CHAPTER 4. ANTICOLLISION AND SUPPLEMENTARY LIGHT
INSTALLATION
400. 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.
401. HAZARDS AND WARNINGS. When installing anticollison 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 darken hangars when activated.
402. REGULATIONS AND OTHER REFERENCES. The requirements for anticollision lights are included in Title 14 of the Code of Federal Regulations (14 CFR) part 23, § 23.1401 and part 27, § 27.1401 for non-transport category aircraft. For part 23 aircraft certificated after March 11, 1996, § 91.205 are required to have an anticollision light. The night VFR requirements for part 23 certificated on or before August 11, 1971, must have an approved white or red anticollison light. Aircraft for which an application for type certificate was made before April 1, 1957, may conform either to the above regulations or to the following standards: Additional information can be found in AC 20-74.
a. Civil Aviation Regulation (CAR) 6, Rotorcraft Airworthiness; Normal Category.
b. Anticollision lights (when installed) should be installed on top of the fuselage or tail in such a location that the light w ill 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.
c. The color of the anticollision light must be either aviation red or aviation white in accordance with the specifications of § 23.1397 or § 27.1397, as applicable.
d. The arrangement of the anticollision light system, (i.e., number of light sources, beam width, speed of rotation and other characteristics, etc.) must give an effective flash frequency of not less than 40, nor 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.
e. 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 di rection within at least 75 degrees above and 75 degrees below the horizontal plane of the aircraft. The minimum light intensity and minimum ef fective intensities are given in §§ 23.1401 and 27.1401 respectively.
f. Supplementary lights may be installed in addition to position and anticollision lights required by applicable regulations; provided that, the required position and anticollision lights are continuously visible and unmistakably recognizable and their conspicuity is not degraded by such supplementary lights.
403. OPERATIONAL CONSIDERATIONS:
CREW VISION. Partial masking of the anticollision light may be necessary to prevent direct Par 400 Page 33
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 propeller disc, nacelle, or wing surface is an application of nonreflective paint on surfaces which present a reflection problem. Perform a night flight-check to assure that any objectionable light reflection, sometimes known as flicker vertigo, has been eliminated. Enter a notation to that effect in the aircraft records.
404. INSTALLATION CONSIDERATIONS.
a. Communication and Navigation. Assure that the installation and operation of any anticollision/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 the RFI disturbance does not usually disrupt the intelligence of audio reception.
b. 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) Assure 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.
405. 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 unsatisfa ctory 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.
406. 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 device, and generator/alternator limitations is contained in Advisory Circular (AC) 43.13-1B Acceptable Methods, Techniques, and Practices-Aircraft Inspection and Repair, (as amended) chapter 11.
Assure that the terminal voltage at each light is within the limits as prescribed by the manufacturer.
407. ALTERATION OF STRUCTURE.
a. 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 4-1.)
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FIGURE 4-1. TYPICAL ANTICOLLISION OR SUPPLEMENTARY LIGHT INSTALLATION
IN A SKIN PANEL (UNPRESSURIZED)
Anticollision Light or Supplementary Light Fuselage Skin Existing Stringer Existing Stringer View A-A Reinforcing Doubler Approximately One Inch Spacing of 1/8” Min.Dia.Rivet Alclad 2024-T3 1 1/2” Edge Distance Min.
b. 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 4-2 for typical installation.)
c. Engineering evaluation is required for installations involving the cutting of complex formed or extruded stiffeners, fuselage frames, or pressurized skin of pressurized aircraft.
d. Vertical stabilizer installations may be made on 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 4-3.)
e. Rudder installations are not recommended because of the possible structural difficulties.
However, if such installations are considered, a FAA engineering evaluation to determine whether the added mass of the light installation will adversely affect the flutter and vibration characteristics of the tail surfaces must be made.
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FIGURE 4-2. TYPICAL ANTICOLLISION OR SUPPLEMENTARY LIGHT INSTALLATION
INVOLVING A CUT STRINGER (UNPRESSURIZED)
Anticollision Light or Supplementary Light Cut Stringer Reinforcing Doubler Alclad 2024-T3 Stringer Stringer Frame Frame Double Flanges at Least the Height of Cut Stringer Flange Stringer and Doubler Existing Rivets Rivets Added as Shown on Frames
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FIGURE 4-3. TYPICAL ANTICOLLISION OR SUPPLEMENTARY
LIGHT INSTALLATION IN A FIN TIP
Mounting Screw Holes for Light to Fairing Anticollision Light or Supplementary Light Approximately One Inch Spacing of 1/8” Min. Dia. Rivet Vertical Stabilizer Light Mounting Fairing Mounting Ring Vertical Stabilizer View A-A B-B NOTE: Skin thickness of mounting ring and fairing are at least equivalent.
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CHAPTER 5. SKI INSTALLATIONS
500. PURPOSE. This chapter provides information for ski installations on small airplane. 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 advisory circular (AC).
501. 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 to the landing g ear and its attachment structure which can cause hidden and/or cumulative damage. Improper rigging and/or weak springs or shock cords 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 airplane s 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 experi enced ski maintenance technicians and operators is strongly recommended when considering any new ski installation or any alteration of an existing ski installation.
502. ADDITIONAL REFERENCE MATERIAL (current editions).
a. Airframe and ski manufacturers’ data, if available.
b. AC 43.13-1, Acceptable Methods, Techniques, and Practices―Airplane Inspection and Repair.
c. AC 43-210, Standardized Procedures for Requesting Field Approval of Data, Major Alterations, and Repairs.
d. Civil Aviation Regulation (CAR) 6, Rotorcraft Airworthiness; Normal Category.
e. FAA Order 8110.54, Instructions for Continued Airworthiness.
f. FAA-H-8083-23, Seaplane, Ski plane, and Float/Ski Equipped Helicopter Operations Handbook.
503. INSTALLATION CONSIDERATIONS.
a. 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, or by contacting the manufacturer. Also determine the need for any required alterations to the airplane to make it eligible for ski operations. (See ski plane-specific entries throughout TCDS A4CE on airspeeds, weight and balance 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/develop approved data from another source.
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b. 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) number 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.
c. Maximum Limit Load Rating.
(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×fl
(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
d. Oversize Ski Installations. This limitation is to assure 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.
e. 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 oversize or "tundra" tires to determine the static rolling radius.
504. FABRICATION AND INSTALLATION.
a. Hub-Axle Clearance. The pedestal hub should fit the axle to provide a clearance of 0.005" minimum to 0.020" 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 5-1.) 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 5-1. TYPICAL HUB
INSTALLATION
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FIGURE 5-2. TYPICAL SKI INSTALLATION
1. Fitting
2. Shock Cord
3. Safety Cable
4. Tape
5. Crust-cutter Cable
6. Fabric removed to facilitate inspection
7. Check Cable
8. Clevis
9. Ski Pedestal
10. Pedestal Height
b. 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 nose of the ski breaks through the crust while taxiing.
c. Cable and Shock Cord Attachment and Attachment Fittings.
(1) Field experience. Service reports indicate that failure of the ski itself is not a predominant factor in ski failures. Rigging (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.
(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 5-2 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 5-3) and attached at separate points on the fuselage when possible. Provide separate means of attaching cables and shock cords at the forward and aft ends of the skis.
(3) Fabrication. Approved skis are normally supplied with cables, shock cord, and fittings. However the specifications in Table 5-1, subparagraphs (a) through (c) below, and Figure 5-3 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" safety or crustcutting cable and its attachment hardware in normal service on skis having a limit load rating of 1,500 pounds or more. The FAA Par 504 Page 41
recommends a minimum cable size of 5/32" for use in fabricating safety or crust-cutting cables for use with skis of 1,500 pounds or greater limit load rating. 1/8" 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 5-1. RECOMMENDED MINIMUM CABLE AND SHOCK CORD SIZES Ski Limit Load Single Safety Double Safety Single Crust- Double Crust- Single Shock Double Shock Rating Cable Cable Cutting Cable Cutting Cable Cord Cord (Pounds) Less than 1,500 1/8" 1/8" 1/8" 1/8" 1/2" 1/2" 1,500-3,000 5/32" 5/32" 5/32" 5/32" 1/2" 1/2" 3,000-5,000 Do Not Use 5/32" 5/32" 5/32" Do Not Use 1/2" 5,000-7,000 Do Not Use 5/32" 5/32" 5/32" 3/4" 3/4" 7,000-9,000 Do Not Use 3/16" Do Not Use 5/32" Do Not Use 3/4"
(a) Make check cable, safety cable, and crust-cutting cable ends by the splice, swage, or nicopress methods. 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, as amended, for more information on cable fabrication.
(b) Shock cord ends may be fabricated by any of the following methods:
1. Make a wrapped splice using a proper size rope thimble and No. 9 cotton cord, 0.041" (minimum) safety wire (ref. National Aerospace Standard NASM20995), 1025 steel, or its equivalent (AISI 4130). Attach with clevis or spring steel snap fastener. (Do not use cast iron snaps.)
2. Use approved spring-type shock cord end fasteners, 1025 steel, or its equivalent (AISI 4130).
(c) Fitting (Figure 5-3) Specifications and Installation:
1. Fittings fabricated for 1/8- inch cable or 1/2-inch shock cord must be at least
0.065" 1025 steel or its equivalent.
2. Fittings fabricated for 5/32- inch cable or 3/4-inch shock cord must be at least
0.080" 1025 steel or its equivalent.
3. An improperly installed fitting may impose excessive eccentric loads on the fitting and attach bolts and result in failure of the fitting or bolts.
4. If attaching cables directly to holes in fittings, radius the hole edges to reduce stress concentration and accelerated wear of the thimble. Stainless steel thimbles are recommended for increased wear resistance.
5. If attaching cables to fittings using clevises, clevis bolt castellated nuts should be used, then properly torqued and safetied with cotter pins. Field experience has shown that diaper-pinstyle quick-releasing safety devices are more prone to failure during operation, and are not recommended.
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FIGURE 5-3. TYPICAL FUSELAGE
FITTINGS
d. Provisions for Inspection. An airplane using fabric-covered landing gear should have at least the lower 4 inches of fabric removed to facilitate inspection of the axle attachment area, and to prevent the entrapment of snow and ice, which can lead to damage and corrosion of the landing gear. (See Item 6 in Figure 5-2.)
505. RIGGING OF SKIS.
a. Location of Attach Fittings on Fuselage or Landing Gear. Locate fittings so the shock cord and cable angles are not less than 20 degrees when measured in the vertical plane with the shock absorber in the fully extended position (see Angle B, Figures 5-4 and 5-5).
NOTE: Do not attach fittings to wing-brace struts, except by special approval (manufacturer or FAA).
b. Main Ski Incidence Angles.
(1) Set cable lengths with the airplane level and no weight on the landing gear.
(2) Adjust length of check cable to provide a ±0- to ±5-degree ski incidence angle (reference Figures 5-4 and 5-6).
(3) Adjust length of safety cable to provide a ±15-degree ski incidence angle (reference Figures 5-5 and 5-6).
FIGURE 5-4. MAIN SKI AT MAXIMUM POSITIVE INCIDENCE (CHECK CABLE TAUT)
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FIGURE 5-5. MAIN SKI AT MAXIMUM NEGATIVE INCIDENCE (SAFETY CABLE TAUT)
FIGURE 5-6. MAIN SKI INCIDENCE ANGLES
c. Tension Required in Main Ski Shock Cords.
(1) Apply sufficient shock cord tension to the forward ends of the skis to prevent flutter and "dumping" throughout the range of airspeeds and attitudes at which the airplane will operate on skis.
Because of the various angles used in attaching the shock cord to the skis, shock cord tension cannot be specified. It is possible to specify the downward force that must be applied to the forward end of the ski in order to overcome the shock cord tension and cause the check cable to slacken when the ski is in the normal flight attitude. That downward force is commonly referred to as the shock cord tension force, or simply the tension force. In most installations on rigid, truss type landing gear, the tension force should be approximately as listed in Table 5-2.
TABLE 5-2. APPROXIMATE MAIN SKI
TENSION FORCES Ski Limit Load Capacity Downward Force (pounds) 1500-3000 3000-5000 5000-7000 7000-9000 20-40 40-60 60-120 120-200 Par 505 Page 44
NOTE: Do not rely upon these tension force values for main ski installations on airplanes with spring steel or other flexible landing gear.
Shock cord tensions great enough to require the downward forces listed in Table 5-2 to overcome them may produce excessive toe-in of the main skis on such airplanes. Variations in gear leg flexibility make it difficult to establish a generic table of tension forces appropriate for all airplanes with flexible landing gear.
(2) The shock cord tension must also be sufficient to return the skis to the normal flight attitude from their maximum negative incidence at all airspeeds up to the airplane's never-exceed speed with skis installed. In the absence of more precise data, each shock cord must be able to produce a nose-up moment about the ski pedestal bearing centerline of M = (0.0000036)(W)(V NE)2 ft•lbs, when the ski is at its maximum negative incidence, where W is the maximum certificated gross weight of the airplane and V NE is its never-exceed speed with skis installed.
d. Springs in Place of Shock Cords. If springs are used in place of shock cords to provide rigging tension, they must be able to withstand extreme cold and slight external scratching without premature fatigue failure, and must not cause skis, rigging, or landing gear to experience flutter or objectionable vibration during an airplane flight and dive tests.
e. Nose Ski Installation. Install the nose ski on an airplane with tricycle landing gear in the same manner as the main skis (see Figure 5-7), except:
(1) Adjust length of safety cable to provide ±5- to ±15-degree ski incidence.
(2) Where it is possible for the nose ski rigging to contact the propeller tips due to vibration, install a 1/4-inch shock cord to hold the rigging out of the propeller arc.
FIGURE 5-7. TYPICAL NOSE SKI INSTALLATION
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