module 7 (maintenance practices) sub module 7.17 (aircraft handling and storage)

8/20/2019 Module 7 (Maintenance Practices) Sub Module 7.17 (Aircraft Handling and Storage)

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PIA TRAINING CENTRE (PTC) Module 7 ‐ MAINTENANCE PRACTICES

Category – B2 Sub Module 7.17 - Aircraft Handling and Storage

PTC/CM/B2 Basic/M7/03 Rev. 007.17 Mar 2014

MODULE 7

Sub Module 7.17

AIRCRAFT

HANDLING

AND

STORAGE


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PTC/CM/B2 Basic/M7/03 Rev. 007.17 - i Mar 2014

Contents

AIRCRAFT HANDLING AND STORAGE .................................. 1

MOVING METHODS ................................................................. 2

AIRCRAFT TOWING ................................................................. 2

AIRCRAFT TAXIING .................................................................. 2

PRECAUTIONS WHEN TOWING / TAXING AIRCRAFT .......... 3

AIRCRAFT JACKING ................................................................ 4

JACKING PRECAUTIONS ........................................................ 7

PARKING AND MOORING AIRCRAFT ................................... 11

CHOCKING OF AIRCRAFT ..................................................... 15

AIRCRAFT STORAGE ............................................................ 16

AIRCRAFT FUELLING PROCEDURES .................................. 20

DEFUELLING .......................................................................... 22

DE-ICING/ANTI-ICING OF AIRCRAFT ................................... 23

GROUND ELECTRICAL SUPPLIES ....................................... 31

GROUND HYDRAULIC SUPPLIES ......................................... 33

GROUND PNEUMATIC SUPPLIES ........................................ 34

EFFECTS OF ENVIRONMENTAL CONDITIONS ON

AIRCRAFT HANDLING AND OPERATION ............................. 36


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PTC/CM/B2 Basic/M7/03 Rev. 007.17 - 4 Mar 2014

AIRCRAFT JACKING

Aircraft may need to be jacked for a variety of purposes. Thesemay include component changes, retraction tests, weighing ofthe aircraft and aircraft rigging checks. Care needs to be takenwhen jacking, to avoid damage to aircraft or equipment.

Jacking points are provided in the wings and fuselage, at strong

points, to enable the whole aircraft to be lifted, and there are,usually, other points, at the nose and main undercarriages, toenable individual wheels to be changed (refer to Fig. 1).

Some aircraft require a jacking pad to be fitted to each jackingpoint, while in some, the jacking pads are built into the structure.Special jacking adapters and beams may be available to liftindividual axles.

In all instances, the Maintenance Manual should be consulted,so that the correct equipment and procedures may be used.

Special Considerations

Because of the position of the jacking points, the C.G. of someaircraft may be well behind, or in front of, the main jackingpoints. It may be necessary to add ballast forward or rear of the

jacking points or to check the fuel load of the aircraft, to bringthe centre of gravity within safe limits as specified in theMaintenance Manual.

Typical Jacking Points

Nose Jacking

Point (Offset)

Main Jacking

Points

Nose Jacking

Point (Offset)


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Mooring (Picketing)

In certain weather conditions, particular in high winds, it wouldbe recommended that the aircraft be parked in a hangar. If theymust be left outside, then smaller aircraft may need to be tieddown. The aircraft may be provided with picketing rings orattachment points at the wings and tail or adjacent to theundercarriage legs (refer to Fig. 2).

Aircraft Picketing PointsFig. 2

View A

View B View C

B C A


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Cables or chains should be attached from the aircraft picketingpoints to prepared anchorages. In some instances the picketingcables are special components and include a tension meter thatis used to apply a pre-load to the cable.

If an aircraft is to be parked for a longer period, then additionalprecautions must be taken. Landing gear down-locks must beinstalled (if so equipped) and all openings such as static vents

and engine intakes should be covered or blanked off (refer toFig. 3) to prevent the ingress of dirt, birds, insects and all formsof precipitation.

Typical Aircraft BlanksFig. 3

Intake Blank

Exhaust Blank

Main Wheel CoversNose Wheel Covers

Pitot-Static Blanks


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CHOCKING OF AIRCRAFT

When aircraft are parked, it is normal to place a chock aheadand behind at least one wheel set. The parking brakes areusually left in the ‘off’ position once chocks are in position, toallow the heat, generated by the brakes, to dissipate evenly.

At high wind speeds, it is normal to chock all the wheels and

apply the brakes (if they have cooled). Some aircraft chocks canbe chained together, to give a more secure hold. During groundruns (and especially those involving high power), it is commonsense to place chocks at the front of all main wheel sets, toreinforce the parking brake.


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AIRCRAFT STORAGE

If an aircraft is de-activated for an extended time it will need tobe protected against corrosion, deterioration and environmentalconditions during its period of storage.

The following notes are based on the storage proceduresapplicable to BAe 146 aircraft that have been de-activated for

periods in excess of 30 days and up to a maximum of 2 years. Itis not intended for the information given here to be complete,but merely to give the student examples of some of the activitiesperformed. Specific details of an aircraft’s storage procedurescan be found in Chapter 10 of the relevant MaintenanceManual.

A list of equipment and materials is normally given. This will,typically, include:

Hydraulic fluid and lubricating oils and greases

Specialised water-displacing fluids and corrosion-preventative compounds

Aircraft covers and blanks

Plastic sheeting and adhesive tape.

Prior to the storage period certain tasks are completed. Thesemay include replacing the tyres with ‘dummy’ tyres (those not

suitable for flight), or the raising of the pressures of the normalones. The various tanks are either filled (water), drained (toilet),or part-filled (fuel). If the aircraft has propellers, they must befeathered, to prevent them rotating in the wind. (they may alsobe restrained by straps).

Generally there would be an initial procedure, this beingrepeated at specified intervals, as shown in Tables 1 (a) and 1(b). If no repeat interval is given, then the item is only doneinitially.

Once the aircraft has been prepared, there are routine, weekly

checks to keep it in good condition.


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PTC/CM/B2 Basic/M7/03 Rev. 00

7.17 - 22 Mar 2014

DEFUELLING

Occasionally, it is necessary to remove fuel from an aircraft, tofacilitate fuel tank maintenance, or because the aircraft is tooheavily loaded for the next flight.

Removing fuel from an aircraft can be accomplished by eitherthe gravity or by the pressure defuelling method.

The gravity method entails draining the fuel into a suitablyearthed container, and this is typical of light aircraft, which arenormally ‘gravity’ refuelled. The fuel removed must be disposedof in the correct manner, with regard to local instructions and tothe environment.

Aircraft that are normally pressure refuelled are normallyequipped with a pressure defuelling facility. Pressure defuelling

is achieved by utilising a small negative pressure (suction),which effectively draws the fuel out of the tank and returns it intothe fuel tanker (bowser).

Current rules will normally only allow the fuel, removed from anaircraft, to be placed into a dedicated defueller vehicle and thefuel will not be permitted to be used in another aircraft. Thisensures that any contamination such as water or debris will notbe transferred to other aircraft.


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7.17 - 23 Mar 2014

DE-ICING/ANTI-ICING OF AIRCRAFT

Ice Types

There are three main types of ice/frost that can affect anaircraft’s performance, Hoar Frost, Rime Ice and Glaze Ice. Thetemperature and weather conditions will determine the type ofice that forms, but all three types can have a detrimental effect.

The Dew Point is the temperature at which moist air becomessaturated and deposits dew if in contact with a colder surface orthe ground. Above ground, condensation into water dropletstakes place.

Hoar Frost is a deposit of ice crystals that form on an objectwhen the dew point is below freezing point. High humidity willnormally produce hoar frost, as these are similar to conditions

that produce dew. Hoar frost can form when the air temperatureis greater than 0°C, but the aircraft skin temperature is less than0°C. This type of frost produces a very rough surface whichleads to turbulent airflow.

Rime Ice is a light coloured opaque rough deposit that has aporous quality. At ground level it forms in freezing fog fromwater droplets with very little spreading. It adds very little weightbut it can disrupt the smooth flow of air over the wing, and block

pitot and static vents.

Glaze Ice can be either transparent or opaque and can form intoa glassy surface due to liquid water flowing over a surfacebefore freezing. It is the most dangerous type of ice found on anaircraft and is dense, heavy and tough. It adheres firmly to a

surface, is difficult to shake off, and if it does breakaway, it doesso in large chunks.

During cold weather operations, it may be necessary to removeice and snow from the aircraft, while it is on the ground, and tokeep it clear long enough, to allow the aircraft’s systems to copewith snow or ice removal. This may not occur until the aircraft isflying.


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7.17 - 24 Mar 2014

On the ground, the aircraft must be cleared of all snow and icefrom its wings, tail, control surfaces, engine inlets and othercritical areas (refer to Fig. 4) before the aircraft can take-off.

Ice formation on an aircraft on the ground may result from anumber of causes:

Direct precipitation from rain, snow and frost

Condensation freezing on external surfaces of integral tanksfollowing prolonged flight at high altitude

After taxing through snow or slush, ice may accumulate onlanding gear, forward facing surfaces and under-surfaces.

Rudder

Elevator

Ailerons

Flaps

Engine Nacelle

Slats

Pitot and

Static

Heads

TCAS

Antenna

VHF

Antenna

Critical Surfaces for De-icing and Anti-icing

Fi . 4


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7.17 - 25 Mar 2014

The formation of ice on aircraft structures can produce manyadverse effects, and if allowed to remain may result in some orall of the following:

Decreased aerofoil lift

Increased aerofoil drag

Increased weight

Decreased engine thrust

Freezing of moisture in control hinges Freezing of micro-switches that affect systems such as the

landing gear retraction

Ingestion of ice into the engine.

Definitions

The terms ‘de-icing‘ and ‘anti-icing’ have specific definitions,and it is essential to know the differences.

De-icing is the removal of ice that has already formed

Anti-icing is the prevention of initial ice formation.

De-Icing and Anti -Icing Methods

The de-icing procedure for removal of ice, frost and snow froman aircraft’s surface can be achieved by mechanical or chemicalmethods. Mechanical methods use blowers, brushes and rubberscrapers whilst chemical methods utilise de-icing fluids.

The anti-icing procedure provides protection against the

formation of ice, frost and snow on aircraft surfaces for a shortperiod known as the ‘Holdover Time’. This is achieved byapplying an anti-icing fluid, but the aircraft must be either clean

or de-iced prior to this anti-icing fluid application. There are twoways of aircraft de-icing and anti-icing:

One Step Method

Two Step Method.


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7.17 - 28 Mar 2014

The Hot Fluid Spray method has been adopted specifically toreduce turn-round time. The FPD fluid is mixed with water inproportion to suit prevailing weather conditions, and heated tobetween of 60ºC (minimum) and 85ºC (maximum).

The fluid is normally sprayed onto the aircraft at a pressure of100 psi (689.5 kN/m2) by use of spray lances. The nozzle of thelance is held close to the aircraft skin, to prevent heat losses.

The heat transfers to the skin of the aircraft, breaking the icebond, and large areas of ice may be flushed away by turning thenozzle sideways. The fluid film remaining on the skin, has onlybeen slightly diluted beyond its original dilution and is effectivein preventing further ice formation.

Hot water de-icing is a method that must not be used below -

70C and may need to be performed in two steps.

Step 1: Snow and ice are normally removed initially with a

jet of hot water not exceeding 95C

Step 2: If necessary a light coating of de-icing fluid is thensprayed on immediately (within 3 minutes) to prevent re-freezing.

On some aircraft, not equipped with aerofoil or propeller de-icing systems, the use of a de-icing paste may be specified. The

paste is spread evenly, by hand, over wing, tail and propellerleading edges. It provides a chemically active surface on whichice may form but not produce a bond. Any ice, which forms, isblown away by the airflow. The paste should be re-appliedbefore each flight in accordance with the AMM.


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7.17 - 29 Mar 2014

Hold Over Times

When used for anti-icing, the FPD fluid should be sprayed ontothe aircraft cold and undiluted, before the onset of icing or afterany hot de-icing. The fluid film will prevent ice and snow fromsticking to the aircraft skin and, given time, will melt any freshprecipitation. Typical times for which the fluid remains effectiveare known as the ‘Hold Over’ time (refer Table 2).

Under extreme cold conditions it may be necessary to heat the

fluid (60C max) to give it sprayability. No significant increase inhold over time is achieved by strengthening the mix of type I(AEA) fluids.

Stations using Kilfrost will normally provide a mix of 50/50 or60/40. It may be difficult to get stronger mixes at short noticeunless the temperature conditions at the stations involved are

below limits for that mix.


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7.17 - 30 Mar 2014

Certain precautions should be observed when applyingchemical anti-icing fluids, and these are:

Anti-icing fluid must NOT be applied on top of a similar,earlier coat

If possible, the engines or the APU should not be operatedduring snow/ice removal

The fluid should not be sprayed directly onto windscreens,

windows, vanes, pitot heads or probes The minimum quantity of fluid should be used in the air

conditioning intake areas

If possible the fluid should not be sprayed onto lubricatedparts, such as landing gear legs

Inspection after De-Icing/Anti-Icing Procedures

The following inspections should be done on completion of a

de-icing procedure:

External surfaces, for signs of residual snow or ice,particularly in the vicinity of control surface gaps and hinges

All protrusions and vents, for signs of damage

Control surfaces for full and free movement by hand. Wherethis is not possible the pilot's controls should be used,bearing in mind that power-operated controls exert largeforces and could cause damage if any part of the control

surface is frozen Landing gear mechanisms, doors, bays and wheel brakes,

for snow and ice deposits

Up-locks and micro-switches, for correct operation

Tyres to ensure that they are not frozen to the ground. Theyshould be freed by the application of hot air to the ice (notthe tyre) and the aircraft moved to a dry area

Engine air intakes for ice and snow deposits

Gas turbine engines for freedom of rotation by hand.Restriction may indicate icing in the compressor region andthe engine should be blown through with hot air immediatelybefore starting until the rotating parts are free

Shock absorber struts and hydraulic jacks for leaks causedby contraction of seals and metal parts

Tyre pressures and shock absorber pressure and extension

Following the inspections an entry should be made in the Tech.Log, indicating that the De-Icing/Anti-Icing procedure has beencompleted.


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7.17 - 31 Mar 2014

GROUND ELECTRICAL SUPPLIES

Ground electrical supplies are normally limited to either 28 voltsdc or 115 volts ac, depending upon the systems of the aircraft.Most modern aircraft have at least one 115 volt ac system (aswell as a 28 volt dc one), so they will normally be supplied with115 volts ac from an external power supply.

Airfields normally supply electricity to aircraft through externalgenerators called Ground Power Units (GPUs), or haveunderground supplies, which are connected to the aircraft viathe air-bridge, or from beneath the ramp surface.

When an external electric supply is required inside the hangar,its generation will normally be through transformer rectifier units. An external power control box may be installed on the hangarwall and the required output for a particular aircraft can be

selected.

To prevent accidentally connecting-up of incorrect supplies, allaircraft have separately-shaped plugs and sockets. The 28 voltdc supply usually has a three-pin connection whilst the 115 voltac utilises a much larger, six-pin plug and socket (refer to Fig.5).

The 28 volt dc connection has two pins which are longer than

the third. The longer pins are the supply connections whilst theshorter pin acts as a safety interlock, to ensure that the power iscut-off, if the cable is inadvertently pulled out without the powerbeing switched off first.

The 115 volt ac connection has six pins, with four pins beinglonger than the other two. The four longer pins provide the threephases and the neutral connection whilst the short pins providethe safety interlock.


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7.17 - 32 Mar 2014

3 PIN EXTERNALPOWER RECEPTACLE

EXTERNAL

SUPPLY SOCKET

EARTH

POSITIVE D.C.

POSITIVE D.C.

3 PIN

PLUG

ACCESS

DOOR

D.C.

A.C. PHASE “A”

A.C. NEUTRAL

A.C. PHASE “C”

A.C. PHASE “B”

NOSEWHEEL

WELLLIGHTS

EXTERNALPOWER

READYLIGHT

SERVICEINTERPHONE

CONNECTION

dc Power Socket and Receptacle

ac Power Receptacle

Ground Electrical Supplies

Fig. 5


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7.17 - 35 Mar 2014

Some aircraft have two separate connections for air supplies atdifferent points on the airframe. The forward connection may befor low-pressure air, which is then fed directly to the conditioningsystem, allowing testing of the air conditioning system and alsoof the pressure hull. The aft connection may be for a higher-pressure bleed air supply that is primarily used to start theengines if the APU is unserviceable.

Whilst some units are dedicated air starter rigs, some can beused both for starting and also for functional testing of the airconditioning and de-icing systems. As with the electric andhydraulic ground power supply rigs, the output of a pneumaticunit must match the aircraft’s system for pressure and flow.


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7.17 - 37 Mar 2014

Most airfields that operate continuously have a plan to deal withexcessive amounts of snow. This plan might include theapplication of heater units or allowing APUs to run for extendedperiods to keep the inside of the aircraft warm.

For aircraft, which are to be left out on the ramp, in sub-zerotemperatures, it may be necessary to drain the potable watertanks, to prevent them freezing overnight. This will involve somecare, as they should not be drained onto the ramp, due to therisk of personnel slipping on the ice.

Other items of equipment that use water, such as heaters andpipe-work, may also need protection in cold temperatures.

High Winds

High winds can cause loose objects to move across the rampand strike the aircraft. These can be light items such as twigsand branches but, on occasions, heavy pieces of groundequipment, that have not been secured correctly, have beenpushed into aircraft, causing major damage.

During very high wind conditions, the smallest objects can belethal, due to the energy they contain.

In certain environments, such as desert climates (or at airfieldsnear seashores), sand and dust, driven by the wind, can entersmall crevices, causing problems with aircraft systems and mayalso block filters. Where extreme conditions exist, such asduring a sand storm, then the blanking of all orifices may haveto be augmented with tape or other methods, to prevent theingress of dust and sand.

Great care must be taken, to ensure suitable entries are madein the Technical Log, for the complete removal of all blankingmaterial, after the storm has abated.


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7.17 - 38 Mar 2014

High Temperature

Certain items of equipment are temperature-sensitive and,when aircraft are operated in environments of extreme high

temperature (+55C), then several extra precautions have to betaken.

Some form of cooling must be provided to ensue that the crewdoes not suffer from heat exhaustion, and reduce theirefficiency. The operating temperature electronic equipmentmust also be kept below a critical level, to ensure its continuedserviceability.

Most of the larger aircraft have an auxiliary power unit (APU),which can provide a supply of bleed air to allow the airconditioning system of the aircraft to operate on the ground.

If an APU is not available, then external air conditioning unitscan be connected to the aircraft to keep the inside cool. Thesecooling rigs should have an air conditioning unit of suitablecapacity for the size of the aircraft that requires cooling.

Some turbo-propeller passenger aircraft have the facility to runan engine, without the propeller turning, to provide airconditioning on the ground.

This facility is known as the ‘Hotel Mode’ and, effectively,enables an engine to operate in a similar manner to an APU,without the need to carry extra weight.

module 7 (maintenance practices) sub module 7.17 (aircraft handling and storage)

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