reinforcement such as that shown in Figure 9-18, at the attachment point. This will allow the fuselage to flex while still maintaining a collapsible structure to absorb the loads encountered in a crash.
919. THRU 922. RESERVED
FIGURE 9-14. TYPICAL WING CARRY-THROUGH INSTALLATION
FIGURE 9-15. TYPICAL HAT SECTION REINFORCEMENT INSTALLATION
Par 918 Page 98
FIGURE 9-16. TYPICAL BULKHEAD REINFORCEMENT INSTALLATION
FIGURE 9-17. TYPICAL STRINGER SECTION REINFORCEMENT INSTALLATION
Par 918 Page 99
FIGURE 9-18. TYPICAL LOCALIZED STRINGER SECTION REINFORCEMENT
INSTALLATION
FIGURE 9-19. TYPICAL ATTACHMENTS TO TUBULAR MEMBERS
Par 918 Page 100
Par 923 Page 101 SECTION 3. STATIC STRENGTH AND TESTING
923. PROOF OF COMPLIANCE. Retrofit harness installations must be proven to meet minimum strength requirements applicable to the aircraft certification basis; otherwise, their ability to provide adequate restraint under accident decelerations is undetermined. Static strength requirements can be demonstrated by static test or stress analysis.
a. Static tests are accomplished by application of the ultimate load to the harness attachment point.
Since TSO and PMA restraints have already been shown to comply with strength requirements, static tests are accomplished to substantiate the airframe attachment. Static testing in operational aircraft is undesirable because there is the risk of airframe damage; however, static testing in a conforming but unserviceable fuselage or cabin section of the same make and model aircraft is an acceptable alternative.
b. Stress analysis is accomplished through engineering data developed for the specific attachment point. This data can be developed by FAA Designated Engineering Representatives (DER) with aircraft structural approval authority.
The DER will perform the analysis, prepare a report, and complete FAA Form 8110-3, Statement of Compliance with the Federal Aviation Regulations, which demonstrates that a specific regulation has been met. The DER will list on FAA Form 8110-3 the data needed to show the structural adequacy of the installation of the harness. Since the DER is only approving the structural aspects of harness attachment, approval for return to service for the installation as a whole is accomplished by the authorized individual or agency on FAA Form 337.
To locate an appropriately authorized DER in your locality, contact the FAA Flight Standards District Office or Aircraft Certification Office having jurisdiction in your geographic area.
NOTE: It is up to the installer to determine which method will be the most efficient. For simple installations, it is possible that the DER could perform stress analysis in just a few hours. The DER may also be able to assist in the design of attachment points.
924. LOAD AND DISTRIBUTION ― AIRPLANES. Table 9-1 provides a reference to determine minimum static test loads based upon certification date, category, standard occupant weight, fitting factors, a nd harness factors. The numbers in each line are multiplied together to obtain the static test load minimum standard.
a. Load. For airplanes type-certificated prior to September 14, 1988, occupant weights were established as 170 pounds for normal category and 190 pounds for utility and acrobatic category airplanes. The additional 20 pounds accounts for a parachute. For aircraft type-certificated on or after this date, 215 pounds is the established weight for the 3 categories.
b. Distribution. In the assessment of a combined shoulder harness-safety belt restraint system, a forward static test load distribution of 40 percent to the shoulder harness and 60 percent to the safety belt has been an acceptable combined static test load distribution. Therefore, demonstration of harness attachment static strength is accomplished by applying 40 percent of the ultimate restraint system load to a single or “Y” type harness attachment, or 20 percent of the load simultaneously to each attachment of a dual independent harness.
Static strength test load requirements for the fifth belt of a 5-point system have not been established for aircraft.
c. Factor. The airplane must be designed to protect each occupant during emergency landing conditions. The critical ulti mate static load is established at 9.0 G’s in the forward direction. If the attachment can sustain this load, it is assumed the lesser loads in upward, sideward, and downward directions will be accommodated.
d. Fitting Factors. Regulations prescribe multiplying factors of safety, fitting factors, that
structural attachments must be subjected to in order to prove minimu m load bearing capabilities. A
1.15 fitting factor for restraint attachments in small aircraft type-certificated prior to September 14, 1969, must be used. For aircraft type-certificated on or after this date, a fitting factor of 1.33 must be used.
925. LOAD AND DISTRIBUTION ― NORMAL CATEGORY HELICOPTERS.
a. Load. For helicopters type-certificated in the normal category, occupant weights are established as 170 pounds.
b. Distribution. In the assessment of a combined shoulder harness-safety belt restraint system, for helicopters type-certificated prior to December 13, 1989, a forw ard static test load distribution of 40 percent to the shoulder harness and 60 percent to the safety belt is the required combined static test load distribution.
c. G Factor. For helicopters type-certificated prior to December 13, 1989, the critical ultimate static load is established at 4.0 G’s in the forward direction. If the attachment can sustain this load, it is assumed the loads in upward, sideward, and downward directions will be accommodated.
NOTE: Due to increased G factors and limited applicability for retrofit harnesses installations, helicopters type-certificated on or after December 13, 1989, are not addressed in this chapter. Additionally, airplanes seat/restraint systems typecertificated after September 14, 1988, must undergo dynamic testing, as prescribed by § 23.562, which is not covered in this chapter.
926. DEMONSTRATING STATIC LOADS.
Two methods are available to demonstrate compliance with static load requirements. One method involves the fabrication of test blocks and application of the ultimate load to the blocks that are being restrained by the harness. The other method involves use of an equation to calculate and simulate the ultimate load at the harness attachment fitting, compensating for horizontal and vertical angles as a result of restraint attachment geometry.
a. Test Blocks. Although AC 23-4, Static Strength Substantiation of Attachment Points for Occupant Restraint System Installations, was cancelled on January 27, 2003, it is still available in various archives and can be used as an acceptable method for fabricating test blocks and applying static loads to restraints. Using this method, deceleration loads imposed upon the restraint by the occupant are accurately duplicated, and the load figures in Table 9-1 can be applied directly to the test blocks. Because of the time-consuming nature of fabricating test blocks for this procedure, it may be desirable to use the second method described below that, in effect, replaces the test blocks with an equation.
b. Calculation. The alternate method is to perform a mathematical calculation to account for the angles that the attachment points are subjected to during decelerations. Increases in angles can result in a significant increase in the load that must be applied to simulate belt loading during occupant decelerations. It is not uncommon for a harness to impose both vertical and horizontal angles that must be compensated for by use of the equation. (See Figures 9-20 and 9-21.) In the case of a “Y” type harness, the horizontal angle is eliminated as long as the attachment is located along the vertical centerline of the occupant.
(1) The equation used to perform the calculation is:
Test Load = [Static Test Minimum] [1/Cosine(vertical angle)] [1/Cosine(horizontal angle)]
(2) Table 9-2 provides 1/Cosine numbers for various angles. These numbers can be inserted into the equation to determine the static load that needs to be applied. For example, using Table 9-1 and Table 9-2, if the airplane is normal category, post-September 14, 1969, pre-September 14, 1988, Par 924 Page 102
Par 926 Page 103 the test load is 814 lbs. If the horizontal angle is 10o and the vertical angle is 15 o, the belt load is calculated as follows.
Test Load = [814][1/Cos(15)][1/Cos(10)] = [814][1.035][1.015] = 855 lbs.
This is not a large increase, but if both angles were 30o, the belt load would be 1086 lbs.
[814][1.155][1.155] = 1086 If there is no angle pr esent in one of the directions, that portio n of the equation is eliminated. For an airplane type-certificated in the normal category prior to September 14, 1969, with a vertical angle of 25 degrees, the equation would be: [704][1.103] = 777 lbs.
c. After obtaining the test load value, the load is applied for a minimu m of 3 seconds, forward (horizontally) when using test blocks, or in the direction of the restraint angles when applying the load to the attachment point(s).
d. Equipment used for measuring test loads must be calibrated to a standard acceptable to the FAA. Load-cells are capable of performing these measurements; however, other equivalent equipment as determined by the user may be acceptable.
927. THRU 930. RESERVED
TABLE 9-1. STATIC TEST REQUIREMENTS TC Basis
Airplanes Category* G Factor Weight Factor (lbs) Fitting Factor Harness Factor (40%) Static Test Minimum Load (lbs) Effective 09/14/88 and on N, U, A 9 215 1.33 .4 1029 N 9 170 1.33 .4 814 Effective 09/14/69 U, A 9 190 1.33 .4 910 N 9 170 1.15 .4 704 Pre 09/14/69 U, A 9 190 1.15 .4 787 Helicopter Pre 12/16/84 N 4 170 1.15 .6 469 Helicopter Post 12/16/84 Pre 12/13/89 N 4 170 1.33 .6 543
• N=Normal, U=Utility, A=Acrobatic
• ** Airplane seat/restraint systems type certificated after September 14, 1988, must undergo dynamic testing, as prescribed by § 23.562, which is not covered in this chapter.
TABLE 9-2. CALCULATED 1/COSINE VALUES Degrees 5 10 15 20 25 30 35 40 50 60 1/Cos Multiplier
1.004 1.015 1.035 1.064 1.103 1.155 1.221 1.305 1.556 2.0
FIGURE 9-20. VERTICAL ANGLE
FIGURE 9-21. HORIZONTAL ANGLE
Par 926 Page 104
Par 931 Page 105 SECTION 4. INSTALLATION AND INSPECTION CHECKLISTS
931. GENERAL. The following checklists are not all-inclusive, but may provide a quick reference for factors to consider when installing retrofit shoulder harnesses and for establishing instructions for continued airworthiness of retrofit harness installations. If available, manufacturer’s instructions take precedence over this AC.
a. Shoulder Harness Installation Checklist.
(1) Locate potential attach points.
(2) Evaluate the geometry of attach points in relation to the occupant and determine the best harness configuration. Short belt lengths are desirable.
(3) Ensure that the configuration will allow unimpeded egress for all occupants. Singlepoint release is mandatory. There should be a means to secure belts and harnesses when not in use to avoid interfering with operation of the airplane or egress from it.
(4) Restraints must allow crewmembers to perform all necessary flight operation functions while seat belts and harnesses are fastened.
(5) Utility and acrobatic category airplane restraints must accommodate an occupant wearing a parachute.
(6) If retractors will be used, ensure that mounting will provide straight-line entry and exit of webbing to prevent binding or frictional drag.
Retractor loading should not impose bending forces upon retractor mounting brackets.
(7) If harness installation will impose loads on the seat back or seat attachment, additional evaluation will be needed for structural integrity.
(8) Refer to the aircraft type certificate to find the certification date and basis to establish minimum static load requirements. Determine the feasibility of performing static tests or stress analysis. Static testing on operational aircraft is not recommended.
(9) Select only restraints that meet OEM, TSO, PMA, or other established industry standards or specifications.
(10) Install restraints using AN, MS, NAS, or other acceptable aircraft hardware with adequate strength properties.
(11) Perform a check to ensure all components function properly.
(12) Complete record entries as required, including FAA Form 3 37, logbook, weight and balance, and equipment list.
b. Shoulder Harness Inspection Checklist.
Inspect restraint system for condition and function at each annual or each required inspection of cabin or cockpit equipment. If questions arise regarding any of the conditions listed below, contact the restraint manufacturer for specific limits.
(1) Inspect stitching on webbing for broken or missing stitches.
(2) Inspect webbing for fraying, fading or cuts. Fraying that causes binding in the retractor is excessive. Fading caused by exposure to sunlight or chemicals may indicate a reduction in strength.
(3) Ensure that TSO, PMA, OEM, or other required identification tags are present and legible on each belt assembly. Tags may not be required for harnesses manufactured prior to March 27, 1987. Contact the aircraft or restraint manufacturer for specific requirements.
(4) If so equipped, check the harness post on the lap belt to make sure the nylon bushing or grommet is present and functional to provide positive harness end fitting engagement. Do not replace the bushing with nylon bundle ties. Contact
the belt manufacturer for replacement bushings/grommets and instructions.
(5) Check the belt buckle for latching and release functions.
(6) Check the retractors to ensure that locking mechanisms engage when webbing is positioned at the normal operating length. Inertia reels should lock when the webbing is accelerated quickly out of the reel. Automatic locking retractors should lock at approximately one-inch increments as the webbing retracts back into the reel.
(7) Inspect buckles, connectors, and fittings for corrosion, cr acks, or other damage.
Check mounting hardware for security and ensure that airframe attachment of end fittings self-align and do not bind.
(8) Inspect quick release end fittings for cotter pins.
(9) If equipped with manual locking inertia reel, check for proper operation and condition.
932. THRU 999. RESERVED
Par 931 Page 106
CHAPTER 10. AIRCRAFT BATTERY INSTALLATIONS SECTION 1. GENERAL 1000. PURPOSE. This chapter contains structural and design considerations for the fabrication of aircraft battery installations.
1001. HAZARDS AND WARNINGS:
HANDLING PRECAUTIONS. Serious injury can result from carelessness while handling and working with batteries. Failure to heed these warnings could result in serious injury or death.
a. All tools must be insulated.
b. Care must be taken with all metal items to include clothing items such as belt buckles, zippers, metal fasteners and wallet chains, as well as jewelry items such as rings, watches, bracelets, and necklaces. All metal or conductive articles should be removed from your person when handling batteries.
c. Wear protective clothing and eye protection. The electrolyte can cause burns if in contact with skin or eyes. Do not touch eyes, nose, or mouth after handling batteries or acid.
d. Do not smoke or hold naked flames near batteries on charge. If allowed to accumulate in a confined space, the gases emitted during charge could cause an explosion. To prevent the accumulation of hydrogen gas in the manifold, do not charge a flooded electrolyte or vented battery on the bench with the cover on.
e. Do not service flooded or vented lead-acid and nickel-cadmium batteries in the same shop area, as cross contamination of acid and alkaline electrolytes may happen.
f. Always pour acid into water, NEVER pour water into acid.
g. Do not use petroleum spirits, trichloroethylene, or other solvents.
h. Know the location and use of emergency eyewash and shower nearest the battery charging area.
1002. ADDITIONAL REFERENCES (current editions).
a. AC 20-106, Aircraft Inspection for the General Aviation Aircraft Owner.
b. AC 43-4, Corrosion Control for Aircraft.
c. AC 120-27, Aircraft Weight and Balance Control.
d. Civil Aviation Regulation 6, Rotorcraft Airworthiness; Normal Category.
e. Federal Aviation Administration (FAA)-H-8083-1, Aircraft Weight and Balance Handbook.
f. FAA-H-8083-19, Plane Sense General Aviation Information.
1003. LOCATION REQUIREMENTS. The battery installation and/or its installation should provide:
a. Accessibility for Battery Maintenance and Removal. The installation should ensure that the battery could be easily installed or removed and serviced without removing seats, fairings, etc.
b. Protection from Engine Heat. If installed in the engine compartment the battery should be protected from extreme heat both during engine operation and after the engine has been shut down.
This kind of protection can be provided by a source of cooling air to the battery box or additional thermal Par 1000 Page 107
protection around the battery. Care should be taken not to interfere with the flow of engine-cooling air.
c. Protection from Mechanical Damage .
Vibration and other shock loads are a major cause of short battery life. Install the battery in a location that will minimize damage from airframe vibration and prevent accidental damage by passengers or cargo.
d. Passenger Protection. Insure that the battery is enclosed within a container/box so that passengers/crew are protected from any fumes or electrolytes that may be spilled as a result of battery overheating, minor crash, or un-intentional inverted flight.
e. Airframe Protection . To minimize damage to adjacent metal structures, fabric covering or electrical equipment can be accomplished by properly locating battery drains and vent discharge lines, and adequately venting the battery compartment. To protect the airframe structure and fluid lines apply asphaltic or rubber-based paint to the areas adjacent to and below the battery or battery box.
1004. AIRCRAFT STORAGE BATTERY DESIGN AND INSTALLATION.
a. Lead Acid.
(1) Each aircraft storage battery, whether approved to a Technical Standards Order (TSO) or not, must be designed as required by regulation and installed as prescribed by the manufacturer.
(2) No explosive or toxic gases emitted by any battery in normal operation, or as the result of any probable malfunction in the charging system or battery installation, may accumulate in hazardous quantities within the airplane.
(3) Corrosive fluids or gases that may escape from the battery may damage surrounding structures or adjacent essential equipment.
b. Nickel Cadmium.
(1) Each aircraft storage battery, whether approved to a TSO or not, must be designed as required by regulation and installed as prescribed by the manufacturer.
(2) Safe cell temperatures and pressures must be maintained during any probable charging and discharging condition. No uncontrolled increase in cell temperature may result when the battery is recharged (after previous complete discharge).
(a) At maximum regulated voltage or power;
(b) During a flight of maximum duration; and
(c) Under the most adverse cooling condition likely to occur in service.
(3) Compliance with paragraph 1004b(2) must be shown by tests unless experience with similar batteries and installations has shown that maintaining safe cell temperatures and pressures presents no problem.
(4) No explosive or toxic gases emitted by any battery in normal operation, or as the result of any probable malfunction in the charging system or battery installation, may accumulate in hazardous quantities within the airplane.
(5) Corrosive fluids or gases that may escape from the battery may damage surrounding structures or adjacent essential equipment.
1005. DUPLICATION OF THE MAN- UFACTURER’S INSTALLATION. The availability of readymade parts and attachment fittings may make it desirable to consider the location and/or type of installation selected and designed by the airframe manufacturer. Appreciable savings in time and work may be realized if previously approved data and/or parts are used.
1006. OTHER INSTALLATIONS. If the battery installation has not been previously approved, or if the battery is to be installed or Par 1003 Page 108
Par 1005 Page 109 relocated in a manner or location other than provided in previously approved data, perform static tests on the completed installation as outlined in chapter 1.
Because of the concentrated mass of the battery, the support structure should also be rigid enough to prevent undue vibration or undue shock, which may lead to early structural failure.
1007. DELIVERY INSPECTION. When the battery is unpacked, a thorough inspection should be made to ensure that no damage occurred during shipment. Inspect the shipping container as well as the battery. Before putting the battery into service, perform a safety check by following these points carefully.
a. Damage. See if any liquid has spilled into the shipping container. This may indicate that a cell is damaged. Check for dented, cracked, or discolored areas on the sides and bottom of the battery case. Check for cracked cell cases or covers.
Do not place a damaged battery into service.
b. Shorting Straps. Some nickel-cadmium batteries are shipped with shorting devices across the main power receptacle output terminals. Before subjecting a battery to electrical service this device must be removed.
c. Electrical Connections. Test all terminal hardware to ensure tightness. Poor electrical contact between mating surfaces may reduce discharge voltage, cause local overheating and damage the battery.
NOTE: Before charging the battery read and become familiar with the manufacturer’s charge procedures.
1008. BATTERY INSTALLATION AND REMOVAL. The following instructions are generic. See the airframe manufacturer’s maintenance manuals or STC for instructions specific to a particular aircraft model.
a. Removal.
(1) Set master switch to the OFF position and tag the switch.
(2) Disconnect any external power supply.
(3) Open battery compartment access panels.
(4) Disconnect battery quick disconnect plug or remove terminal bolts and disconnect battery cables from battery terminals. Always disconnect the ground cable first and install the ground cable last.
(5) Disconnect battery ventilation tubes, if any.
(6) Unlock battery hold down clamps or remove battery hold down bars. Disengage battery.
(7) Carefully remove battery.
WARNING: Batteries are heavy.
Use appropriate lifting devices or equipment. Use battery handles where provided.
b. Installation.
(1) Inspect the battery for damage.
Cracks in metal or plastic containers are not permitted. Dents in metal containers that impinge on the interior plastic container are not acceptable.
(2) Set master switch to the OFF position and tag (explain what should be on the tag “Do not turn on master switch”).
(3) Disconnect any external power supply and tag (explain what should be on the tag “Do not connect external power”).
(4) Open battery compartment access panels.
(5) Ensure the battery container or tray is clean and dry. Treat and paint any corrosion areas.