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.
the towing lugs on the main landing gear. When an aircraft is towed in this manner, a steering bar is attached to the nosewheel to steer the aircraft.
The following towing and parking procedures are typical of one type of operation. They are examples, and not necessarily suited to every type of operation. Aircraft ground-handling personnel should be thoroughly familiar with all procedures pertaining to the types of aircraft being towed and local operating standards governing ground handling of aircraft. Only competent persons properly checked out should direct an aircraft towing team.
1. The towing vehicle driver is responsible for operating his vehicle in a safe manner and obeying emergency stop instructions given by any team member.
2. The person in charge should assign team personnel as wing walkers. A wing walker should be stationed at each wingtip in such a position that he can ensure adequate clearance of any obstruction in the path of the aircraft. A tail walker should be assigned when sharp turns are to be made, or when the aircraft is to be backed into position.
3. A qualified person should occupy the pilot's seat of the towed aircraft to observe and operate the brakes as required. When necessary, another qualified person is stationed to watch and maintain aircraft hydraulic system pressure.
4. The person in charge of the towing operation should verify that, on aircraft with a steerable nosewheel, the locking scissors are set to full swivel for towing.
The locking device must be reset after the tow bar has been removed from the aircraft. Persons stationed in the aircraft should not attempt to steer or turn the nosewheel when the tow bar is attached to the aircraft.
5. Under no circumstances should anyone be permitted to walk or ride between the nosewheel of an aircraft and the towing vehicle, nor ride on the outside of a moving aircraft or on the towing vehicle.
In the interest of safety, no attempt to board or leave a moving aircraft or towing vehicle should be permitted.
6. The towing speed of the aircraft should not exceed that of the walking team members. The aircraft's engines usually are not operated when the aircraft is being towed into position.
7. The aircraft brake system should be charged before each towing operation.
Aircraft with faulty brakes should be towed into position only for repair of brake systems, and then only with personnel standing by ready with chocks for emergency use. Chocks must be immediately available in case of an emergency throughout any towing operation.
8. To avoid possible personal injury and aircraft damage during towing operations, entrance doors should be closed, ladders retracted, and gear downlocks installed.
9. Prior to towing any aircraft, check all tires and landing gear struts for proper inflation. (Inflation of landing gear struts of aircraft in overhaul and storage is excluded.)
10. When moving aircraft, do not start and stop suddenly, For added safety, aircraft brakes must never be applied during towing except in emergencies, and then only upon command by one of the tow team members.
11. Aircraft should be parked in specified areas only. Generally, the distance between rows of parked aircraft should be great enough to allow immediate access of emergency vehicles in case of fire, as well as free movement of equipment and materials.
12. Wheel chocks should be placed fore and aft of the main landing gear of the parked aircraft.
13. Internal or external control locks (gust locks or blocks) should be used while the aircraft is parked.
14. Prior to any movement of aircraft across runways or taxiways, contact the airport control tower on the appropriate frequency for clearance to proceed.
15. An aircraft should not be parked in a hangar without immediately being statically grounded.
Taxiing Aircraft As a general rule, only rated pilots and qualified airframe and powerplant technicians are author- 519
Lights Meaning Flashing green - Cleared to taxi.
Steady red. _ _Stop.
Flashing red Taxi clear of runway in use.
Flashing white. Return to starting point.
Alternating red and green... Exercise extreme caution.
FIGURE 11-32. Standard taxi light signals.
ized to start, run up, and taxi aircraft. All taxiing operations should be performed in accordance with applicable local regulations. Figure 11-32 contains the standard taxi light signals used by control towers to control and expedite the taxiing of aircraft. Refer to the following section, "Taxi Signals," for detailed instructions on taxi signals and related taxi instructions.
FIGURE 11-33. The taxi signalman.
Taxi signalman FIGURE 11-34. Position of the taxi signalman.
Taxi Signals Many ground accidents have occurred as a result of improper technique in taxiing aircraft.
Although the pilot is ultimately responsible for the aircraft until the engine is stopped, a taxi signalman can assist him around the flight line. In some aircraft configurations, the pilot's vision is obstructed while he is on the ground. He cannot see obstructions close to the wheels nor under the wings, and has little idea of what is behind him.
Consequently, he depends upon the taxi signalman for directions. Figure 11-33 shows a taxi signalman indicating his readiness to assume guidance of the aircraft by extending both arms at full length above his head, palms facing each other.
The standard position for a signalman is slightly ahead of and in line with the aircraft's left wingtip.
As the signalman faces the aircraft, the nose of the aircraft is on his left (figure 11-34). He must stay far enough ahead of the wingtip for the pilot to see him easily. He should follow a foolproof test to be sure the pilot can see his signals. If he can see the pilot's eyes, the pilot can see his signals.
Figure 11-35 shows the standard aircraft taxiing signals published in the Airmen's Information Manual by the Federal Aviation Administration.
It should be emphasized that there are other standard signals, such as those published by the Armed Forces. In addition, operating conditions in many areas may call for a modified set of taxi 520
FLAGMAN DIRECTS PILOT TO SIGNALMAN'S POSITION SIGNALMAN DIRECTS
SIGNALMAN IF TRAFFIC TOWING
CONDITIONS REQUIRE
STOP COME AHEAD EMERGENCY STOP CUT ENGINES
START ENGINES PULL CHOCKS INSERT CHOCKS SLOW DOWN ALL CLEAR (O.K.) LEFT TURN RIGHT TURN NIGHT
OPERATION FIGURE 11-35. Standard FAA hand taxi signals.
START ENGINE ENGAGE ROTOR STOP ROTOR STOP
MOVE BACK MOVE FORWARD MOVE RIGHT MOVE LEFT
TAKE OFF ANDIN( GO UP GO DOWN
DIRECTIOI
SWING TAIL SWING TAIL
TO RIGHT TO LEFT FIGURE 11-36. Helicopter operating signals.
manner as day signals with the exception of the stop signal. The stop signal used at night is the emergency stop" signal. This signal is made by crossing the wands to form a lighted "X" above and in front of the head.
FIGURE 11-37. Night operations with wands.
signals. The signals shown in figure 11-35 represent a minimum number of the most commonly used signals. Whether this set of signals or a modified set is used is not the most important consideration, as long as each flight operational center uses a suitable, agreed-upon set of signals.
Figure 11-36 illustrates some of the most commonly used helicopter operating signals.
The taxi signals to be used should be studied until the taxi signalman can execute them clearly and precisely. The signals must be given in such a way that the pilot cannot confuse their meaning.
It should be remembered that the pilot receiving the signals is always some distance away, and must often look out and down from a difficult angle.
Thus, the signalman's hands should be kept well separated, and signals should be overexaggerated rather than risk making indistinct signals. If there is any doubt about a signal, or if the pilot does not appear to be following the signals, the "stop" signal should be used and the series of signals begun again.
The signalman should always try to give the pilot an indication of the approximate area in which the aircraft is to be parked. The signalman should glance behind himself often when walking backward to prevent backing into a propeller or tripping over a chock, fire bottle, tiedown line, or other obstruction.
Taxi signals are usually given at night with the aid of illuminated wands attached to flashlights (figure 11-37). Night signals are made in the same
JACKING AIRCRAFT The aviation technician must be familiar with the jacking of aircraft in order to perform maintenance and inspection. Since jacking procedures and safety precautions vary for different types of aircraft, only general jacking procedures and precautions are discussed. Consult the applicable aircraft manufacturer's maintenance instructions for specific jacking procedures.
Extensive aircraft damage and serious personal injury have resulted from careless or improper jacking procedures. As an added safety measure, jacks should be inspected before use to determine the specific lifting capacity, proper functioning of safety locks, condition of pins, and general serviceability. Before raising an aircraft on jacks, all workstands and other equipment should be removed from under and near the aircraft. No one should remain in the aircraft while it is being raised or lowered, unless maintenance manual procedures require such practice for observing leveling instruments in the aircraft.
The aircraft to be jacked must be located in a FIGURE 11-38. Typical tripod jack.
Jacking Complete Aircraft Prior to jacking the aircraft, an overall survey of the complete situation should be made to determine if any hazards to the aircraft or personnel exist. Tripod jacks of the appropriate size for the aircraft being jacked should be placed under the aircraft jacking points and perfectly centered to prevent them from cocking when the aircraft is raised. The legs of the jacks should be checked to see that they will not interfere with the operations to be performed after the aircraft is jacked, such as retracting the landing gear.
At least three places or points are provided on aircraft for jacking purposes; a fourth place on some aircraft is used to stabilize the aircraft while it is being jacked at the other three points. The two main places are on the wings, with a smaller one on the fuselage near either the tail or the nose, depending on the landing gear design.
Most aircraft have jack pads located at the jack points. Others have removable jack pads that are inserted into receptacles bolted in place prior to jacking. The correct jack pad should be used in all cases. The function of the jack pad is to ensure that the aircraft load is properly distributed at the jack point and to provide a convex bearing surface to mate with the concave jack stem. Figure 11-40 FIGuRE 11-39. Typical single-base jack. illustrates two types of jack pads.
level position, well protected from the wind.
A hangar should be used if possible. The manufacturer's maintenance instructions for the aircraft being jacked should be consulted for the location of the jacking points. These jacking points are usually located in relation to the aircraft center of gravity so the aircraft will be well balanced on the jacks. However, there are some exceptions to this. Wing jack pad assembly On some aircraft it may be necessary to add weight to the nose or tail of the aircraft to achieve a safe balance. Sandbags are usually used for this purpose.
Tripod jacks similar to the one shown in figure 11-38 are used when the complete aircraft is to be jacked.
A small single-base jack similar to the one shown in figure 11-39 is used when only one wheel is to be raised. The jacks used for jacking aircraft must be maintained in good condition; a leaking or damaged jack must never be used. Also, each jack Forward jack fitting has a maximum capacity, which must never be exceeded. FIGURE 11-40. Typical jack pads.
Wing jack pad assembly FIGURE 11-41. Jacking a complete aircraft.
Prior to jacking, determine if the aircraft configuration will permit jacking. There may be equipment or fuel which has to be removed if serious structural damage is to be avoided during jacking. If any other work is in progress on the aircraft, ascertain if any critical panels have been removed. On some aircraft the stress panels or plates must be in place when the aircraft is jacked to avoid structural damage.
Extend the jacks until they contact the jack pads. A final check for alignment of the jacks should be made before the aircraft is raised, since most accidents during jacking are the result of misalined jacks.
When the aircraft is ready to be raised, a man should be stationed at each jack. The jacks should be operated simultaneously to keep the aircraft as level as possible and to avoid overloading any of the jacks. This can be accomplished by having the crew leader stand in front of the aircraft and give instructions to the men operating the jacks.
Figure 11-41 shows an aircraft being jacked.
Caution should be observed, since on many jacks the piston can be raised beyond the safety point;
therefore, never raise an aircraft any higher than is necessary to accomplish the job.
The area around the aircraft should be secured while the aircraft is on jacks. Climbing on the aircraft should be held to an absolute minimum, and no violent movements should be made by persons who are required to go aboard. Any cradles or necessary supports should be placed under the fuselage or wings of the aircraft at the earliest possible time, particularly if the aircraft is to remain jacked for any length of time.
On collet-equipped jacks, the collet should be kept within two threads of the lift tube cylinder during raising, and screwed down firmly to the cylinder after jacking is completed to prevent settling.
Before releasing jack pressure and lowering the aircraft, make certain that all cribbing, workstands, equipment, and persons are clear of the aircraft, that the landing gear is down and locked, and that all ground locking devices are properly installed.
Jacking One Wheel of an Aircraft When only one wheel has to be raised to change a tire or to grease wheel bearings, a low single-base jack is used. Before the wheel is raised, the remaining wheels must be chocked fore and aft to prevent movement of the aircraft. If the aircraft is equipped with a tailwheel, it must be locked. The wheel should be raised only high enough to clear the concrete surface. Figure 11-42 shows a wheel being raised using a single-base jack.
COLD WEATHER SUGGESTIONS When an aircraft is to be exposed to extreme cold for any length of time, extra care should be taken to see that the aircraft is prepared for winter. All covers for engines, air-conditioning system intakes, pitot and static system openings, and ram air inlets should be installed to prevent snow and ice accumulations. Small covers should be conspicuously marked or tagged so that they are not likely to be overlooked betore flight.
If the aircraft is to be parked in snow or ice 525
Main landing gear jack pad Nose landing gear jack pad FIGURE 11-42. Jacking one wheel.
conditions, it sometimes saves time and man-hours to paint around doors and frequently opened access panels with one of the inhibited glycol antifreeze compounds. The glycol may be painted on surfaces under snow covers to prevent the cover freezing to the surface. It can also be used full strength on wing or tail surfaces themselves to prevent frost. However, if snow is expected, painting exposed surfaces is rarely useful, since the slush that forms will be more troublesome than dry snow.
Another timesaver can be parking the wheels on planking rather than on ice or packed snow, or when sleet or slush may be expected to freeze tires to the ground. Sand can be used for such a purpose but should be confined to wheel areas and not distributed where it may be drawn into the engines on starting.
Flaps and spoilers should be retracted. Aircraft with movable horizontal stabilizers should have them set at approximately zero. All water and waste systems should be drained or serviced with an antifreeze solution when applicable.
If an aircraft is to be parked for a long period of time, leaving a window partially open will permit circulation of the air inside and help prevent frosting of the windows. The best way to remove snow is to sweep off as much as possible. One method is to throw a line over the fuselage and drag the snow off. A brush or broom can be used on wing and tail surfaces. Do not damage vortex generators on aircraft that have them.
A certain amount of snow may freeze to the aircraft surfaces which cannot be brushed off. It is important that all surfaces are entirely free of ice, snow, or frost before takeoff.
Most commercial facilities have spray equipment for applying deicing fluids, which are usually diluted with water and sometimes heated. Glycol antifreeze compounds, often identified by military specification numbers, have been materially improved. The compound recommended for commercial use is MIL-A-8243A. This is ethylene glycol and propylene glycol in approximately 3:1 ratio, with added corrosion inhibitor and a wetting agent. It has low toxicity, causes no damage to aircraft metals, and has no effect on most plastics, paint, or rubber.
If hot air is used for deicing, particularly from a ground starter unit, skin areas should not be overheated. A large flow of warm air is more effective than a blast of hot air. Any temperature under the boiling point of water is safe.
Should the last layer of ice or snow be melted from the fuselage, or from the leading edges of the wing, by internal heating from ground sources, the water will probably run down and refreeze in unheated areas, and must be removed again.
Whatever the deicing method, inspect the trailing edge mechanism areas of the wing and tail to be sure that water or slush has not run down inside to refreeze.
When conditions warrant, preheating is used on the following sections or parts of the aircraft:
accessory section, nose section, Y-drain valve, all oil lines, oil tank sump, starters, instruments, tires, cockpits, and elevator trim tabs.
Check all drain valves, oil tank sumps, oil drains, fuel strainers, vent lines, and all main and 526
auxiliary control hinges and surfaces, for the existence of ice or hard snow. Thoroughly check all deicing equipment to ensure proper operation.
Alcohol tanks must be checked for proper level of deicing alcohol.
The use of an external heater is permissible at temperatures below 0° C. for heating oil and engine(s). If a heater is not available for heating the oil, the oil can be drained, heated, and put back into the system.
When starting a reciprocating engine in cold weather, try to catch the engine on the first starting attempt to prevent ice forming on the spark plugs. If ice should form, remove the spark plugs, bake, and reinstall.
In freezing weather, ice may form on the propellers while the engine is warming up. Using the propeller deicer (if available) during warm-up eliminates this condition. The turbine engine should be easier to start in very bad weather than the average piston engine. Turbine engines do not require oil dilution, priming, or lengthy warm-up.
Turbine engine compressor rotors should be checked to see that ice has not formed inside. This is particularly necessary when an engine has shut down in driving rain or snow. Be very careful when running engines if icy conditions exist. With icy pavement, chocks slide very easily, and once the aircraft is in motion it is difficult to stop.
After a flight, the oil is diluted prior to shutdown of reciprocating engines equipped with an oil dilution system, if temperatures near or below freezing are expected before or at the time of the next start. When it is necessary to dilute the oil, consult the manufacturer's instructions for the applicable aircraft. These instructions should be strictly followed; otherwise the engine can be When fueling aircraft, the fuel tanks should be left about 3 to 5 percent below maximum capacity.
This allows for expansion in the event the aircraft is brought into the hangar prior to the next flight.
Fuel expands approximately 1 percent for each 10° C. increase in temperature. If fuel tanks are filled to the normal levels, at a temperature of approximately 0° C. to 10° C., and later brought into a warm hangar (20° C.), the ensuing expansion will overflow the tanks, causing a fire hazard.
Tires should be inflated to load standards, regardless of possible rise in pressure under warmer conditions. Underinflation quickly causes overheat that would result in more tire damage and more possibility of blowout than a slight amount of overinflation. If a tire is frozen to the ground, it should be thawed with warm air or water and, moved before it re-freezes.
It is easy to exceed nose gear towing load limits in snow or slush. If the airplane must be towed in deep snow, it should be pulled by cables attached to the main landing gear lugs.
The aircraft battery should require no special attention other than the normal routine servicing.
CHAPTER 12
HANDTOOLS AND MEASURING DEVICES
INTRODUCTION This chapter contains information on some of the handtools used by an aviation mechanic. It outlines the basic knowledge required in using the most common handtools and measuring instruments used in aircraft repair work. This information, however, cannot replace sound judgment on the part of the individual. There are many times when ingenuity and resourcefulness can supplement the basic rules. A sound knowledge is required of these basic rules and of the situations in which they apply. The use of tools may vary, but good practices for safety, care, and storage of tools remain the same.
GENERAL-PURPOSE TOOLS Hammers and Mallets Figure 12-1 shows some of the hammers that the aviation mechanic may be required to use.
Metal-head hammers are usually sized according to the weight of the head without the handle.
Occasionally it is necessary to use a soft-faced hammer, which has a striking surface made of wood, brass, lead, rawhide, hard rubber, or plastic.
Ball peen Straight peen Cross peen Tinners mallet Riveting hammer FIGURE 12-1. Hammers.
These hammers are intended for use in forming soft metals and striking surfaces that are easily damaged. Soft-faced hammers should not be used for rough work. Striking punch heads, bolts, or nails will quickly ruin this type hammer.
A mallet is a hammerlike tool with a head made of hickory, rawhide, or rubber. It is handy for shaping thin metal parts without denting them.
Always use a wooden mallet when pounding a wood chisel or a gouge.
When using a hammer or mallet, choose the one best suited for the job. Ensure that the handle is tight. When striking a blow with the hammer, use the forearm as an extension of the handle. Swing the hammer by bending the elbow, not the wrist.
Always strike the work squarely with the full face of the hammer.
Always keep the faces of hammers and mallets smooth and free from dents to prevent marring the work.
The screwdriver can be classified by its shape, type of blade, and blade length. It is made for only one purpose, i.e., for loosening or tightening screws or screwhead bolts. Figure 12-2 shows several different types of screwdrivers. When using the common screwdriver, select the largest screwdriver whose blade will make a good fit in the screw which is to be turned.
A common screwdriver must fill at least 75 percent of the screw slot. If the screwdriver is the wrong size, it cuts and burrs the screw slot, making it worthless. A screwdriver with the wrong size blade may slip and damage adjacent parts of the structures.
The common screwdriver is used only where slotted head screws or fasteners are found on aircraft. An example of a fastener which requires the use of a common screwdriver is the airlock fastener which is used to secure the cowling on some aircraft.
The two types of recessed head screws in common use are the Phillips and the Reed and Prince.