4-14 Figure 4-16. VOR Rabbit Ear Fig ure 4-17. VOR Blades
4-15 Figure 4-18. Transponder/DME Probe Fig ure 4-19. DME/Transponder Blade
5-1 CHAPTER 5. ANTICOLLISION AND SUPPLEMENTARY LIGHT INSTALLATION
5.1 Purpose. This chapter gives procedures and standards to be used when replacing older rotating beacon assemblies and wing lights with strobe or other anticollision systems.
This chapter assumes that the newer units have FAA approval in the form of a Parts Manufacturer Approval (PMA) or Technical Standard Order (TSO) and not an experimental or aviation unit.
5.2 Hazards and Warnings. When installing anticollision lights, take care to ensure the unit is properly grounded, the airframe structure can support the new unit, and the aircraft wiring is of the correct size. Mechanics should take special precautions to protect their eyes when testing the new unit. Strobe lights are especially hazardous in dark or darkened hangars when activated.
5.3 Regulations and Other References. The operational requirements for anticollision lights can be found in 14 CFR § 91.205. Information regarding installation requirements for nontransport category aircraft is included in 14 CFR §§ 23.1401 and 27.1401. Additional information can be found in AC 20-30, Aircraft Position Light and Anticollision Light Installations; AC 20-74, Aircraft Position and Anticollision Light Measurements; and Civil Air Regulation (CAR) 6, Rotorcraft Airworthiness; Normal Category. Aircraft for which an application for type certificate (TC) was made before April 1, 1957, may conform to either the above regulations or to the following standards:
5.3.1 Anticollision lights, when installed, should be installed on top of the fuselage or tail in such a location that the light will not impair the flight crewmembers’ vision and will not detract from the conspicuity of the position lights. If there is no acceptable location on top of the fuselage or tail, a bottom fuselage or wing tip installation may be used.
5.3.2 The color of the anticollision light must be either aviation red or aviation white in accordance with the specifications of 14 CFR § 23.1397 or 14 CFR § 27.1397, as applicable.
5.3.3 The arrangement of the anticollision light system (i.e., number of light sources, beam width, speed of rotation, other characteristics, etc.) must give an effective flash frequency of no less than 40 but not more than 100 cycles per minute. The effective flash frequency is the frequency at which the aircraft’s complete anticollision light system is observed from a distance and applies to each sector of light, including any overlaps that exist when the system consists of more than one light source. In overlaps, flash frequencies may exceed 100 but not more than 180 cycles per minute.
5.3.4 The system must consist of enough lights to illuminate the vital areas around the aircraft, considering the physical configuration and flight characteristics of the aircraft. The field of coverage must extend in each direction within at least 75 degrees above and 75 degrees below the horizontal plane of the aircraft. The minimum light intensity and minimum effective intensities are given in 14 CFR §§ 23.1401 and 27.1401, respectively.
5.3.5 Supplementary lights may be installed, in addition to position and anticollision lights required by applicable regulations, provided that the required position and anticollision
5-2 lights are continuously visible and unmistakably recognizable and their conspicuity is not degraded by such supplementary lights.
5.4 Operational Considerations: Crew Vision. Partial masking of the anticollision light may be necessary to prevent direct or reflected light rays from any anticollision or supplementary light from interfering with crew vision. Determine if the field of coverage requirements are met. An acceptable method of preventing light reflection from the propeller disc, nacelle, or wing surface is an application of nonreflective paint on surfaces that present a reflection problem. Perform a night flight check to ensure that any objectionable light reflection, sometimes known as flicker vertigo, has been eliminated.
Enter a notation to that effect in the aircraft records.
5.5 Installation Considerations.
5.5.1 Communication and Navigation. Ensure that the installation and operation of any anticollision or supplementary light does not interfere with the performance of installed communication or navigation equipment. Capacitor discharge light (strobe) systems may generate radio-frequency interference (RFI). This radiated interference can be induced into the audio circuits of communication or navigation systems and is noticeable by audible clicks in the speaker or headphones. The magnitude of RFI disturbance does not usually disrupt the intelligence of audio reception.
5.5.2 Precautions. RFI can be reduced or eliminated by observing the following precautions during installation of capacitor discharge light systems:
1. Locate the power supply at least 3 feet from any antenna, especially antennas for radio systems that operate in the lower frequency bands.
2. Ensure that the lamp unit (flash tube) wires are separated from other aircraft wiring, placing particular emphasis on coaxial cables and radio equipment input power wires.
3. Make sure that the power supply case is adequately bonded to the airframe.
4. Ground the shield around the interconnecting wires between the lamp unit and power supply at the power supply end only.
5.6 Markings and Placards. Identify each switch for an anticollision/supplementary light and indicate its operation. The aircraft should be flight tested under haze, overcast, and visible moisture conditions to ascertain that no interference to pilot vision is produced by operation of these lights. If found unsatisfactory by test or in the absence of such testing, a placard should be provided to the pilot stating that the appropriate lights be turned off while operating in these conditions.
5.7 Electrical Installation. Install an individual switch for the anticollision light or supplementary light system that is independent of the position light system switch. Data for the installation of wiring, protection devices, and generator/alternator limitations is contained in AC 43.13-1, Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair, Chapter 11, Aircraft Electrical Systems. Ensure that the terminal voltage at each light is within the limits as prescribed by the manufacturer.
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5.8 Alteration of Structure.
5.8.1 The simplest light installation is to secure the light to a reinforced fuselage skin panel.
The reinforcement doubler shall be of equivalent thickness, material, and strength as the existing skin. (Install as shown in Figure 5-1.)
Figure 5-1. Typical Anticollision or Supplementary Light Installation in a Skin Panel (Unpressurized)
5.8.2 When a formed angle stringer is cut and partially removed, position the reinforcement doubler between the skin and the frame. The doubler is to be equivalent to the stringer in thickness and extend lengthwise beyond the adjacent fuselage frames. The distance between the light and the edge of the doubler is to be twice the height of the doubler flange (see Figure 5-2, Typical Anticollision or Supplementary Light Installation Involving a Cut Stringer (Unpressurized), for typical installation).
5-4 Figure 5-2. Typical Anticollision or Supplementary Light Installation Involving a Cut Stringer (Unpressurized)
5.8.3 Engineering evaluation is required for installations involving the cutting of complex formed or extruded stiffeners, fuselage frames, or pressurized skin of pressurized aircraft.
5.8.4 Vertical stabilizer installations may be made on the aircraft if the stabilizer is large enough in cross-section to accommodate the light installation and if aircraft flutter and vibration characteristics are not adversely affected. Locate such an installation near a spar, and add formers as required to stiffen the structure near the light. A typical installation is shown in Figure 5-3, Typical Anticollision or Supplementary Light Installation in a Fin Tip.
5-5 Figure 5-3. Typical Anticollision or Supplementary Light Installation in a Fin Tip N ote: Skin thickness of the mounting ring and fairing are at least equivalent.
5.8.5 Rudder installations are not recommended because of the possible structural difficulties.
However, if such installations are considered, an FAA engineering evaluation must be made to determine whether the added mass of the light installation will adversely affect the flutter and vibration characteristics of the tail surfaces.
6-1 CHAPTER 6. SKI INSTALLATIONS
6.1 Purpose. This chapter provides information about ski installations on small airplanes.
The information provided for main ski and nose ski installations applies to wheel replacement skis only. Tire-cushioned skis other than tail skis, wheel penetration skis, and hydraulically adjustable or retractable skis involve special considerations and cannot be installed by relying solely on data in this AC.
6.2 Hazards and Warnings. Operation of ski planes exposes the airplane and its occupants to additional risks not associated with wheel-equipped landplanes. The additional weight and surface area of skis impose additional ground and air loads on the airplane. Ground handling, taxiing, takeoff, and landing can place significant side loads and twisting moments on the landing gear and its attachment structure, which can cause hidden or cumulative damage, or both. Improper rigging, weak springs or shock cords, or all, can cause the skis to “dump,” or rotate nose down in flight, possibly rendering the airplane uncontrollable or causing it to break up in flight. Skis with weak springs or shock cords may rotate nose down and “dig,” or penetrate the snow, during takeoff or landing on uneven or drifted snow, which could result in an accident. In-service failure of ski attachment hardware, springs, shock cords, or cables creates a high risk of those parts or a ski itself entering the propeller arc, which has resulted in complete loss of airplanes in flight. For these reasons, proper installation, rigging, periodic inspection, and maintenance of skis and their attaching parts are of utmost importance to safety.
Consultation with experienced ski maintenance technicians and operators is strongly recommended when considering any new ski installation or any alteration of an existing ski installation.
6.3 Additional References (current editions).
• Airframe and ski manufacturers’ data, if available.
• AC 43.13-1, Acceptable Methods, Techniques, and Practices―Airplane Inspection and Repair.
• AC 43-210, Standardized Procedures for Obtaining Approval of Data Used in the Performance of Major Repairs and Major Alterations.
• Civil Air Regulation (CAR) 6, Rotorcraft Airworthiness; Normal Category.
• FAA Order 8110.54, Instructions for Continued Airworthiness Responsibilities, Requirements, and Contents.
• FAA-H-8083-23, Seaplane, Skiplane, and Float/Ski Equipped Helicopter Operations Handbook.
6.4 Installation Considerations.
6.4.1 Determining Eligibility of an Airplane. Only an airplane approved for operation on skis is eligible for ski installations in accordance with this chapter. Eligibility can be determined by referring to the aircraft specifications, Type Certificate Data Sheets (TCDS), aircraft listing, summary of Supplemental Type Certificates (STC), or by contacting the
6-2 manufacturer. Also, determine the need for any required alterations to the airplane to make it eligible for ski operations. Refer to ski plane-specific entries throughout TCDS A4CE on airspeeds, Weight and Balance (W&B) limitations and additional placards, and the Required Equipment listing for the first model in Aircraft Specification A-790 for examples. If the airplane is not approved in a ski plane configuration by type design, then skis cannot be installed by relying solely on data in this AC. Contact FAA engineering for approval or obtain or develop approved data from another source.
6.4.2 Identification of Approved Model Skis. Determine that the skis are of an approved model by examining the identification plates or placards displayed on the skis. Skis of approved models will have such plates or placards, and the Technical Standard Order (TSO)-C28;
an aircraft component, accessory, or equipment type certificate (TC) number; or an airplane part number (if the skis have been approved as part of the airplane) will be engraved or imprinted on each plate or placard.
6.4.3 Maximum Limit Load Rating.
6.4.3.1 Known Limit Landing Load Factor. Before installation, determine that the maximum limit load rating (L) of the ski, as specified on its identification plate or placard, is at least equal to the maximum static load on it (S) times the limit landing load factor (fl) previously determined from drop tests of the airplane by its manufacturer. This requirement can be expressed by the following equation:
L = S x fl
6.4.3.2 Unknown Limit Landing Load Factor. In lieu of a value fl determined from such drop tests, a value of fl determined from the following formula may be used:
9000 η = 2.80 + (W + 4000) where “W” is the certificated gross weight of the airplane
6.4.4 Oversize Ski Installations. This limitation is to ensure that the oversize skis will not adversely affect the performance, stability, controllability, and spin recovery behavior of the airplane or impose excessive loads on it.
6.4.5 Landing Gear Moment Reactions: Landing Gear Bending Moments. In order to avoid excessive bending moments on the landing gear and attachment structure, the ski pedestal height measured from the bottom surface of the ski to the axle centerline must not exceed 130 percent of the static rolling radius of the standard tire approved for the airplane when the tire is installed on the standard wheel at the approved inflation pressure. Do not use oversized or “tundra” tires to determine the static rolling radius.
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6.5 Fabrication and Installation.
6.5.1 Hub-Axle Clearance. The pedestal hub should fit the axle to provide a clearance of
0.005 inch minimum to 0.020 inch maximum. Hubs may be bushed to adjust for axle size, using any ferrous or nonferrous metal, hard rubber, or fiber. If rubber or fiber bushings are used, use retaining washers of sufficient size on each side to retain the hub if the bushing should slip or fail (see Figure 6-1). Field experience has shown that the use of good quality, low-temperature grease, particularly modern synthetic-based grease, improves ski operation and wear protection when used on the axle-to-hub or axle-to-bushing faying surfaces.
Figure 6-1. Typical Hub Installation
6-4 Figure 6-2. Typical Ski Installation
6.5.2 Crust-Cutter Cables. Crust-cutter cables are optional. However, when operating in severe crust conditions, it is advisable to have this cable installed to prevent the shock cord from being cut if the ski’s nose breaks through the crust while taxiing.
6.5.3 Cable and Shock Cord Attachment and Attachment Fittings.
6.5.3.1 Field Experience. Service reports indicate that failure of the ski itself is not a predominant factor in ski failures. Rigging, which is improper tension and terminal attachments, and cast-type pedestal material failures are predominant.
Failures of the safety cable and shock cord attachment fittings usually occur at the ski end and not at the fuselage end.
6.5.3.2 Separating Attachment Points. It is strongly recommended that tension cords and safety cables be attached to entirely separate fittings at their fuselage ends. Although the attachment fitting detail shown in Figure 6-2 may be adequate for some installations where alternate attachment locations are unavailable, we recommend that each cord and cable be attached to its own fitting (such as the right-hand fitting in Figure 6-3, Typical Fuselage Fittings) and attached at separate points on the fuselage when possible. Provide a
6-5 separate means of attaching cables and shock cords at the forward and aft ends of the skis.
6.5.3.3 Fabrication. Approved skis are normally supplied with cables, shock cords, and fittings. However, the specifications in Table 6-1, paragraphs 6.5.3.3.1 through 6.5.3.3.3, and Figure 6-3 may be used for fabricating and installing cables, shock cord assemblies, and fuselage fittings.
Note: Field experience indicates that accelerated wear and damage can occur to a 1/8-inch safety or crust-cutting cable and its attachment hardware in normal service on skis having a limit load rating of 1,500 pounds or more. The FAA recommends a minimum cable size of 5/32 inch for use in fabricating safety or crust-cutting cables for use with skis of a 1,500 pounds or greater limit load rating. 1/8-inch cables may be suitable for use on airplanes with light-weight skis and maximum certificated weights less than 1,500 pounds, such as those meeting the definition of light sport aircraft.
Table 6-1. Recommended Minimum Cable and Shock Cord Sizes Ski Limit Load Rating (Pounds) Single Safety Cable Double Safety Cable Single Crust-Cutting Cable Double Crust-Cutting Cable Single Shock Cord Double Shock Cord Less than 1,500 1/8 inch 1/8 inch 1/8 inch 1/8 inch 1/2 inch 1/2 inch 1,500–3,000 5/32 inch 5/32 inch 5/32 inch 5/32 inch 1/2 inch 1/2 inch 3,000–5,000 Do Not Use 5/32 inch 5/32 inch 5/32 inch Do Not Use 1/2 inch 5,000–7,000 Do Not Use 5/32 inch 5/32 inch 5/32 inch 3/4 inch 3/4 inch 7,000–9,000 Do Not Use 3/16 inch Do Not Use 5/32 inch Do Not Use 3/4 inch
6.5.3.3.1 Make check cable, safety cable, and crust-cutting cable ends by the splice method or swaging, such as the Nicopress process. Cable clamps may be used if adjustable lengths are desired, but they are not recommended. Use standard airplane hardware only. (Hardware used to attach cables must be compatible with cable size.) Refer to AC 43.13-1, Chapter 7, Aircraft Hardware, Control Cables, and Turnbuckles, for more information on cable fabrication.
6.5.3.3.2 Shock cord ends may be fabricated by any of the following methods:
1. Make a wrapped splice using a properly sized rope thimble and No. 9 cotton cord, 0.041 inch (minimum) safety wire (refer to Aerospace Industries Association (AIA) National Aerospace Standard (NAS) NASM20995, Wire, Safety or Lock), 1025 steel, or its equivalent