(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)
FIGURE 6-3. TYPICAL OXYGEN INSTALLATION IN LIGHT TWIN AIRCRAFT
Par 618 Page 59 SECTION 3. AIRWORTHINESS COMPLIANCE CHECK SHEET: OXYGEN SYSTEM
INSTALLATION IN UNPRESSURIZED AIRCRAFT
618. GENERAL. Oxygen system installations made in accordance with FAA-approved airframe manufacturer, or other FAA-approved installations, may be accepted without further investigation. On other installations, the following points should be checked to determine if the installation is satisfactory.
619. APPLICABLE FEDERAL AVIATION REGULATIONS. Determine if the installation complies with the re gulations listed in paragraph 602.
620. STRUCTURAL REQUIREMENTS.
a. If changes or alterations of the aircraft structure are made (mounting of oxygen cylinder), determine if the original strength and integrity of the structure is retained.
b. If gages are added to the instrument panel or an outside filler valve installed on the fuselage, determine if the structural integrity of the panel and airframe or its supporting structure is retained.
c. Determine if the extent of the modification has affected the center of gravity (CG) of the aircraft evaluated.
d. Check whether all lines are properly routed and supported.
621. HAZARDS TO THE AIRCRAFT OR ITS OCCUPANTS. Determine if the design of the oxygen system is evaluated to ensure that the aircraft and its occupants are safe from hazards identified in paragraph 601.
622. OPERATING ASPECTS.
a. When required by the operating rules for the use of supplemental oxygen, determine if the system’s capacity is sufficient to supply oxygen to all combinations of crew and passengers.
b. Determine if the oxygen system provides the required flow.
c. Determine if the oxygen regulator controls are accessible to a member of the flightcrew in flight.
d. Determine if there is a means, readily available to the crew in flight, to turn on and shut off the oxygen supply at the high pressure source.
e. Check whether there is a means to allow the crew to readily determine during flight the quantity of oxygen available in each source of supply.
623. DETAIL DESIGN STANDARDS. Determine if:
a. All parts are suitable for use with oxygen.
b. The regulator is located as close as physically possible to the oxygen cylinder and minimizes the use of fittings.
c. No lines are 100 percent visible during normal operation solid metal lines.
d. Each breathing device has a device attached that visually shows the flow of oxygen.
e. The lines that pass through potential fire zones are stainless steel.
f. When oxygen system components are added to the baggage compartments, there are provisions to protect the system components from shifting cargo.
g. Where oxygen components are installed, the compartment is placarded against the storage of oil or hydrocarbons.
h. A smoke detector is installed where oxygen cylinders are installed in a closed, nonaccessible compartment.
i. The cargo area weight limitations placard is updated.
j. All oxygen outlets are placarded.
k. “No Smoking When Oxygen Is In Use” placards and other appropriate placards (i.e., operation instructions) are visible to the crew and occupants of the aircraft.
624. INSTRUCTIONS FOR CONTINUED AIRWORTHINESS. Determine if:
a. There are written instructions concerning system operation, maintenance, and cylinder changing procedures.
b. There are written instructions in the use of the oxygen equipment in the AFM or placards.
NOTE: Any changes to the AFM must be approved by the FAA.
c. There are written inspection and test schedules and procedures.
d. Mechanical drawings and wiring diagrams are available, as required.
e. Written instructions are available concerning oxygen cylinder hydrostatic testing requirements and cylinder replacement requirements.
f. There is a scheduled (annual) check of a constant flow system manifold output pressure for recommended output pressure.
g. The guidance contained in AC 43.13-1 (current edition), paragraphs 9-47 to 9-51 is considered in the design of the oxygen maintenance program.
625. RECORDKEEPING. Determine if:
a. A maintenance record entry has been made.
(Reference § 43.9.)
b. The equipment list and weight and balance has been revised. (Ref erence Order 8310.6, chapter 1.)
626. THRU 699. RESERVED
Par 623 Page 60
CHAPTER 7. ROTORCRAFT EXTERNAL-LOAD-DEVICE
INSTALLATIONS CARGO SLINGS AND EXTERNAL RACKS SECTION 1. GENERAL
700. PURPOSE. This section contains structural and design information for the fabrication and installation of a cargo sling used as an external load attaching means for a Class B rotorcraft-load combination operation under Title 14 of the Code of Federal Regulations (14 CFR) part 133. As an external-load attaching means, a "cargo sling" includes a quick-release device (hook) and the associated cables, fittings, etc., used for the attachment of the cargo sling to the rotorcraft.
Part 133, § 133.43(d) specifies the requirements for the quick-release device.
701. HAZARDS AND WARNINGS. Particular attention should be paid to the effect of the sling load on the lateral as well as the fore and aft center of gravity (CG) of the rotorcraft. Use TC PMA, T50 or Designated Engineering Representative approved parts.
702. REFERENCES. It is the installer’s responsibility to ensure that the latest revisions of any regulations, advisory circulars, manufacturer’s data, etc., are used in any cargo sling or rack installation. Reference Title 14 of the Code of Federal Regulations part 27 and Civil Aviation Regulation 6, Rotorcraft Airworthiness; Normal Category.
703. INSTALLATION CONSIDERATIONS.
a. Location of Cargo Release in Relation to the Rotorcraft's CG Limits. An ideal location would be one that allows the line of action to pass through the rotorcraft's CG at all times. (See Figure 7-1, Illustration A.) However, with most cargo sling installations, this ideal situation is realized only when the line of action is vertical or near vertical and through the rotorcraft’s CG (See Figure 7-1, Illustration B.)
(1) Whenever the line of action does not pass through the rotorcraft's CG due to the attachment method used, acceleration forces, or aerodynamic forces, the rotorcraft-load combined CG will shift from the rotorcraft's CG position.
Depending upon the factors involved, the shift may occur along either or both the longitudinal or lateral axes. The amount of shif t is dependent upon the force applied (F) and the length of the arm of the line of action. Their product (F x Arm) yields a moment which can be used to determine the rotorcraft-load combined CG (See Figure 7-1, Illustration C.) If the rotorcraft-load CG is allowed to shift beyond the rotorcraft's approved CG limits, the rotorcraft may become violently uncontrollable.
Par 700 Page 61
FIGURE 7-1. LOCATION OF CARGO RELEASE IN RELATION TO THE ROTORCRAFT’S
CENTER OF GRAVITY
(2) Thus, any attachment method or location which will decrease the length of the arm will reduce the distance that the combined CG will shift for a given load (F) and line of action angle.
(See Figure 7-1, Illustration D.)
b. Maximum External Load. The maximum external load (including the weight of the cargo sling) for which authorization is requested may not exceed the rated capacity of the quick-release device.
704. FABRICATION AND INSTALLATION.
a. Static Test. The cargo sling installation must be able to withstand the static load required by § 133.43(a). Conduct the test as outlined in chapter 1. If required during the test, supports may be placed at the landing gear to airframe attach fittings to prevent detrimental deformation of the landing gear due to the weight of the aircraft.
b. Sling-Leg Angles of Cable-Supported Slings. The optimum sling-leg angle (measured from the horizontal) is 45 to 60 degrees. Minimum tension in a sling leg occurs with a sling-leg angle of 90 degrees, and the tension approaches infinity as the angle approaches zero. Thus, larger sling-leg angles are desirable from a standpoint of cable strength requirements. Slings should not be attached in such a manner as to provide sling-leg angles of less than 30 degrees.
c. Minimum Sling-Leg Cable Strength.
(1) An analysis which considered the effects of 30-degree sling angles showed that the minimum cable strength design factor required would be 2.5 times the maximum external load for each leg regardless of the number of legs. Although this is the minimum strength required by part 133, it may be desirable to double this value to allow for deterioration of the sling-leg cables in service. This Par 703 Page 62
will result in a cable strength equal to five times the maximum external load.
Example: Maximum external load 850 pounds Minimum required sling-leg cable strength 850 x 2.5 = 2125 Minimum desired sling-leg cable strength 850 x 2.5 x 2 = 4250
(2) A 3/16-inch, nonflexible 19-wire cable (MIL-W-6940) provides a satisfactory cable strength. For convenience, the cable sizes desired for various loads have been calculated and are tabulated in Table 7-1 based on a factor of 5:
TABLE 7-1. CABLE LOAD TABLE Aircraft Cable Size For Each Cargo Sling Leg
Maximum External Load (pounds)
MIL-C-5693 and MIL-W-6940
MIL-W-1511
MIL-C-5424 100 200 300 400 500 600 700 800 900 1,000 1,200 1,400 1,600 1,800 2,000 1/16 3/32 7/64 1/8 5/32 5/32 3/16 3/16 3/16 7/32 7/32 ¼ 1/4 5/16 5/16 3/32 1/8 1/8 1/8 5/32 3/16 3/16 3/16 7/32 7/32 1/4 1/4 9/32 5/16 11/32 3/32 1/8 1/8 5/32 3/16 3/16 3/16 7/32 7/32 7/32 ¼ 9/32 5/16 5/16 3/8
d. Sling Installation.
(1) Attach the cargo sling to landing gear members or other structure capable of supporting the loads to be carried. Install the quick-release device in a level attitude with the throat opening facing the direction as indicated on the quick-release device.
When cables are used to support the quick-release device, make sure the cables are not twisted or allowed to twist in the direction to un-lay the cable.
(2) Some cargo release devices are provided with a fitting to permit installation of a guideline to assist in fully automatic engagement of the load target ring or load bridle. Secure the guideline to the quick-release device with a shear pin of a definite known value which will shear if a load becomes entangled on or over the guideline.
Provision should also be made for cable-supported slings to be drawn up against the fuselage into a stowage position to prevent striking or dragging the release on the ground when not in use.
e. Installation of Release Controls. See Figure 7-2 for typical wiring diagram of the electrical controls.
(1) Install a cargo release master switch, readily accessible to the pilot, to provide a means of deactivating the release circuit. The power for the electrical release circuit should originate at the primary bus. The "auto" position of the release master switch on some cargo release units provides for automatic release when the load contacts the ground and the load on the release is reduced to a preset value.
(2) Install the cargo release switch on one of the pilot's primary controls. It is usually installed on the cyclic stick to allow the pilot to release the load with minimum distraction after maneuvering the load into the release position.
Par 704 Page 63
FIGURE 7-2. TYPICAL CARGO SLING WIRING DIAGRAM
(3) Install the emergency manual release control in a suitable position that is readily accessible to the pilot or other crewmember. Allow sufficient slack in the control cable to permit complete cargo movement without tripping the cargo release.
(4) The manual ground release handle, a feature of some cargo release units, permits opening of the cargo release by ground personnel.
(5) Label or placard all release controls as to each function and operation.
f. Functional Test.
(1) Test the release action of each release control of the quick-release device with various loads up to and including the maximum external load. This may be done in a test fixture or while installed on the rotorcraft, if the necessary load can be applied.
(2) If the quick-release device incorporates an automatic release, the unit should not release the load when the master switch is placed in the "automatic" position until the load on the device is reduced to the preset value, usually 80 to 120 pounds.
FIGURE 7-3. TYPICAL CARGO SLING INSTALLATION NO. 1
Par 704 Page 64