main landing gear zones), that is: The in-flight aerodynamic conditions. The accessibility for ground maintenance operations. The exhaust duct noise projection on the ground.

Which is the engine technology most extensively used today, for aircraft auxiliary power units?. Electrical Generator. Turbomachinery Engine. Fuel Cells. Diesel Engine.

Which are key features for the fire protection design strategy in a typical APS installation?. An adequate APU compartment drainage system. The use of fireproof titanium firewalls of 0.4 mm thickness. The installation of the APU in a fire compartment with a fire dectecion & estinguishing system. A manual (non-automataic) APU fire detection & extinguishing system for APU ground use.

Which of the following statements are correct?. The APU Air Intake Door has an actuator controlled by the DMM. Same as in a propulsive power plant, the APU shall be installed in a Fire Compartment. The APU engine shall be mounted on the A/C structure with a Suspension System designed to withstand the corresponding inertial loads. The APU Air Intake usually has an electrically actuated flap door that is kept closed while the APU is not operating. The Exhaust Muffler outlet at the very rear end point of the fuselage, is the most favorable location for its pressure effect for in-flight APU starts.

The primary step for the Certification of the APU system in the aircraft is: To achieve the certification of the aircraft electrical & pneumatic systems to be supplied by the APU. APU Engine Type Certificate delivered by the certification authority. To achieve the APU Qualification obtained by the manufacturer for the engine by TSO C77B. The qualification of the APU by a TSO delivered by the Certification Authority.

Which is the primary test platform for certification of the integrated A/C & APU system?. The APU engine test cells. The Compatibility Tests Rig. The Icing Tests rig. The Flight Tests aircrafts.

The normal duration of the development cycle for a new APU system in a large transport aircraft is: The duration of the typical A/C’s: Electrical duty cycle + ECS duty cycle – the MES time. 6 to 7 years. Minimum to 10 years.

Which is an alternative technology to the rotating engine APU, for A/C auxiliary power generation?. Electric Generator. Turbomachinery Engine. Fuel Cells. Diesel Engine.

Which is not a function of the APU system?. To supply electrical & pneumatic power to the aircraft systems while in flight. Run the A/C systems relieving the main engines. Assist the main engines re-start in windmilling. Avoids the main engines running or a GPU running on ground.

Which of the following functions correspond to the FCS?. Stability Augmentation. Thrust Setting. Center of Gravity Control. Flight Envelope Protection. Load Alleviation. Flutter Suppression (manoeuvre and gust). Thrust Vectoring. Abnormal Position Recovery, including post stall.

Two of the following statements are correct. Which ones are they?. Artificial feel systems are required to provide good handling qualities in irreversible FCS. In an “irreversible” FCS, pilot cannot reconfigure the system after a failure. In a “fly by wire” FCS, pilot controls parameters rather than surface position. In a “direct link” FCS, there is a linear relation between control surface displacement and stick forces.

Identify drawbacks of the Fly By Wire systems in the list below. They require the use of hydraulic systems to provide power to the actuators. They require a high degree of redundancy. They require the use of digital computers. High development cost and high system clearance effort. SW development complexity and inherent computing delays. Safety critical SW certified against Common Mode Failures (testing + specification).

Which of the following statements are true for all types of Fly By Wire FCS: A mechanical back-up system is required to control the aircraft after a total FBW system failure. Configuration changes are easy to implement in comparison with mechanically signaled FCS. A/C response is tailored depending on flight phase by FC Computer.

Which of the following statements do not apply to the concept of Control Configured Vehicles: Allows control of aircraft with highly nonlinear aerodynamics. Highly manoeuvrability and flight to high angles of attack. Automatic prevention of stall departure / spinning. Automatic structural protection and gust alleviation. Use of the FCS to actively compensate for deficiencies in the aerodynamics of the basic airframe.

What is the main disadvantage of the Linear Electro Mechanical Actuator for its application in Primary FCS?. They require local hydraulic pumps that make the design heavy and complex. The mechanical signaling circuit is prone to jamming. They have a slow response to input commands. If there is a mechanical jamming, control surface remains in the last commanded position.

Identify two inputs to the FCS design from the following list: Interface Documents. Compliance checklist. Maintenance concept. Technical direction. Preliminary Design. Flight Physics. Loads. Regulation. Reliability.

Identify why kerosene type fuels (Jet A-1/JP-8) are safer than wide-cut fuel types (JetA/JP-4). Kerosene Type Fuels have higher freezing temperature. Density of Kerosene Type Fuels is higher. Kerosene are less volatile. The vapor pressure of kerosene type fuel is lower.

Identify what is the purpose of the fuel vent subsystem (choose two): Maintain the fuel tank temperature. Allow fuel thermal expansion inside the tanks without external leakage. Avoid fuel tank overpressure or underpressure during climbs and dives. Increases the fuel tank pressure.

For certification of the fuel system is essential to demonstrate that (choose one): The fuel reserves are higher than 5% of the fuel tank contents. The aircraft can be refueled in flight. The fuel supply of the engines is maintained across the entire flight envelope.

What are the advantages of the Boom/Receptacle Air Refuelling Systems compared with probe and drogue Air Refueling System systems (choose two): It allows simultaneous air refuelling of two receiver aircraft. None, they are fully compatible between them. Allows higher fuel transfer flow rates minimizing the time in contact. Reduces the receiver pilot work load when in contact.

What are the advantages of the Probe and Drogue Air Refuelling Systems compared with Boom/Receptacle Air Refueling System systems (choose three): Allows higher fuel transfer flow rates minimizing the time in contact. None, they are fully compatible. It allows simultaneous air refuelling of two receiver aircraft. Normally minimizes the modification of the aircraft and fuel system due to the air refueling installation. No need for additional operators.

In terms of safety, which is the main concern in air refuelling operations?. Transferring fuel is always the big safety concern. Lack of fuel transfer in flight will not allow the receiver to make a safe landing. Several aircraft are flying in close proximity, increasing the pilot workload and hence the risk of collision.

The purpose of fire detection systems is: To eliminate the possibility of a fire in the aircraft. To sense and indicate the possibility of a fire in the aircraft. To signal presence and local fire in the aircraft. To extinguish a fire in the aircraft.

Why do current fire extinguishing substances (Halon based) have to be replaced in the future? (choose one). Density of halon’s is too high compared with new substances considered equivalent for fire extinguishing. They are considered risk substances for human health. Because Halon based extinguishing substances have destructive effects on the earth’s ozone layer.

What is the purpose of the self sealing fuel tanks? (choose one). They avoid fuel tank explosion sealing the tank after projectile impact. They reduce the risk of fire in hot areas around the fuel tanks by minimizing fuel leakage in case of a threat impact.

What are the main factors to be considered in the selection of foams?. Density. Color. Resistance to fuel exposure. Resitance to water exposure. Conductivity. Porosity.

What are the differences today between OBIGGS for civil airliners and OBIGGS for military airplane (choose two). Civil ones are more demanding than military ones. There is not any difference. The purpose of civil ones is to minimize the risk of tank explosion in case of fuel system failures, and military ones is to minimize the risk of tank explosion in case of external military threats. For military application Limiting Oxygen Concentration LOC = 9% and civil LOC = 12%.

Ground testing allows: Test individual elements. Test all aspects of the complete A/C and of the man/machine interface. Modeling, simulation, individual elements or the complete A/C are tested as far as possible.

Flight testing allows: Test individual elements. Test all aspects of the complete A/C and of the man/machine interface. Modeling, simulation, individual elements or the complete A/C are tested as far as possible.

Identify what tests are performed during pre-flight test phase: Structural loads tests. Functional tests. Taxi tests.

The Nose Wheel arrangement of an airplane is shown in attached figure: Statically neutral, Dynamically neutral suitable only for steered mounting and shimmy damper required. Statically neutral, Dynamically stable, Stable in reverse when wheel casters right around, Normally Shimmy damper required unless twin wheels coupled in rotation used. Statically unstable. Dynamically Stable. Unstable in reverse. Must be locked or steered. Shimmy damper required, except from t=R to t=1.2R (usually shimmy free).

The slip dynamics of a braked Wheel is shown in figure: A wheel working in “A” means that there is no any point of the tire footprint slipping. In “B” it achieves “optimum slip” with maximum friction coefficient and “C” is actually slippering. A wheel working in “A” means that it is slipping. In “B” it achieves “optimum slip” with maximum friction coefficient and “C” there is no any point of the tire footprint slipping.

Brake by wire system control typically has critical partitions as: Brake by wire systems do not use brake order computer control. The command is mechanically transmitted by to the Brake Valve. Only Antiskid computer is used to carry on antiskid function. Beside non-commanded brake order generated from computer caused by SW error or HW failure at take-off, brake availability at landing could also be critical. A back up brake control (emergency system) torque limited (without antiskid protection) is normally needed. The are no critical failure modes as at aircraft level the effects are normally limited to Hazardous, by declaring accelerate-stop and landing distances specified in the Aircraft Flight Manuals with sufficient length margin to avoid worse effects under loss of braking failure modes. The Software is typically designed with DAL B (Development Assurance Level B).

For aircraft designs required to operate in unpaved airfields: Radial tyres are normally used because they are lighter than Bias Tyres. Bias tyres are normally used because sidewall thickness and better retreadability. Sidewall thickness contributes to minimize punches when operating underinflated when sidewall is more exposed to ground contamination.

Select the correct response(s): The Longitudinal position of Main gear, if too fwd, compromised static stability during aircraft loading and high authority of nose wheel steering. Static stability during loading refers to the aircraft’s ability to maintain a stable balance on the ground when the aircraft is being loaded or unloaded. Compromised Stability: If the main gear is positioned too far forward, the aircraft can become tailheavy during loading. The Longitudinal position of Main gear, if too fwd, compromised static stability during aircraft loading and low authority of nose wheel steering.

Which are the key features of the Solid State Power Controller?. Mechanical trip device activated by the heating. Electronic component based on power semiconductors: IGBT and MOSFET. Remote control/monitor capability. Protects installations from short circuits and overloads. High MTBF (Mean Time Between Failures). High reliability/ Low power dissipation / No vibrations / Programmable / High life cycles.

The purpose of electrical distribution systems is: Reduce the size and volume of electrical power sources. Ensure a maximum availability of the bus-bars. Participate in the connection/disconnection of the power sources. Ensure the electrical network configurations. Ensure the electrical network reconfigurations. Ensure the protection against short-circuit, overvoltage. Ensure the electrical protections in order to avoid power source paralleling (AC) and propagation of defaults.

Identify two drawbacks of the conventional protection devices (fuse and Circuit breakers): They require a high volume. They are general use devices. Ambient temperature dependency. Complex to monitor or no monitoring capability. No arc-fault detection capability.

What type of main generator disconnection could perform crew with cockpit push-buttons?. Electrical disconnection (line contactor opening). A mechanical disconnection P/B is installed on the electrical overhead panel. It sends a signal to the generator that mechanically disconnect it from the Accesory Gearbox (AGB).

Regulated converters advantages compared with unregulated converters are: Higher efficiency. Cheaper. Simpler and more reliable. Less volume.