FIGURE 11-16. CO2 fire extinguisher.
for use. When pouring oil into the tanks, be sure that cleaning rags or pieces of rag or other foreign substances do not get into the tanks. Foreign material in the oil system restricts the flow of oil and can cause engine failure.
Lubricating oil is nonexplosive, very difficult to ignite in bulk, and is not normally capable of spontaneous combustion. However, if oil is ignited, a hotter fire results than that from gasoline. The vapor of the oil, however, is explosive when mixed with air in certain proportions. Vapors of many petroleum products are highly toxic when inhaled or ingested. It is therefore necessary to take all precautions when handling lubricating oil.
MAINTENANCE SAFETY Good housekeeping in hangars, shops, and on the flight line is essential to safety and efficient maintenance. The highest standards of orderly work arrangements and cleanliness should be observed during the maintenance of aircraft. Where continuous work shifts are established, the outgoing shift should remove and properly store personal tools, rollaway boxes, all workstands, maintenance stands, hoses, electrical cords, hoists, crates, and boxes that are superfluous to the work to be accomplished.
Safety Lanes Pedestrian walkways or fire lanes should be painted around the perimeter inside the hangars.
This should be done as a safety measure to prevent accidents and to keep pedestrian traffic out of work areas.
Power Cords I. Power cords should be heavy industrial type which are able to resist abrasion and impact.
2. Power cords should not be run over by any equipment.
3. Lights should be explosion proof.
4. Connections should be locking type to prevent accidental disconnection.
5. All lights or equipment should be switched "off"', , to prevent arching before connecting or disconnecting.
6. Power cords should be straightened, coiled, and properly stored when not in use.
Disregard of the above suggestions may result in explosions and fires with damage into millions of dollars and loss of life.
Compressed Air System Compressed air is like electricity-an excellent tool as long as it is under control.
1. Air hoses should be inspected frequently for breaks and worn spots. Unsafe hose should be replaced immediately.
2. All connections should be kept in a ino leak condition".
3. In line oilers, if installed, should be maintained in operating condition.
4. The system should have water sumps installed FIGURE 11-17. Dry chemical extinguisher. tervals. and they should be drained at regular in- 507
5. Air used for paint spraying should be filtered to remove oil and water.
6. Never use compressed air to clean hands or clothing. Pressure can force debris into the flesh leading to infection.
7. Never use compressed air for "horse play".
8. Air hoses should be straightened, coiled, and properly stored when not in use.
Spilled Oil and Grease Oil, grease, and other substances spilled on hangar or shop floors should be immediately cleaned or covered with an absorbent material to prevent fire or personal injury. Drip pans should be placed beneath engines and engine parts wherever dripping exists. Waste oil and dirty cleaning fluid should be stored in containers for future salvage. Under no circumstances should oil or cleaning fluid be emptied into floor drains. Fumes from this type "disposal" may be ignited and cause severe property damage.
Aircraft Tire Mounting To prevent possible personal injury, tire dollies and other appropriate lifting and mounting devices should be used in mounting or removing heavy aircraft tires. When inflating tires on wheels equipped with locking rings, tire cage guards should always be used.
should be inflated in tire cage guards. Becaus of possible personal injury, extreme caution is required to avoid overinflation of high-pressure tires.
Pressure regulators should be used on high pressure air bottles to eliminate the possibility of overinflation of tires.
Tire cages need not be used when adjusting pressure in tires installed on aircraft.
Welding should not be performed except in designated areas. Any part to be welded should be removed from the aircraft, if possible. Repair would then be accomplished in the welding shop under controlled environment. A welding shop should be equipped with proper tables, ventilation, tool storage, and fire prevention and extinguishing equipment.
Welding on an aircraft should be performed outside if possible. If welding in the hangar is necessary, these precautions should be observed:
1. No open fuel tanks or work on fuel systems should be in progress.
2. No painting in progress.
3. No aircraft within 35 feet.
4. Immaculate housekeeping should prevail around the welding area.
5. Only qualifed welders should be permitted to do the work.
6. The area should be roped off and placarded.
7. Fire extinguishing equipment of a minimum rating of 20B should be in the immediate area with 80B rated equipment as a backup.
8. There should be trained fire watches in attendance at the above equipment.
9. Aircraft should be in towable condition, with a tug attached, aircraft brakes off, and a qualified operator on the tug with mechanics available to assist in the towing operation. Hangar doors should be opened
SERVICING AIRCRAFT OXYGEN SYSTEMS Before servicing any aircraft, consult the specific aircraft maintenance manual to determine the proper type of servicing equipment to be used Two persons are required to service an aircraft with gaseous oxygen. One man should be stationed at the control valves of the servicing equipment and one man stationed where he can observe the pressure in the aircraft system. Communication between the two men is required in case of an emergency. Aircraft should not be serviced with oxygen during fueling, defueling, or other main tenance work which could provide a source of ignition. Oxygen servicing of aircraft should be accomplished outside hangars.
Oxygen Hazards Gaseous oxygen is chemically stable and is nonflammable; however, combustible materials ignite more rapidly and burn with greater intensity in an oxygen-rich atmosphere. In addition, oxygen combines with oil, grease, or bituminous material to form a highly explosive mixture which is sensitive to impact. Physical damage to, or tailure oi, oxygen containers, valves, or plumbing can result in explosive rupture, with danger to life and property.
It is imperative that the highest standard of housekeeping be observed in handling oxygen and that only authorized persons be permitted to service aircraft.
In addition to aggravating the fire hazard, liquid oxygen will cause severe "burns" (frostbite) if it comes in contact with the skin because of its low temperature. (It boils at - 297° F.)
Only oxygen marked ¿Aviators Breathing Oxygen" which meets Federal Specification BB-0-925a.
Grade A or equivalent may be used in aircraft breathing oxygen systems.
AIRCRAFT TIEDOWN Aircraft tiedown is a very important part of aircraft ground handling. The type of tiedown will 508
be determined by the prevailing weather conditions. In normal weather a limited or normal tiedown procedure is used; but when storm conditions are anticipated, a heavy weather or storm condition tiedown procedure should be employed.
Normal Tiedown Procedure Small aircraft should be tied down after each flight to preclude damage from sudden storms. The direction in which aircraft are to be parked and tied down will be determined by prevailing or forecast wind direction.
Aircraft should be headed, as nearly as possible, into the wind, depending on the locations of the fixed, parking area tiedown points. Spacing of tiedowns should allow for ample wingtip clearance (figure 11-18). After the aircraft is properly located, lock the nosewheel or the tailwheel in the fore-and-aft position.
Tiedown Anchors All aircraft parking areas should be equipped for three-point tiedowns. This is facilitated at most airports by use of tiedown anchors installed in concrete parking areas. Tiedown anchors, sometimes called "pad eyes," are ringlike fittings installed when the parking area is poured. They are normally set flush with the surface of the concrete or no more than one inch above it. There are several types of tiedown anchors in use. The type selected is usually determined by the material used in aircraft parking areas, since it may be a Major axis +
- 10 FIGURE 11-18. Diagram of tiedown dimensions.
concrete paved surface, a bituminous paved surface, or an unpaved turf area.
Location of tiedowns is usually indicated by some means such as white or yellow paint markings or by surrounding the tiedown anchor with crushed stone.
Tiedown anchors for small single-engine aircraft should provide a minimum holding power (strength) of approximately 3,000 pounds each.
Although this minimum can be achieved when stake-driven tiedowns are used in dry or turfed areas, such stakes will almost invariably pull out Manila Nylon Dacron Yellow Polypropylene Size (Twist) (Braid) (Twist) (Braid) (in.) Minimum Minimum Minimum Minimum Minimum Minimum tensile tensile tensile tensile tensile tensile strength strength strength strength strength strength (lbs.) (Ibs.) (Ibs.) (Ibs.) (Ibs.) (Ibs.)
• 3/16 960 850 730 800 600 1/4 600 1,500 1,440 980 1,300 1,100 5/16 1,000 2,400 2,200 1,650 1,900 1,375 3/8 1,350 3,400 3,120 2,300 2,750 2, 025 7/16 1,750 4,800 4,500 2,900 1/2 2,650 6,200 5,500 3,800 4,200 3,800 5/8 4,400 10,000 3/4 5,400 9,000 FIGURE 11-19. Comparison of common tiedown ropes.
when the ground becomes soaked from torrential rains which accompany hurricanes and some thunderstorms.
Tiedown Ropes Tiedown ropes capable of resisting a pull of approximately 3,000 pounds should be used to Release lever Lock Unlock FIGURE 11-21. A multipurpose tiedown chain.
secure light aircraft. Cable or chain tiedown is usually preferred for tying down large aircraft.
Manila ropes should be inspected periodically for mildew and rot. Nylon or Dacron tiedown ropes are preferable to manila rope. The objection to manila rope is that it shrinks when wet, is subject to mildew or rot, and has considerably less tensile strength than either nylon or Dacron. Various types of commonly used tiedown rope are compared in figure 11-19.
Tiedown Cable Starwheel Tiedown cables are often used to secure aircraft, especially in the case of large aircraft. Most cable-type tiedowns are accomplished with some form of tiedown reel designed for rapid and reliable securing of all types of aircraft. Figure Locking handle 11-20 illustrates the operation of a typical cable tiedown reel.
Locking cam In A of figure 11-20 the cable is released by D depressing the release lever to provide cable slack.
FIGURE 11-20. Operation of a cable tiedown reel. One end of the cable is then attached to the 510
Up through Back down This one must be under and around back through (A) Tying a bowline knot.
Over Ov
- Under Under (B) Tying a square knot.
FIGURE 11-22. Knots commonly used for aircraft tiedown.
aircraft tiedown ring and the other end to a SECURING LIGHT AIRCRAFT tiedown anchor. The starwheel on the reel (B of figure 11-20) is then turned clockwise to remove excess slack from the cable. The locking handle is then secured to the bar when the cable has been adjusted for the desired tautness (C of figure 11-20). Finally, as shown in D of figure 11-20, the locking cam is secured to complete the tiedown procedure.
Tiedown Chains The chain-type tiedown sometimes is used as a better and stronger tiedown to secure the heaviest aircraft. This tiedown assembly is composed of an all metal quick-release mechanism, a tensioning device, and a length of chain with hooks (figure 11-21).
Light aircraft are most often secured with ropes tied only at the aircraft tiedown rings provided for securing purposes. Rope should never be tied to a lift strut, since this practice can bend a strut if the rope slips to a point where there is no slack.
Manila rope shrinks when wet; about 1 inch of slack should be provided for movement. Too much slack will allow the aircraft to jerk against the ropes. Tight tiedown ropes put inverted flight stresses on the aircraft, many of which are not designed to take such loads.
A tiedown rope holds no better than the knot.
Antislip knots such as the bowline or square knots are quickly tied and are easy to untie (figure 11-22). Aircraft not equipped with tiedown fittings 511
should be secured in accordance with the manufacturer's instructions. Ropes should be tied to outer ends of struts on high-wing monoplanes, and suitable rings should be provided where structural conditions permit, if the manufacturer has not already provided them.
4. Attach tiedown reels to airplane tiedown loops and to tiedown anchors or tiedown stakes. Use tiedown stakes for temporary tiedown only. If tiedown reels are not available, 4-inch wire cable or 1½-inch manila line may be used.
SECURING HEAVY AIRCRAFT The normal tiedown procedure for heavy aircraft can be accomplished with rope or cable tiedown. The number of such tiedowns should be governed by anticipated weather conditions.
Most heavy aircraft are equipped with surface control locks which should be engaged or installed when the aircraft is secured. Since the method of locking controls will vary on different type aircraft, check the manufacturer's instructions for proper installation or engaging procedures. In case high winds are anticipated, which may damage the control surfaces or locking devices, control surface battens can also be installed to prevent damage.
Figure 11-23 illustrates four common tiedown points on heavy aircraft.
In general, the normal tiedown procedure for heavy aircraft should include the following:
1. Head airplane into prevailing wind whenever possible.
2. Install control locks, all covers and guards.
3. Chock all wheels fore and aft.
Aft fuselage Nose landing gear tiedown ring tiedown loop Underside of wing tiedown Toop Main gear wheel tiedown loop FIGURE 11-23. Common tiedown points.
AIRCRAFT TIEDOWN FOR STORM CONDITIONS Each year many aircraft are needlessly damaged by windstorms because of negligence and improper tiedown procedures. A storm can turn a local airport into a junkyard in a matter of minutes. If an aircraft is damaged during a windstorm, the chances are it was improperly secured or was not tied down at all.
Most windstorm damage occurs during the early summer months, but can continue with lessening frequency throughout the year. As a general rule, the large and very severe windstorms cause less damage than the small local ones. This is because there is usually sufficient advance warning for the former, but the latter build up quickly and give little warning of their coming.
According to available weather records, Tampa, Florida, is the storm center of this country, with an average of 94 thunderstorms a year. Santa Fe, New Mexico, is second with a yearly average of 73.
Other cities are less frequently visited by such storms. The Pacific Coast States average only one to four such storms a year. Generally speaking, thunderstorms and tornadoes are accompanied by high surface winds which account for most of the damage to aircraft on the ground.
Although most storms are generated in the daytime, many sections of the United States, including the Southwest, the lower Michigan Peninsula, and an extensive area centered in eastern Nebraska, are plagued with night storms during the summer months. Thunderstorms are bothersome in the Central States during the months of July, August, and September. On the other hand, in the winter the greatest storm activity takes place in the lower Mississippi Valley.
The map in figure 11-24 shows the yearly average number of days with thunderstorms based on observations from all U. S. Weather Bureau first-order stations in the United States. A thunderstorm day is considered any day during which one or more thunderstorms occur. It should be realized, however, that there probably are variations which do not show on this map because 512
20 50 1O 20 80 80 FIGURE 11-24. Map showing average number of thunderstorm days per year.
of the local nature of thunderstorms and the sparsity of observations from some areas. July and August are the months with the greatest number of thunderstorms over most sections of the United States, while December and January have the least number.
Thunderstorms are not the only concern of aircraft owners, fixed-base operators, airport service crews, etc., from a tiedown sense. There are also hurricanes and tornadoes. Figure 11-25 is a map showing the tornado frequency in the various states during a recent 10-year period.
A map showing the principal storm belts in the continental U.S.A. is presented in figure 11-26.
Precautions Against Windstorm Damage The best protection against windstorm damage is, of course, to fly the aircraft out of the impending storm area when there is sufficient time. The next best protective measure is to secure the aircraft in a stormproof hangar or other suitable shelter. The remaining alternative is to assure that the aircraft is tied down securely. When securing aircraft, fasten all doors and windows properly to minimize damage inside the aircraft. Engine openings (intake and exhaust) for both reciprocating and gasturbine type should be covered to prevent entry of foreign matter. Pitot-static tubes should also be covered to prevent damage.
Be prepared for the worst storm conditions; for example, pouring rain, and gusty winds with intermittent sheets of water flowing across the runways, ramps, and parking areas, with perhaps no hangar facilities available. With such conditions in mind, responsible service crews should plan in advance by becoming familiar with their aircraft manufacturer's instructions for the following: (1) Tiedown ropes; (2) installation of tiedown rings for attachment of tiedown ropes; (3) securing nosewheel type aircraft vs. tailwheel type aircraft;
and (4) aircraft weights and relative wind velocities that would make varied tiedown procedures necessary for pending weather emergencies.
The following suggestions will materially reduce aircraft damage from windstorms:
1. Partially disassembled aircraft which are outdoors (particularly light aircraft with 513
£OI 16 12 14 17 32 28 116 80 20 139 20 96 10 186 64 62 377 90 50 00~ 8+1 191 2560 1215 989 266 e+z 138 .C 80 187 58 99 149 90 167 87 1102 175 915 412 Fairbanks
•0 Honolulu S ALASKA HAWAI!
UPPER NUMBER - Number of tornadoes LOWER NUMBER- Number of tornado days FiGurE 11-25. Tornado frequency during a recent 10-year period.
engines removed) should be hangared as soon as storm warnings are received.
Loose wings should never be tied against a fuselage; they should be stored inside a hangar.
2. Whenever possible, fly aircraft out of anticipated storm danger zones. If impossible, hangar the aircraft in a stormproof hangar.
3. Observe the minimum recommended strength for tiedown ropes.
4. A single row of properly secured sandbags or spoiler boards (2" X 2') on the top of a wing's leading edge will serve as an effective spoiler and reduce the lifting tendency of the wings. Do not overload the wings with sandbags. If the anticipated winds will exceed the lift-off speed of the aircraft, the makeshift spoilers should run the entire length of the wings.
Another means for tying down light aircraft (of various types and sizes) utilizes continuous lengths of parallel wire ropes passed through U-bolt anchors secured to ground tiedown points (figures 11-27 and 11-28). Tiedown chains are attached to the wire rope with round-pin galvanized anchor shackles. This allows tiedown chains to "float" along wire rope and gives a variable distance between anchor points so that a variety of aircraft can use a vertical tiedown without loss of space.
The vertical anchor significantly reduces impact loads that may occur during gusty wind conditions.
The distance between ropes will depend upon the types of aircraft which use the tiedown area.
The diagram in figure 11-28 shows a proper vertical anchor using wire rope tiedown line, straight link coil chain for connection between the wire rope and aircraft wing. One link on the free end is then passed through a link of the taut portion, and a safety snap is used to keep the link from passing back through. Any load on the chain is borne by the chain itself instead of the snap.
Primary hurricane danger zone.
Fringe area.
Tornado belt.
FIGURE 11-26. Storm belts in the continental U.S.
FIGURE 11-27. Typical aircraft tiedown using a wire rope system.
FIGURE 11-28. Wire rope tiedown line using vertical anchor chain.
Securing Multiengine Aircraft Multiengine aircraft will obviously require stronger tiedown facilities because of the additional weight of these aircraft. The anchor should be capable of a holding power of 4,000 pounds each for the lighter executive twin-engine aircraft.
Much higher load capacity is required for the heavier transport-type aircraft.
Do not depend on the weight of the multiengine aircraft to protect it from damage by windstorms.
It is possible for a sudden, severe windstorm to move, damage, or even overturn such aircraft.
Multiengine aircraft should, therefore, always be tied down and chocked when left unattended for any length of time. Gust locks should be used to protect control surfaces. If the landing gear uses downlock safety pins, these pins should be inserted at the time the aircraft is being secured.
Securing Helicopters Structural damage can occur from high-velocity surface winds. Therefore, if at all possible, helicopters should be evacuated to a safe area if tornadoes or hurricanes are anticipated.
When possible, helicopters should be secured in hangars. If not, they should be tied down securely.
Helicopters that are tied down can usually sustain winds up to approximately 65 m.p.h.
For added protection, helicopters should be moved to a clear area so that they will not be damaged by flying objects or falling limbs from surrounding trees.
If high winds are anticipated with the helicopter parked in the open, the main rotor blades should be tied down. Detailed instructions for securing and mooring each type of helicopter can be found in the applicable maintenance manual. Methods of securing helicopters will vary with weather conditions, the length of time the aircraft is expected to remain on the ground, and location and characteristics of the aircraft. Wheel chocks, control locks, rope tiedowns, mooring covers, tip socks, tiedown assemblies, parking brakes, and rotor brakes are used to secure helicopters.
Typical mooring procedures are as follows:
1. Head the helicopter in the direction from which the highest forecasted wind or gusts are anticipated.
2. Spot the helicopter slightly more than rotor-span distance from other aircraft.
3. Place wheel chocks ahead of and behind all wheels (where applicable). On helicopters equipped with skids, retract the handling wheels, lower the helicopter to rest on the skids, and install wheel position lockpins.
4. Install a tiedown assembly on the end of the blade (figure 11-29 and align the blade over the tail boom. Secure the tiedown straps under the structural tubes of the tail boom. Tie the straps snugly without strain.
During wet weather, provide some slack to avoid the possibility of the straps tightening 516
FIGURE 11-29. Securing helicopter blades and fuselage.
5. Fasten the tiedown ropes or cables to the forward and aft landing gear cross tubes and secure to ground stakes or tiedown rings.
Securing Seaplanes and Aircraft on Skis Aircraft mounted on floats or skis should be secured to tiedown anchors or "deadmen" sunk under the water or ice. When warning of an impending storm is received and it is not possible to fiy the aircraft out of the storm area, some compartments of the seaplane can be flooded, partially sinking the aircraft. In addition, the aircraft should be tied down securely to anchors:
Seaplanes tied down on land have been saved from high-wind damage by filling the floats with water in addition to tying the aircraft down in the usual manner. Operators of ski-equipped aircraft sometimes pack soft snow around the skis, pour water on the snow, and permit the skis to freeze to the ice. This, in addition to the usual tiedown procedures, aids in preventing damage from windstorms.
MOVEMENT OF AIRCRAFT General Movement of large aircraft on an airport and about the flight line and hangar is usually accomplished by towing with a tow tractor (sometimes called a "mule or tug"). In the case of small aircraft, most moving is accomplished by hand, by pushing on certain areas of the aircraft surface.
Aircraft may also be taxied about the fight line, but usually only by certain qualified persons.
Towing of Aircraft Towing aircraft can be a hazardous operation, causing damage to the aircraft and injury to personnel, if done recklessly or carelessly. The following paragraphs outline the general procedure for towing aircraft; however, specific instructions for each model of aircraft are detailed in the manufacturer's maintenance instructions and should be followed in all instances.
Before the aircraft to be towed is moved, a qualified man must be in the cockpit to operate the brakes in case the tow bar should fail or become unhooked. The aircraft can then be stopped, preventing possible damage.
Some types of tow bars available for general use (figure 11-30) can be used for many types of towing operations. These bars are designed with sufficient tensile strength to pull most aircraft, but are not intended to be subjected to torsional or twisting loads. Although many have small wheels that permit them to be drawn behind the towing vehicle going to or from an aircraft, they will suffer 517
Tow hitch plate.
Locking pin.
Spreader plate.
End hooks. Tubing.
Locking pin hole.
Tailwheel Main wheel FIGURE 11-30. A front or rear tow bar.
less damage and wear if they are loaded aboard the vehicle and hauled to the aircraft. When the bar is attached to the aircraft, all the engaging devices should be inspected for damage or malfunction before moving the aircraft.
Some tow bars are designed for towing various types of aircraft; however, other special types can be used on a particular aircraft only. Such bars are usually designed and built by the aircraft manufacturer.
When towing the aircraft, the towing vehicle speed must be reasonable, and all persons involved in the operation must be alert.
When the aircraft is stopped, the brakes of the towing vehicle alone should not be relied upon to stop the aircraft. The man in the cockpit should coordinate the use of the aircraft brakes with those of the towing vehicle. A typical tow tractor (or tug) is shown in figure 11-31.
The attachment of the tow bar will vary on different types of aircraft. Aircraft equipped with tailwheels are generally towed forward by attaching the tow bar to the tow rings on the main landing gear. In most cases it is permissible to tow the aircraft in reverse by attaching the tow bar to the tailwheel axle. Anytime an aircraft equipped with a tailwheel is towed, the tailwheel must be unlocked or the tailwheel locking mechanism will be damaged or broken.
Aircraft equipped with tricycle landing gear are generally towed forward by attaching a tow bar to the axle of the nosewheel. They may also be towed forward or backward by attaching a towing bridle or specially designed towing bar to FIGURE 11-31. Tow tractor.