AIRCRAFRT TAXIING / TOWING AND ASSOCIATED SAFETY PRECAUTIONS

TOWINGTo move an aircraft without starting the engines, in order to position it•For servicing or •To enable passengers or •Cargo to be loaded, and if this operation is not carried out properly, severe damage can be caused to the aircraft..

TOWING LIGHT AIRCRAFT• Great care should be exercised when manhandling light aircraft.• On aircraft having a nose-wheel landing gear, a steering arm should be fitted to the nose wheel to guide the aircraft, and force should be applied only to those parts of the structure, which are designed to accept it. • Force should not be applied to trailing edges of wings or control surfaces, to streamlined wires, or to areas which are marked to prohibit the application of force; • An engine should always be regarded as ‘live’, and therefore, a propeller should not be used to push or pull the aircraft.

• It is better to push an aircraft backwards rather than forwards, since the leading edges of the wings and tail plane are stronger than trailing edges

• But struts and undercarriages on some aircraft are suitable for pushing the aircraft forwards.

• The flat of the hands should be used when pushing, so as to spread the load over the largest area, and when pushing on struts or undercarriages the force should be applied as near to the end fittings as possible

• On aircraft with steerable nose wheel connected to the rudder pedals, care must be taken not to exceed the turning limits, which are normally marked on the nose undercarriage leg.

• On this type of aircraft it is also important that the rudder controls are not locked during towing operation.

• On aircraft, which are fitted with a tailskid instead of a tail wheel it is customary to raise the tail by lifting on the tail plane struts near to the fuselage fittings, so that the aircraft is balanced at the main wheels;

• On some aircraft it may be advisable to place the propeller in a horizontal position, to prevent it striking the ground when the tail is lifted.

• When towing a light aircraft by means of a tractor, the correct tow-bar should be connected between the towing attachment at the base of the nose undercarriage leg and the tractor, and a person familiar with the aircraft brake system should be seated in the cockpit to operate the brakes in an emergency; the brakes should not normally be applied unless the aircraft is stationary.

• A safe speed, depending on conditions in the vicinity.

• A close watch should be kept on the wing tips and tail, particularly in confined spaces, to ensure that they do not come in to contact with other stationary or moving objects.

TOWING LARGE AIRCRAFT

•Large multi engine aircraft usually moved by towing with a tow-bar attached to the nose undercarriage leg, a special tow tug (cradle) often being required to provide sufficient Tractive effort (slow moving).

•The tow-bar is fitted with a shear-pin or bolt, which will shear at a predetermined load to prevent excessive force being applied to the nose undercarriage.

ESSENTIAL REQUIREMENTS FOR TOWING

The centre of gravity (C of G) of the aircraft must be determined before towing, to ensure that there is sufficient weight on the nose wheel.

Adverse fuel distribution, and the aircraft being in a non-standard condition (e.g. with an engine removed), could affect the C of G position,. Ballast may sometimes be required to achieve a safe C of G position, but the maximum towing weight must not be exceeded.

Before towing is commenced the undercarriage ground locks should be installed, the steering should, if applicable, be disconnected or disabled (usually by removing a steering disconnection pin, by inserting a lock-out pin or by tripping the associated circuit breaker), and the nose undercarriage shock absorber should be checked for normal extension.

In addition, the brake pressure should be checked and, if necessary, built up to the minimum safe pressure (this is often accomplished by operation of an electrically-driven hydraulic pump, which wheel complete freedom of movement complete freedom of movement, but particular attention must be paid to any limits imposed on aircraft having bogie under carriages.

When towing the aircraft, two qualified pilots or suitably trained and authorized members of the towing crew should be stationed in the cockpit, to operate the brakes `and any other aircraft systems which may be required, and to keep a look–out and monitor progress.

These persons should be in telephonic communication with the outside ground crew and with the tractor driver. Ground crew should be located at the wing tips and tail to guide the aircraft past any obstructions, and one person should be in overall control of the operation.

The aircraft brakes should be released before the tractor moves off, and towing speed should be kept down to a safe speed.

The radii of turns should be kept as large as possible, to minimize tire scrubbing and twisting loads on the main undercarriage legs, and care should be taken not to exceed any towing force limits which may be specified in the relevant Maintenance Manual for various nose wheel steering angles.

Before stopping, the aircraft should be towed in a straight line for a short distance in order to remove any tyre stresses imposed by turning.

Once stationary the aircraft brakes may be re-applied. The tractor and tow-bar may be removed, and the nose-wheel steering links refitted and safety locked.

In circumstances where the towing load exceeds the nose wheel limitations, towing bridles should be attached to the main undercarriage legs and the aircraft should be towed using two tractors, one connected to each main undercarriage leg.

In an emergency it may be necessary to move an aircraft from a runway while it has one or more deflated tires. Provided that there is one sound tire on axle the aircraft may be towed to the maintenance area, but

• Sharp turns should be avoided,

• Towing speed should be kept to an absolute minimum,

• Brakes should be applied very carefully.

• If an axle is not supported by a sound tire, however, the aircraft may only be moved the shortest distance necessary to clear the active runway

• The wheels with deflated tires must be removed and serviceable components fitted before towing is continued.

• After any tire failure the associated wheel must be inspected and it may also be necessary to inspect the wheels and tires which have not failed if the aircraft has landed or been towed with a deflated tire.

JACKING OF AIRCRAFT

An aircraft may have to be jacked up for a variety if reasons,•Servicing, •Weighing, •Changing wheels, •Retraction tests, (care is necessary to avoid damaging the aircraft.)

Jacking points are provided

in the wings and fuselage to enable the whole aircraft to be lifted, usually, at the nose and main undercarriages to enable individual wheels to be changed. Some aircraft require a jacking pad to be fitted to each jacking point in the wings and fuselage, adapters to be fitted to the jacks while in other cases special stirrups or beams may be required to lift individual axles.

Because of the position of the jacking points, the centre of gravity of some aircraft may, although satisfactory for flight, fall behind the main jacking points and thus be unsatisfactory for jacking purposes. In these cases it may be to add ballast forward of the main jacking points to bring the centre of gravity within limits specified in the relevant Maintenance Manual.

Each jacking or steadying point may have a load limit, which, if exceeded, could result in structural damage

Safety Measures

To avoid exceeding the limiting load at the jacking points it is sometimes necessary to fit hydraulic or electrical load cells to the jacks,

Ballast may have to be used to avoid exceeding the loading limit at a steadying point.

Micro switches fitted to the undercarriage legs and operated by the extension or contraction of the shock absorbers, are used to arm or disarm various electrical circuits on an aircraft.

If the aircraft is jacked up these circuits should, therefore, be isolated by tripping the appropriate circuit breakers or by removing the associated fuses, as necessary.

As a safety precaution, light aircraft normally be jacked inside a hangar, But large aircraft may be jacked in the open provided that they are headed into wind and that the surface is level and strong enough to support the weight of the aircraft at the jacking points.

A maximum safe wind speed for jacking is generally specified in the relevant Maintenance Manual.

Procedure For Satisfactory Jacking of Aircraft,

• Strictly adhere to any additional precautions or actions specified in the Maintenance manual for particular aircraft.

• One person should be located at each jacking position and a co-ordinator should supervise the operation.

• On large aircraft the levelling station should also be manned, and all ground crew concerned should be in communication with the co-ordinator, headphones being used when necessary.

• ‘A bottle’ jack and an adapter or special fitting are often used when raising a single undercarriage or part of a bogie beam for the purpose of changing a wheel.

• The remaining wheels should be chocked front and rear to prevent aircraft movement, • Sometimes be specified that a tail support is located at the rear fuselage jacking point when raising a nose undercarriage.

• The jack should be raised only sufficiently to lift the unserviceable wheel a few inches clear of the ground

• Before lowering an aircraft to the ground, all ground equipment, work stands, supports, etc., should be moved clear of the aircraft structure to prevent inadvertent damage,

• The wheels should be rotated by hand to check that the brakes are free

.

• The jacks should be lowered slowly by opening their pressure release valves, and, to guard against failure of a jack, the locking nuts on the jack rams should be unscrewed while the jacks are lowered and kept within 50 mm (2 in) of the jack heads.

• The jacks should be fully lowered after the aircraft is resting on its wheels and the pressure release valves should be closed.

• Chocks should then be placed in position, the jacks, jacking pads and adapters should be removed from the aircraft,

• Any electrical circuits which were disarmed as a safety measure should be reinstated.

LEVELLING OF AIRCRAFT

For some purposes, such as rigging or weighing, an aircraft must be levelled laterally and longitudinally, and a number of different methods may be employed.

1.SPIRIT LEVEL

• Many aircraft are levelled by use of a spirit level, which is placed at jigged positions on the airframe structure.

• On light aircraft the longitudinally level position is generally obtained by placing the spirit level on two pegs or on the heads of two partially withdrawn screws on the side of the fuselage, and adjusting the jacks (or the shock absorber extension or tyre pressures, if the aircraft is resting on its wheels) until the spirit level is centred.

• The laterally level position is obtained by placing the spirit level on the centre-section spar boom (or other nominated position), and again adjusting the jacks or tyre pressures until the level is centred.

• With some large aircraft a spirit level may be used in conjunction with special fittings, which are secured to locations in the centre fuselage or in one of the wheel bays;

• These fittings must be removed before flight and should have warning streamers attached. If adjustments have been necessary to level an aircraft laterally, the longitudinal level should be re-checked.

Note: In cases where tyre pressures are adjusted to level the aircraft, care must be taken not to over-inflate to completely deflate a tyre.

2. PLUMB BOB

• On many aircraft a plumb bob is used in conjunction with a levelling plate.

• The plumb bob is suspended from a fixed position in the cabin roof or upper part of a wheel bay, and hangs over a levelling plate, which may be a permanent fixture or a separate fitting accurately located on the cabin floor or lower part of the wheel bay.

• The levelling plate is marked with a zero position and scales indicating the adjustments required about the lateral and longitudinal axes to centre the plumb bob.

3. ENGINEERS TRANSIT

The most accurate means of levelling an aircraft is by the use of an engineers transit (theodolite) in conjunction with range poles or scales located on the aircraft’s lateral and longitudinal axes.

The transit is set up below the aircraft centreline and between the lateral levelling points, and levelled horizontally.

Range poles or scales are then located at the four marked levelling points on the lower surfaces of the fuselage and wings.

Sightings are first taken on the lateral range poles or scales, and the main jacks are adjusted until identical readings are obtained.

Sightings are then taken on the longitudinal range poles or scales, and the nose jack is adjusted until identical readings are again obtained. The aircraft is then considered level and the transit can be removed.

Note: The transit method is also employed when checking alignment of the aircraft structure.

POINTS TO BE CONSIDERED

•Check that the aircraft weight, fuel state and centre of gravity are within the limits specified in the aircraft Maintenance Manual

•Head the aircraft into wing if it is to be jacked in the open, chock the main wheels front and rear, and release the brakes

•If jacking an aircraft in a restricted space, ensure that there is adequate clearance above every part of the aircraft to allow for its being raised, and adequate access and lifting space for cranes or other equipment, which may be required

• Connect earthing cable to the earth points on the aircraft

•Install the undercarriage ground locks

•Fit jacking pads to the aircraft jacking points and adapters to jacks as required. Load cells should also be fitted to the jacks at positions where a maximum jacking load is specified

•Position the jacks at each jacking point and raise them until the adapters are located centrally in the jacking pads.

• Care must be taken to ensure that the jacks are vertical, and that the weight is evenly distributed over the legs of each jack

• Remove the wheel chocks and slowly raise the aircraft, maintaining it in a horizontal attitude as nearly as possible, until the undercarriage legs are fully extended and the wheels are a few inches off the ground.

• As a safety measure the locking nuts on the jack rams should be kept in close proximity to the jack shoulders as the jacks are raised

• Tighten the jack ram locking nuts, and place supports under the outer wings and rear fuselage as indicated in the Maintenance Manual. • The positioning of these supports is most important, as they are usually shaped to fit the under surface of the wing or fuselage and must be located at a strong point such as a rib or frame; they are not intended to support the weight of an aircraft

AIRCRAFT STORAGE METHODS

Under normal operating conditions the interior parts of an engine are protected against

•Corrosion by the continuous application of lubricating oil,

•Operating temperatures are sufficient to dispel any moisture, which may tend to form; after shutdown the residual film of oil gives protection for a short period.

•When not in regular service, however, parts which have been exposed to the products of combustion, and internal parts in contact with acidic oil, are prone to corrosion.

•If engines are expected to be out of use for an extended period they should be ground run periodically or some form of anti-corrosive treatment applied internally and externally to prevent deterioration.

The maximum storage times quoted in the Leaflet are generally applicable to storage under cover in temperate climates, and vary considerably for different storage conditions.

Times may also vary between different engines, and reference must be made to the appropriate Maintenance Manual for details.

INSTALLED TURBINE ENGINES

Installed turbine engines which are to be out of use for a period of up to seven days require no protection apart from fitting covers or blanks to the intake, exhaust and any other apertures, to prevent the ingress of dust, rain, snow, etc.

A turbine engine should not normally be ground run for the purpose of preservation, since the number of temperature cycles to which it is subjected is a factor in limiting its life.

For storage periods in excess of seven days additional precautions may be necessary to prevent corrosion.

SHORT-TERM STORAGE

The following procedures will normally be satisfactory for a storage period of up to one month.

FUEL SYSTEM

The fuel lines and components mounted on the engine must be protected from the corrosion which may result from water held in suspension in the fuel.

The methods used to inhibit (prevent) the fuel system depend on the condition of the engine and whether it is installed in an aircraft or not. (Refer to appropriate Maintenance Manual )

On completion of inhibiting, the fuel cocks must be turned off.

LUBRICATION SYSTEMS

Some manufacturers recommend that all lubrication systems (engine oil, gear box oil, starter oil, etc.) of an installed engine should be drained, Filters removed and cleaned

•Some are recommend that the systems should be filled to the normal level with clean system oil or storage oil.

•The method recommended for a particular engine should be ascertained from the appropriate Maintenance Manual

EXTERNAL TREATMENT

Exterior surfaces should be cleaned as necessary to detect corrosion, then dried with compressed air.

Any corrosion should be removed, affected areas re-treated, and any damaged paintwork made good in accordance with the manufacturer’s instructions. Desiccant or vapour phase inhibitor should be inserted in the intake and exhaust, and all apertures should be fitted with approved covers or blanks.

LONG-TERM STORAGE

For the protection of turbine engines which may be in storage for up to six months, the short-term preservation should be applied and , in addition, the following actions taken:

• Grease all control rods and fittings• Blank off all vents and apertures on the engine, • wrap greaseproof paper round all rubber parts which may be affected by the preservative• spray a thin coat of external protective over the whole engine forward of the exhaust unit.

At the end of each successive six months storage period an installed engine should be re-preserved for a further period of storage.

Alternatively, the engine may be removed from the aircraft and preserved in a moisture vapour proof envelope.

UNINSTALLED ENGINES (PISTON AND TURBINE)Engines which have been removed from aircraft for storage, or uninstalled engines which are being returned for repair or overhaul, should be protected internally, and sealed in “Moisture Vapour Proof” (MVP) envelopes. This is the most satisfactory method of preventing corrosion, and is essential when engines are to be transported overseas.A piston engine should be drained of all oil, the cylinders inhibited , drives and inside of crankcase sprayed with cylinder protective, and all openings sealed.A turbine engine should be drained of all oil, fuel system inhibited, oil system treated as recommended by the manufacturer, and blanks fitted to all openings.Particular care should be taken to ensure that no fluids are leaking from the engine, and that all sharp projections, such as locking wire ends, are suitably padded to prevent damage to the envelope.

UNINSTALLED ENGINES (PISTON AND TURBINE)

Engines which have been removed from aircraft for storage, or uninstalled engines which are being returned for repair or overhaul, should be protected internally, and sealed in “Moisture Vapour Proof” (MVP) envelopes.

This is the most satisfactory method of preventing corrosion, and is essential when engines are to be transported overseas.

A piston engine should be drained of all oil, the cylinders inhibited , drives and inside of crankcase sprayed with cylinder protective, and all openings sealed.

A turbine engine should be drained of all oil, fuel system inhibited, oil system treated as recommended by the manufacturer, and blanks fitted to all openings.

Particular care should be taken to ensure that no fluids are leaking from the engine, and that all sharp projections, such as locking wire ends, are suitably padded to prevent damage to the envelope.

The MVP envelope should be inspected to ensure that it is undamaged, and placed in position in the engine stand or around the engine, as appropriate.

The engine should then be placed in the stand, care being taken not to damage the envelope at the points where the material is trapped between the engine attachment point and the stand bearers.

• Vapour phase inhibitor or desiccant should be installed in the quantities and at the positions specified in the relevant maintenance Manual, and a humidity indicator should be located in an easily visible position in the envelope.

• The envelope should then be sealed (usually by adhesive) as soon as possible after exposure of the desiccant or vapour phase inhibitor.

The humidity indicator should be inspected after 24 hours to ensure that the humidity is within limits (i.e. the indicator has not turned pink). An unsafe reading would necessitate replacement of the desiccant and an examination of the MVP envelope for damage or deterioration. After a period of three years storage in an envelope the engine should be inspected for corrosion and re-preserved.

INSPECTION PROCEDURE

• Engine is storage should be inspected periodically to ensure that no deterioration has taken place.• Engines which are not preserved in a sealed envelope should be inspected at approximately two-weekly intervals.• Any corrosion patches should be removed and the protective treatment re-applied, but if external corrosion is extensive a thorough inspection may be necessary.• Envelopes on sealed engines should be inspected at approximately monthly intervals to ensure that humidity with in the envelope is satisfactory. • If the indicator has turned pink the envelope should be unsealed, the desiccant renewed and the envelope resealed.

EQUIPMENT AND MATERIALS USED

EQUIPMENT

• The spraying equipment should be of a type approved by the engine manufacturer, • Should be operated in accordance with the instructions issued by the manufacturer of the equipment. • A special nozzle is required, and this should be checked immediately before use to ensure that the spray holes are unblocked. • Correct operation of the spray gun may be checked by spraying a dummy cylinder and inspecting the resultant distribution of fluid.

MATERIALS

Only the types of storage and inhibiting (preventing) oil recommended by the manufacturer should be used for preserving an engine. American manufacturers generally recommend oils and compounds to American specifications, and British manufacturers generally recommend British Specifications

BLANKS

• Approved blanks or seals should be used whenever possible.

• These are normally supplied with a new or reconditioned engine, and should be retained for future use.

• Pipe connections are usually sealed by means of a screw-type plug or cap such as AGS 2108; these items are usually coloured for visual identification.

• Large openings such as air intakes are usually fitted with a specially designed blanking plate secured by the normal attachment nuts, and the contact areas should be smeared(applied) with grease before fitting, to prevent the entry of moisture. • Adhesive tape may be used to secure waxed paper where no other protection is provided, but should never be used as a means of blanking off by itself, since it may promote corrosion and clog small holes or threads.

REMOVAL FROM STORAGE

For an engine which was not installed in an aircraft during storage the installation procedure described in the appropriate Maintenance Manual should be carried out, followed by a thorough ground run and check of associated systems.

For an engine which was installed in an aircraft during storage the following actions should be taken:-

•Remove all masking, blanks and desiccant.

•Clean the engine as necessary, e.g. remove excess external protective and surplus grease from controls.

•Ensure fire extinguisher spray pipe holes are clear.

•Replace any components, which were removed for individual storage, as necessary.

•Drain out all storage oil, oil filters and refill with normal operating oil.

•Piston engines; remove sparking plug blanks and turn engine slowly to drain excess oil from the cylinders, then fit plugs and connect leads.

•Turbine engines; prime the fuel system in accordance with the manufacturer’s requirements.

•Prime the engine lubricating oil system.

Start the engine and carry out a check of the engine and associated systems.

RECORDS

Appropriate entries must be made in the engine log book giving particulars of inhibiting procedures or periodic ground running. Such entries must be signed and dated by an appropriately licensed engineer or Approved Inspector.

REFUELLING / DEFUELLING PROCEDURES

Before refuelling it should be ensured that the refuelling vehicle contains the correct grade of fuel, as shown at the refuelling points on the aircraft.Precautions should be taken to provide a path to earth for any static electrical which may be present or which may build up as a result of the fuel flow.The aircraft and the refuelling vehicle should be earthed to a point, which is known to be satisfactory, and the earthing wire on the refuelling pipe should be connected to the earth point provided on the aircraft before connecting the refuelling pipe or removing the tank filler cap.

The earthing wire should remain in position until after the refuelling pipe is disconnected or the tank filler cap is replaced, as appropriate.When draining fuel into buckets, containers or tanks, these should also be bonded to the aircraft and / or the refuelling vehicle. No radio or radar equipment should be operated while re-fuelling or de-fuelling is taking place, and only those electrical circuits essential to these operations should be switched on.

When pressure re-fuelling, a float switch or fuel level shut-off valve is often used to cut off fuel flow when the tanks are full, or have reached a pre-set level.

Since pressure re-fuelling rates are very high, failure of these components could cause rapid build-up in pressure and serious damage to the tanks.

The tanks of some aircraft are fitted with pressure relief valves which can be checked manually prior to refuelling, but when this is not the case persons engaged in refuelling operations should be prepared to shut off the supply instantly, should the automatic cut-off system fail to operate.

Note: When refuelling, the wheel chocks should be moved a short distance away from the tyres, to prevent them being trapped when the tyres absorb the additional weight.

Particular care should be taken when refuelling high-winged light aircraft, since the upper wing surface will not normally be safe to walk on and the filer cap may not be within easy reach.

A step ladder or stand should be used to gain access to the filler cap and assist in preventing damage to the wing surface. Use of the steps will also facilitate correct locking of the filler cap.

When a spillage of fuel has occurred, care should be taken to ensure that all traces of fuel and vapour are removed.

Any residual (remaining) fuel should be mopped up and any fuel-soaked(saturated) lagging or fabric should be removed and cleaned.

The effects of the fuel on other such as cables, seals, bearings and windows should also be considered and the appropriate action should be taken.

After refuelling an aircraft it is usually recommended that fuel is checked for contamination, Drain valves are provided in the tank, sumps, pipelines and filters, by means of which a small quantity of fuel may be drained into a glass jar and checked for the presence of water, sediment and microbiological contamination. Because of the slow rate of settlement of water in turbine fuels it is usually the sample is taken.

With turbine-engined aircraft, samples may also be taken to determine the specific gravity of the fuel in the tanks.

DE-ICING / ANT-I ICING PROCEDURES

INTRODUCTION

This gives general guidance on the removal of Frost, Ice Snow from aircraft before flight.

GENERAL

•Any deposits of ice, snow or frost external surfaces of an aircraft may drastically affect its performance. •This can be due to reduced aerodynamic lift and increased aerodynamics drag resulting from the disturbed airflow over the aerofoil surfaces, or due to the weight of the deposit over the whole aircraft. •The operation of an aircraft may be also seriously affected by the freezing of moisture in controls, hinges and micro switches, or by the ingestion of ice into the engine.

• The measures taken to remove frozen deposits on the ground must also be such as to provide adequate protection during the initial stages of flight.

• Freezing Point Depressant (FPD) types FPD anti-icing compounds are known to be effective in retarding the formation of frost, snow or ice

• However, that the need for a close inspection of an aircraft prior to take-off still remains

• The aircraft de-icing systems are designed to remove or prevent the accretion of ice on a specific area of the wings, tail and engine nacelles in flight and would nor normally be effective in removing deposits which have accumulated while the aircraft is stationary. Their use on the ground may, in some instances, also cause a different type of unsatisfactory situation by melting parts of the deposit, which would then freeze elsewhere. The use of cabin heating to remove deposits from the fuselage is also not recommended for the same reason.

When aircraft are moved so as to be under cover during inclement weather, any melted snow or ice may freeze again when the aircraft is subsequently moved into sub-zero temperatures. Complete protection could be provided by placing aircraft in heated hangars, but due to the size of modern transport aircraft and the need to meet schedules involving quick turnaround times this is not often practicable. Removal of frost, ice and snow from aircraft is therefore often necessary and maintenance crews need to be familiar with the methods of ground de-icing in current use

There are two main types of de-icing /anti –icing fluids,Type I fluids (un-thickened)Type II fluids (thickened)

 TYPE I FLUIDS (UN-THICKENED)These fluids have high glycol content and a low viscosity. The de-icing performance is good, however, they provide only limited protection against refreezing. TYPE II FLUIDS (THICKENED)These fluids have a minimum glycol content of approximately 50% and due to the thickening agent have special properties, which enable the fluid to remain on the aircraft surfaces until take-off. The de-icing performance is good and, in addition, protection is provided against refreezing and / or build up of further accretions, when exposed to freezing precipitation.

PRE-FLIGHT PREPARATION

The whole aircraft should be inspected to ensure that it is free from deposits of frost, ice and snow. When necessary, a de-icing fluid should be used. The objectives of using such fluids are to achieve effective removal of any frost or ice and to provide a measure of protection against any further formation. Only fluids approved for the purpose should be used.

The ability of the fluid to achieve the above objectives under varying atmospheric conditions is dependent upon the correct mixture strength and methods of application, both of which should be strictly in accordance with recommended procedures. For example, while fluid diluted with water may effectively remove ice, its ability to prevent further formation will be significantly reduced, and under certain conditions the fact that the aircraft surfaces are wetted may actually enhance the accumulation of wet snow.

Where adequate advise on approved fluids, mixture strength and methods of application is not given in the relevant aircraft Maintenance Manuals, guidance should always be sought from the aircraft, manufacturer and from the suppliers of the fluid. The following information is only intended as general information and should not be used to override that which is contained in the aircraft maintenance Manuals.

Advances in the composition of de-icing fluids have led to the production of a dual-purpose anti-icing barrier fluid (DTD 900/4907) which is capable of removing ice and snow and delaying deposits re-forming. When used as a de-icing agent, this fluid should be mixed with the required volume of water and applied at a temperature of approximately 70C by the method described in paragraph 5.2. It is however, strongly recommended that refractometer readings be taken so that the Precise concentration of the solution can be determined.

Note: Pocket refractometers are available which permit on-site measurement of fluid concentration as a refractive index, which can be converted to fluid/water proportions accurately by means of a chart.

Note: Kilfrost ABC is normally available in a solution of 50/50, 60/40 or 70/30. it may be difficult to get stronger solutions at short notice unless the temperature conditions at the aerodrome involved are below limits for that solution mix (Refer Table 2)

FROST DEPOSITS AND METHODS OF TREATMENTA deposit of frost is best removed by the use of a frost remover or, in severe conditions, a de-icing fluid (e.g. Kilfrost ABC or similar proprietary fluids). These fluids normally contain either ethylene glycol and isopropyl alcohol or diethylene glycol (or propylene glycol) and isopropyl alcohol, and may be applied by spray or by hand. The process is not lengthy, as one application is usually sufficient, provided that it is applied with in the two hours prior to flight.Note: De-icing fluids may adversely affect glazed oanes ir the exterior finish of aircraft, particularly when the paint is new. Only the type of fluid recommended by the aircraft manufacturer should therefore be used and any instructions relating to its use should be strictly observed.

De-icing fluids, particularly those with an alcohol base, may cause dilution or complete washing out of oils and greases from control surface bearings, etc., allowing the entry of water which could subsequently freeze, jamming controls. Spray nozzles should not, therefore, be directed at lubrication points or sealed bearings and an inspection of areas where fluid may be trapped is usually necessary. The maintenance Schedule may specify re-lubrication in these areas whenever de-icing fluids are used.

Frost may also be removed from aircraft surfaces using a mobile unit capable of supplying large quantities of hot air through a delivery hose and nozzle. The air is blown on to the wings, fuselage and tail surfaces and either blow away or melts any frost deposits. Operators using this equipment should ensure that any melted frost is dried up and not allowed to accumulate in hinges, micro switches, etc., where re-freezing could occur.

Mixture strength (Glycol/water)

Kilfrost ABC Hoechst 1704 Mil. Spec. Fluids 8243

30/70 - - -11C

40/60 - - -18C

50/50 -7 1/2C -7 1/2C 35C

60/40 -10C -10C -

70/30 -13C -13C -

100% -28C -28C -

LOWER TEMPERATURE LIMITS

ICE AND SHOW DEPOSITS AND METHODS OF TREATMENT

Probably the most difficult deposit to deal with is deep wet snow when ambient temperatures are slightly above freezing point. This deposit should be removed with a brush or squeegee, care being taken not to damage aerials, vents, stall warning vanes, pilot probes, vortex generators, etc., which many be concealed by the snow. Light dry snow in sub-zero temperatures should be blown off whenever possible; the use of hot air is not recommended. Since this would melt the snow, which would then freeze and require further treatment. Moderate or heavy ice and residual snow deposits should be removed with a de-icing fluid, which may be successfully applied to any aircraft by spraying; in severe conditions it may be necessary to spray a final application immediately before flight. The aircraft nose and cockpit canopy should normally be left dry to ensure that the windscreen does not become contaminated with fluid, which could cause smearing and reduced vision. Windscreens should be cleared by wiping with an alcohol soaked cloth or by use of the windscreen anti-icing system.Note: * No attempt should be made to remove ice deposits or break an ice bond by force.* It is essential that removal of deposits proceed symmetrically.

Cold Fluid Spray.

A cold fluid spray is the simplest method of applying de-icing fluid, but suffers from several disadvantages which must be considered in relation to the particular circumstances.

In very severe conditions one sprayed application of cold fluid may not be sufficient to remove all the ice and snow; brushing or rubbing thickly iced areas is usually necessary, followed by a second or even third application of fluid. As the ice and snow melts, the fluid is diluted , becomes less effective and is prone to freezing again quite quickly. This may have serious consequences If the diluted fluid is allowed to run into control surface and landing gear mechanisms. Under these conditions the cold spray method may be both prolonged and expensive.

HOT FLUID SPRAY

Many airline operators have dispensed with the use of cold spraying techniques except at small airports and in an emergency. They have adopted a hot fluid spraying system which was developed specifically to reduce turnaround times and to inhibit the bonding of ice and snow to aircraft surfaces for a period of time. The equipment used consists of a static unit, in which quantities of both water and de-icing fluid are heated, and a mobile unit, which houses an insulated tank, a pump, an hydraulically-operated boom-mounted platform and several spray lances.

In this system hot fluid pumped from the static unit to the insulated tank on the mobile unit, the proportions of water and de-icing fluid being adjusted to suit prevailing weather conditions. The mobile unit is then driven to the site of operations, the optimum number and disposition of units being found by experience on a particular aircraft type.

The fluid is normally sprayed on at a temperature of 70C and a pressure of 700 kN/m2 (100 lbf/in2), holding the nozzle close to the aircraft skin to prevent heat losses. Heat is transferred to the aircraft skin, thus breaking the ice bond, and large areas of ice may be flushed away by turning the nozzle sideways. In this way, time is saved and the dilution of fluid with ice and snow reduced to a minimum. The film of fluid left on the aircraft skin, being only slightly further diluted, is effective in preventing ice re-forming. Note: Overheating, in the de-icing rig, of most de-icing fluid will result in a gelled formation being deposited on the aircraft which will not shear off on take-off and may, therefore, have an adverse aerodynamic effect.

HOT WATER DE-ICINGHot water de-icing should not be carried out at temperatures below -7C, and the second step must be performed within three minutes of the beginning of step 1, if necessary area by area.Step 1 – Snow and ice is initially removed with a jet of hot water at a maximum temperature of 95C.Step 2 – A light coating of de-icing fluid is then immediately applied to the aircraft to prevent re-freezing.

HIGH PRESSURE SPRAYS

High-pressure sprays used for de-icing are capable of causing damaged to pitot static probes and other sensing devices. A carelessly directed spray could also result in the ingress of a considerable quantity of fluid into engine intakes, drains or vents, possible resulting in cabin smoke or malfunction of an associated aircraft system. Where covers or bungs are provided they should be fitted during de-icing operations. Where this is not possible care must be taken to prevent direct impingement of the spray on any vents or probes.

High-pressure sprays can also cause erosion of the aircraft skin and some aircraft manufacturers recommend a maximum impingement pressure, which is quoted in the appropriate Maintenance Manual and should not be exceeded.

DE-ICING OF AIRCRAFT WITH ENGINES OPERATING

Aircraft ‘taxi-through’ de-icing facilities are presently being used which de-ice aircraft with the engines operating. Winter environmental conditions and the manner of application create potentially unsafe conditions if an incorrect de-icer solution is inadvertently sprayed into the engine / APU inlets or contacts the exhausts when the engines or APU are operating. APU and engine bleeds should be closed during such operations to minimise the risk of contamination of the cabin environment.

De-icing fluids have a flashpoint of 139 to 156C in their undiluted state which is within the engine / APU operating range. The numerous de-icing fluids available also include some which have toxic characteristics that could affect personnel or passengers if ingested by the air-conditioning system.Some aircraft manufacturers issue instructions which contain precautions concerning fluids and techniques for de-icing aircraft with engines operating. A safety hazard could exist if the manufacturer’s instructions are not followed.Safeguards should include procedures which ensure that de-icing fluids are diluted below critical flashpoints and that such fluids are prevented from entering air ducts, air-conditioning systems, and engines / APU inlets or exhaust.

Fire and emergency equipment should be readily available at all times.

ANTI-ICING MEASURES

When used as an anti-icing agent, the FPD fluid should be sprayed onto the aircraft cold and undiluted, either before the onset of icing conditions or after hot de-icing has been carried out. This will leave a film of fluid approximately 0.5 mm (0.020 in) thick on the surfaces sprayed and give protection overnight in all but the most severe weather conditions. The fluid prevents ice and snow from sticking to the aircraft skin and given time will melt any fresh precipitation. Newly fallen snow may be quickly removed by blowing, and heavy ice deposits, such as those produced by freezing rain, may be removed by a light and economical spray of hot fluid. Excess fluid will shear off during the take-off run (but see paragraph (b.2 Note).On some aircraft not equipped with an aerofoil de-icing system, the use of a de-icing paste may be specified. This paste is intended to prevent the accumulation of frozen deposits which may result from inadvertent flight into icing conditions. When spread smoothly by hand over the leading edges of the wings and tail unit the paste presents a chemically active surface, on which ice may from but may not bond. Any ice which does from may ultimately be blown off in the air stream.The paste should be reactivated before each flight in accordance with the manufacturer’s instructions.

WARNING: It is important to note that de-icing pastes do not constitute an approved method of de-icing otherwise unprotected aircraft for intended flights into known or forecast icing conditions.

INSPECTION AFTER DE-ICING OPERATIONS

It is important to carry out an inspection of an aircraft after completion of de-icing operations. The aircraft should also be continually monitored between de-icing and departure to ensure no further ice build-up has occurred. The presence of ice in certain areas may not be obvious to personnel handling the de-icing equipment.Note: The effective duration of anti-icing fluids depends on concentration /temperature of application, column of snow and ice, etc., subsequent temperature and time.All external surfaces should be examined for signs of residual snow or ice, particularly in the vicinity of control surface gaps and hinges. This is especially important where control surfaces are sealed by ‘curtains’ of the Westland –Irvine type. Drainage or pressure sensing holes and radiator honey combs should be checked to ensure that they are not blocked. Where it has been necessary to physically remove a layer of snow all protrusions and vents should be examined for signs of damage.

Where possible, control surfaces should be moved by hand to ascertain that they have full and free movement. Where this is not possible the pilot’s controls should be gently operated, bearing in mind that power-operated controls exert considerable force on the control surface and could cause damage if any part of the circuit is frozen. If any restriction is found, the control cables, pulleys, fairleads, hinges, etc., should be examined and any frozen deposits treated with de-icing fluid until smooth control operation is achieved.

The landing gear mechanism, doors bays and wheel brakes should be inspected for snow or ice deposits, and the operation of unlocks and micro switches checked. In very sever conditions it is possible for the tyres to become frozen to the ground; they may be freed by the application of warm air to the ice (not the tyre) and the aircraft should then be moved to a dry area.Snow or rain can enter jet engine intakes after flight and freeze in the compressor when the engine has cooled. If compressors cannot be turned by hand for this reason, the engine should be blown through with hot air immediately before starting, until the rotating parts are free.The low temperatures associated with icing conditions may also introduce problems apart from those associated with the clearance of precipitation.Contraction of metal parts and seals can lead of fluid leakage and particular attention should be given to landing gear shock absorber struts and hydraulic jacks.

Tyre and shock absorber strut pressures reduce with temperature and may require adjustment in accordance with the loading requirements.

TECHNICAL LOGS

An entry should be made in the Technical Log as required by British Civil Airworthiness Requirements, Section A, Chapter A6-8, unless an alternative company procedure has been agreed by the CAA

ELECTRICAL, HYDRAULIC AND PNEUMATIC GROUND SUPPLIES

ELECTRICAL

The purpose to connect an external electrical power supply to an aircraft,

•Either for engine starting purposes or •To permit operation of the aircraft systems and equipment.

Certain precautions must be observed when connecting the external supply, to prevent damage to the aircraft electrical system.

Most light aircraft have direct current (d.c.) electrical systems, and although alternating current (a.c) is provided for the operation of certain equipment It is not usual for the aircraft to have provision for the connection of a.c. external power.

The external power socket is, therefore, usually for the connection of a d.c. supply, which may be provided solely by batteries or from a generator and battery set.

The following actions should be taken when connecting an external d.c. supply to a typical light aircraft:

•Check the voltage and polarity of the ground supply•Check that the external power plug and socket are clean, dry and undamaged•Check that the external supply and the aircraft batteries master switch are off and connect the external supply, ensuring that the plug is fully home in the socket

Switch on the external supply and the aircraft battery master switch, and carry out the servicing operations for which the external power was required

To disconnect the external supply, switch off the battery master switch, switch off the external supply, disconnect the external power plug, and if the aircraft electrical system is to be used (e.g. after engine starting), switch the battery master switch on again.

Most large aircraft are provided with multi-pin plugs or sockets, by means of which external d.c. or a.c. power may be connected into the aircraft electrical system.

The external supply is usually provided by a towed or self-propelled unit, which has its own power-driven generator and can provide d.c. power at various voltages and a.c. power at a particular

voltage, frequency and phase rotation

Procedure of connecting the external power to aircraft

•Check that the external supply is compatible with the aircraft system (i.e. it has the same voltage, frequency and phase rotation as the aircraft system), and is switched off.•Check that the external plug and socket are clean, dry and undamaged.•Connect the external plug/socket, ensuring that it is fully mated and secure, and switch on the external power supply.•Check the voltage and frequency of the external supply on the aircraft electrical system instruments, and perform the operations specified in the relevant maintenance manual to engage the external supply with the aircraft a.c. system.

To disconnect the external supply, disengage it from the aircraft a.c. system, switch off the external power at source, and remove the external power plug/socket.

HYDRAULIC(MIL-H 5606)

MAINTENANCE

•The appropriate Maintenance Manual should be consulted before any work is carried out on the hydraulic system of any particular aircraft. •Failure to observe the precautions detailed by the manufacturer could lead to damage to the aircraft, and, possibly, to physical injury.

•Even when the aircraft pumps are stationary, high pressures are maintained in parts of the system by the accumulators, and no disconnections should be made while the system is pressurised.

Any specific instructions regarding the isolation of electrical circuits, or the fitting of hydraulic safety locks during servicing, should be carefully followed.

CLEANLINESS.

•With a modern hydraulic system cleanliness is of the utmost importance.

•The filters fitted in the aircraft system will normally protect the components from the effects of particle contamination,•It is important that any ground equipment used for servicing purposes is kept scrupulously(thoroughly) clean, and that the fluid is filtered to a similar standard. •Contamination from other fluids must be also be avoided, and provision is usually made for taking fluid samples. •Whenever a connection is broken, or a component is removed, precautions must immediately be taken to prevent the ingress (enter) of foreign matter or moisture. •If it is necessary to top-up the system, fluid should be poured directly from a new fluid container into the reservoir, or a sealed dispensing rig should be used. When the system is topped-up from a can, any unused fluid should be discarded

SAMPLING

•Samples of the system fluid should be taken at the periods specified in the approved Maintenance Schedule, and whenever contamination is suspected. •If a fluid sampling kit is available it should be used strictly in accordance with the manufacturer’s instructions, but, if such a kit is not available, the sample should be sent to a laboratory for examination.•The bottle into which the fluid is drained must be scrupulously clean, to avoid adding to any contamination that may already be present in the sample. •The bottle should be washed with soap and water to give a clean, bright finish, rinsed in clean water, then in filtered alcohol, and dried with clean dry air. •It is usually recommended that plastic sheet is interposed between the bottle and the cap, to prevent the formation of loose particles when the cap is screwed on.

•When taking a sample, a suitable service should be operated to circulate the fluid, and a small quantity should be drained from the sampling point before filling the sample bottle.

•Every precaution should be taken to prevent contamination of the sample, and any instructions contained in the Maintenance Manual, or in the test kit, should be carefully followed.

The parameters to be tested acidity, specific gravity, viscosity, water content, particle contamination,

and acceptable values are specified in the appropriate Maintenance Manual.

If slight contamination is present, the fluid should be circulated by operation of the services, and a further sample taken. If heavy contamination is found, the affected system should be flushed or drained, and re-filled with clean fluid.

FLUSHING

Flushing is normally required

•After extensive removal •A replacement of pipelines or components, This is carried out by operating the particular service a number of times, so that any particle contamination may be trapped by the filters. When it is necessary to flush the main system, the filters should be changed and the fluid should be circulated by operating the largest hydraulic jacks a number of times.

Either an auxiliary pump, or an external hydraulic test rig, may be used for flushing, but, if an auxiliary pump is used, it is normally recommended that it is subsequently removed and inspected for possible damage.

DRAINING THE SYSTEM

The hydraulic system should be drained

•whenever components which are not provided with self-sealing couplings have to be removed, •and also when overheating or mechanical failure of a pump, or the introduction of extraneous fluids or foreign matter, has resulted in contamination of the system.•It is common practice to disconnect the engine-driven pump from the system before commencing draining, so as to prevent the formation of air locks in the pump and to maintain lubrication when the pump is rotated.•The hydraulic system should be made electrically safe (by the tripping of circuit-breakers or the removal of fuses, as appropriate),

•The hydraulic pressure should be released by operating one of the services, and the air pressure should be released from the accumulators and reservoir. •The reservoir filler cap should be removed, and fluid should be drained into a clean container of suitable capacity, by means of the system drain cock. •Drained fluid should be returned, in appropriately identified containers, for reclamation by an approved process.•If fluid contamination is the reason for draining , it will also be necessary to remove the filters, and to clean or replace the filter elements as appropriate. Cleaning is usually by an ultrasonic cleaning process, but washing in “trichloroethylene” may also be permissible as a temporary measure.

FILLING THE SYSTEM

Occasions•Initial installation, •whenever the fluid has been drained, •The system should be filled and primed. •Filling may be carried out through the reservoir filler neck,• Through a priming connection in the ground-servicing bay, using an external priming rig. The system is pressurized for priming purposes by using either an aircraft electrically operated pump, or an external hydraulic test rig.To ensure correct operation of the system, all air must be removed fro the pipelines and components. Some components are held by slackening the pipe connections, allowing fluid to escape, then retightening; some components are fitted with bleed valves, and others are purged by operating the service and forcing any trapped air to return to the reservoir.The aircraft should be jacked in accordance with the relevant Maintenance Manual, and the accumulators should be charged with air nitrogen, as appropriate. Ground electrical power should be connected, and the appropriate fluid and pump overheat warning lamps should be tested.

The reservoir filler cap should be removed, the should be completely filled with fluid, and the quantity indicators should be checked. The system should be pressurised to normal system pressure, using the electrically operated pump or test rig as appropriate, and one of the services should be operated until the reservoir fluid level has stabilised. Trapped air should be released from the reservoir, and fluid added to keep the level at maximum. This process should be repeated for each service, bleeding being carried out where appropriate, and careful watch being kept on the pump and fluid temperatures. Fluid bled or drained from components must not be returned to the system.

After each service has been primed, the fluid level should again be checked. In some systems the fluid level depends on the positions of various actuators, and, before checking the fluid level, it is necessary to make the appropriate selections, and to ensure that all accumulators and reservoirs are fully charged.When filling and priming are completed, all connections should be checked for tightness, and locked. Electrical power (and the hydraulic test rig, if used) should be disconnected, and the aircraft should be lowered to the ground. Engines should be run to check correct operation of the hydraulic services.

REPLENISHMENT OF LIQUIDS

On modern aircraft, replenishment of engine oil, hydraulic fluid, de-icing fluid, water, and other systems containing liquids, is achieved by the use of servicing trolleys which are specially designed for the task and are connected into the system by quick-release couplings; alternatively, and with older aircraft, these systems may be replenished by removing the tank filler cap and pouring in the required liquid. Whichever method is used, the utmost care should be taken to ensure that only the approved liquids are used, and that no foreign matter is allowed to enter the system. Servicing trolleys should be inspected regularly for cleanliness, and their delivery pipes should be capped when not in use; all utensils should be kept scrupulously clean, and should, preferably, be retained for use with one particular liquid.

The quantity of liquid in a system may be indicated by a sight glass, by use of a dip-stick, by its visible level in a filter fitted in the filler opening, or in some cases, by means of a contents gauge, the transmitter unit for which is mounted in the tank. When required, the system should be replenished to the ‘full’ level; no system should be overfilled, as this could affect system operation.

Precautions applicable to the replenishment of systems containing liquid are outlined in paragraphs 1) to 4) below:

Some systems are pressurized in normal use, and this pressure should be released before replenishing with liquid. When replenishing a hydraulic system, it may be necessary to pre-set the hydraulic services to specified positions to prevent overfilling.

Some liquids, such as methanol, synthetic lubricating oils and hydraulic fluid, may be harmful or even toxic if their vapours are breathed in or if they come into contact with the skin or eyes. Particular note should be taken of any warnings of dangers to health which may be contained in the relevant Maintenance Manuals, and the recommended procedures for the handling of these liquids should be observed.The liquids mentioned in paragraph 3) may also have an adverse effect on paintwork, adhesives and sealant, and thus inhibit corrosion prevention schemes. Care should be taken not to spill any of these liquids, but if a spillage does occur, immediate steps should be taken to mop it up and clean the affected area

LUBRICATIONLubrication should be carried out in accordance with a schedule approved for the particular aircraft, the intervals normally being related to flying hours, with certain positions requiring additional lubrication after ground de-icing operations and after cleaning the aircraft.

The lubricant to be used, and the method of application, are usually annotated on a diagram of the aircraft in the appropriate chapter of the aircraft Maintenance Manual. The method of annotation is often by the use of mimic diagrams (e.g. an oil can for oiling or a grease gun for greasing) and the type of lubricant is indicated by a symbol.The utensils used for lubrication purpose should be kept scrupulously clean, and should only be filled with new lubricant. Each utensil or container should be clearly marked with the lubricant it contains, and should be kept solely for that lubricant.

When lubricating a component, care should be taken to ensure that the quantity applied is adequate but not excessive; in some cases a particular quantity may be specified in the Maintenance Manual (e.g. “apply 8 drops of oil..”) but normally a quantity sufficient to cover the bearing surfaces, as evidenced by the exuding of new lubricant, should be applied. The lubricating point should be wiped clean and dry with a lint-free cloth before applying the oil grease, and any excess exuding from the component should be wiped off to prevent the accumulation of dirt or foreign matter.Effects of environmental conditions on aircraft handling and operation

Weather OperationsParticular care is essential in the operation of aircraft when temperatures are likely to fall below freezing point at ground level. When snow or ice present towing and taxying should be carried out with extreme caution and aircraft movements should be kept to a minimum; parking areas should, if possible, be cleared of snow and ice, so as to prevent aircraft tyres from freezing to the ground. If sand or grit is used increase the tractive effort of tractors or assist the braking of aircraft, care should be taken to prevent materials being drawn into operating engines; taxiways and hard standing should be swept to remove any sand or grit after the snow and ice have melted.AFTER FLIGHT. When parking an aircraft, all covers, plugs and ground locks should be fitted as soon as possible. If the airframe is wet or affected by snow or ice, the surface under the covers should be given a light coating of anti-freeze liquid; anti-freeze liquid should not, however, be applied to the windows, since it has an adverse effect on plastics materials. Engine covers should be fitted as soon as the engine has cooled sufficiently, but in the case of turbine engines an inspection should be made for the presence of ice in the air intake, since this could melt while the engine is hot, drain to the lowest part of the compressor, and subsequently re-freeze when the engine cools, locking the lower compressor