EFTA01122646.pdf

http://www.Boeing-727.com System Descriptions Air Conditioning APU Autopilot Electrics Fire Protection Flight Controls Fuel System GPWS Hydraulics Ice & Rain Protection Landing Gear & Brakes Oxygen Pitot Static System Pneumatics Powerplant Pressurisation Windows Yaw Dampers Page 1 Of 78 EFTA01122646  http://www.Boeing-727.com System Descriptions AIR CONDITIONING The pneumatics system provides compressed air at a constant flow rate to the two air conditioning packs. In these units the air temperature is modified to keep the cabin and cockpit comfortable. In normal operation some of the air from the left pack provides conditioned air to the cockpit. The rest of the air from the left pack mixes with the air from the right pack in a distribution duct and provides conditioned air to the passenger cabin. The air is exhausted through the pressurisation system at a flow rate that allows the cabin to be pressurised. The air conditioning packs are located beneath the floor in the centre fuselage area. An air conditioning pack valve controls the flow of air from the pneumatics system into each pack. The pack valves are controlled by two switches on the Flight Engineers panel. In each pack the air is split into three paths. In one path the air passes through a refrigeration unit, then to a set of mixing valves. The mixing valves mix the refrigerated air with air from the other two paths. This allows the air to be delivered to the cabin at the proper temperature. The second path to the mixing valves delivers hot air directly. The third path is through only a portion of the refrigeration unit, and It reaches the mixing valves at a moderate temperature. The refrigeration unit is called an air cycle machine. It operates on the same principle as any other refrigeration device, except that it uses air instead of freon for refrigeration. The usual compression cooling and expansion seen in any refrigeration cycle is accomplished in the air cycle machine by a compressor, the secondary heat exchanger and an expansion turbine. The work extracted by the turbine is transmitted by a shaft to the compressor. A primary heat exchanger cools the air before it reaches the compressor, and thus increases the efficiency of the air cycle machine. Page 2 Of 78 EFTA01122647  http://www.Boeing-727.com System Descriptions a Supply Duct Temp 190' F 1250'F Pack 140' FE Fan Dist ution ct 99 ' C Water Seperator Air Source Cold Air ACM Water Seperator Warm Air Anti Ice Valve Air Conditioning System The primary and secondary heat exchangers are normally cooled by air picked up by two inlets on the bottom of the fuselage. The air passes through the primary and secondary heat exchangers and out through a set of louvers at each heat exchanger. Doors at the inlets control the airflow through the heat exchangers. The cooling door and louvers on each pack are interconnected and driven by a single motor. Pack temperature is most vitally affected by the position of the cooling doors. The pack cooling doors are controlled switches on the Flight Engineer's panel. On some aircraft the cooling door switches have positions to open and close, and are spring loaded to a centre off position. Some are on open, off and close with no spring loading. Others are equipped with automatic operated pack cooling doors which will modulate to keep the pack at the proper temperature. These doors have the open and close positions, but the centre position is auto. The centre position is not spring loaded. When the cooling door switch is left in the auto position the cooling doors will remain open while the airplane is on the ground or the flaps are not up. Once flaps are retracted, the associated pack temperature will be automatically regulated to a temperature schedule bias altitude. Below 10,000 feet the temperature is kept at 125 degrees C. From 10.000 feet to 30,000 feet the temperature decreases linearly to 45 degrees C, and remains at 45 degrees C as altitude increases further. This schedule should be used if the doors must be controlled manually. To provide additional cooling for low speed flight and ground operation, an electric fan for each pack is used to force air through the heat exchangers. Page 3 Of 78 EFTA01122648  http://www.Boeing-727.com System Descriptions This fan will operate when the pack is on and the inboard flaps are not fully retracted, or when a pack is on and the airplane is on the ground. The ground cooling fan has its own motor driven air inlet door on the side of the fuselage that remains open when the fan is in operation. When a pack fan is started. It draws a very heavy load from the electrical system, and when stabilised, fan consumes about ten kilowatts of power. These are the highest loads on the electrical system. To monitor the operation of the air cycle machines, each has a temperature transmitter at the outlet off its compressor. The temperature sensed is displayed on a pack temperature gauge for each pack. As more air is directed through cycle machine to provide more cooling, more compression is required from the compressor. This results in a higher compressor outlet temperature. Therefore, the pack temperature gauge monitors air cycle machine workload. To protect the compressor from excessively high temperature an over temperature sensor at the outlet of the compressor will cause the pack to shut down if the temperature reaches the limiting value. Another temperature limiting sensor located at the inlet to the turbine. This uses the temperature of the air as an indication of the energy in the air. If the temperature of the air, and thus the energy entering the turbine becomes too high, the pack will shut down to prevent an overspeed. In order to return the pack to operation after the temperature in the pack has reduced, a reset button on the pack control panel is provided. The pack cannot be returned to operation until the button has been pressed. If the pack fan is operating when an air conditioning pack trips off, the fan will continue to operate. The fan will stop when the pack temperature drops, the pack switch Is turned off, and the reset button is pressed. To allow unattended ground operation of the air conditioning system in the 727, the pack trip off sensing and the pack valves are powered from the battery transfer bus. Should the AC electrical power fail, the pack cooling fans will stop. Hot air from the APU will overheat the pack and a pack trip will occur, providing the battery transfer bus is powered. This is one reason for leaving the battery switch on. As air is cooled it will hold loss moisture. To remove this condensation a water separator is installed downstream of the air cycle machine turbine. The water separator swirls the air over an impingement surface causing the moisture to drop out. This water can be seen coming from the lower fuselage on humid days. The air cycle machine is capable of lowering air temperatures below freezing, which would cause the moisture in the water separator to freeze. To prevent ice accumulation from blocking the water separator, a sensor monitors the temperature. If the temperature gets too low, a water separator anti-ice valve is opened which allows warm air to bypass the air cycle machine and keep the temperature above freezing. 35F. The air conditioning units are controlled by switches on the Flight engineers panel. Each switch opens and closes its pack valve at a rate that will not overload the air cycle machine. The pack valves are powered from the battery transfer bus. Each air mix valve set is actually three valves ganged together, one hot, one Page 4 Of 78 EFTA01122649  http://www.Boeing-727.com System Descriptions intermediate, and one cold. These valves operate together to provide the proper mixing of hot, cool, and cold air. There is a set of three valves for each air conditioning pack. As the outside air temperature drops, the temperature of the cooling air passing through the heat exchangers is low enough to provide sufficient temperature drop in the conditioned air. To compensate, the intermediate valve opens, allowing air to bypass the turbine and flow directly from the secondary heat exchanger into the cabin or cockpit. The turbine slows as a result of this bypassing action causing the compressor to be driven at a slower speed. This allows some of the compressed air to bypass the compressor, flowing directly from the primary heat exchanger to the secondary heat exchanger. The restriction to airflow caused by the air cycle machine is reduced as a result of this bypassing, reducing the need for high- pressure bleed air. Reducing the need for high stage bleed air improves engine efficiency, reducing the amount of fuel being used by the engine. The temperatures in the cabin and cockpit are normally controlled by automatic temperature regulators. Each regulator provides signals to a motor which drives the associated air mix valve. Each temperature regulator receives inputs from a temperature sensor in the cockpit or cabin and a temperature selector on the flight engineer's panel. The temperature sensor in the forward cabin provides temperature signals to the automatic temperature regulator for the right pack, and the cockpit temperature and left temperature selector position are sent to the temperature regulator for the left pack. The position of each air mix valve is shown on an indicator next to the associated temperature selector on the Flight Engineer's panel. The air mix valve moves to the full cold position automatically when the associated pack valve is closed. Conditioned air flowing from the air mix valves enters a common distribution duct. From this ducting a small portion of the air is directed into the cockpit. The remainder going to the passenger cabin. Both packs supply the distribution ducting; therefore the same distribution ratio of air to the cabin and cockpit would result whether one or both packs are in operation. The air to the passenger cabin flows through risers between the windows to keep the cabin walls warm. The air in the cabin eventually flows out through a grill along the floor line into the lower fuselage where it is exhausted through the pressurisation valves (outflow). Duct temperature is automatically restricted when the temperature control is operating in the automatic range. A temperature sensor in the duct downstream of each air mix valve signals the associated automatic temperature regulator if the temperature reaches a limiting value. When this limiting temperature is reached, a circuits called the topping circuit, prevents the mixing valve from moving toward a higher temperature position. If an automatic temperature regulator fails to control the temperature of the air satisfactorily, the associated air mix valve can be controlled manually.- To operate the air mix valve manually, spring tension must be overcome and the Page 5 Of 78 EFTA01122650  http://www.Boeing-727.com System Descriptions selector rotated to the manual position. In this position the automatic temperature regulator is cut out. Holding the selector lightly against spring tension to the cool position will cause the air mix valve to move towards cold. In the warm position, the valve will move towards hot. To prevent the air from a pack getting too hot, should the automatic temperature regulator fail, a second temperature sensor is installed downstream of each mixing valve. When the limiting temperature is reached, the associated air mix valve will move to the full cold position, and the duct overheat light next to the associated temperature controller will illuminate. If the automatic temperature regulator and the duct overheat protection both fail, to prevent the duct temperature from rising, a third temperature sensor will cause the pack to trip. If the overheat and pack trip are on the left portion of the systems the location of the supply duct temperature transmitter near the right air mix valve will prevent the temperature indication from reaching the trip off temperature. To regain control of the temperature regulating networks and turn off the trip lights after an overheat has occurred, a reset button is installed on the temperature control panel. Once the temperature has reduced, pressing the button will return the temperature control system to normal operation. A temperature gauge on the flight engineers panel is used to monitor the temperature of the air being supplied to the cabin at two locations. The air temperature selector can be used to select the temperature in the forward and aft supply ducts, the main supply distribution duct, and in the forward and aft cabins. Air is tapped off at the cold side of the left air conditioning pack and delivered to the individually controlled outlets above the passengers, the lavatories, and the cockpit. This in referred to as the gasper system. To increase the flow of gasper air, a fan is installed in the gasper ducting. A switch on the flight engineers air conditioning control panel turns the gasper fan on or off. If the left air conditioning pack is not operating when the gasper fan is on, cabin air is recirculated through the gasper system. Conditioned air flows through the airplane and exhausts through three principal exit systems. First of these is the normal pressurisation outflow valve. Operation of this valve will be covered under pressurisation. Some air flows into the electronic equipment compartment and circulates through the various electronic components; it passes through electronic equipment and circuit breaker panels in the cockpit, the electronic equipment bay, and the weather radar compartment. This air absorbs the heat generated by these units and carries it overboard through an exhaust system on the forward right side of the fuselage. In normal flight, cabin differential pressure provides necessary airflow through this system. Since the electronic equipment operates continuously, a means of inducing airflow on the ground and at low cabin pressure differential pressure is required. To provide this flow, an electric fan has been installed in the exhaust duct. This fan comes on automatically at low cabin differential pressure. The exhaust to this system has a large and small outlet. So that unrestricted flow can be achieved at low cabin differentials, both outlets are Page 6 Of 78 EFTA01122651  http://www.Boeing-727.com System Descriptions used. As the flow rate increases, a flow rate sensitive valve closes preventing excessive loss of air at high differential pressures. A warning light on the lower right corner of the flight engineers panel will alert the crew to inadequate cooling of electronic equipment. A sensor in the cooling air outlet monitors airflow through the cooling system. If cooling airflow becomes inadequate the "no equipment cooling" light will come on. The cargo compartments on the 727 are class D cargo compartments, which are designed to confine a fire without endangering the safety of the airplane or the occupants. No air circulates through them although a small amount of air flows through the equalisation valves to maintain equal pressure between the cargo compartment and the surrounding cavities, should cabin pressure vary. If a fire develops, it will smother itself as the oxygen in the compartment is consumed. To maintain temperature in the forward cargo compartment, conditioned air from the cabin flows around an airtight inner shell then is discharged through the cargo heat outflow valve. Approximately 30% of the air in the aircraft will exit through this valve. A switch on the flight engineers panel controls the cargo heat outflow valve. In the normal position the valve is open, permitting air circulation around the forward cargo compartment. If a pressurisation problem should occur, closing the switch can stop the flow of air through this exit. Without airflow around the forward cargo compartment the temperature within the compartment will drop rapidly to a much lower value. The air that passes from the cabin to the pressurisation outflow valve in the aft fuselage of the airplane heats the aft cargo compartment. An automatic pack trip system is incorporated in the 727 200 series aircraft. With the system armed before takeoff, loss of thrust on any engine will trip off both packs. This allows the engines to develop somewhat higher thrust for the remainder of the takeoff and initial climb. In addition, both pack fans will stop, thereby reducing the electrical load. To arm the auto pack trip system, the airplane must be on the ground, the flaps must be out of the up position, the auto pack trip switch must be in the normal position, and all engines must be above 1.5 EPR. When the flaps reach the up position after takeoff the auto pack trip system will be deactivated. After takeoff, and when clear of obstacles the auto pack trip switch should be returned to the coot position. This will deactivate the auto pack trip system. Should any engine lose power below 1.3 EPR both packs will trip off, both pack valves will close, both pack fans will stop and both pack trip lights will illuminate. In addition, an engine fail light will illuminate on each side of the pilot's glare shield. These engine fail lights can be extinguished by pressing on either light cap. When a substantial power reduction is anticipated, such as a noise abatement takeoff. The flight engineers should anticipate the thrust reduction and place the auto pack trip switch to cut out prior to reducing thrust to remove the possibility of an inadvertent auto pack trip. The airplane is equipped with a means of controlling the temperature in the aft cabin without affecting the temperature of the forward cabin. This is done through the aft cabin zone temperature system. A single switch operates two Page 7 Of 78 EFTA01122652  http://www.Boeing-727.com System Descriptions valves in this system. This allows warm air from the right air conditioning pack to enter the forward or aft cabin bringing about the requested change in aft cabin temperature. Should the aft cabin ducting overheat an amber light on the panel will illuminate. Both zone control valves will close and the needle will centre. The flight engineer can monitor the use of this system with the air temperature selector. APU The auxiliary power unit, or APU in the Boeing 727 is a small turbine engine mounted between the main wheel wells. it draws air from the wheel well area for combustion and cooling and exhausts through louvers in the top of the right wing root. Most of the accessories are mounted on the left hand side of the unit. The components of most interest are the APU starter (electric), hour meter, fuel control unit, 3-speed switch (3 psi oil, 35%, 95%) Generator, tacho generator (RPM) note that these last two components are interchangeable with there brothers on the engine. Power for starting the APU comes directly from the airplane battery. The battery switch must be on when operating the APU, if the switch is turned off the APU will shutdown. The APU uses fuel from the number 2 tank. The APU fuel shutoff valve is located at the tank. It is opened or closed by the APU master switch. Operation of either APU fire switch or activation of the auto fire shutdown circuitry will also close this valve The controls for the unit may be found in the flight deck at the flight engineers auxiliary panel and in the left hand wheel well. It contains controls for starting and stopping the APU, fire detection and protection, generator operation, and gauges for monitoring electrical load and exhaust temperature. There is a three-position control switch marked Off, ON and Start. It remains in the OFF position when the APU is shut down and in the ON position when the APU is operating. It must be held in the START position against spring pressure when starting the APU. ON is the normal operating position. Selecting this position prior to starting will open the APU fuel valve. After the fuel valve is opened, positioning the master switch to START will initiate the automatic starting sequence. When the APU crank light comes on, the automatic starting sequence has begun. Once the light is on, the master switch may be released to the ON position. During the start sequence, if the EGT does not rise within 15 seconds or there is no frequency an the AC meter within 30 seconds, the APU fire shutoff handle should be pulled to interrupt the start sequence. The APU crank light goes out when the starter releases. Click here to view starting sequence. Self-contained lubrication system requires no crew monitoring. The APU will not operate if the oil pressure fails. An exhaust temperature gauge located in the lower right corner of the APU control panel shows APU turbine exhaust temperature in degrees C. The temperature will vary widely depending on bleed air loads. The green band is the normal operating range, and the red radial is the maximum operating temperature. Page 8 Of 78 EFTA01122653  http://www.Boeing-727.com System Descriptions The APU is governor controlled to maintain 100% RPM, thus it can be geared to drive an AC generator directly. This generator can supply electrical power to all airplane systems for ground operation. Bleed air is extracted from the APU compressor to be used for airplane air conditioning and for engine starting on the ground. An APU bleed air valve is installed on the APU to control flow of bleed air from the APU to the bleed air distribution system. The APU bleed air valve will open if the APU has reached operating RPM and either or both Engine No.2/APU BLEED switches are in the OPEN position. An APU light is located on the door warning annunciator at the flight engineers panel. This light will come on any time the fuel valve is open if the number 1 DC electrical bus is powered. For maintenance personnel external control of the APU, a second APU control panel is located in the left wheel well between the fuselage and the gear strut. It is not used for normal operation. The start switch on this panel will start the APU if the battery switch and APU master switch in the cockpit are on. The stop switch will shut the APU down. Also the panel contains a fire switch, a fire warning light, and a bottle discharge button. These controls permit fighting an APU fire without going to the cockpit. The APU will shut down automatically for the following reasons; loss of oil pressure or overspeed will cause the fuel to be cut off at the fuel control in the APU. The fire detection loop, if it reaches the warning temperature, will close the fuel shutoff valve in the number 2 tank and at the fuel control and the APU will stop. Heat sensitive probes in the turbine exhaust provide other protection. First, these probes cause the APU to be unloaded by modulating the APU bleed air valve toward close; if closing the bleed air valve fails to solve the high exhaust temperature, the probes will cause the fuel control to reduce fuel flow until the temperature is lowered sufficiently or the APU flames out. Page 9 Of 78 EFTA01122654  http://www.Boeing-727.com System Descriptions APU SchEmatic To API) Control Circuit To Pnournailc Manifold APU Fuel Shutoff Valve On the 200 series aircraft a turbine and compressor assembly called a flow multiplier is used to improve the airflow from the APU. It draws in additional air from the right wheel well adding it to the APU compressed air output. This higher volume of air makes it possible for the APU to supply air to both air conditioning packs. During single pack operation however, the flow multiplier shut off valve remains closed and the turbine is bypassed. A FLOW MULTIPLIER OVERHEAT light on some airplanes and a BLEED AIR light on others warns of an overheat in the output of the flow multiplier compressor. The overheat will cause the APU bleed air valve to close. Cycling the number two engine bleed switches will reset the APU bleed air valve. Further protection is provided by a fusible plug, which should it melt. It will close the flow multiplier shutoff valve, preventing compressed air from reaching the flow multiplier turbine. Pressures in the pneumatic ducts can be read on the duct pressure gauge under most conditions. The duct pressures will read zero, when either air conditioning pack is turned on, if the APU is the only source of air in the pneumatic ducting (200 Series). Turning either pack switch on prevents APU bleed air from reading on the duct pressure transmitters. The APU on the Boeing 727 can be used for ground operation only. Electrical loads and EGT limits must be observed for all operations. The EGT limits are red radial for maximum and the green band for continuous operation. The electrical load limit is 165 amps, the higher rating is due to the improved Page 10 Of 78 EFTA01122655  http://www.Boeing-727.com System Descriptions cooling of the APU installation. The APU should be operated without pneumatic load for at least one minute after start or prior to shut down. A pretty good piece of kit, most of the problems you experience are to do with starting (3 speed switch or over-speed switch) occasionally the shorting link on the exhaust disconnect link. Extensive troubleshooting will require the test set, (not a great deal you can do down route). It's manufactured by Allied Signal (Garrett). APU Starter is limited to 1 min on 4 min off Max time for APU fire test AC Busses powered 30 sec- 45 sec. Battery power 60 sec. Max APU generator load 165 amps One pack on for cooling (100 Series) Two packs on for heating Two packs on for cooling (If flow multiplier installed) Normal operating EGT Green Band (Marked @ 700) Max Operating Red Radial line (Marked 750 - 790) APU EGT Operating GTCP85-98 and 98C 98CK Maximum 760 °C 710 °C Continuous 710 °C 663 °C AUTOPILOT The Autopilot (NP) can control the aircraft in a climb, cruise decent and approach phases of flight or as directed manually by the pilot via the control knob. It may also be directed by signals from the VHF, GPS, and INS navigation systems. It can also find and maintain a pre selected heading, altitude, pitch attitude or operate in a split axis configuration. It requires 115V AC for operation from the aircraft generators or an external source. If using the latter you need to operate the ground test switch. Electrical interlocks prevent selection or operation unless all the proper conditions for correct functioning are satisfied. INTERLOCKS Mandatory interlocks are at least one yaw damper switched on and it's disengage flag out of view, turn and pitch controller in neutral detent, operating vertical gyro if these conditions are correct you will be able to engage the aileron switch. To engage the elevator switch the aileron switch must be engaged and the cruise stabilizer trim switch must be in the normal position. Page 11 Of 78 EFTA01122656  http://www.Boeing-727.com System Descriptions The autopilot will disengage if any of the following actions or conditions occur. Yaw damper positioned to off, capt or co pilot press autopilot release switch, power to vertical gyro is lost, switching compass source or power to A/P aileron (roll) is lost. Elevator channel disengage will occur if the stabilizer trim switch is activated, pitch channel selector is switched (A or B) cruise trim switch is activated, A/P and cruise trim cut out switches positioned to cut out, electrical power to the NP elevator (pitch) is lost. NP mode will return to manual (turn and pitch knob) if any of the following occur reference VHF/GPS/INS is switched, turn and pitch controller moved out of detent, ILS frequency is switched while in approach mode. ELECTRICS AC POWER Modern transport aircraft use 400-hertz alternating current to power much of their electrical equipment for several reasons. Voltages are easily converted from high to low or low to high. The higher frequencies used in aircraft electrical systems allow components to be smaller, but develop the same power as the 60 hertz devices normally found in the home and industry. Power for the electrical system is supplied by the three engine driven generators, and as a backup on the ground, APU generator, or an external power source. Normally all of the electrical power in the airplane is produced by the engine driven AC generators. An AC generator must be rotated at a constant speed throughout the operating RPM range of the engine. This is necessary to maintain the appropriate frequency output of the generator. A generator drive unit, called a constant speed drive, or CSD, which is a hydro mechanical device between the engine drive pad and the generator, accomplishes this function for each generator. Each generator drive unit contains its own integral oil supply and pumps. So that the oil pressure within the unit can be monitored, a low oil pressure light for each unit is included on the flight engineers electrical panel. The amber light will come on if the oil pressure in a unit is too low. To cool the generator drive oil an air-cooled heat exchanger is installed in each drive system. Engine fan stage bleed air continuously provides the required cooling airflow for the heat exchangers. There is an oil temperature gauge for each generator drive unit. These gauges have two scales. Oil "IN" temperature is indicated on the lower scale, which is calibrated from 40 degrees to 160 Page 12 Of 78 EFTA01122657  http://www.Boeing-727.com System Descriptions degrees Celsius. The upper scale is calibrated from 0 degrees to 30 degrees Celsius, and indicates the rise in the temperature of the oil as it passes through the generator drive unit. Above each temperature gauge is a toggle switch for selecting either the "IN" or "RISE" temperature scale. The "IN" temperature is sensed downstream of the oil cooler as it enters the generator drive. This gives an indication of oil cooler efficiency. The rise temperature is the difference between oil in and oil out temperatures and is an indication of heat generated within the drive unit in rotating the generator, or the workload of the generator drive unit. The rise temperature caution range is 20 degrees to 30 degrees C. If the "IN" temperature reads between 127 degrees and 140 degrees C the operating time limit is two hours. With the "IN" temperature between 140 degrees and 160 degrees C. Operating time limit is 50 minutes. To the left of each low pressure light is the disconnect switch for the associated generator drive unit. These switches are red guarded and safety wired. The switch under the guard has two positions, Normal and Disconnect. The Disconnect position is momentary contact and spring loaded to the normal position. The generator drive unit can be disconnected by opening the guard and moving the disconnect switch to the disconnect position. This action disengages the mechanical coupling for the generator drive unit from the engine drive pad. Also this action trips the associated generator breaker, breaking the electrical connection between the generator and its load bus. The generator drive can only be reconnected on the ground by maintenance personnel. The generators each produce three phase, 400 hertz. 115 volt AC electrical power. The voltage produced by a generator depends on there being a magnetic field in the generator. Current flowing from the voltage regulator produces this field. The generator's output voltage is sampled by the voltage regulator which adjusts the current to the field so that the generator's output, when not in parallel, will be 115 volts. plus or minus 5 volts. Under certain abnormal or emergency conditions it is necessary to reduce the voltage output of the generator to a minimum. The field relay performs this function by interrupting the current flow from the voltage regulator to the generator. With the field relay open, only residual voltage of 10 to 17 volts will be produced if the generator is rotating. Each generator has a field relay controlled by the field switch on the electrical panel. The light next to the field switch will be on when the field relay is open. When the generator is producing full voltage, it may be connected to its load bus by closing the generator breaker. The load bus is a distribution point for the power produced by the generator. Heavy load items, such as air conditioning pack fans, galleys, and hydraulic "B" pumps are powered directly from the load busses. Power is also sent to the various circuit breaker panels to power electrical equipment throughout the airplane. Each generator breaker is closed with a switch labelled GEN. Page 13 Of 78 EFTA01122658  http://www.Boeing-727.com System Descriptions When a generator is connected to its load bus through the generator breakers the generator breaker light next to that generator switch will be out. When the generator is not connected to its load bus the light will be on. To equalise the loads on the generators, and to protect the electrical system if one generator should fail, the three load buses are connected together by a third set of relays. These bus tie breakers are connected to a common circuit referred to variously as the "tie bus" or the synch bus. The tie bus shuttles power among the three AC load buses as power requirements change, but only when the bus tie breakers are closed. If a generator should fail the tie bus will power the AC load bus associated with that generator through its bus tie breaker. Since we are dealing with alternating current, we must be certain that the voltages of the various sources we are joining in parallel are "in phase". By this we mean that the positive and negative portions of the two voltages that we are connecting occur at the same time. If we joined the voltage sources when they were not "in phase", serious damage could be done to a generator. In practice, the bus tie breakers are left closed so a single power source could power all three AC load buses. To protect against connecting a generator out of phase, automatic protective circuits prevent the generator breakers from being closed unless the associated generator is in phase with the other generators already powering the system. The bus tie breakers do not have this protective feature. Some AC powered items are considered to be more critical to safe flight. These are powered through the essential AC bus, which can be supplied by any of the three generators directly without the necessity of its generator breaker being closed. The selected generator's field relay must be closed so that the generator will be able to supply electrical power. The essential power selector switch on the upper right side of the electrical panel controls the selection of a power source for the essential AC bus. Normally generator three supplies the essential power, with the other two generators available. The essential AC bus is also powered when external power or the APU is supplying the airplane. Preferences for essential sources are eng 3, 1, 2 in that order. It's due to the loads on each bus, 3 being the lightest load, 2 the heaviest Red warning lights show failure of the selected essential AC power source. There is a steady red light on the essential power selector panel and a flashing red light, labelled "WARN - PUSH TO RESET", on the pilot's centre instrument panel. The flashing red light can be extinguished by pressing the light cap, but the steady red light will not go out until the essential AC bus is powered from another source. Certain of the captain's instruments are protected even further. They are powered from the standby AC bus. As long as the essential AC bus is Page 14 Of 78 EFTA01122659  http://www.Boeing-727.com System Descriptions powered, it powers the standby AC bus. In the event of a failure of essential AC power in flight the standby bus will automatically be powered by a static inverter. The static inverter is powered from the battery bus. On the ground the standby AC bus may be powered from the static inverter, however, it is necessary to select "STANDBY" with the essential power selector to do so. This is normally done when standby AC power is required, but AC power is not available from the airplane's generators or an external power source. The essential power selector must be depressed before it can be rotated to the "STANDBY" position. When the selector is moved to the standby position on the ground or in flighty the essential AC bus will no longer be powered even if it were powered previously. The last major AC bus is the AC transfer bus. Normally this bus is powered from the number 3 AC load bus, but under certain conditions can be powered from an external power source. Distribution of electrical power is through the various circuit breaker panels. The lower portion of the P 6 panel is divided into three sections. P6-11, P6-12, and P6-13. These sections are associated with the three AC load buses. 1, 2, and 3 respectively. On each panel is a power light, which glows continuously when the associated bus is powered. The rest of the P6 panel and the P18 panel contain the systems sections with the circuit breakers for those systems. The upper portion of the P 6 panel is divided from top to bottom into four main sections, P6-1, P6-2, P6-3, and P6-4. The other main circuit breaker panel is P-18, which is located on the left sidewall above the first observer's seat. The P18 panel is further subdivided into four main sections numbered from bottom to top. In general these panels are: P 18-1. Radio equipment; P18-2, light instruments, autopilot, and interphone; P18-3. Passenger accommodation and P18-4. Cockpit lighting, service lights, and exterior lighting. Isolated groups at circuit breakers related to lighting are installed in several other cockpit locations. There are also some circuit breakers, which are inaccessible to the crew located in the electronic equipment compartment. On the right side of the flight engineers panel is an AC meters selector. Each of the three engine driven generators, the APU generator, or the external power can be sampled as well as the voltage and frequency on the synch bus. When a generator is rotating with its field relay open, it will produce 10 to 17 volts residual voltage. This voltage can be read an the voltmeter lower scale by selecting that generator and pushing the residual volts button. When the generator field relay is closed the generator field is energised by the voltage regulator. Now normal voltage can be read on the top scale of the voltmeter. It should read 115 volts plus or minus 5 volts. Above the AC meters selector is a frequency meter. This meter will indicate the frequency of the power source selected by the AC meters selector. When selected to generators 1, 2, or 3. the frequency desired is 400 hertz plus or minus 9 hertz. If the frequency is not 400 hertz, it can be adjusted using the frequency knob on the left panel. The knob for each generator allows adjustment of the Page 15 Of 78 EFTA01122660  http://www.Boeing-727.com System Descriptions frequency within about a 15-hertz spread. Frequency will be indicated only when the generator field relay is closed. Just above the meters selector are two white lights labelled "SYNCHRONIZED WHEN LIGHTS ARE OUT'. These lights are used when connecting generators in parallel with the bus tie breakers. Automatic paralleling protection is provided when the generators are brought online normally since the generator breakers are used. If the generator breakers cannot be used because an abnormal or emergency procedure requires the bus tie breakers to be used, the manual paralleling procedure outlined here must be used. After one generator is connected to the synch bus. Selection of another with the AC meters selector will cause the synch lights to flash in unison. They are indicating the synchronisation of the selected generator in comparison to the synch bus. Before closing the bus tie breaker, which places that generator in parallel with any other on the synch bus, the frequency of that generator is adjusted with its frequency knob to 400 hertz so that the lights are flashing slowly. When the lights are out. The generator is synchronized and can be safely paralleled. SYNCHRONALED WHEN LIMITS • Alit OUT 410 OEN 2 GEN 3 GEN I • EXT TE- POWER AC METERS When an electrical load is sustained by an engine driven generator, the load is indicated in kilowatts on its kilowatt meter. There is one for each engine driven generator. The maximum continuous load for a single generator that is not operating in parallel is 36 kilowatts. It can sustain an overload of 54 kilowatts for 5 minutes. Two generators operating in parallel are limited to 54 kilowatts total load, and 3 generators in parallel may be operated continuously with a total load of 102.5 kilowatts. The loads on paralleled generators should be nearly equal, indicating that the generators are sharing the loads equally. Another electrical quantity which can be read on the meters is kilovolt-amperes reactive, or KVARS. The KVAR button is shown in yellow. When the KVAR button is pushed and held, it changes the three meters to read kilovolt amperes reactive. A measure of reactive power. All three meters should show the same readings for reactive power. Page 16 Of 78 EFTA01122661  http://www.Boeing-727.com System Descriptions When certain electrical system faults occurs lights an the electrical fault annunciator panel on the flight engineer's auxiliary panel will indicate the type of fault and the system involved. The reset button on the panel is used to put out the annunciator lights when required. The test button is used to test the annunciator lights. OTHER POWER SOURCES The system may be powered by the APU generator which in identical to the engine driven generators but is geared directly to the APU accessory drive. When the APU is operating at 100% RPM, the APU generator will be providing 400 hertz power. The controls for the APU generator are located on the flight engineers auxiliary panel. There is a field switch and a generator breaker switch. Both of these switches are three position lever lock switches. The amber light associated with the field switches is a field off light. The amber light associated with the generator breaker is a generator circuit open light. The AC ammeter located on the APU control panel indicates the AC load on the APU generator in amps. This ammeter will also indicate external power load in amps if an external power unit is being used. The maximum electrical load when using the APU generator is limited to 165 amps. APU voltage and frequency can be read on the AC meters with APU selected. When the APU is running at normal speed and its generator field relay is closed, closing its generator breaker will connect the APU generator directly to the airplane's synch bus. The individual load buses will be powered from the synch bus if the bus tiebreakers are closed. In normal operation the bus tie breakers are left closed and the transfer of power sources is done with the generator breakers, or in the case of external power, the external power contactor. With all bus tie breakers closed, AC buses 1,2, and 3 are now powered by the APU generator. An external power unit may be used to provide electrical power to the airplane systems. An AC connected light on the flight engineers electrical panel comes on when external power is plugged into the nose of the airplane. This light signifies that power is available but it does not show whether the power is actually energising the airplane's AC buses. By selecting external power with the AC meters selector, the voltage and frequency of the external power can be monitored. Approximately 115 volts and 400 hertz should be indicated before external power is accepted. The external power source can be connected to the airplane electrical system by means of the external power switch. The switch is held in the ON position by a solenoid. A temporary loss AC power will allow the switch to return to the centre OFF position. Moving the switch to the ON position will connect the external power to the synch bus. As with APU power, the bus tie breakers must be closed for the power from the synch bus to reach the three AC load buses. ESSENTIAL POWER Essential power can be supplied on the ground when either the APU or an Page 17 Of 78 EFTA01122662  http://www.Boeing-727.com System Descriptions external power source is powering the AC load buses. Power from the number 3 AC load bus is tapped off and supplied to a pair of relays which, when the proper conditions are met, will allow the essential power selector to supply AC power to the essential AC bus. There are certain requirements, which must be met before the essential AC bus can be powered by selecting APU or external power on the essential power selector. When the number 3 AC bus is powered from any source. The essential AC bus will be energized from that bus with APU selected, only if the APU is running and its field relay is closed. To power the essential AC bus from the external power position. External power must be powering the buses. With the external power switch off, the external power position of the essential power