Aircraft Handling Ground Connections

Transcription

1 Aircraft Handling Ground Connections Contents Ground Connections... 2 Electrical Power Connection... 3 Pneumatic Power Connection... 6 Conditioned Air Connection... 8 External Hydraulic Source Connection... 9 ETBN Ground Connections Page 1 of 11 EASA Part 66

2 Ground Connections During certain ground operations and when the aircraft is undergoing maintenance it is often necessary to operate systems which would usually be powered by the engines in flight or the Auxiliary Power Unit (APU) in normal ground operations. These systems rely on power or supplies form the engine Electrical, Pneumatic and Hydraulic sources. To power these systems while the engines and APU are inoperative, external sources must be connected to the aircraft systems. It is essential that the external equipment and its output are compatible with the aircraft system requirements and will not damage or contaminate the aeroplane system. ETBN Ground Connections Page 2 of 11 EASA Part 66

3 Electrical Power Connection As previously stated, it is often necessary to connect an external electrical power supply to an aircraft, either for engine starting purposes or to permit operation of the aircraft systems and equipment. Certain precautions must be observed when connecting the external supply, to prevent damage to the aircraft electrical system. Most light aircraft have direct current (dc) electrical systems and although alternating current (ac) may be provided for the operation of certain equipment it is not usual for the aircraft to have provision for the connection of ac external power. The external power socket is, therefore usually for a connection of a dc supply, which may be provided solely by batteries or from a generator and battery set. The following actions should be taken when connecting an external dc supply to a typical light aircraft: 6. To disconnect the external supply, switch of the battery master switch, switch off the external supply, disconnect the external power plug and if the aircraft electrical system is to be used (e.g. after engine starting), switch the battery master switch to on again. Close and latch the access door. 3 PIN SOCKET 1. Check the voltage and polarity of the ground supply. 2. Check that the external power plug and socket are clean, dry and undamaged. 3. Check that the external supply and the aircraft battery master switch is off and connect the external supply, ensuring that the plug is fully home in the socket. EXTERNAL SUPPLY PLUG ACCESS DOOR 4. Check flight deck switch positions for critical systems introduction of electrical power may cause unintended operation. DC EXTERNAL SUPPLY 5. Switch on the external supply and the aircraft battery master switch and carry out the servicing operations for which the external power was required. ETBN Ground Connections Page 3 of 11 EASA Part 66

4 Electrical Power Connection Most large aircraft are provided with multi-pin plugs or sockets in an accessible location, by means of which external dc and ac power may be connected into the aircraft electrical system. The external supply is usually provided by a towed or self propelled unit known as a Ground Power Unit (GPU), which has its own power driven generator and can provide dc power at various voltages and ac power at a particular voltage, frequency and phase rotation. The example shown has two power receptacles, each with an AC Connected light to indicate that the GPU is delivering power and is properly connected, and a Power Not In Use light which indicates that the supply is not connected to the aircraft system and it is safe to shut down the GPU. The plug should never be connected or removed with the GPU delivering power (plug and socket live), and the GPU should never be shut down or disconnected while the aircraft systems are using ground power. AC CONNECTED LIGHT POWER NOT IN USE LIGHTS AC CONNECTED LIGHT EXTERNAL SUPPLY PLUG EXTERNAL POWER RECEPTACLE No 1 EXTERNAL POWER RECEPTACLE No 2 EXTERNAL POWER RECEPTACLE DOOR AC EXTERNAL SUPPLY ETBN Ground Connections Page 4 of 11 EASA Part 66

5 Electrical Power Connection Aircraft electrical systems vary considerably and the checks which are necessary after connecting the external power will vary between aircraft, but the following procedure is applicable in most cases: 1. Check that the external supply is compatible with the aircraft system (i.e. it has the same voltage, frequency and phase rotation as the aircraft system) and is switched off. 2. Check that the external plug and socket are clean dry and undamaged. 3. Connect the external plug/socket, ensuring that it is fully mated and secure and switch on the external power supply. 4. Check the voltage and the frequency of the external supply on the aircraft electrical system instruments (some aircraft automatically check the quality of the power and indicate its acceptability with a External Power Available light on the flight deck). 5. Check flight deck switch positions for critical systems introduction of electrical power may cause unintended operation. 5. Perform the operations specified in the relevant maintenance manual to engage the external supply with the aircraft ac system. 6. To disconnect the external supply, disengage it from the ac system, switch off the external power at source and remove the external power plug/socket. Close and latch the access panel. ETBN Ground Connections Page 5 of 11 EASA Part 66

6 Pneumatic Power Connection On an aircraft, pneumatic power can be used for engine starting, pressurisation and air-conditioning, anticing, and operation of other systems (alternate hydraulics, flight controls etc.). To use and test these systems on the ground a source of compressed air must be connected to the aircraft. This external source may be a mechanically driven compressor (electrical or diesel) but for large aircraft which have a high volumetric demand, a small gas turbine unit is commonly used. These external sources may be fixed plant in the hangar or vehicle mounted units for portability. FLANGE CHECK VALVE As with Electrical power the quality of the air supply must be compatible. Typically the pressure required will be around PSI ( kg/cm 2 ) and the temperature not more than about 200 C. Volumetric requirement for starting an engine may be as high as 450 lb/min (205 kg/min). Connection is via a coupling, which is standard to most aircraft types, usually located in the belly area of the aircraft for easy access. Larger aircraft may have multiple adaptors to allow more than one start truck to be connected to meet their needs. A typical process for connection is as follows, but always check the AMM for type specific information. ACCESS DOOR CONNECTOR WARNING ENSURE THAT THE GROUND CART HOSE IS DEPRESSURIZED PRIOR TO REMOVAL. REFER TO AMM / 201. CAUTION DO NOT EXCEED 50 PSIG AND/OR 232 C (450 F) ENSURE APU, LEFT AND RIGHT ENGINES ARE NOT RUNNING PRIOR TO GROUND CART HOOK - UP 1. Check that the external supply is compatible with the aircraft system (i.e. correct pressure, temperature and volume) and is switched off. UNDER WING FUSELAGE AREA 2. Check that the external hose and coupling, and the aircraft receptacle are clean and undamaged. ETBN Ground Connections Page 6 of 11 EASA Part 66

7 Pneumatic Power Connection 3. Connect the external hose, ensuring that it is fully mated and secure, and switch on the external power unit. 4. Check flight deck switch positions and circuit breakers for critical systems as per the AMM introduction of pneumatic power may cause unintended operation of systems and components including movement of control surfaces. 5. Check the pressure on the aircraft flight deck instruments (some aircraft automatically check the quality of the supply and indicate its acceptability with a Pneumatic Power Available light). 6. Perform the operations specified in the relevant maintenance manual to introduce the external supply to the aircraft system (e.g. open isolation and cross feed valves). PNEUMATIC COUPLING 7. To disconnect the external supply, close the supply/isolation valves, shut down the start truck/ground source. Disconnect the hose, and ensure the aircraft check valve has closed. Close the access panel. Caution The pneumatic system components will be hot after operation of the system. Exercise caution when handling them. PNEUMATIC CART CONNECTED TO AN AIRCRAFT ETBN Ground Connections Page 7 of 11 EASA Part 66

8 Conditioned Air Connection When an aircraft is parked in a hot environment for an extended period it is often more economical to supply conditioned air from an external source, rather than running the APU. Cooled air is introduced into the conditioned air manifolds via a ground connection downstream of the air conditioning packs. The aircraft environmental control system will have no control over the external system so it must be ensured that the aircraft is in a suitable configuration before external conditioned air is introduced. Failure to observe this may damage components of the aircraft system and could possibly lead to pressurisation of the cabin which can cause injury. The conditioned air connection is a large volume low pressure receptacle, protected from leakage by a check valve which closes when the aircraft Packs are supplying conditioned air. PACK 1 GROUND SERVICE CONNECTOR CONDITIONED AIR MANIFOLDS FROM WATER SEPARATOR CONDITIONED AIR MANIFOLD AIR CONDITIONING EQUIPMENT BAY PACK 2 GROUND SERVICE CONNECTOR GROUND SERVICE CONNECTOR SWING CHECK VALVE TO CONDITIONED AIR PLENUM ETBN Ground Connections Page 8 of 11 EASA Part 66

9 External Hydraulic Source Connection Primary hydraulic power is normally provided by engine driven pumps. Alternate power is usually supplied by electrically, or pneumatically driven pumps. It is not always appropriate to operate these alternate sources in a hanger during maintenance so an external source may be connected to each aircraft system in these circumstances. Often, the external source can be regulated to a specific delivery pressure and flow rate so that initial testing may be performed at a safer value below normal system operating pressure. Cleanliness is imperative when maintaining aircraft hydraulic systems and components. Because the hydraulic power ground service unit or rig exchanges fluid with the aircraft, it must be maintained to the same high standards to prevent cross contamination. The rig must also be filled with the same type of fluid as is used in the aircraft. As the hydraulic system is a circulatory system, the ground service rig, must be able to handle both pressure (output) and return (input) flows. To prevent the system reservoir being filled from the rig, it may need to be pressurised with air as it would be in flight. For these reasons the hydraulic power supply rig will have multiple connections into the aircraft system. The rig is a self-contained hydraulic system with an electrically driven pump unit, a reservoir, filtration, pressure and flow regulation, cooling and protective features. Rigs of differing capacity and output are available and must be selected with regard to the requirements of the aircraft system. Most large commercial aircraft require a pressure of either 3000 or 5000 psi and a flow of up to 50 gallons per minute. ETBN Ground Connections Page 9 of 11 EASA Part 66

10 External Hydraulic Source Connection Connection to the aircraft system may by means of quick release or threaded couplings to specific points in the aircraft system. Both halves of the coupling are protected by a self sealing valve to prevent loss of fluid and contamination when uncoupled. Protective caps or blanks should be fitted to both halves of the coupling when disconnected. The connections for each system may be centrally located or distributed around the aircraft depending on the configuration of the systems. GROUND SERVICE DISCONNECT FOR THE RETURN LINE The pressure connection is usually to the aircraft pressure manifold or pressure module, upstream of the pressure filter to offer a further level of protection against contamination. The return connection draws fluid either from the return module or from the reservoir. In some instances the reservoir must be pressurised and the rig may also provide a regulated air supply. A typical process for connection is as follows, but always check the AMM for type specific information. A 1. Check that the external supply rig is compatible with the aircraft system (i.e. correct pressure, flow, fluid type and couplings) and is switched off. 2. Remove blanks immediately prior to connection. Check that the external hoses and couplings, and the aircraft connections are clean and undamaged. SEE A SYSTEM 1 SEE A CONNECTIONS SYSTEM 2 SEE B SEE B CONNECTIONS GROUND SERVICE DISCONNECT FOR THE PRESSURE MODULE B ETBN Ground Connections Page 10 of 11 EASA Part 66

11 External Hydraulic Source Connection 4. Connect the external hoses, ensuring that are fully tightened and secure and switch on the external power unit. 4. Check flight deck switch positions and circuit breakers for critical systems as per the AMM introduction of pneumatic power may cause unintended operation of systems and components including movement of control surfaces. 5. Check the pressure on the aircraft flight deck instruments. 7. Perform the operations specified in the relevant maintenance manual to introduce the external supply to the aircraft system (e.g. open isolation valves). 8. To disconnect the external supply, isolate the supply, shut down the ground rig. Disconnect the hoses and blank all connections. Close any access panels. 9. Depressurise reservoir and check hydraulic system contents, replenish as required. Caution The hydraulic system and its components may remain pressurised after shut down. Even residual pressure can cause serious injury. Caution The hydraulic system components will be hot after operation of the system. Exercise caution when handling them. Caution Hydraulic fluids are usually irritants. Always handle with care and observe all safety precautions. Note; Ground Service should not be confused with Servicing the replenishment of the systems. ETBN Ground Connections Page 11 of 11 EASA Part 66