AIRCRAFT OXYGEN SYSTEMS

Oxygen Systems      

During the maintenance of the oxygen system, the aircraft manufacturer's information must be followed along with the safety requirements men­tioned earlier. Some general rules concerning oxygen system maintenance that must be followed are: keep hands, tools and working area clear of grease, dirt, water and all foreign matter. All oxygen system components must be keep clean and dry until they are installed. The use of com­pounds on fitting threads is normally not allowed unless the aircraft service manual calls for their use. Always check the oxygen cylinder for con­tamination, the hydrostatic test date, and for being completely empty. If the cylinder is found to be completely empty the cylinder generally needs to be sent for a complete inspection by an FAA ap­proved repair station. After a thorough inspection of all the components in the system, an operational check should be performed to ensure the system is functioning normally. The specific inspection procedures for the aircraft that is being serviced will be in the aircraft's service manual; follow these closely.

The following instructions are to serve as a guide for the in­spection and maintenance of aircraft oxygen systems. The information is applicable to both portable and permanently-installed equipment.

7.7.1 Aircraft Gaseous Oxygen Systems: The oxygen in gaseous systems is supplied from one or more high or low-pressure oxy­gen cylinders. Since the oxygen is compressed within the cylinder, the amount of pressure in­dicated on the system gauge bears a direct re­lationship to the amount of oxygen contained in the cylinder. The pressure-indicating line connection is normally located between the cylinder and a pressure-reducing valve.

NOTE: Some of the gaseous oxygen systems do not use pressure-reducing valves. The high pressure is reduced to a useable pressure by a regulator. This regulator is located between the high- and low-pressure system.

CAUTION: Oxygen rich environ­ments are dangerous.

7.7.2   Portable Oxygen Systems: The three basic types of portable oxygen systems are: demand, pressure demand, and continuous flow. The components of these systems are identical to those of a permanent installation with the exception that some parts are minia­turized as necessary. This is done in order that they may be contained in a case or strapped around a person's shoulder. It is for this port­ability reason that special attention be given to assuring that any storage or security provision for portable oxygen equipment in the aircraft is adequate, in good condition, and accessible to the user.

NOTE: Check portable equipment including its security provisions fre­quently, since it is more susceptible to personnel abuse than a permanently installed system.

INSPECTION

Hands, clothing, and tools must be free of oil, grease, and dirt when working with oxygen equipment. Traces of these organic materials near compressed oxy­gen may result in spontaneous combustion, explosions, and/or fire.

Oxygen Tanks and Cylinders: In­spect the entire exterior surface of the cylinder for indication of abuse, dents, bulges, and strap chafing.

(1)       Examine the neck of cylinder for cracks, distortion, or damaged threads.

(2)       Check the cylinder to determine if the markings are legible.

(3)       Check the date of the last hydro­static test. If the periodic retest date is past, do not return the cylinder to service until the test has been accomplished.

(4)       Inspect the cylinder mounting bracket, bracket hold-down bolts, and cylin­der-holding straps for cracks, deformation, cleanliness, and security of attachment.

(5)       In the immediate area where the cylinder is stored or secured, check for evi­dence of any types of interference, chafing, de­formation, or deterioration.

 Lines and Fittings:

(1)       Inspect oxygen lines for chafing, corrosion, flat spots and irregularities, i.e., sharp bends, kinks, and inadequate security.

(2)       Check fittings for corrosion around the threaded area where lines are joined. Pres­surize the system and check for leaks. See paragraph 7.9.2(2) (d)

CAUTION: In pressurizing the sys­tem, actuate the valve slowly to avoid surging which could rupture the line.

Regulators, Valves, and Gauges:

(1)       Examine all parts for cracks, nicks, damaged threads or other apparent damage.

(2)       Actuate the regulator controls and the valve to check for ease of operation.

(3)       Determine if the gauge is function­ing properly by observing 'the pressure build-up and the return to zero when the system oxygen is bled off.

Masks and Hoses:

(1)       Check the oxygen mask for fabric cracks and rough face seals. If the mask is a full-face model, inspect the glass or plastic for cleanliness and state of repair.

(2)       When appropriate, with due regard to hygienic considerations, the sealing quali­ties of an oxygen mask may be tested by placing a thumb over the connection at the end of the mask tube and inhaling very lightly. Re­move the thumb from the disconnect after each continuous inhalation. If there is no leakage,, the mask will adhere tightly to the face during inhalation, and definite resistance to inhalation will be noticeable.

(3)       Flex the mask hose gently over its entirety and check for evidence of deteriora­tion or dirt.

(4)       Examine the mask and hose storage compartment for cleanliness and general con­dition.

(5)       If the mask and hose storage com­partment is provided with a cover or release mechanism, thoroughly check the operation of the mechanism.

MAINTENANCE.

Oxygen Tanks, Cylinders, and Hold Down Brackets.

(1)       Remove from service any cylinders that show signs of abuse, dents, bulges, cracks, distortion, damaged threads, or defects which might render them unsafe. Typical examples of oxygen cylinder damage..

(2)       When replacing an oxygen cylinder, be certain that the replacement cylinder is of the same size and weight as the one removed.

AIRTCRAFT PREVENTION OF OXYGEN FIRES OR EXPLOSIONS

Prevention Of Oxygen Fires Or Explosions

Safety precautions for oxygen servicing are similar to those required for fuelling or refuelling an aircraft. The airplane and service cart should be electrically grounded and all vehicles should be kept a safe distance away. There should be no smoking, open flame or items which may cause sparks within 50 feet or more depending upon the ventilation of the area during servicing operations. Since the clothing of a person involved in servicing an oxygen system is likely to be permeated with oxygen, no one should smoke within ten or fifteen minutes after completing the oxygen servicing.

The most important consideration when servic­ing any type of oxygen system is the necessity for absolute cleanliness. The oxygen should be stored in a well ventilated part of the hangar away from any grease or oil, and all high pressure cylinders not mounted on a service cart should be stored upright, out of contact with the ground and away from ice, snow or direct rays of the sun. Protective caps must always be in place to prevent possible damage to the shutoff valve. The storage area for oxygen should be at least 50 feet away from any combustible material or separated from such material by a fire resistant partition. When setting up an oxygen storage area, you should be sure that it meets all of the requirements established by your insurance company and by both Federal and State Occupational Safety and Health Act (OSHA).

Because of the extreme incompatibility of oxygen and any form of petroleum products, it is a good idea to set aside some tools to be used exclusively with oxygen equipment. Any dirt, grease or oil that may be on the tools or on any of the hoses, adapters, cleaning rags, or even on your clothing is a possible source of fire.

AIRCRAFT REPLACING TUBING, VALVES AND FITTINGS

Replacing Tubing, Valves And Fittings

It is extremely important when installing any oxygen line in an aircraft that no petroleum product is used as a thread lubricant, and that the lines are thoroughly cleaned of any trace of oil that was used in the flaring or presetting operation. Trichloroethylene or some similar solvent may be used to clean the tubing and fittings, and after they are thoroughly clean, they should be dried either with heat or by blowing them dry with water­ pumped dry air or dry nitrogen.

Tapered pipe threads must never be lubricated with a thread lubricant that contains any form of petroleum. Oxygen-compatible thread lubricant that meets specification MIL-T-5542 maybe used, or the male threads may be wrapped with Teflon tape and the fittings screwed together.

Before any tubing or fitting is replaced in an oxygen system, the part must be thoroughly cleaned and inspected. Check the part for evidence of corrosion or damage, and degrease it with a vapour degreaser or ultrasonic cleaner. Flush the new line with stabilized trichloroethylene, acetone, or some similar solvent, and dry it thoroughly with water-pumped dry air or nitrogen. If neither water pumped air nor nitrogen are available, the part may be dried by holding it at a temperature of about 250 °F until it is completely dry. When the parts are dry, close them with properly fitting protective caps or plugs, but never use tape in any form to seal the lines or fittings, as small particles of the tape are likely to remain when it is removed. 

AIRCRAFT FILLING A LIQUID OXYGEN SYSTEM

 Filling A Liquid Oxygen System

Service carts for liquid oxygen normally carry the LOX in 25- or 100-liter containers. Servicing systems from these carts is similar to that described in the previous section on gaseous oxygen systems. And here again, cleanliness and care are of the utmost importance. Liquid oxygen has such a low boiling point that it must not be spilled on your skin; it would be sure to cause serious frostbite. Protective clothing and an eye shield must be worn.

Before servicing an empty LOX system or one that hasn't been in use for some time, you should purge it for a few hours with heated water pumped dry air or nitrogen.

Attach the service cart to the aircraft system and, after placing the build-up and vent valve in the vent position, open the valve on the service cart. As the LOX flows from the service cart into the warm converter, it vaporizes rapidly and cools the entire system. Considerable gaseous oxygen is released during the filling procedure, and it vents to the outside air through the build-up and vent valve. This venting of the gaseous oxygen will continue until liquid oxygen starts to flow out of the vent valve. A steady stream of liquid indicates that the system is full.

Be sure that the system vents freely as it is being filled and that frost forms only on the outlet and the hoses. If any frost forms on the supply con­tainer, it could be an indication of an internal leak, and since the pressure can build up extremely high, any trace of a leak demands that the equip­ment be shut down immediately and the cause of the frosting determined.

When you attach the liquid oxygen cart to the aircraft system, open the valve fully, then close it slightly. If you do not do this, it is possible that the oxygen flowing through the valve could cause the valve to freeze in the open position and it may be difficult or impossible to close.

There are two ways LOX converters are serviced. Some are permanently installed in the aircraft and are serviced from an outside filler valve. The build-up and vent valve is placed in the vent position, the service cart is attached to the filler valve, and liquid oxygen is forced into the system until liquid runs out of the vent line. When the system is full, the build-up and vent valve is returned to the build-up position to build up pressure in the converter. Other installa­tions have quick-disconnect mounts for the con­verters so the empty converter can be removed from the aircraft and replaced with a full one. Exchanging converters allows oxygen servicing to be done much more quickly and safely than can be done by filling the converter in the aircraft.

Inspecting the masks and hoses disposable masks such as those used with many of the portable systems should be replaced

with new masks after each use, but the permanent masks used by crew members are normally retained by the individual for his exclusive use. These masks are fitted to the face to exclude leakage and are usually treated as personal flight gear. They should be occasionally cleaned with a lukewarm detergent bath by washing them with a cloth wet with the detergent solution and then allowing them to dry at room temperature. The face portion of the mask may be disinfected with a mild antiseptic.

Check the masks and hoses for leaks, holes or rips, and replace them rather than attempting to repair any damaged component. When storing the mask in the airplane, be sure to protect it from dust and dampness, and especially from any type of grease or oil.

OXYGEN SYSTEM SERVICING, INSPECTION AND MAINTENANCE PRACTICES

Oxygen System Servicing, Inspection And Maintenance Practices

 INTRODUCTION

Oxygen system requires some careful maintenance activities. This week highlight different type of  servicing, inspection and maintenance procedures.

  Oxygen System Servicing: GENERAL

Care and attention to detail is the mark of professional aviation maintenance, and nowhere is this characteristic more important than when servicing aircraft oxygen systems. Compressed gaseous oxygen demands special attention be­cause of both its high storage pressure and its extremely active chemical nature.

When possible, all oxygen servicing should be done outdoors, or at least in a well ventilated area of the hangar. Oxygen systems having removable or portable supply cylinders should have these containers removed from the operation, and all electrical work within the aircraft should be suspended during the servicing. In all cases the manufacturer's service information must always be used while performing service, maintenance or inspection on aircraft oxygen systems.

Servicing Gaseous Oxygen Systems

  Leak Testing Gaseous Oxygen Systems:  Leaks should be searched out by using a special leak detector material which is a form of non-oily soap solution. Spread this solution over every fitting and at every place a leak could possibly occur, and the presence of bubbles will indicate a leak. If a leak is found, release the pressure from the system, and check the fittings for proper torque. It is especially true of flare less fittings where over tightening can intensify a leak. If the fitting is properly torqued and still leaks, remove the fitting and examine all of the sealing surfaces for indication of damage. It may be necessary to replace the fitting and reflare the tube or install a new flare less fitting.

Draining The Oxygen System: Draining of the oxygen system should normally be done after the high pressure bottle has been removed or isolated from the system. Either out­doors or in a well ventilated hangar, open the aircraft's doors and windows, then bleed the system's pressure off by opening the appropriate fitting to allow the oxygen pressure to bleed off. Normally a system will require purging after the system has been drained. All the safety precau­tions mentioned later in this chapter should be followed during any oxygen draining procedure.

 Filling An Oxygen System: Fixed base operators who do a considerable amount of oxygen servicing will usually have one of the larger oxygen servicing carts such as the one seen in Figure 7.1. This cart carries six large cylinders, each holding approximately 250 cubic feet of aviators breathing oxygen. A seventh cylinder, facing the opposite direction and filled with compressed nitrogen, is normally carried to charge hydraulic accumulators and de-icer cylinders. Fittings on the nitrogen cylinders are different from those on the oxygen cylinders, to minimize the possibility of using nitrogen to fill the oxygen system, or of servicing the other systems with oxygen.

If you ever fill a low-pressure oxygen system from a high-pressure supply, be sure the proper regulator is installed and the output pressure is adjusted to that required for the system.

Various manufacturers of oxygen equipment use different types of connections between the supply and the aircraft, and a well equipped ser­vice cart should have the proper adapters. These adapters must be kept clean and protected from damage. Never improvise when adapting a supply cart to the aircraft. Leakage during the filling operation is not only costly, but it is hazardous as well.

Before filling any aircraft oxygen system, be sure that all of the cylinders are of the approved type, and that they have all been hydrostatically tested within the required time interval.

No oxygen system should be allowed to become completely empty. When there is no pressure in­side the cylinder, air can enter, and most air contains water vapour. When the water vapour is mixed with the oxygen and expanded through the small orifices in the system, the water is likely to freeze and shut off the flow of oxygen to the masks. Water in a cylinder can also cause it to rust on the inside and weaken it so it will fail with catastrophic results. A system is considered to be empty when the pressure gets down to 50 to 100 psi. If the system is ever allowed to get completely empty, the valve should be removed and the cylinder cleaned and inspected by an FAA-approved repair station.

When filling an airplane from a large supply cart, start with the cylinder having the lowest pressure. The pressure should be written on the container with chalk or a record kept with the cart. Momen­tarily crack the valve on the cylinder and allow some oxygen to purge all of the moisture, dirt and air from the line; then connect the line to the aircraft filler valve and slowly open the valve on the cylinder. Most all filler valves have restrictors that prevent too high a flow rate into the cylinder. When the pressure in the aircraft system and that in the cylinder with the lowest pressure stabilizes and there is no more flow, mark this pressure on the cylinder with chalk and close the cylinder valve. Slowly open the valve on the cylinder having the next lowest pressure and allow oxygen to flow into the system until it again stabilizes. Continue this procedure until the pressure in the aircraft system is that which is required.

The ambient temperature determines the pres­sure that should be put into the oxygen system, and a chart similar to the one in should be used to determine the pressure needed. For example, if the ambient temperature is 90 °F and you want a stabilized pressure in the system of 1,800 psi, you should allow the oxygen to flow until a pressure of 2,000 psi is indicated on the system pressure gauge. When the oxygen in the system drops to its standard temperature of 70 °F, the pressure should stabilize at 1,800 psi. If the ambient temperature is low, you must stop filling the system at a lower pressure, because the oxygen will expand and the pressure will rise when it warms up to its standard temperature.\

Purging A Gaseous Oxygen System: If the oxygen system has been opened for servic­ing, you should purge it of any air that may be in the lines. To purge a continuous flow system, plug masks into each of the outlets, turn on the oxygen supply valve, and allow the oxygen to flow through the system for about ten minutes. Diluter demand and pressure demand systems may be purged by placing the regulators in the EMERGENCY posi­tion and allowing the oxygen to flow through them for about ten minutes. After the system has been thoroughly purged, fill the cylinders to the re­quired pressure.

AIRCRAFT MISCELLANEOUS EQUIPMENT

MISCELLANEOUS EQUIPMENT

Parachutes. With reasonable care, parachutes can remain in service indefinitely. They should not be carelessly tossed about, left in aircraft to become wet, or left where someone may tamper with them. They should not be placed where they may fall on oily floors or be subject to acid fumes from adja­cent battery chargers.

(1)       When repacking is scheduled, to comply with the 120-day requirement in Ti­tle 14 of the Code of Federal Regulation (14 CFR) part 105 section 105.43 a careful in­spection of the parachute shall be made by a qualified parachute technician (rigger). If re­pairs or replacements of parts are necessary to maintain the airworthiness of the parachute as­sembly, such work must be done by the origi­nal parachute manufacturer or by a qualified parachute rigger, certificated in accordance with 14 CFR, part 65.

(2)       The lead seal should be inspected periodically to ensure the thread has not been broken.  If broken, or broken and retied or appears to have been tampered with, the para­chute must be repacked by a properly certified rigger.

Safety Belts. All seat belts and re­straint systems must conform to standards es­tablished by the FAA. These standards are contained in Technical Standard Order TSO C22 for seat belts and TSO C 114 for re­straint systems.

(1)       Safety belts eligible for installation in aircraft must be identified by the proper TSO markings on the belt. Each safety belt must be equipped with an approved metal to metal latching device. Airworthy type certificated safety belts currently in aircraft may be removed for cleaning and reinstalled. However, when a TSO safety belt is found un­airworthy, replacement with a new TSO-approved belt or harness is required.

(2)       The webbing of safety belts, even when mildew-proofed, is subject to deteriora­tion due to constant use, cleaning, and the effects of aging. Fraying of belts is an indication of wear, and such belts are likely to be unair­worthy because they can no longer hold the minimum required tensile load.

AIRCRAFT LIFE PRESERVERS

LIFE PRESERVERS

Inflatable life preservers are subject to general deterioration due to aging. Experience has indicated that such equipment may be in need of replacement at the end of 5 years due to porosity of the rubber-coated material. Wear of such equip­ment is accelerated when stowed on board air­craft because of vibration which causes chaf­ing of the rubberized fabric. This ultimately results in localized leakage. Leakage is also likely to occur where the fabric is folded be­cause sharp corners are formed. When these corners are in contact with the carrying cases, or with adjacent parts of the rubberized fabric, they tend to wear through due to vibration.

Life preservers should be inspected in accor­dance with the manufacturer's specification, unless climate, storage, or operational condi­tions indicate the need for more frequent inspections.

LIFE PRESERVER -INSPECTION

Life preservers should be inspected at 12-month intervals for cuts, tears, or other damage to the rubberized material:. Check the mouth valves and tubing for leakage, corro­sion, and deterioration: Remove^. the CO₂ cyl­inder and check the discharge mechanism by operating the lever to ascertain that the pin op­erates freely. Check the gaskets and valve cores of the cylinder container and the pull cord for deterioration. If no defects are found, inflate the preserver with air to a 2 psi pressure and allow to stand for 12 hours. If the pre­server still has adequate rigidity at the end of that time, deflate and fit with C02 cylinders having weights not less than that indicated on them by the manufacturer. All cylinders made in accordance with joint Army-Navy Specifi­cation MIL-C-00601 D are' so stamped and have a minimum permissible weight stamped on them. The use of such CO₂ cylinders is recommended. Having fitted the preserver with an adequately-chaiged cylinder, mark the preserver to indicate the date of inspection and patch it to the container. It is recommended that the aforementioned procedure be repeated every 12-month period, utilizing the C0₂ car­tridge. for inflation. Carbon dioxide permeates the rubberized fabric at a faster rate than air and will indicate if the porosity of the material is excessive. The following checks and in­spections should be completed:

a.         Check for abrasions, chafing, and soiling across folded cell areas and around metal parts. Condemn the life preserver when unsuitable conditions are found.

b.         Check for separation of cell fabric and loose attachments along the edges of patches and sealing tapes. Repair if practicable.

c.         Check for deterioration in areas where oil and grease are noted. Condemn deterio­rated cells. If deterioration is not noted, clean the areas with mild soap and water and rinse with clear water.'

d.         Inspect the snaps and/or buckles to ensure proper operation.

e.         Inspect the instruction panel for read­ability.

f.          Inspect all stitching for gaps, pulls, and tears.

g.         Visually inspect the cell containers for snags, cuts, loose stitching, and oil and grease spots. Repair or replace as necessary.

h.         Inspect the hardware for rusted or broken parts and cotter pins for damage. En­sure that pins are smooth and free of burrs.

i.          Check the inflator discharge lever for proper operation. Move the inflator dis­charge lever slowly through a normal cycle of operation to ensure freedom of 'operation and to make certain that the piercing pin has suffi­cient movement to discharge the CO_Z cylinder. The point of the pin should move past the sur­face of the gasket in the inflator. In the un-op­erated position, the end paint should be slightly below the gasket surface.

j.          Check the installation of the inflator stem gaskets and check the stem caps for tightness.. Ensure that the inflator is centred on the stem.

k.         Check rescue light. Inspect and test.

(1)    Replace the battery if it shows any signs of encrustation.

(2)    Inspect for proper installation and physical condition of the lamp, wire, and bat­tery.

(3)    Check the light assembly for proper operation and water insulation and flotation.

(4)    Pull the sealing plug (where appli­cable) from the battery. Let water flow through the open ports. Make sure the battery is activated and power is supplied to the light.

(5)    Fill out the inspection record and serviceable parts tag. Attach to the vest.

  l.        Deflate the life preserver and repack in container and secure.

m.        The accessories listed below will be required for all life preservers:

(1)    One Recognition Light: Remove when returning to serviceable or reparable storage. Remove for replacement of defective light, repair, or salvage of preserver.

(2)    One Recognition Light Battery: Remove when returning to serviceable or repa­rable storage.

n.         Record the inspection data on data cards.

o.         Life preserver inspected and found sea worthy. Include the inspector's signature.

p.         Inspection record. Upon completion of 12-month inspection and tests, each flota­tion cell will be marked to indicate the date the inspection was accomplished. The inspection stencil will consist of 1/8-inch letters and nu­merals and will be applied to the patches on the cells (example: 4/3/97). To facilitate determination of the next 12-month inspection period, enter the date it is due in the blank be­side the word inspect on the inspection data card provided in the inspection data pocket on the cell container. Repack, close, and seal the container.

 REPAIR OF LIFE PRESERVERS

Leaks may be disclosed by immersion in soapy water. Repair leaks by the use of patches in accordance with the recommendations of the manufacturer. Clean corroded metal parts and replace missing or weakened lanyards. Life preservers which do not retain sufficient rigid­ity after the 12-hour period, because of general deterioration and: porosity of the fabric, are be­yond economical repair and should be re­placed.

AIRCRAFT SPECIAL INSPECTIONS

SPECIAL INSPECTIONS

Life rafts in storage or in service shall be unpacked and thoroughly inspected for mildew whenever weather or other conditions warrant. The ex­tent of a special inspection will be determined by the inspector or maintenance chief follow­ing a review of the circumstances or conditions to which the life rafts have been subjected. The inspector or maintenance chief may direct a complete overall inspection and inflation test of the life rafts, regardless of the last date of inspection, if it is considered that another in­spection is warranted.

INSPECTION RECORD

The date the inspection was completed will be stencilled on the flotation tube at the left of the cylinder. The size of lettering will not be less than 1/4-inch or greater than 1/2-inch in height. Previous inspection dates will not be removed or obliterated, but will be arranged in colum­nar form with the latest date at the top. After the inspection is completed, fill out the raft's in­spection record in accordance with part 43 sec­tion 43.9, and attach the parts tag to the survival equipment. The date on the tag will reflect the same date as stenciled on the flotation tube and will be used to determine the next due date of inspection and test.

RAFT REPAIRS

Repairs. The service life for flotation equipment will be determined by condition rather than age. Equipment passing tests and inspections may remain in service indefinitely since the inflation tests and material inspec­tions will identify and condemn equipment having more than minor installation defects. However, the service life for life rafts operat­ing under normal usage and environmental conditions is anticipated by the manufacturers to be 8 to 10 years, and it is appropriate to base life raft's parts replacement programs upon this estimate. It is not considered advisable or economical to perform major repairs on life rafts.

Life Rafts.       Life rafts with any of the following conditions should be condemned rather than repaired:

(1)       Life rafts over 3-1/2 years of age and requiring major repair or more than two miⁿor repairs.

(2)       A rip or tear across an air retaining seam.

(3)       Rafts on which oil, grease, or any other foreign substance has caused a deteriora­tion of the rubberized fabric.

(4)       Rafts on which a heavy mildew condition has caused deterioration of the rub­berized fabric.

(5)       Rafts on which porous flotation tubes allow diffusion of air. A porous area is located by a soap test on the inflated raft. Higher diffusion is indicated by the excessive loss of pressure after a soap test has failed to locate a specific area of injury on the raft.

(6)       Rafts requiring internal repair or opening of air retaining seams for repair.

(7)       Rafts with an excessive number of injuries that would not, in the judgment of competent inspectors, justify repair.

Patches. Holes or abrasions which are 2 inches or less, in diameter_. (in air retaining chambers) will be repaired by the application of an outside patch. Holes exceeding 2 inches in length or diameter, will require an inside patch as well as an outside patch. Inside and outside patches should be round or rectangular and manufactured of fabric (specification MIL-C-6819). Cement should conform to Class 1 of specification MIL-C-5539. Patch as follows:

(1)       Outside patches.

(a)       With a rubber solvent thoroughly clean the area to be patched.

(b)       From the material referenced, fabricate a patch.

(c)       When two fabric surfaces are to be bonded, apply two coats of extra light ce­ment, two coats of light cement, and three coats of heavy cement to each surface. Rubber coated tape and seam crossover patches with protective backing do not require cement. Each coat of cement should be thoroughly dry to the touch before the next coat is applied. Start the bonding of fabric surfaces while the last coat of cement is slightly tacky. To ensure proper adhesion when bonding two cemented sur­faces, the areas to be bonded should remain tacky during application. This is accomplished by brushing the cemented area with a cloth moistened with solvent.

NOTE: If difficulty in the drying of heavy cement is encountered due to atmospheric conditions, six additional coats of light cement may be substi­tuted for the three coats of heavy ce­ment.

(d)       After applying the patch, thor­oughly roll it with a hand roller, rolling from the centre to the outer edge, to ensure that all air pockets are removed and a firm bond is se­cured.

(e)       Thoroughly dust with talc. Allow to cure for 60 hours before performing leak tests and storing.

(2)       Inside Patches.

(a)       Cut a rectangular patch , allowing at least 1-1/2 inches to extend beyond the edge of the injury in all di­rections.

(b)       Mark the centre line on the side of the patch that is to be attached to the raft. Mark cross lines on each end of the patch l-1/2 inches from the ends. When the patch is applied to the injury on the inside, the longitu­dinal edges of the injury will coincide with the centre line, and cross lines on the ends of the patch will coincide with the ends of the injury.

c)         To ensure that the inside surface of the raft is properly powdered in the area of repair, pass a small handful of talc through the opening in the raft and place it approximately 12 inches from the injury. This should be ac­complished before the inside area is cemented, exercising care to prevent distribution of the talc prior to completion of the repair.

(d)       Using cleaning solvent, cleanse an area on the inside surface of the fabric slightly larger than the patch to be applied. En sure that the repaired area is thoroughly dry, both inside and outside; apply two coats of extra light cement, two coats of light cement, and three coats of heavy cement (or six addi­tional coats of light cement in lieu of the heavy cement) to the cleansed area, allowing each coat to dry thoroughly before applying succes­sive coats.

NOTE: Since it is impossible for the repairman to visually observe the ce­menting     that is being accomplished on the inside of the raft, exercise care to ensure that each coat of cement com­pletely covers the area to be repaired.

(e)       The inside patch should be ce­mented simultaneously with the application of cement to the inside of the raft. Apply the same number of coats as directed in para­graph 9 42b(2)(d) to the side of the patch that is applied to the injured fabric of the raft. En­sure that each coat is thoroughly dry before applying the next coat.

(f)        To aid in adhesion, prior to ap­plying the patch, the inside area to be repaired and cemented surface of the patch should be cleaned with a cloth moistened with rubber solvent. The cement will then become tacky.

(g)       Apply the patch. Fold the patch lengthwise in the shape of the letter "U" and insert the patch between the. tom edges of the injury on the life rafts. Position the patch so that the fabric at the end of the tear will coin­cide with a cross line and the centre line on the patch follows one edge of the torn fabric. At­tach one edge of the torn fabric along the centre line on the patch.

(h)       Inspect the repair for wrinkles. Working from the attached edge of the fabric to the edge of the patch, remove the wrinkles with_. a stitcher. Lay the opposite edge of the torn fabric on the patch so that it butts the edge of the torn fabric that has already been applied to the patch. Remove the wrinkles. Thor­oughly roll the patch with a 2 inch rubber roller.

          NOTE: The surface under the patch should be as smooth as possible so that the torn edge of the fabric may be at­tached to the patch instead of at­tempting to attach the patch to the fabric.

(i)         Scatter the handful of talc that was placed inside the tube by grasping the sides of the flotation tube and pulling them apart.

(j)         Prepare and attach the outside patch as outlined in "OUTSIDE PATCHES," sub-paragraphs 9-42b(1)(a)-(e).

(k)       Allow to cure for at least 60 hours before performing leak tests and storing.

(3)       Seams and Tapes.

(a)       Remove all old or dead cement from the area that will require re-cementing. Dampen the repair area with a solvent moistened cloth; then roll or rub off the old cement.

(b)       Apply cement to the surface as outlined in "OUTSIDE PATCHES," sub­paragraph 6.6.2(1), 6.6.3(a)-(e).

(c)       Roll thoroughly with a roller to ensure that all air pockets are removed and a firm bond is secured.

(d)       Allow to dry and apply talc over the seam as previously outlined.

(e)       Allow to cure for at least 60 hours before performing leak tests and storing.