11-16 flight and landing load factors of 14 CFR §§ 23.337, 23.341, and 23.473.
In lieu of a calculated determination of these loads, the down load factors referenced above may be used.
5. Supporting structure of other mass items should be designed to the critical flight or landing load factors of 14 CFR § 23.321, § 23.471, § 27.321, or § 27.471. The values shown in 14 CFR § 23.561 or § 27.561 may be used in lieu of determination of these values.
11.31.5 Determine if the equipment is installed so that it does not adversely affect another structure (either primary or secondary).
11.31.6 Confirm whether means are provided to permit proper inspections of the installation and related adjacent parts as components.
11.32 Hazards to the Aircraft and its Occupants.
1. Confirm whether the parts of the airplane adjacent to the battery are protected against corrosion from any products likely to be emitted by the battery during servicing or flight.
Note: Methods that may be used to obtain protection include acid-proof paint that will resist corrosive action by emitted electrolyte, drain to discharge corrosive liquids clear of the aircraft, positive pressure vents to carry corrosive fumes and flammable gases outside the aircraft, enclosed battery cases that would contain any amount of electrolyte that might be spilled, or a combination of these methods.
2. Determine whether the battery container or compartment is vented in such a manner that any explosive gases released by the battery during charging or discharging are carried outside the airplane.
3. Confirm that the battery container or compartment is vented in such a manner that any noxious gases emitted by the battery are directed away from the crew and passengers.
4. Verify whether the battery connector terminals or other exposed parts are protected against electrical contact with the battery container or compartment.
5. Determine if adequate provision is made for the drainage of spilled or excess battery fluid.
11.33 Operating Aspects. If a battery is the only source of electrical power, determine if the battery has sufficient capacity to supply the electrical power necessary for dependable operation of all electrical equipment essential to the safe operation of the airplane.
11.34 Detail Design Standards. Verify that the battery is accessible for inspection or servicing on the ground.
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11.35 Recordkeeping.
1. Confirm that a maintenance record entry has been made.
2. Determine if the equipment list and W&B has been revised.
11-18 Section 5. Instructions for Continued Airworthiness
11.36 Lead-Acid Batteries.
11.36.1 Airworthiness Limitations.
11.36.1.1 Battery Inspection. To ensure continued airworthiness, the battery should be removed and the capacity tested. Follow the battery manufacturer’s recommended instructions for continued airworthiness (ICA) to determine service periods.
11.36.1.2 Connector/Wiring Inspection. Check for mechanical integrity, resiliency, pitted or corroded mating surfaces, burn marks, condition, and type of wiring.
11.36.1.3 Electrolyte Levels. Electrolyte levels must be maintained just over the plates at all times. Replenish consumed water with distilled or demineralized water.
11.36.1.4 Sump Jar Maintenance. Inspect the electrolyte levels and the sump jar every 100 flight-hours.
11.36.2 Capacity Test. The capacity test should be performed as follows:
1. Check for proper battery installation per the STC or the manufacturer’s ICA when performing annual and 100-hour inspections and when replacing the battery after a capacity test.
2. Stabilize the battery at 15 °C (59 °F) or higher for at least 24 hours.
3. Remove the battery from the aircraft and charge it according to the recommended charging instructions. Allow the battery to stand on an open circuit for 1 hour.
4. Connect the fully charged battery to a capacity tester that incorporates a load resistance, ammeter, voltmeter, and a timer.
5. Discharge the battery at the C1 rate to 1.75 volts per cell (10 volts for a 12-volt battery and 20 volts for a 24-volt battery). Note the discharge time.
6. The battery is considered airworthy if it meets 80 percent of its C1 (1 hour) capacity rating. However, it is recommended to return batteries to service when their capacity is above the minimum (i.e., 85 percent minimum or 51 minutes to end point voltage).
7. If the battery fails to meet the minimum runtime, continue using the constant current C1 method in the manufacturer’s ICA. Allow the battery to stand on an open circuit for 1 hour.
8. Repeat the discharge test as indicated. If the failure persists, replace the battery.
9. If the battery is found to be airworthy, it must be recharged with constant potential (CP) prior to reinstalling it in the aircraft.
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11.37 Nickel-Cadmium Batteries.
11.37.1 Airworthiness Limitations. To ensure continued airworthiness, the battery should be removed and inspected per the manufacturer’s recommendations.
11.37.1.1 Connector/Wiring Inspection. Check for mechanical integrity, resiliency, pitted or corroded mating surfaces, burn marks, condition, and type of wiring.
11.37.1.2 Voltage Regulator. Periodic checks to correct out-of-tolerance regulators and replacement of defective units will reduce the possibility of inadvertent increases in charging voltage with the resultant rise in charge current and battery temperature and water consumption.
11.37.1.3 Battery. Inspect the can and cover for dents, damage, epoxy coating separation, vent tube obstruction, latch function, and cover seal condition.
Remove the battery cover and clean the top of the cells and connectors with a nylon brush. Verify torque on every intercell connection. If disassembly is required, discharge the battery first.
11.37.1.4 Electrolyte Levels. Electrolyte levels should be adjusted during the last 15 minutes of the topping charge and while the current is still flowing because the cells are at their most uniform electrolyte level at this time. Replenish electrolyte levels with distilled, deionized, or demineralized water only. Refer to the component maintenance manual for the syringe/nozzle specifications to ensure that the proper nozzle and syringe assembly are used to level the cells.
Using the incorrect nozzle may impact battery serviceability and longevity.
11.37.1.5 Electrical Leakage. Determine if external leakage is of such a magnitude that a complete battery cleaning is required. Follow the manufacturer’s recommended procedures.
11.37.1.6 Sensor Assembly. Inspect the battery for proper placement of thermostats, heaters, thermistors, or other sensor elements. Inspect wiring and receptacle for insulation damage, corrosion, and crimping or other defects. If the sensor/harness assembly fails testing or is damaged, it must be replaced.
Perform a functional test on the temperature sensor assembly at least once each calendar year.
11.37.2 Capacity Test. The capacity test must be performed in accordance with the manufacturer’s recommendations.
12-1 CHAPTER 12. ADDING OR RELOCATING INSTRUMENTS
12.1 Purpose. This chapter contains structural and design guidance to consider when aircraft alterations are to be accomplished by the addition or relocation of instruments.
12.2 Hazards and Warnings. The rapid advance of technical progress in the aviation industry has resulted in a virtual explosion of high-tech aftermarket instrumentation. In many instances, these innovations are marketed without the support of a proper certification process. As a result, much of the equipment purported to be the most advanced may not be certificated or even eligible for certification for installation on aircraft, which uninformed purchasers have chosen the equipment for installation.
Note: The burden of provision of and compliance with approved data falls entirely on the technician approving the aircraft for return to service.
12.3 Additional References. Before initiating an alteration involving the addition or relocation of instruments, the regulatory basis of the aircraft must be considered.
Chapter 1, General, provides guidance to be considered on the subject of certification basis. For this chapter, the following additional references are provided:
12.3.1 Department of Commerce (DOC), Aeronautics Branch, Aeronautics Bulletin 7a, section 71 provides regulatory requirements for electrical equipment applicable to the 24 makes and 115 models of aircraft certificated under the provisions of that document.
Section 72(B) of the same document provides additional regulatory requirements for instrumentation to be installed on the aircraft listed therein.
Note: Exercise care in using Bulletin 7a as a basis of proof for certification data.
Subsequent changes in ownership and production of some makes and models (M/M) may have also resulted in changes of the certification basis.
12.3.2 Civil Air Regulation (CAR) 18 and the related Civil Aeronautics Manual (CAM) 18, Maintenance, Repair, and Alteration of Certificated Aircraft, Aircraft Engines, Propellers, and Instruments, established and maintained the standards and practices for all maintenance, repair, and alteration of aircraft applicable under the provisions of the CAR.
That document remained in effect until the advent of the systemic changes dictated by the Federal Aviation Act of 1958 and the resultant documentary changes.
12.3.3 CAR 6, Rotorcraft Airworthiness; Normal Category.
12.4 Preparation. Before initiating any alteration involving the addition or relocation of instruments, the regulatory basis of the aircraft must be considered. For the purposes of this chapter the following references are provided:
• CAR 3.661 through 3.676 provides the regulatory basis for installation of instruments in CAR 3, Airplane Airworthiness—Normal, Utility, Acrobatic, and Restricted Purpose Categories, airplanes.
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• CAR 4a .532 thr ough 4a.537 provide the regulatory basis for supplemental variations for installation of instruments in CAR 4, Airplane Airworthiness, non-air carrier (NAC) airplanes.
• T itle 14 CFR § 23.1321 provides the regulatory basis for the arrangement and visibility of instruments in 14 CFR part 23 airplanes.
12.4.1 Structure. Chapter 2, Structural Data, provides guidance for determining structural integrity. Paragraphs 3.3 and 3.4 provide information pertinent to instrument panel installations.
12.4.2 Location. In the absence of specific regulatory requirements, for installation of instruments required for operation under instrument meteorological conditions (IMC), the recommended configuration is in the form of the basic “T” (see Figure 12-1).
Figure 12-1. The Basic “T” Visual Meteorological Conditions (VMC) Instrument Configuration
12.4.2.1 The aircraft attitude indicator is located at the top center of the installation.
12.4.2.2 The airspeed indicator is located adjacent to and left of the attitude indicator.
12.4.2.3 The altimeter is located adjacent to and to the right of the attitude indicator.
12.4.2.4 The directional indicator is located adjacent to and immediately below the attitude indicator.
Note: As instrument panel installations have become more complex, the basic “T” has become more difficult to accomplish. With the relocation of the directional indicator, the relationship of the Air Speed Indicator (ASI)-Attitude Indicator (ATI)-Altitude Indicator (ALT) combination is assumed.
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12.5 Installation. Throughout the development of the complexity of aircraft, the requirements for the mounting of all instruments have remained the same. All instruments must be mounted so they are visible to the crewmember primarily responsible for their use.
12.5.1 Structure. Before initiating changes to instrument panel installations, determine the load-bearing requirements of the component. In some aircraft, the instrument panel is stressed as the primary structure; with the majority, the panel is treated as the secondary structure with load-bearing responsibilities limited to instruments and equipment installed. Regardless of the structural nature, the altering technician is responsible for the installation to its original or properly altered state.
12.5.1.1 In all cases, where available, refer to the manufacturer’s instructions for continued airworthiness (ICA) when considering alterations to any structure.
For aircraft manufactured before the regulatory requirement for the manufacturer to provide such information, refer to AC 43.13-1, Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair, Chapter 4, Metal Structure, Welding, and Brazing, Section 4, Metal Repair Procedures, and/or Chapter 3, Communication, Navigation, and Emergency Locator Transmitter System Installations, of this AC for methods and techniques of retaining structural integrity.
12.5.1.2 If those sources are not available or applicable, we recommend that the altering individual have a Designated Engineering Representative (DER) approve the data before accomplishing the task.
12.5.2 Instrument Plumbing. The majority of CAR 3 and CAR 4 general aviation aircraft use instrumentation identified as “wet” gauges. This term has nothing to do with what is being measured by the gauge but rather the material to be measured is delivered directly to the gauge. Typical “wet” systems are fuel pressure, engine oil pressure, and, when so equipped, hydraulic pressure. While not usually considered “wet” systems, the airspeed and vacuum systems use this same system. The tubing used is generally thin-walled seamless aluminum or stainless steel. However, flexible rubber and/or neoprene lines are prevalent in airspeed and vacuum sensing lines.
12.5.2.1 The most reliable source of information on the material used in a particular aircraft is the manufacturer’s ICA. If that source is not available, AC 43.13-1, Chapter 8, Engines, Fuel, Exhaust, and Propellers, provides inspection and maintenance guidance on fuel lines while Chapter 9, Aircraft Systems and Components, provides the same level of information on hydraulic systems.
12.5.2.2 The installation of remote sensing systems per 14 CFR part 23 has replaced the “wet” systems with system pressures being remotely measured by transducers and electrically transmitted to the flight deck indicators.
12.5.2.3 Aircraft with long histories of alteration may contain a mixture of mechanical and/or electrical analogue instruments and digital presentations.
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12.5.3 Venturi Vacuum Source. A venturi is a relatively low-cost means of producing the vacuum to operate gyroscopic instruments, such as the turn and bank, directional gyro, and artificial horizon. It is mounted on the exterior of the fuselage, parallel with the longitudinal axis of the aircraft. As the aircraft moves through the air, an area of reduced pressure, a partial vacuum, is created in the throat of the venturi. The venturi throat is connected by a tube to the gyro instrument case, resulting in a reduction of pressure within the case. Ambient air, entering the instrument through the inlet port of the case, passes over the gyro rotor, causing it to spin rapidly, and causes the instrument to activate. Venturis are available in sizes providing 2, 4, and 9 inches of mercury (inHg) of vacuum.
12.5.3.1 The vacuum requirement for the operation of each instrument is generally provided on the data plate attached to its case. If it is not, obtain the data from the manufacturer or another acceptable source, such as Army/Navy and Air Force/Navy (AN) and MS standards.
12.5.3.2 If the vacuum available exceeds the requirements of the installation, it will be necessary to install an in-line regulator to adjust the flow within requirements.
12.5.4 Pumped Vacuum Source. Current aviation technology has produced durable light-weight, mechanically-driven pump and control systems for providing instrument operating vacuum. Selection of the correct pump remains dependent on the vacuum requirements of the system being driven. Control is provided by either the system itself or an in-line regulator. Production and aftermarket standby vacuum systems are available to provide operating capabilities in the event of failure of the primary mechanically-driven system.
12.5.5 Calculating Vacuum Loads. When a venturi vacuum source is selected, do not assume the venturi selected will provide sufficient flow and negative pressure to operate the instrument package. Even within the M/M of the venturi selected, tolerance may be insufficient to meet the requirements of the system selected. Therefore, it is essential that the vacuum load requirements be carefully evaluated.
12.5.5.1 Gyroscopic Instruments. Gyroscopic instruments require optimum value of airflow to produce their rated rotor speed. For instance, a specific bank and pitch indicator required approximately 2.30 cubic feet per minute (CFM) flow and a resistance, or pressure drop, of 4 inHg. If the altering technician has selected a 2 inHg Venturi, the resultant vacuum would be insufficient to drive the instrument.
12.5.5.2 Examples. The following vacuum driven items are examples for the purposes of calculation:
12-5 Table 12-1. CFM/Vacuum Values Instrument Flow Vacuum Bank and Pitch Indicator 2.3 CFM 4.0 inHg Directional Gyro Indicator 1.3 CFM 4.0 inHg Turn and Bank Indicator 0.5 CFM 2.0 inHg Total flow required 4.10 CFM
12.5.5.3 Table of Instruments. The above listed instruments are listed in Tables 12-2 and 12-4, Differential Pressure Across the Instrument Inlet and Outlet of the Example Instrument Packages. Optimum values are shown in Table 12-4. The negative pressure air source must deliver not only the optimum vacuum value for the instruments but must also have sufficient volume capacity to accommodate the total flow requirements of the various instruments it serves.
Note: The example components listed above and in Tables 12-2 and 12-4 are accepted as viable, and the operating parameters related to them are accurate. The nomenclature and the related properties have no effect on the resulting computations.
Table 12-2. Instrument Air Consumption for Example Vacuum-Driven Autopilot and Instrument Installations Instrument Air Consumption at Sea Level Differential Drop inHg Suction (Optimum) Cubic Feet per Minute Automatic Pilot System (Type A-2, A-3, and A-3A) Directional gyro control unit across mount assembly 5.00 2.15* Bank and climb gyro control unit across mount assembly 5.00 3.85* Total ― 6.00* Automatic Pilot System (Type A-4) Directional gyro control unit 5.00 3.50* Bank and climb gyro control unit 5.00 5.00* Total ― 8.50* Bank and pitch indicator 4.00 2.30 Directional gyro indicator 4.00 1.30 Turn and bank indicator 2.00 0.50 Note: Asterisk (*) indicates it includes air required for operations of pneumatic relays.
12-6 Table 12-3. Equivalent Straight Tube Line Drops for Each 90-Degree Elbow Installed in Any Given System (By O.D.)
Tubing Size Pressure Drop in a 90˚ Elbow in Terms of Length of Straight Tube Equivalent to a 90˚ Elbow O.D.
Inch Wall Thickness Inch Feet 1/4 X 0.035 0.28 3/8 X 0.035 0.46 1/2 X 0.042 0.62 5/8 X 0.042 0.81 3/4 X 0.049 0.98 1 X 0.049 1.35 Table 12-4. Differential Pressure Across the Instrument Inlet and Outlet of the Example Instrument Packages Instrument Suction in inHg Minimum Optimum Maximum Automatic Pilot System (Type A-2, A-3, and A-3A) Directional gyro control unit across mount assembly 4.75 5.00 5.25 Bank and climb gyro control unit across mount assembly 4.75 5.00 5.25 Gauge reading (differential gauge in B and C control unit) 3.75 4.00 4.25 Automatic Pilot System (Type A-4) Directional gyro control unit 3.75 5.00 5.00 Bank and climb gyro control unit 3.75 5.00 5.00 Bank and pitch indicator 3.75 4.00 5.00 Directional gyro indicator 3.75 4.00 5.00 Turn and bank indicator 1.80 2.00 2.20
12.5.5.4 Calculation of Equivalent Straight-Line Pressure Drop Due to Routing. In addition to the effects of the instrumentation itself, consideration must be given to the parasitic resistance to flow provided by the routing of the tubing providing the source pressure to the instruments. For this problem, assume the example system has four right-angle elbows and 20 feet of 1/2-inch O.D. x
0.042-inch tubing.
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12.5.5.5 Solution to the Stated Problem (Step-by-Step).
12.5.5.5.1 Flow Requirements. Accept the flow requirements of the example instruments listed in paragraph 12.5.5.2 as 4.10 CFM. The pressure drop for one 90-degree 1/2-inch O.D. elbow is equivalent to 0.62 feet of straight tubing.
Therefore, the pressure drop of the four 90-degree elbows is equivalent to
2.48 feet of tubing (see Table 12-3, Equivalent Straight Tube Line Drops for Each 90-Degree Elbow Installed in Any Given System (By O.D.)).
12.5.5.5.2 Pressure Drop. Determine the pressure drop through 22.48 feet (20 feet plus the above 2.48 feet) of 1/2-inch O.D. x 0.42-inch tubing at 4.10 CFM flow (see Figure 12-2, Pressure Drop Data for Smooth Tubing).
Figure 12-2. Pressure Drop Data for Smooth Tubing
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1. The pressure drop for each 10-foot length of that tube is 0.68 inHg.
2. Divide 22.48 feet of tubing to determine the number of 10-foot lengths
(i.e., 22.48 divided by 10 equals 2.248).
3. Multiply the number of sections (2.248) by 0.68 inHg to obtain the pressure drop through the system (0.68 x 2.248 = 1.53 inHg).
4. The pump must, therefore, be capable of producing a minimum pressure differential of 5.63 inHg (i.e., 4.10 inHg) for maximum instrument usage + 1.53 inHg (determined) at a flow of 4.10 CFM.
12.5.5.5.3 Filters. Filters are used to prevent dust, lint, or other foreign matter from entering the instrument and vacuum system. Filters may be located at the instrument intake port or the manifold intake port when instruments are interconnected. Determine if the flow capacity of the filter is equal to or greater than the flow capacity of the vacuum system. If it is not, the restriction will create a pressure drop in the system. AC 43.13-1, Chapter 12, Aircraft Avionics Systems, paragraph 38 provides additional guidance on the installation and maintenance of venturi and engine-driven vacuum and instrument systems.
12.5.5.5.4 Electrical Supply for Instruments. AC 43.13-1, Chapter 11, Aircraft Electrical Systems, provides information on the inspection and installation of electrical systems.
12.5.5.5.5 Instrument Lighting. The regulatory requirements for instrument lighting have changed little as certification specifications have developed.
1. CAR 3.696 and 3.697 provide two paragraphs simply stating that instrument lights (1) should be installed safely, (2) provide sufficient illumination to make instruments and controls easily readable, and (3) shall be installed in such a manner as not to shine in the pilot’s eyes.
2. CAR 4a.577 adds that instrument lighting shall be equipped with a rheostat control for dimming unless it can be shown a non-dimming light is satisfactory.
3. Title 14 CFR § 23.1381 consolidates the language of the earlier regulatory requirements with no appreciable changes.
12.5.5.5.6 Magnetic Direction Indicator. The magnetic compass is commonly referred to as the whiskey compass. The maximum deviation limitations of magnetic compasses have changed little since 1928.
1. CAR 3.666 specifies that the Magnetic Direction Indicator must be installed so that its accuracy is not excessively affected by the airplane’s vibration or magnetic field. After compensating for this in the installation, the deviation level in flight must not exceed 10 degrees on any heading.