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
Par 505 Page 45
f. Tail Ski Installation.
(1) When installing a tail ski on an airplane with conventional landing gear, use a tail ski that has been appr oved on an airplane of approximately the same weight and whose tail wheel bears approximately the same fraction of that weight when the airplane is in the three-point attitude (within 10 percent), or select the tail ski as outlined in paragraphs 501 and 503. Some types of tail ski require that the tail wheel be removed to install the rest on its upper surface “ski.”
(2) Adjust the length of the limiting cable (reference Figure 5-8) to allow the ski to turn approximately 35 degrees either side of the straightforward position with the weight of the airplane resting on the ski.
(3) The shock cord (reference Figure 5-8) must be of a length that will hold the ski in the straight-forward position during flight.
FIGURE 5-8. TYPICAL TAIL SKI INSTALLATION
506. DOCUMENTATION.
a. Airplane or Ski Manufacturer's Data.
Comply with the requirements for placards, markings, and manuals required to operate the airplane as a skiplane, as listed in the approved or accepted documents discussed in paragraph 503a.
b. Performance Information. The following Paragraphs contain the minimum additional performance data required for airplanes equipped with new or altered ski installations. Consult AC 43-210 (current edition) chapter 4, for additional guidance regarding approved Aircraft Flight Manual (AFM) supplements.
(1) For an airplane that requires an approved AFM, obtain FAA approval for an AFM supplement that adds the following or similar information to the Perf ormance section of the Manual.
(a) Takeoff. Under the most favorable conditions of smoothly packed snow at temperatures approximating 32° F, the skiplane takeoff distance is approximately 10 percent greater than that shown for the landplane.
NOTE: In estimating takeoff distance for other conditions, caution should be exe rcised as lower temperatures or other snow conditions will usually increase these distances.
(b) Landing. Under the most favorable conditions of smoothly packed snow at temperatures approximately 32° F, the skiplane Par 505 Page 46
landing distance is approximately 20 percent greater than that shown for the landplane.
NOTE: In estimating landing distances for other conditions, caution should be exercised as other temperatures or other snow conditions may either decrease or increase these distances.
(c) Climb Performance. In cases where the landing gear is fixed (both landplane and skiplane), where climb requirements are not critical, and the climb reduction is small (30 to 50 feet per minute), the FAA will accept a statement of the approximate reduction in climb performance placed in the performance information section of the AFMS. For larger variations in climb performance, where the minimum requirements are critical, or the landing gear of the landplane is retractable, appropriate climb data should be obtained to determine the changes and new curves, tables, or a note should be incorporated into the AFMS.
(2) For an airplane that does not require an AFM, make the information in paragraph 506b(1) available to the pilot in for form of placards, markings, manuals, or any combination thereof. One type of acceptable manual is an approved Supplementary AFM.
507. FLIGHT AND HANDLING OPERA- TIONAL CHECKS. Accomplish an operational check in accordance with Title 14 of the Code of Federal Regulations (14 CFR) part 91, § 91.407(b), to determine the takeoff, landing, and ground handling characteristics. Ensure that the ski angles during tail high and tail low landings will not cause the skis to dig in or fail from localized stress. Verify that ground control is adequate to satisfactorily complete a landing run with a turnoff at slow speed.
In flight, the skis must ride steady with check cables taut, and must not produce excessive drag or unsatisfactory flight characteristics. Enter a notation of this check in the airplane records.
508. MAINTENANCE (INCLUDING IN- SPECTION).
a. Inspection and Repa ir Data Sources.
Contact the airplane and ski manufacturers for any specific inspection and ma intenance instructions they may have developed. Refer to AC 43.13-1 (as amended), chapter 9, for more information.
b. Instructions for Continued Airworthiness (ICA). The modifier (developer of the ski installation or alteration) must provide instructions for future inspection, maintenance, and repair of the added or altered parts, and is also responsible for assessing the need for any changes to the product-level ICA (changes that affect the airplane as a whole when the skis are installed). For simple airplane/ski combinations where skis of the same model have been approved on similar airplanes with appropriate ICA, it may only be necessary to reference those ICA in the maintenance records of the newly altered airplane and/or in Block 8 of the FAA Form 337 documenting the ski installation. For complex ski installations requiring special considerations, the modifier may need to develop new installation-specific ICA. In either case, the modifier must ensure that adequate and appropriate ICA is available to the skiplane owner or operator. Consult current editions of AC 43-210, chapter 5, and FAA Order 8110.54, for additional guidance regarding ICA.
c. Interchanging of Skis and Wheels. A person appropriately authorized by 14 CFR part 43, § 43.3, must perform a new weight and balance computation when the skis are initially installed. The FAA recommends that the airplane be weighed for this initial computation. After the initial installation, removing the skis and reinstalling the wheels or vice versa is considered a preventive maintenance operation if it does not involve complex assembly operations or a new weight and balance computation (ref. part 43, appendix A, paragraph (b)(4)(c)(18)).
NOTE: During subsequent weight and balance changes to the airplane, be sure to update its weight and Par 506 Page 47
Par 508 Page 48 balance records and its equipment list to account for all approved ski, wheel, and float installations.
d. Periodic Inspection Required. Seasonally removed and installed equipment items such as skis should be inspected at installation to comply with §§ 91.407(a) and 91. 409(a), and part 43, appendix D, paragraphs (e)(1) and (e)(10), if they were not installed on the airplane at the time of the last inspection. All available data described in this paragraph should be used during the inspection.
509. THRU 599. RESERVED
CHAPTER 6. OXYGEN SYSTEM INSTALLATIONS IN
NONPRESSURIZED AIRCRAFT SECTION 1. GENERAL
600. PURPOSE. This chapter provides data for acceptable means of gaseous oxygen system installations in nonpressurized aircraft. For other oxygen system installations (i.e., liquid oxygen), installers should contact their local Flight Standard District Office (FSDO) for assistance in applying for a Supplemental Type Certificate (STC).
601. HAZARDS AND WARNINGS TO
CONSIDER WHEN INSTALLING AN OXYGEN SYSTEM.
a. Oxygen itself does not burn, but materials that burn in air will bur n much hotter and more vigorously in an oxygen rich environment.
b. Oil and grease burn with explosive violence in the presence of oxygen.
c. Rapid release of high-pressure oxygen in the presence of foreign particles can cause temperatures sufficient to ignite combustible materials and materials that would not normally burn in air.
d. Pressurized oxygen cylinder failures, particularly aluminum-lined composite cylinders, have the potential of producing violent explosions.
602. ADDITIONAL REFERENCES (current editions).
a. Title 14 of the Code of Federal Regulations (14 CFR) part 23, Airworthiness Standards: Normal, Utility, Acrobatic, and Commuter Category Airplanes.
b. Title 14 CFR part 43, Maintenance, Preventive Maintenance, Rebuilding, and Alteration.
c. Title 14 CFR part 91, General Operating and Flight Rules.
d. Civil Aviation Regulations (CAR) 3, Airplane Airworthiness; Normal, Utility, and Acrobatic Categories.
e. CAR 6, Rotorcraft Airworthiness; Normal Category.
f. Advisory Circular (AC) 27-1, Certification of Normal Category Rotorcraft.
g. AC 43.13-1, Acceptable Methods, Techniques, and Practices―Aircraft Inspection and Repair.
h. Society of Automotive Engineers Aerospace Information Report (SAE AIR) No. 825B, Oxygen Equipment for Aircraft and SAE AIR 822, Oxygen Systems for General Aviation.
i. Handbook Bulletin for Airworthiness (HBAW) 02-01B, Maintenance of Pressure Cylinders in Use as Aircraft Equipment.
j. FAA Order 8310.6, Airworthiness Compliance Check Sheet Handbook.
603. THRU 606. RESERVED
Par 600 Page 49 (and 50)
Par 607 Page 51 SECTION 2. INSTALLATION OF THE OXYGEN SYSTEM
607. SYSTEM REQUIREMENTS. Gaseous oxygen systems may be a higher pressure system with the oxygen stored at 1850 psi or a low pressure system with the oxygen st ored at 425 psi. All oxygen systems contain a storage tank, a regulation system, and a distribution system. The main difference in system type is in the regulation of the oxygen to the user (re: paragraph f below).
a. Cylinders. Install oxygen cylinders conforming to Interstate Commerce Commission (ICC) requirements for gas cylinders which carry the ICC or DOT 3A, 3AA, or 3HT designation followed by the service pressure metal-stamp on the cylinder.
b. Tubing/Lines.
(1) In systems having low pressure, use seamless aluminum alloy or equivalent having an outside diameter of 5/16 inch and a wall thickness of
0.035". Double flare the ends to attach to fittings.
(2) In high-pressure systems (1800 psi), use 3/16-inch O.D., 0.035" wall thickness, seamless copper alloy tubing meeting Specification WWT-779a type N, or stainless steel between the filler valve and the pressure-reducing valve. Silversolder cone nipples to the ends of the tubing to attach the fittings in accordance with Specification MIL-B-7883.
(3) Use 5/16-inch O.D. aluminum alloy tubing after the pressure-reducer (low-pressure side).
NOTE: Any lines that pass through potential fire zones should be stainless steel.
NOTE: If lines are located behind upholstery or not 100 percent visible during normal operations, they should be solid metal lines or highpressure flexible lines.
c. Fittings. All fittings must be manufactured from materials that are compatible for use with oxygen systems. Fittings should not be made of mild steel or materials that are prone to corrosion when in contact with another material.
(1) High Pressure. Intercylinder connections are made with regular flared or flareless tube fittings with stainless steel. Usually fittings are of the same material as the lines. Mild steel or aluminum alloy fittings with stainless steel lines are discouraged. Titanium fittings should never be used because of a possible chemical reaction and resulting fire.
(2) Low Pressure. Fittings for metallic low-pressure lines are flared or flareless, similar to high pressure lines. Line assemblies should be terminated with "B" nuts in a similarly manner to a manufactured terminating connection. Universal adapters (AN 807) or fr iction nipples used in conjunction with hose clamps are not acceptable for use in pressurized oxygen systems.
d. Valves. Each system must contain a slowopening/closing shutoff valve that is accessible to a flight crewmember to turn on and shut off the oxygen supply at the high pressure source.
e. Regulators. The cylinder or system pressure is reduced to the individual cabin outlets by means of a pressure-reducing regulator that can be manually or automatically controlled. The regulator should be mounted as close as possible to the cylinders and certificated for aviation environment.
f. Types of Regulators. The four basic types of oxygen systems, classified according to the type of regulator employed, are:
(1) Continuous-flow Type. The constant flow type provides the same output pressure or flow regardless of altitude. Continuous-flow oxygen systems provide protection for passengers up to 25,000 feet mean sea level (MSL) and a continuous flow of 100 percent oxygen to the user. They may be automatic or manual in their operation.
(2) Diluter-demand Type. This type dilutes pure oxygen with ambient air and maintains the proper portion of oxygen in the breathing gas depending on altitude. Oxygen concentration is automatically diluted proportionate to the specific altitude’s predetermined human oxygen consumption requirement. Such systems only supply oxygen, mixed with cabin air, during inhalation.
(3) Demand Type. This type uses highpressure compressed oxygen that feeds a supply of oxygen to a ‘high-to-low’ pressure regulator at the individual crew station. The regulator, after reducing the higher pressure, automatically cycled lowpressure breathing oxygen to the wearer only on demand. Section 23.1441 requires aircraft that are certified to operate above 25,000 feet to be equipped with a demand system to supply required crewmembers.
(4) Pressure-demand Type. This type is not likely to be included on small general-aviation models. Aircraft certified to exceed 40,000 feet must have a pressure-demand system, which delivers pressurized oxygen to pilots such as high altitude Oxygen breathing system (above 40,000 feet) using anthropomorphic facial measurements of aircrew to produce a mask that would satisfactorily contain the pressure required to allow breathing under pressure, while maintaining an airtight face-seal and also remaining relatively comfortable to the wearer.
g. Flow Indicators.
(1) A pith-ball flow indicator, vane, wheel anemometer, or lateral pressure indicator which fluctuates with changes in flow or any other satisfactory flow indicat or may be used in a continuous flow-type system.
(2) An Air Force/Navy flow indicator or equivalent may be used in a diluter-demand type system. Each flow indicator should give positive indication when oxygen flow is occurring.
h. Relief Valve.
(1) A relief valve is installed in lowpressure oxygen systems to safely relieve excessive pressure, such as that caused by overcharging.
(2) A relief valve is installed in highpressure oxygen systems to safely relieve excessive pressure, such as that caused by heating.
i. Gauge. Provide a pressure gauge to show the amount of oxygen in the cylinder during flight.
j. Masks. Only approved masks designed for the particular system should be used.
608. INSTALLATION AND DESIGN CON- SIDERATIONS. Oxygen systems present a hazard. Therefore, foll ow the precautions and practices listed below:
a. Remove oil, grease (including lip salves, hair oil, etc.), and dirt from hands, clothing, and tools before working with oxygen equipment.
b. Prior to cutting the upholstery, check the intended route of the system.
CAUTION: Ensure all system components are kept completely free of oil or grease during installation and locate components so they will not contact or become contaminated by oil or oil lines.
c. Keep open ends of cleaned and dried tubing capped or plugged at all times, except during attachment or detachment of parts. Do not use tape, rags, or paper.
d. Clean all lines and fittings that have not been cleaned and sealed by one of the following methods:
(1) A vapor-degreasing method with stabilized trichlorethylene conforming to Specification MIL-T-7003 or carbon tetrachloride.
Blow tubing clean and dry with a stream of clean, dried, water-pumped air, or dry nitrogen (watervapor content of less than 0.005 milligrams per liter Par 607 Page 52
Par 608 Page 53 of gas at 700º F and 760 millimeters of mercury pressure).
(2) Flush with naptha conforming to Specification TT-N-95; blow clean and dry off all solvent with water-pumped air; flush with antiicing fluid conforming to Specification MIL-F-5566 or anhydrous ethyl alcohol; rinse thoroughly with fresh water; and dry thoroughly with a stream of clean, dried, water-pumped air, or by heating at a temperature of 250º to 300º F for one-half hour.
(3) Flush with hot inhibited alkaline cleaner until free from oil and grease; rinse thoroughly with fresh water; and dry thoroughly with a stream of clean, dried, water-pumped air, or by heating at a temperature of 250º to 300º F for one-half hour.
e. Install lines, fittings, and equipment above and at least 6 inches aw ay from fuel, oil, and hydraulic systems. Use deflector plates where necessary to keep hydraulic fluids away from the lines, fittings, and equipment.
f. Allow at least a 2-inch clearance between the plumbing and any flexible control cable or other flexible moving parts of the aircraft. Provide at least a 1/2-inch clearance between the plumbing and any rigid control tubes or other rigid moving parts of the aircraft.
g. Allow a 6-inch separation between the plumbing and the flight and engine control cables, and electrical lines. When electrical conduit is used, this separation between the plumbing and conduit may be reduced to 2 inches.
h. Route the oxygen system tubing, fittings, and equipment away from hot air ducts and equipment. Insulate or provide space between these items to prevent heating the oxygen system.
i. Mount all plumbing in a manner that prevents vibration and chafing. Support a 3/16-inch O.D. copper line each 24 inches and a 3/16-inch O.D. aluminum each 36 inches with cushioned looptype line support clamps (AN-742) or equivalent.
j. Locate the oxygen supply valve (control valve) so as to allow its operation by the pilot during flight. The cylinder shutoff valve may be used as the supply control valve, if it is operable from the pilot’s seat. Manifold plug-in type outlets, which are incorporated in automatic systems, may be considered oxygen supply valves since the pilot can control the flow of oxygen by engaging and disengaging the plug-in type oxygen mask.
k. Filler connections, if provided, are recommended to be located outside the fuselage skin or isolated in a manner that would prevent leaking oxygen from entering the aircraft. Careful evaluation should also be made of any nearby source of fuel, oil, or hydrau lic fluid under normal or malfunction conditions. Each filler connection should be placarded. Additionally, any valve (aircraft or ground servicing equipment) associated with high pressure should be slow acting.
NOTE: Locate th e oxygen shutoff valve on or as close as practicable to the cylinder to prevent loss of oxygen due to leakage in the system.
609. EQUIPMENT LOCATION AND MOUNT- ING. Determine the weight/load factors and center of gravity (CG) limits for the installation prior to commencing the installation.
a. Mount the cylinder in the baggage compartment or other suitable location in such a position that the shutoff valve is readily accessible.
Provide access to this valve from inside the cabin so that it may be turned on or off in flight.
b. Fasten the cylinder brackets securely to the aircraft, preferably to a frame member or floorboard using AN bolts with fiber or similar locking nuts.
Add sufficient plates, gussets, stringers, crossbracing, or other reinforcements, where necessary, to provide a mounting that will withstand the inertia forces, stipulated in chapter 1.
c. When cylinders are located where they may be damaged by baggage or stored materials, protect them with a suitable guard or covering.
d. Provide at least 1/2-inch of clear airspace between any cylinder and a firewall or shroud isolating a designated fire zone.
e. Mount the regulator close to the cylinder to avoid long high-pressure lines.
f. Store the masks in such a way that there will be a minimum delay in removing and putting them into use.
610. THREAD COMPOUND. Use anti-seize or thread-sealing compound conforming to Specification MIL-T-5542-B, or equivalent.
a. Do not use compound on aluminum alloy flared tube fittings having straight threads. Proper flaring and tightening should be sufficient to make a flared tube connection leakproof.
b. Treat all male-tapered pipe threads with antiseize and sealing compound (MIL-T-5542-B, or tetrafluroethylene tape MIL-T-27730), or equivalent.
c. Apply the compound in accordance with the manufacturer's recommendation. Make sure that the compounds are carefully and sparingly applied only to male threads, coating the first three threads from the end of the fitting. Do not use compound on the coupling sleeves or on the outside of the tube flares.
611. FUNCTIONAL TEST. Before inspection plates, cover plates, or upholstering are replaced, make a system check including at least the following:
a. Open cylinder valve slowly and observe the pressure gauge.
b. Open supply valve and remove one of the mask tubes and bayonet f ittings from one of the masks in the kit. Plug the bayonet into each of the oxygen outlets. A small flow should be noted from each of the outlets. This can be detected by holding the tube to the lips while the bayonet is plugged into an outlet.
c. Check the complete system for leaks. This can be done with a soap solution made only from a mild (castile) soap or by leak-detector solution supplied by the oxygen equipment manufacturer.
d. If leaks are found, close the cylinder shutoff valve and reduce the pressure in the system by plugging a mask tube into one of the outlets or by carefully loosening one of the connections in the system. When the pressure has been reduced to zero, make the necessary repairs. Repeat the procedure until no leaks are found in the system.
WARNING: Never tighten oxygen system fittings with oxygen pressure applied.
e. Test each outlet for leaks at the point where the mask tube plugs in. This can be done by using a soapy solution over each of the outlets. Use the solution sparingly to prevent dogging the outlet by soap. Remove all residue to prevent accumulation of dirt.
f. Examine the system to determine if the flow of oxygen through each outlet is at least equal to the minimum required by the pertinent requirements at all altitudes at which the aircraft is to be operated. This can be accomplished by one of the following methods:
(1) In a continuous flow system when the calibration (inlet pressure vs. flow) of the orifices used at the plug-in outlets is known, the pressure in the low-pressure distribution line can be measured at the point which is subject to the greatest pressure drop. Do this with oxygen flowing from all outlets.
The pressure thus measured should indicate a flow equal to or greater than the minimum flow required.
(2) In lieu of the above procedure, the flow of oxygen, through the outlet that is subject to the greatest pressure drop, may be measured with all other outlets open. Gas meters, rotometers, or other suitable means may be used to measure flows.
(3) The measurement of oxygen flow in a continuous flow system which uses a manually Par 609 Page 54
Par 611 Page 55 adjusted regulator can be accomplished at sea level.
However, in a continuous flow system which uses an automatic-type regulator, it may be necessary to check the flow at maximum altitude which will be encountered during the normal operation of the aircraft. The manufacturer of the particular continuous-flow regulator used should be able to furnish data on the operating characteristics of the regulator from which it can be determined if a flight check is necessary.
(4) Checking the amount of flow through the various outlets in a diluter-demand or straightdemand system is not necessary since the flow characteristics of the particular regulator being used may be obtained from th e manufacturer of the regulator. However, in such systems the availability of oxygen to each regulator should be checked by turning the lever of the diluter-demand regulator to the "100 percent oxygen" position and inhaling through the tube via the mask to determine whether the regulator valve and the flow indicator are operating.
g. Provide one of the following acceptable means or equivalent to indicate oxygen flow to each user by:
(1) Listening for audible indication of oxygen flow.
(2) Watching for inflation of the rebreather or reservoir bag.
(3) Installing a flow indicator.
612. OPERATING INSTRUCTIONS. Provide instructions appropriate to the type of system and masks installed for the pilot on placards. Include in these instructions a graph or a table which will show the duration of the oxygen supply for the various cylinder pressures and pressure altitudes (Table 6-1).
613. THRU 617. RESERVED
TABLE 6-1. TYPICAL OXYGEN DURATION TABLE
ACTUAL DURATION IN HOURS AT VARIOUS ALTITUDES Number of Persons 8000 Ft.
10,000 Ft.
12,000 Ft.
15,000 Ft.
20,000 Ft.
Pilot only 7.6 hr 7.1 hr 6.7 hr 6.35 hr 5.83 hr Pilot and 1 Passenger
5.07 hr 4.74 hr 4.47 hr 4.24 hr 3.88 hr Pilot and 2 Passengers
3.8 hr 3.55 hr 3.36 hr 3.18 hr 2.92 hr Pilot and 3 Passengers
3.04 hr 2.84 hr 2.68 hr 2.54 hr 2.34 hr Pilot and 4 Passengers
2.53 hr 2.37 hr 2.24 hr 2.12 hr 1.94 hr NOTE: The above duration time is based on a fully charged 48 cubic-foot cylinder. For duration using 63 cubic-foot cylinder, multiply any duration by 1.3.
FIGURE 6-1. TYPICAL FLOOR MOUNTING
Regulator Alternate Location Cylinder Bracket Floor Large area washer AN bolt and self-locking nut Oxygen cylinder bracket Reinforce floor, if necessary, to withstand the added load.
Like aluminum or plywood of sufficient thickness.
FIGURE 6-2. TYPICAL BAGGAGE COMPARTMENT MOUNTING
.032 aluminum FastenersHinge Typical example of shroud Bracket Bulkhead WasherSelf-locking Nut Doubler Cylinder support block – Cut to fit contour of cylinder base.
Secure with countersunk machine screw or wood screw.
NOTE: Enclose cylinder and valve with shroud to prevent damage from baggage.
Par 612 Page 56
Par 612 Page 57 (and 58)