PЗ Stabilizing Load windings Damper feedback Ref Bias _P4 ¿ RE + Input signal Output signa
• +
d. c. bias Ref Bias Load windings Stabilizing Damper feedback winding From generator damper windings FIGURE 9-44. First stage of a magnetic amplifier voltage regulator.
These units are shown in figure 9-43. Potentiometer Pl is adjusted so that, at rated bus voltage, there is a zero potential difference between points A and B on the bridge circuit. For any other input voltage, the voltage drop across the glow tubes causes a potential to exist between points A and B.
For example, if the generator voltage is low, the current flow through the arms of the bridge will be reduced. The voltage across R4 will be less than the fixed voltage across V1; consequently, point B will be at a higher potential than point A.
This gives an error signal used as an input to the first mag-amp (magnetic amplifier) stage. For high input voltages the error signal polarity is reversed.
The second unit in the system is the magnetic amplifier. The circuitry for the first stage of a typical mag-amp voltage regulator is shown in figure 9-44. This unit consists of two reactors, supply voltage transformers and rectifiers, and the following windings: reference, d.c. bias, damper circuit, load circuit, and feedback circuit. The d.c.
bias winding fixes the operating level of the reactors and is adjusted by potentiometers P5 and P6.
Potentiometer P6 regulates the magnitude of the bias voltage, and P5 regulates the magnitude of biasing current on each reactor to overcome the slight differences in the two cores and the associated rectifiers. If the bias voltage is properly adjusted and if a zero error signal input exists, the voltages developed across R5 and R6 will be equal and the output will be zero.
The damper circuit is connected into the circuit and is used as a stabilizing winding. Its source of power is the damper winding of the generator.
The generator damper winding is energized through transformer action by a changing generator excitation current and is, therefore, proportional to the rate of change of excitation. This current is used as a feedback signal in the first magnetic amplifier stage because its polarity always opposes the error signal input.
R5 R6 DC Bias adj P7 To gen. exciter regulator winding E, = Input signal FIGURE 9-45. Second mag-amp stage of voltage regulator.
The magnitude of the damper feedback current is adjusted with potentiometer P4. Its function is to establish the recovery time of the regulator and to provide stable operation. The potentiometer should be adjusted to provide fast voltage recovery during stable operation under normal load conditions.
Next, the feedback winding receives a voltage that is proportional to the output voltage; this provides stability during steady load conditions.
A look at the circuit will disclose that the load winding receives its power from transformerrectifier terminals T1 and T2. The current fow through these windings and load resistors R5 and R6 is regulated by the degree of magnetization of the reactor cores, established by the current flow in the various control windings.
Figure 9-44 also illustrates that, when the input signal is not zero, the currents through R5 and Ro will not be equal. The unequal currents in these resistors provide a potential difference which is the output signal for this stage, the polarity of which depends on the polarity of the error signal input.
All of the units in the regulator have been discussed except the output stage, which is referred to as the second stage of the regulator.
This is a three-phase, full-wave, magnetic amplifier, as shown in figure 9-45. The output of the first stage, which we have just discussed, is fed into the control winding of the second stage. The output of this stage is the generator exciter-regulator field voltage. The magnitude of this voltage is established by the magnitude and polarity of the input signal, the bias current which is adjustable by P7, and also by the feedback current which is proportional to the output.
This type of regulator has a distinct advantage 422
FIGURE 9-46. Constant-speed drive.
over other types, since it will function on a very small change in voltage. Because of the operating characteristica of this type of regulator, variations in the output voltage will be within 1 percent.
The various adjustments on the unit, with the exception of those on P1, have been discussed.
Adjustments on PI are to be accomplished only on the bench, when the regulator is being calibrated.
Potentiometer P1 is located in the center of the front face of the regulator adjacent to the voltmeter jacks, The potentiometer may be adjusted while the regulator is installed on the aircraft to set the bus voltage to the desired value.
The voltage regulator is divided into three main parts: the voltage error detector, the preamplifier, and the power amplifier. These three units work together in a closed-loop circuit with the generator exciter regulator winding to maintain nearly constant voltage at the generator output terminals.
The function of the error detector is to sample the generated voltage, compare it with a fixed standard, and send the error to the preamplifier.
The detector includes a three-phase rectifier; a variable resistor for voltage adjustment, and a bridge consisting of two voltage reference tubes and two resistors. In operation, if the generator voltage ranges above or below its rated value, a current will flow either in one direction or the other, depending on the polarity developed in the bridge circuit.
The preamplifier receives an error signal from the voltage error detector. With the use of magnetic amplifiers, it raises the signal to a sufficient level to drive the power amplifier to full output, required for proper excitation.
The power amplifier delivers a signal to the exciter regulator winding; its magnitude depends on the signal from the preamplifer. This will raise or lower the voltage of the exciter regulator winding, which, in turn, will raise or lower the output voltage of the generator.
ALTERNATOR CONSTANT-SPEED DRIVE Alternators are not always connected directly to the airplane engine like d.c. generators. Since the various electrical devices operating on a.c. supplied by alternators are designed to operate at a certain voltage and at a specified frequency, the speed of the alternators must be constant; however, the speed of an airplane engine varies. Therefore, some alternators are driven by the engine through a constant-speed drive installed between the engine and the alternator.
A typical hydraulic-type drive is shown in figure 9-46. The following discussion of a constantspeed drive system will be based on such a drive, found on large multiengine aircraft.
The constant-speed drive is a hydraulic transmission which may be controlled either electrically or mechanically.
The constant-speed drive assembly is designed to deliver an output of 6,000 r.p.m., provided the input remains between 2,800 and 9,000 r.p.m. If the input, which is determined by engine speed, is below 6,000 r.p.m., the drive increases the speed in order to furnish the desired output. This stepping up of speed is known as overdrive.
In overdrive, an automobile engine will operate at about the same r.p.m. at 60 m.p.h. as it does in conventional drive at 49 m.p.h. In aircraft, this principle is applied in the same manner. The constant-speed drive enables the alternator to produce the same frequency at slightly above engine-idle r.p.m. as it would at takeoff or cruising r.p.m.
With the input speed to the drive set at 6,000
r.p.m., the output speed will be the same. This is known as straight drive and might be compared to an automobile in high gear. However, when the input speed is greater than 6,000 r.p.m., it must be reduced to provide an output of 6,000 r.p.m. This is called underdrive, which is comparable to an automobile in low gear. Thus, the large input, caused by high engine r.p.m., is reduced to give the desired alternator speed.
As a result of this control by the constant-speed drive, the frequency output of the generator varies from 420 c.p.s. at no load to 400 c.p.s. under full This, in brief, is the function of the constantspeed drive assembly. Before discussing the various units and circuits, the overall operation of the transmission should be discussed.
cylinder block gear, which it drives, as well as to the makeup and scavenger gear pumps E.
The makeup (charge) pump delivers oil (300
p.s.i.) to the pump and motor cylinder block, to the governor system, and to the pressurized case, whereas the scavenger pump returns the oil to the external reservoir.
The rotating cylinder assembly B consists of the pump and motor cylinder blocks, which are bolted to opposite sides of a port plate. The two other major parts are the motor wobbler A and the pump wobbler C. The governor system is the unit at the top of the left side in the illustration.
The cylinder assembly has two primary units.
The block assembly of one of the units, the pump, contains 14 cylinders, each of which has a piston and pushrod. Charge pressure from the makeup pump is applied to each piston in order to force it outward against the pushrod. It, in turn, is pushed against the pump wobble plate.
If the plate remained as shown in part A of figure 9-48, each of the 14 cylinders would have equal pressure, and all pistons would be in the same relative position in their respective cylinders.
But with the plate tilted, the top portion moves outward and the lower portion inward, as shown in part B of the illustration. As a result, more oil enters the interior of the upper cylinder, but oil will be forced from the cylinder of the bottom If the pump block were rotated while the plate remained stationary, the top piston would be forced inward because of the angle of the plate.
This action would cause the oil confined within the cylinder to be subjected to increased pressure great enough to force it into the motor cylinder block assembly.
Before explaining what the high-pressure oil in the motor unit will do, it is necessary to know something about this part of the rotating cylinder block assembly. The motor block assembly has 16 Hydraulic Transmission The transmission is mounted between the generator and the aircraft engine. Its name denotes that hydraulic oil is used, although some transmissions may use engine oil. Refer to the cutaway view of such a transmission in figure 9-47. The input shaft D is driven from the drive shaft on the accessory section of the engine. The output drive F, on the opposite end of the transmission, engages the drive shaft of the generator.
The input shaft is geared to the rotating cylinders, each with its piston and pushrod. These are constantly receiving charge pressure of 300
p.s.i. The position of the piston depends upon the point at which each pushrod touches the motor wobble plate. These rods cause the wobble plate to rotate by the pressure they exert against its sloping surface.
This is how the action works: the piston and pushrod of the motor are pushed outward as oil is forced through the motor valve plate from the pump cylinder. The pushrods are forced against the motor wobble plate, which is free to rotate but 424
FICURE 9-47. Cutaway view of a hydraulic transmission.
cannot change the augle at which it is set. Since the pushrods cannot move sideways, the pressure exerted against the motor wobble plate's sloping face causes it to rotate.
In the actual transmission, there is an adjustable wobble plate. The tilt of the pump wobble plate is determined by the control cylinder assembly. For example, it is set at an angle which causes the motor cyliaders to turn the motor wobble plate faster than the motor assembly, if the transmission is in overdrive. The result described is produced by the greater pressure in the pump and motor cylinders.
With the transmission in underdrive, the angle is arranged so there is a reduction in pumping action. The subsequent slippage between the pushrods and motor wobble plate reduces the output speed of the transmission. When the pump wobble plate is not at an angle, the pumping action will be at a minimum and the transmission will have what ia known as hydraulic lock. For this condition, the input and output speed will be about the same, and the transmission is considered to be in straight drive.
To prevent the oil temperature from becoming excessively high within the cylinder block, the 425
FIGURE 9-48. Wobble plate position.
makeup pressure pump forces oil through the center of this block and the pressure relief valve.
From this valve, the oil flows into the bottom of the transmission case. A scavenger pump removes the oil from the transmission case and circulates it through the oil cooler and filter before returning it to the reservoir. At the start of the cycle, oil is drawn from the reservoir, passed through a filter, and forced into the cylinder block by the makeup pressure pump.
The clutch, located in the output gear and clutch assembly, is an overrunning one-way, sprag-type device. Its purpose is to ratchet if the alternator becomes motorized; otherwise, the alternator might turn the engine. Furthermore, the clutch provides a positive connection when the transmission is driving the alternator.
There is another unit of the drive which must be covered, the governor system. The governor system, which consists of a hydraulic cylinder with a piston, is electrically controlled. Its duty is to regulate oil pressure flowing to the control cylinder assembly, as shown in figure 9-49.
The center of the system's hydraulic cylinder is FIGURE 9-49. Control cylinder.
speed drive Constant 1Estiat Estat snan Generator Oil out Oil in FIGURE 9-50. Electrical hydraulic control circuit.
slotted so the arm of the pump wobble plate can be connected to the piston. As oil pressure moves the piston, the pump wobble plate is placed in either overspeed, underspeed, or straight drive.
Figure 9-50 shows the electrical circuit used to govern the speed of the transmission. First, the main points of the complete electrical control circuit will be discussed (figure 9-50 and 9-51).
Then, for simplification, two portions, the overspeed circuit and the load division circuit, will be considered as individual circuits.
Note, then, in figures 9-50, that the circuit has a valve and solenoid assembly O and a control cylinder E, and that it contains such units as the tachometer generator D, the rectifier C, and adjustable resistor B, rheostat A, and the control coil Q.
Since it is driven by a drive gear in the transmission, the tachometer (often called tach) generator, a three-phase unit, has a voltage proportional to the speed of the output drive. Its voltage is changed from a.c. to d.c. by the rectifier. After rectification, the current flows through the resistor, rheostat, and valve and solenoid. Each of these units is connected in series, as shown in figure 9-51.
Under normal operating conditions, the output of the tach generator causes just enough current to enter the valve and solenoid coil to set up a magnetic field of sufficient strength to balance the spring force in the valve. When the alternator speed increases as the result of a decrease in load, the tach generator output increases also. Because of the greater output, the coil in the solenoid is sufficiently strengthened to overcome the spring force. Thus, the valve moves and, as a result, oil pressure enters the reduced speed side of the control cylinder.
In turn, the pressure moves the piston, causing the angle of the pump wobble plate to be reduced.
The oil on the other side of the piston is forced back through the valve into the system return.
Since the angle of the pump wobble plate is smaller, there is less pumping action in the transmission. The result is decreased output speed.
To complete the cycle, the procedure is reversed.
With the output speed reduction, tach generator output decreases; consequently, the flow of current 427
Constant speed drive Generator To load • Oil out Oil in FIGURE 9-51. Speed control circuit.
to the solenoid diminishes. Therefore, the magnetic field of the solenoid becomes so weak that the spring is able to overcome it and reposition the valve.
If a heavy load is put on the a.c. generator, its speed decreases. The generator is not driven directly by the engine; the hydraulic drive will allow slippage. This decrease will cause the output of the tach generator to taper off and, as a result, weaken the magnetic field of the solenoid coil. The spring in the solenoid will move the valve and allow oil pressure to enter the increase side of the control cylinder and the output speed of the transmission will be raised.
There are still two important circuits which must be discussed: the overspeed circuit and the load division circuit. The generator is prevented from overspeeding by a centrifugal switch (S in figure 9-52) and the overspeed solenoid coil R, which is located in the solenoid and valve assembly. The centrifugal switch is on the transmission and is driven through the same gear arrangement as the tach generator.
The aircraft d.c. system furnishes the power to operate the overspeed coil in the solenoid and coil assembly. If the output speed of the transmission reaches a speed of 7,000 to 7,500 r.p.m., the centrifugal switch closes the d.c. circuit and energizes the overspeed solenoid. This component then moves the valve and engages the latch which holds the valve in the underdrive position. To release the latch, energize the underdrive release solenoid.
The load division circuit's function is to equalize the loads placed on each of the alternators, which is necessary to assure that each alternator assumes its share; otherwise, one alternator might be overloaded while another would be carrying only a small load.
In figure 9-53, one phase of the alternator provides power for the primary in transformer G, whose secondary supplies power to the primaries of two other transformers, J and J2. Rectifiers K then change the output of the transformer secondaries from a.c. to d.c. The function of the two capacitors, L, is to smooth out the d.c.
pulsations.
The output of the current transformer F depends 428
CHAPTER 10
INSPECTION FUNDAMENTALS
GENERAL Inspections are visual examinations and manual checks to determine the condition of an aircraft or component. An aircraft inspection can range from a casual walkaround to a detailed inspection involving complete disassembly and the use of An inspection system consists of several processes, including: (1) Reports made by mechanics or by the pilot or crew flying an aircraft and (2) regularly scheduled inspections of an aircraft. An inspection system is designed to maintain an aircraft in the best possible condition.
Thorough and repeated inspections must be considered the backbone of a good maintenance program. Irregular and haphazard inspection will invariably result in gradual and certain deterioration of an aircraft. The time which must eventually be spent in repairing an aircraft thus abused often totals far more than any time saved in hurrying through routine inspections and maintenance.
It has been proven that regularly scheduled inspections and preventive maintenance assure airworthiness. Operating failures and malfunctions of equipment are appreciably reduced if excessive wear or minor defects are detected and corrected early. The importance of inspections and the proper use of records concerning these inspections cannot be overemphasized.
Airframe and engine inspections may range from preflight inspections to detailed inspections. The time intervals for the inspection periods vary with the models of aircraft involved and the types of operations being conducted. The airframe and engine manufacturer's instructions should be consulted when establishing inspection intervals.
Aircraft may be inspected using flight hours as a basis for scheduling, or on a calendar inspection system. Under the calendar inspection system, the appropriate inspection is performed on the expiration of a specified number of calendar weeks. The calendar inspection system is an efficient system from a maintenance management standpoint.
Scheduled replacement of components with stated hourly operating limitations is normally accomplished during the calendar inspection falling nearest the hourly limitation.
In some instances, a flight-hour limitation is established to limit the number of hours that may be flown during the calendar interval.
Aircraft operating under the flight-hour system are inspected when a specified number of flight hours are accumulated. Components with stated hourly operating limitations are normally replaced during the inspection that falls nearest the hourly limitation.
REQUIRED INSPECTIONS Federal Aviation Regulations (FAR) provide for the inspection of all civil aircraft at specific intervals, depending generally upon the type of operations in which they are engaged, for the purpose of determining their overall condition. Some aircraft must be inspected at least once each 12 calendar months, while inspection is required for others after each 100 hours of flight. In other instances, an aircraft may be inspected in accordance with an inspection system set up to provide for total inspection of the aircraft over a calendar or flight-time period In order to determine the specific inspection requirements and rules for the preformance of inspections, reference should be made to the Federal Aviation Regulations which prescribe the requirements for the inspection and maintenance of aircraft in various types of operations.
INSPECTION TECHNIQUES Before starting an inspection, be certain all plates, access doors, fairings, and cowling have been opened or removed and the structure cleaned. When opening inspection plates and 461
cowling, and before cleaning the area take note of any oil or other evidence of fluid leakage.
CHECKLIST Always use a checklist when performing the inspection. The checklist may be of your own design, one provided by the manufacturer of the equipment being inspected, or one obtained from some other source. The checklist should include the following:
1. Fuselage and hull group.
a. Fabric and skin-for deterioration, distortion, other evidence of failure, and defective or insecure attachment of fittings.
b. Systems and components-for proper installation, apparent defects, and satisfactory operation.
c. Envelope gas bags, ballast tanks, and related parts- for condition.
2. Cabin and cockpit group.
a. Generally-for cleanness and loose and security.
proper operation.
e.
charge.
e.
f. Engine controls-for defects proper travel, and proper safetying.
g. Lines, hoses, and clamps-for leaks, condition, and looseness.
h. Exhaust stacks-for cracks, defects, and proper attachment.
i. Accessories-for apparent defects in security of mounting.
j- All systems-for proper installation, general condition defects, and secure attachment.
k. Cowling-for cracks and defects.
Ground runup and functional checkcheck all powerplant controls and systems for correct response, all instruments for proper operation and indication.
4. Landing gear group.
a. All units-for condition and security of attachment.
b. Shock absorbing devices for proper oleo fluid level.
c. Linkage, trusses, and members-for undue or excessive wear, fatigue, and distortion.
d. Retracting and locking mechanismfor proper operation.
e. Hydraulic lines-for leakage.
f. Electrical system--for chafing and proper operation of switches.
g. Wheels-for cracks defects, and condition of bearings.
h. Tires-for wear and cuts.
i. Brakes-for proper adjustment.
j. Floats and skis-for security of attachment and obvious defects.
Wing and center section.
a. All components-for condition and security.
b. Fabric and skin-for deterioration, distortion, other evidence of failure, and security of attachment.
c. Internal structure (spars, ribs compression members) -for cracks, bends, and security.
d. Movable surfaces-for damage or obvious defects, unsatisfactory fabric or skin attachment and proper travel.
e. Control mechanism-for freedom of movement, alignment, and security.
f. Control cables- for proper tension, fraying, wear and proper routing through fairleads and pulleys,
6. Empennage group.
a. Fixed surfaces--for damge or obvious defects, loose fasteners, and security of
b. Movable control surfaces-for damage or obvious defects, loose fasteners, loose fabric, or skin distortion.
c. Fabric or skin-for abrasion, tears, cuts or defects, distortion, and deterioration.
7. Propeller group.
a. Propeller assembly-for cracks, nicks, bends, and oil leakage.
b. Bolts-for proper torquing, and safety-
tions and obvious defects.
d. Control mechanisms-for proper operation, secure mounting, and travel.
Communication and navigation group.
a. Radio and electronic equipment-for proper installation and secure mounting,
b. Wiring and conduits-for proper routing, secure mounting, and obvious defects.
c. Bonding and shielding for proper installation and condition.
d. Antennas-for condition, secure mounting and proper operation.
9. Miscellaneous.
a. Emergency and first-aid equipmentfor general condition and proper stowage.
b. Parachutes, life rafts, flares, etc.-inspect in accordance with the manufacturer's recommendations.
c. Autopilot system-for general condition, security of attachment, and proper operation.
AIRCRAFT LOGS "Aircraft logs" as used in this handbook is an inclusive term which applies to the aircraft logbook and all supplemental records concerned with the aircraft. The logs and records provide a history of maintenance and operation, control of maintanance schedules, and data for time replacements of components or accessories.
The aircraft logbook is the record in which all data concerning the aircraft is recorded. Information gathered in this log is used to determine the aircraft condition, date of inspections, time on airframe and engines. It reflects a history of all significant events occurring to the aircraft, its components, and accessories, and provides a place for indicating compliance with FAA Airworthiness Directives or manufacturers' serv.
ice bulletins.
SPECIAL INSPECTIONS raft. occasions atlined on the ature and are mechanic with AS such, they aing any one of follow the + maintenance manual.
Hard or Overweight Landing Inspection The structural stress induced by a landing depends not only upon the gross weight at the time but also upon the severity of impact. However, because of the difficulty in estimating vertical velocity at the time of contact, it is hard to judge whether or not a landing has been sufficiently severe to cause structural damage. For this reason, a special inspection should be performed after a landing is made at a weight known to exceed the design landing weight or after a rough landing, even though the latter may have occurred when the aircraft did not exceed the design landing weight.
Wrinkled wing skin is the most easily detected sign of an excessive load having been imposed during a landing. Another indication which can be detected easily is fuel leaks along riveted seams. Other possible locations of damage are spar webs, bulkheads, nacelle skin and attachments, firewall skin, and wing and fuselage stringers.
If none of these areas show adverse effects, it is reasonable to assume that no serious damage has occurred. If damage is detected, a more extensive inspection and alignment check may be necessary.
Severe Turbulence Inspection When an aircraft encounters a gust condition, the airload on the wings exceeds the normal wingload supporting the aircraft weight. The gust tends to accelerate the aircraft while its inertia acts to resist this change. If the combination of gust velocity and airspeed is too severe, the induced stress can cause structural damage.
A special inspection should be performed after a flight through severe turbulence. Emphasis should be placed upon inspecting the upper and lower wing surfaces for excessive buckles or wrinkles with permanent set. Where wrinkles have occurred, remove a few rivets and examine the rivet shanks to determine if the rivets have sheared or were highly loaded in shear.
Inspect all spar webs from the fuselage to the tip, through the inspection doors and other accessible openings. Check for buckling, wrinkles, and sheared attachments. Inspect for buckling in the area around the nacelles and in the nacelle skin, particularly at the wing leading edge.
Check for fuel leaks. Any sizeable fuel leak is an indication that an area may have received overloads which have broken the sealant and opened the seams.
If the landing gear was lowered during a period of severe turbulence, inspect the surrounding surfaces carefully for loose rivets, cracks, or buckling. The interior of the wheel well may give further indications of excessive gust conditions.
Inspect the top and bottom fuselage skin. An excessive bending moment may have left wrinkles of a diagonal nature in these areas.
Inspect the surface of the empennage for wrinkles, buckling, or sheared attachments, Also, inspect the area of attachment of the empennage to the fuselage.
The above inspections cover the critical areas. If excessive damage is noted in any of the areas mentioned, the inspection should be continued until all damage is detected.
PUBLICATIONS Aeronautical publications are the sources of information for guiding aviation mechanics in the operation and maintenance of aircraft and related equipment. The proper use of these publications will greatly aid in the efficient operation and maintenance of all aircraft. These include manufacturers' service bulletins, manuals, and catalogs, as well as FAA regulations, airworthiness directives, advisory circulars, and aircraft, engine and propeller specifications.
Bulletins Service bulletins are one of several types of publications issued by airframe, engine, and component manufacturers.
The bulletins may include: (1) The purpose for issuing the publication; (2) the name of the applicable airframe, engine, or component; (3) detailed instructions for service, adjustment, modification or inspection, and source of parts, if required; and (4) the estimated number of manhours required to accomplish the job.
Maintenance Manual The aircraft maintenance manual provided by the manufacturer contains complete instructions for maintenance of all systems and components installed in the aircraft. It contains information for the mechanic who normally works on units, assemblies, and systems, while they are installed in the aircraft, and not for the overhaul mechanic.
A typical aircraft maintenance manual contains:
(1) A description of the systems such as electrical, hydraulic, fuel, control, etc.; (2) lubrication instructions setting forth the frequency and the lubricants and fluids which are to be used in the various systems; (3) pressures and electrical loads applicable to the various systems; (4) tolerances and adjustments necessary to proper functioning of the airplane; (5) methods of leveling, raising, and towing; (6) methods of balancing control surfaces;
(7) identification of primary and secondary structures; (8) frequency and extent of inspections necessary to the proper operation of the airplane;
(9) special repair methods applicable to the airplane; (10) special inspection techniques requiring X-ray, ultrasonic, or magnetic particle inspection; and (11) a list of special tools.
Overhaul Manual The manufacturer's overhaul manual contains brief descriptive information and detailed step-bystep instructions covering work normally performed on a unit away from the aircraft. Simple, inexpensive items, such as switches and relays, on which overhaul is uneconomical, are not covered in the overhaul manual.