JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
CONTENTS
1 INTRODUCTION ... 1-1 2 SAFETY PRECAUTIONS ... 2-1 2.1 FIRE ... 2-12.1.1 The ‘Fire Triangle’ ... 2-2 2.1.2 Classes of Fire ... 2-2 2.1.3 Fire Extinguishants and their Uses ... 2-3
2.2 FIRST AID ... 2-5
2.3 WORKSHOP AND HANGAR SAFETY ... 2-5
2.3.1 Machinery ... 2-5 2.3.2 Electricity ... 2-6 2.3.3 Noise... 2-7 2.3.4 High-Pressure Gases ... 2-7 2.3.5 Gas Bottle Identification ... 2-8 2.3.6 High-Pressure Gas Replenishing ... 2-8 2.3.7 Oxygen Systems ... 2-9 2.3.8 Aviation Oils and Fuels ... 2-10 2.3.9 Chemical and Physiological Hazards ... 2-11 2.3.10 Lifting and Shoring ... 2-11 2.3.11 Slinging ... 2-12
2.4 FLIGHT-LINE SAFETY ... 2-13
2.4.1 Towing and Taxying ... 2-14 2.4.2 Parking ... 2-15 2.4.3 Marshalling... 2-16 2.4.4 Fuelling ... 2-17 2.4.5 Weather Radar ... 2-18 3 WORKSHOP PRACTICES ... 3-1 3.1 CARE OF TOOLS ... 3-1 3.2 CONTROL OF TOOLS... 3-2
3.3 CALIBRATION OF TOOLS AND EQUIPMENT... 3-3
3.3.1 General Notes on Calibration ... 3-3 3.3.2 Procedures... 3-4
3.4 USE OF WORKSHOP MATERIALS ... 3-6
3.5 STANDARDS OF WORKMANSHIP ... 3-7
4 TOOLS ... 4-1
4.1 COMMON HAND TOOLS ... 4-1
4.1.1 Engineer’s Rule ... 4-1 4.1.2 Scriber ... 4-2 4.1.3 Key-Seat Rule ... 4-2 4.1.4 Fitter’s Square ... 4-3 4.1.5 Combination Set ... 4-4 4.1.6 Surface Plates and Tables ... 4-5 4.1.7 V Blocks ... 4-5 4.1.8 Surface Gauge (Scribing Block) ... 4-6 4.1.9 Dividers ... 4-7 4.1.10 Callipers ... 4-7 4.1.11 Hammers ... 4-8
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
4.1.12 Punches ... 4-9 4.1.13 Metal-Cutting Chisels... 4-10 4.1.14 Bench Vice ... 4-12 4.1.15 Hand Vice ... 4-13 4.1.16 Hacksaws ... 4-14 4.1.17 Sheet Metal Shears and Snips ... 4-15 4.1.18 Files ... 4-16 4.1.19 Filing Techniques ... 4-19 4.1.20 Hand Brace (Hand Drill) ... 4-21 4.1.21 Twist Drills ... 4-22 4.1.22 Stop, and Press (Dimpling), Countersinking Tools ... 4-27 4.1.23 Reamers ... 4-29 4.1.24 Internal Screw Thread, Cutting Taps ... 4-32 4.1.25 External Screw Thread, Cutting Dies ... 4-34 4.1.26 Screwdrivers ... 4-36 4.1.27 Pliers ... 4-38 4.1.28 Wire Snips (Nippers)... 4-39 4.1.29 Spanners, Sockets and Wrenches ... 4-394.2 COMMON POWER TOOLS ... 4-45
4.2.1 Electrically Powered Pillar Drills ... 4-45 4.2.2 Electrically Powered Hand Drills ... 4-46 4.2.3 Pneumatically Powered Hand Drills ... 4-46 4.2.4 Pneumatically Powered Riveting Hammers ... 4-48 4.2.5 Pneumatic Miller (Microshaver) ... 4-49 4.2.6 Nibblers ... 4-49 4.2.7 Pneumatic Tool Maintenance ... 4-50 4.2.8 Abrasive Wheels ... 4-50
4.3 PRECISION MEASURING INSTRUMENTS ... 4-52
4.3.1 External Micrometers ... 4-52 4.3.2 Internal Micrometers ... 4-56 4.3.3 Micrometer Depth Gauge... 4-57 4.3.4 Vernier Micrometers ... 4-58 4.3.5 Vernier Callipers ... 4-60 4.3.6 Vernier Height Gauge ... 4-61 4.3.7 Vernier Protractor ... 4-62
4.4 MISCELLANEOUS MEASURING TOOLS ... 4-63
4.4.1 Gauge Blocks ... 4-63 4.4.2 Dial Test Indicator (DTI) ... 4-64 4.4.3 Feeler Gauges ... 4-64 4.4.4 Screw Pitch and Radius Gauges ... 4-65 4.4.5 Go/No-Go Gauges ... 4-65 4.4.6 Straight Edges ... 4-65
4.5 LUBRICATION METHODS AND EQUIPMENT ... 4-66
4.5.1 Lubrication Methods ... 4-66 4.5.2 Lubrication Equipment ... 4-69
5 ENGINEERING DRAWING, DIAGRAMS AND STANDARDS ... 5-1
5.1 TYPES OF DRAWING ... 5-1
5.2 METHODS OF DRAWING SOLID OBJECTS ... 5-2
5.2.1 Pictorial Projections ... 5-3 5.2.2 Orthographic Projections ... 5-4
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
5.2.3 Sectional Views ... 5-5 5.2.4 Exploded Views ... 5-6 5.2.5 Drawing Lines, Symbols and Abbreviations... 5-7 5.2.6 Conventional Representations ... 5-9 5.2.7 General and Geometric Tolerances ... 5-95.3 DRAWING IDENTIFICATION SYSTEM... 5-10
5.3.1 Title Block ... 5-11 5.3.2 Drawing Number ... 5-11 5.3.3 Handed Parts ... 5-11 5.3.4 Sheet Numbers ... 5-11 5.3.5 Drawing Changes... 5-11 5.3.6 Part Referencing ... 5-12 5.3.7 Validation of Modification/Repair Drawings ... 5-12 5.3.8 Summary of Recommended Drawing Information ... 5-13
5.4 AUXILIARY DIAGRAMS AND CHARTS ... 5-14
5.4.1 Electical Wiring Diagrams ... 5-14 5.4.2 Component Location Diagrams ... 5-15 5.4.3 Schematic Diagrams ... 5-16 5.4.4 Block Diagrams ... 5-17 5.4.5 Logic Flowcharts ... 5-17
5.5 MICROFILM,MICROFICHE AND COMPUTERISED PRESENTATIONS .... 5-19
5.5.1 Microfilm ... 5-19 5.5.2 Microfiche ... 5-19 5.5.3 Computer CD-ROM ... 5-20 5.5.4 Supplementary Information ... 5-20
5.6 AERONAUTICAL STANDARDS ... 5-21
5.6.1 Air Transport Association Specification No. 100 ... 5-21 5.6.2 International Organisation for Standardisation (ISO) ... 5-24 5.6.3 British Standards (BS) ... 5-24 5.6.4 Military Standard (MS) ... 5-24 5.6.5 Air Force and Navy (AN) ... 5-24 5.6.6 National Aerospace Standard (NAS) ... 5-24
6 FITS AND CLEARANCES ... 6-1
6.1 DIMENSIONS ... 6-1
6.1.1 Allowances ... 6-1 6.1.2 Tolerances ... 6-2
6.2 DRILLING SIZES FOR HOLES ... 6-3
6.3 CLASSES OF FITS ... 6-3
6.3.1 Newall System ... 6-4 6.3.2 British Standards System ... 6-5
6.4 SCHEDULE OF FITS AND CLEARANCES ... 6-5
6.4.1 Limits for Wear ... 6-6 6.4.2 Limits for Ovality ... 6-6 6.4.3 Limits for Bow ... 6-7 6.4.4 Limits for Twist ... 6-8
7 RIVETING ... 7-1
7.1 TYPES OF SOLID RIVET ... 7-1
7.1.1 Rivet Materials ... 7-2 7.1.2 Basic Rivet Location Terminology ... 7-2
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
7.2 TYPES OF RIVETED JOINTS ... 7-4 7.3 CLOSING SOLID RIVETS ... 7-4
7.4 CLOSING HOLLOW RIVETS ... 7-5
7.4.1 Tucker-pop ... 7-5 7.4.2 Chobert... 7-5 7.4.3 Avdel ... 7-6 7.4.4 Cherry Max ... 7-7 7.4.5 Hi-Lok ... 7-8 7.4.6 Rivnuts ... 7-8
7.5 INSPECTION OF RIVETED JOINTS ... 7-9
7.6 RIVET REMOVAL PROCEDURE ... 7-10
8 PIPES AND HOSES... 8-1
8.1 PIPE BENDING ... 8-1
8.1.1 Simple Bending Jigs ... 8-2 8.1.2 Hand Pipe-Bending Machines ... 8-2
8.2 PIPE FLARING ... 8-3
8.2.1 Flaring Tool ... 8-3 8.2.2 Standard Flared Pipe Couplings ... 8-4 8.2.3 Flareless Couplings ... 8-5
8.3 INSPECTION AND TESTING OF PIPES AND HOSES ... 8-6
8.3.1 Bore Testing of Pipes ... 8-7 8.3.2 Hydraulic Pressure Testing of Pipes ... 8-7 8.3.3 Pneumatic and Oxygen Pressure Testing of Pipes ... 8-7 8.3.4 Cleaning After Test ... 8-7 8.3.5 Testing Flexible Hoses ... 8-8
8.4 INSTALLATION AND CLAMPING OF PIPES ... 8-8
8.4.1 Pipe Supports ... 8-8
8.5 CONNECTION OF PIPES ... 8-9
8.6 MAINTENANCE OF PIPES AND HOSES ... 8-9
8.7 PIPE IDENTIFICATION TAPE ... 8-10
9 SPRINGS ... 9-1
9.1 INSPECTION AND TESTING OF SPRINGS ... 9-1
10 BEARINGS ... 10-1
10.1 CLEANING AND INSPECTION OF BEARINGS ... 10-1 10.2 INSPECTION OF BEARINGS ... 10-2
10.2.1 Normal Fatigue ... 10-2 10.2.2 Excessive Loads ... 10-2 10.2.3 Installation and Misalignment ... 10-3 10.2.4 Loose Fit ... 10-3 10.2.5 Brinelling ... 10-3 10.2.6 Overheating and Lubrication Failure ... 10-4 10.2.7 Contamination and Corrosion ... 10-5
10.3 SAFETY PRECAUTIONS ... 10-5 10.4 STORAGE ... 10-5
11 TRANSMISSIONS ... 11-1
11.1 GEARS ... 11-1 11.2 BELTS AND PULLEYS ... 11-1
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
11.3 CHAINS AND SPROCKETS ... 11-2 11.4 SCREW JACKS ... 11-3 11.5 LEVERS ... 11-4
11.5.1 Push-Pull Rod Systems... 11-5
12 CONTROL CABLES ... 12-1
12.1 SWAGING OF END FITTINGS ... 12-1 12.2 INSPECTION AND TESTING OF CONTROL CABLES ... 12-1
12.2.1 Cable Wear ... 12-1 12.2.2 Bowden and Teleflex Cable Systems ... 12-3
12.3 INSPECTION OF CONTROL CABLE PULLEYS ... 12-4
13 SHEET METAL WORK... 13-1
13.1 MARKING OUT... 13-2 13.2 FORMING OF SHEET METAL PARTS ... 13-3
13.2.1 Cutting ... 13-3 13.2.2 Bending and Calculation of Bend Allowance ... 13-4
13.3 INSPECTION OF SHEET METAL WORK ... 13-8
14 WELDING, SOLDERING AND BONDING ... 14-1
14.1 WELDING ... 14-1 14.2 METHODS OF WELDING ... 14-1
14.2.1 Oxy-Acetylene Flame ... 14-1 14.2.2 Manual Metal Arc ... 14-2 14.2.3 Metal Arc Gas-Shielded (MAGS) ... 14-2 14.2.4 Tungsten Arc Gas-Shielded (TAGS) ... 14-2 14.2.5 Flash Butt Welding ... 14-3 14.2.6 Spot Welding... 14-3 14.2.7 Seam Welding ... 14-3
14.3 INSPECTION AND TESTING OF WELDS ... 14-3 14.4 SOLDERING ... 14-4 14.5 METHODS OF SOLDERING ... 14-4
14.5.1 Hard Soldering (Brazing and Silver Soldering) ... 14-4 14.5.2 Soft Soldering ... 14-5 14.5.3 Using Indirectly Heated (Electric) Soldering Irons... 14-6 14.5.4 Active and Passive Fluxes ... 14-8 14.5.5 Flux Removal ... 14-10
14.6 INSPECTION AND TESTING OF SOLDERED JOINTS ... 14-10 14.7 BONDING ... 14-10 14.8 METHODS OF BONDING ... 14-11
14.8.1 Thermoplastic Adhesives ... 14-11 14.8.2 Thermosetting Adhesives ... 14-12
14.9 INSPECTION AND TESTING OF BONDED JOINTS... 14-12
15 AIRCRAFT MASS AND BALANCE ... 15-1
15.1 DEFINITIONS... 15-1 15.2 MASS AND BALANCE ... 15-2
15.2.1 Mass and Balance Documentation ... 15-3
15.3 FREQUENCY OF WEIGHING ... 15-4
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
15.4 WEIGHING REQUIREMENTS ... 15-4 15.5 CENTRE OF GRAVITY LIMITS (CGENVELOPE)... 15-5 15.6 RECORDS ... 15-5 15.7 CALCULATION OF MASS AND CG OF ANY SYSTEM ... 15-5 15.8 PRINCIPLES OF WEIGHT AND BALANCE OF AIRCRAFT ... 15-7 15.9 CALCULATION OF MASS AND CG OF AIRCRAFT ... 15-7 15.10 AIRCRAFT WEIGHING METHODS... 15-815.10.1 Preparation for Weighing ... 15-9 15.10.2 Weighing on Aircraft Jacks ... 15-9 15.10.3 Calculation of Aircraft’s CG ... 15-10 15.10.4 CG as Percentage Standard Mean Chord (SMC) ... 15-12
15.11 CHANGES IN BASIC WEIGHT ... 15-12
15.11.1 Examples of Alterations to Dry Operating Mass ... 15-13
15.12 LOADING OF AIRCRAFT (TYPICAL AIRCRAFT LOAD SHEET) ... 15-15
16 AIRCRAFT HANDLING AND STORAGE ... 16-1
16.1 MOVING METHODS ... 16-2
16.1.1 Moving by Hand and Steering Arm ... 16-2 16.1.2 Using a Bridle and Steering Arm ... 16-2 16.1.3 Using a Purpose-Made Towing Arm ... 16-3 16.1.4 Precautions when Towing Aircraft... 16-3 16.1.5 Taxiing Aircraft... 16-4
16.2 AIRCRAFT JACKING ... 16-5
16.2.1 Special Considerations ... 16-5 16.2.2 Aircraft Jacks ... 16-6 16.2.3 Jack Maintenance and General Notes ... 16-7 16.2.4 Jacking Precautions... 16-8 16.2.5 Jacking Procedures ... 16-8 16.2.6 Trestles... 16-9 16.2.7 Lowering Aircraft off Jacks ... 16-10
16.3 SLINGING ... 16-10
16.3.1 Lifting Tackle ... 16-11
16.4 PARKING AND MOORING AIRCRAFT... 16-12
16.4.1 Parking ... 16-12 16.4.2 Mooring (Picketing) ... 16-13 16.4.3 Typical Small Aircraft Procedures ... 16-14 16.4.4 Large Aircraft Procedures ... 16-14 16.4.5 Chocking of Aircraft ... 16-15
16.5 AIRCRAFT STORAGE ... 16-16 16.6 AIRCRAFT FUELLING PROCEDURES ... 16-20
16.6.1 Fuelling Safety Precautions ... 16-20 16.6.2 Refuelling ... 16-21 16.6.3 Checking Fuel Contents ... 16-21 16.6.4 Defuelling. ... 16-22
16.7 GROUND DE-ICING/ANTI-ICING OF AIRCRAFT ... 16-23
16.7.1 Ice Types ... 16-23 16.7.2 Definitions ... 16-25 16.7.3 De-Icing and Anti-Icing Methods ... 16-25 16.7.4 Chemical De-Icing ... 16-26
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
16.7.5 Treatment of Frost Deposits ... 16-26 16.7.6 Removal of Ice and Snow Deposits ... 16-27 16.7.7 Hold Over Times ... 16-29 16.7.8 Inspection after De-Icing/Anti-Icing Procedures ... 16-30
16.8 GROUND ELECTRICAL SUPPLIES ... 16-31 16.9 GROUND HYDRAULIC SUPPLIES ... 16-33
16.9.1 Safety, Health and Servicing Precautions ... 16-33 16.9.2 Rig Maintenance ... 16-34
16.10 GROUND PNEUMATIC SUPPLIES ... 16-34
16.11 EFFECTS OF ENVIRONMENTAL CONDITIONS ON HANDLING ... 16-35
16.11.1 Cold and Wet ... 16-35 16.11.2 Snow and Ice ... 16-36 16.11.3 High Winds... 16-36 16.11.4 High Temperature ... 16-37
17 PREVENTATIVE MAINTENANCE TECHNIQUES ... 17-1
17.1 TYPES OF DEFECTS ... 17-1
17.1.1 External Damage ... 17-2 17.1.2 Inlets and Exhausts ... 17-3 17.1.3 Liquid Systems ... 17-3 17.1.4 Gaseous Systems ... 17-4 17.1.5 Dimensions ... 17-5 17.1.6 Tyres ... 17-5 17.1.7 Wheels ... 17-6 17.1.8 Brakes... 17-6 17.1.9 Landing Gear Locks ... 17-7 17.1.10 Indicators ... 17-7 17.1.11 External Probes ... 17-8 17.1.12 Handles and Latches ... 17-8 17.1.13 Panels and Doors... 17-8 17.1.14 Emergency System Indication ... 17-9 17.1.15 Lifed Items ... 17-9 17.1.16 Light Bulbs ... 17-9 17.1.17 Permitted Defects... 17-9
17.2 LOCATIONS OF CORROSION IN AIRCRAFT ... 17-10
17.2.1 Exhaust Areas ... 17-10 17.2.2 Engine Intakes and Cooling Air Vents ... 17-10 17.2.3 Landing Gear ... 17-10 17.2.4 Bilge and Water Entrapment Areas ... 17-11 17.2.5 Recesses in Flaps and Hinges ... 17-11 17.2.6 Magnesium Alloy Skins ... 17-11 17.2.7 Aluminium Alloy Skins ... 17-11 17.2.8 Spot-Welded Skins and Sandwich Constructions ... 17-12 17.2.9 Electrical Equipment ... 17-12 17.2.10 Control Cables ... 17-12
17.3 CORROSION REMOVAL,ASSESSMENT AND REPROTECTION ... 17-13
17.3.1 Cleaning and Paint Removal ... 17-13 17.3.2 Ferrous Metals ... 17-14 17.3.3 Aluminium and Aluminium Alloys ... 17-14 17.3.4 Alclad ... 17-15 17.3.5 Magnesium Alloys ... 17-16
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
17.3.6 Acid Spillage ... 17-16 17.3.7 Alkali Spillage ... 17-16 17.3.8 Mercury Spillage ... 17-1717.4 PERMANENT ANTI-CORROSION TREATMENTS ... 17-18
17.4.1 Electro-Plating ... 17-18 17.4.2 Sprayed Metal Coatings ... 17-18 17.4.3 Cladding ... 17-18 17.4.4 Surface Conversion Coatings ... 17-19
17.5 NON-DESTRUCTIVE TESTING/INSPECTION (NDT/NDI)TECHNIQUES 17-20
17.5.1 Visual/Assisted Visual Inspections ... 17-21 17.5.2 Remote Viewing Instruments ... 17-22 17.5.3 Penetrant Flaw Detection (PFD) ... 17-25 17.5.4 Ultrasonic Flaw Detection (UFD)... 17-34 17.5.5 Eddy Current Flaw Detection (ECFD) ... 17-40 17.5.6 Magnetic Particle Flaw Detection (MPFD) ... 17-46 17.5.7 Radiographic Flaw Detection (RFD) ... 17-52 17.5.8 Miscellaneous Radiation Techniques ... 17-57
17.6 DISASSEMBLY AND RE-ASSEMBLY TECHNIQUES ... 17-58
17.6.1 Complete Airframes ... 17-58 17.6.2 Replacement of Major Components/Modules ... 17-59 17.6.3 Replacement of Minor Components/Modules ... 17-60 17.6.4 Disassembly and Re-assembly of Major Components .. 17-60 17.6.5 Disassembly and Re-assembly of Minor Components .. 17-60 17.6.6 Basic Disassembly and Re-assembly Techniques ... 17-61 17.6.7 Small Part and Component Identification ... 17-62 17.6.8 Discarding of Parts ... 17-63 17.6.9 Freeing Seized Components ... 17-63 17.6.10 Use of Correct Tools ... 17-63 17.6.11 ‘Murphy’s Law’ ... 17-64
18 ABNORMAL EVENTS ... 18-1
18.1 TYPES OF ABNORMAL OCCURRENCES ... 18-1 18.2 TYPES OF DAMAGE ... 18-1 18.3 LIGHTNING STRIKES ... 18-2
18.3.1 Effects of a Lightning Strike ... 18-2 18.3.2 Inspection ... 18-2
18.4 EXAMPLE OF A POST LIGHTNING STRIKE PROCEDURE ... 18-3
18.4.1 Basic Protection ... 18-3 18.4.2 Strike Areas ... 18-4 18.4.3 Signs of Damage ... 18-5 18.4.4 External Components at Risk ... 18-5 18.4.5 Electrical Components at Risk ... 18-6 18.4.6 Examination of External Surface ... 18-6 18.4.7 Functional Tests ... 18-7 18.4.8 Examination of Internal Components ... 18-8 18.4.9 Return the Aircraft to Service ... 18-9
18.5 HIGH INTENSITY RADIATED FIELDS (HIRF)PENETRATION ... 18-9
18.5.1 Specific Testing – HIRF ... 18-10 18.5.2 Protection against HIRF Interference ... 18-11
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
18.6.1 Example of Post Heavy Landing Inspection ... 18-12
18.7 FLIGHT THROUGH SEVERE TURBULENCE ... 18-14
19 MAINTENANCE PROCEDURES ... 19-1 19.1 MAINTENANCE PLANNING ... 19-1 19.2 MODIFICATION PROCEDURES ... 19-2 19.2.1 Major Modifications ... 19-2 19.2.2 Minor Modifications ... 19-2 19.3 STORES PROCEDURES ... 19-3 19.4 CERTIFICATION AND RELEASE PROCEDURES ... 19-3
19.4.1 Interface with Aircraft Operation ... 19-4
19.5 MAINTENANCE INSPECTION/QUALITY CONTROL AND ASSURANCE 19-5 19.6 ADDITIONAL MAINTENANCE PROCEDURES ... 19-6 19.7 CONTROL OF LIFE-LIMITED COMPONENTS ... 19-6
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
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JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
1
INTRODUCTION
Most accidents are, in the main, caused by human carelessness and accidents in the work place are among the main causes of death and disability.
They are, additionally, the cause of a great loss of man-hours and, thus, cost companies (and individuals) large amounts of money.
All personnel should be aware, not only of the potential for accidents and injury, wherever they work, but also of the legislation and information that is available in an attempt to prevent accidents actually happening.
While it is incumbent upon companies (in accordance with The Management of Health and Safety at Work Regulations 1992), to ensure that all personnel receive adequate training in Health and Safety matters, this Module contains a reminder of some of the general safety precautions which are necessary, when working in the aerospace industry.
The Module continues with further topics, which are concerned with the practices recommended for the safe and efficient maintenance of aircraft and aerospace components.
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
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JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
2
SAFETY PRECAUTIONS
Aircraft, by their very nature and design, make for a dangerous working environment. The danger is further increased by the wide variety of machines, tools and materials required to support and maintain aircraft.
Personal safety starts with being appropriately dressed for the work being undertaken, combined with the correct use of eye and ear protection whenever necessary.
Technicians should only operate equipment with which they are familiar and which they can operate safely. Hand tools should be kept in good working order. Good ‘housekeeping’ in workshops, hangars, and on flight line ramps is essential to safe and efficient maintenance.
Pedestrian and fire lanes should be clearly marked and NEVER obstructed. They should always be used to keep non-technical personnel clear from the work area. Any spillage of oils, greases and fuels should be immediately covered with absorbent material and cleaned up, to prevent fire or injury. Spillage should be prevented, from running into floor drains.
It is very important, that all personnel know the location of the fixed points where fire fighting equipment and First Aid treatment are available. They must also be aware of the types of emergency that can occur in the workplace (whether in the workshop, hangar or on the ramp), and of the procedures to be followed in any emergency.
2.1 FIRE
WARNING: ALWAYS ENSURE THAT CORRECT FIRE PRECAUTIONS ARE OBEYED AND THAT ESCAPE ROUTES ARE NOT OBSTRUCTED. LETHAL FUMES AND SMOKE CAN BE PRODUCED BY CERTAIN MATERIALS AND THEY CAN BURN VERY RAPIDLY.
Personnel, engaged in the maintenance, overhaul and repair of aircraft, should be fully conversant with the precautions required to prevent outbreaks of any fire. They should be qualified in the operation of any fire protection equipment that is provided, and should know the action to be taken in the event of discovering a fire.
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
2.1.1 The ‘Fire Triangle’
Fire results from the chemical reaction that occurs when oxygen combines rapidly with fuel to produce heat, (and light). Three essentials of this process form the ‘Fire Triangle’ (refer to Fig.1).
As can be seen, a fire requires three components to burn, and the removal of any one of these components will extinguish the fire. The requirements of the three components, forming the ‘Fire Triangle’, are:
Fuel: a combustible material, which may be a solid, liquid or gas
Oxygen: in sufficient volume to support the process of combustion
Heat: of sufficient intensity to raise the temperature of the fuel to its ignition (or kindling) point.
2.1.2 Classes of Fire
There are, generally, four classes of fires, each determined by the type of material that is being burned. In alphabetical, order the classes of fire are:
Class A: often known as solid fires, which occur in materials such as paper, wood, textiles and general rubbish.
Class B: often described as liquid fires, and include fires in materials such as internal combustion engine fuels, alcohol, oils, greases and oil-based paints.
Class C: include fires involving flammable gases and electrical fires (which can occur in fuse boxes, switches, appliances, motors and generators).
Class D: refer to fires of high intensity, which may occur in such metals as magnesium, potassium, sodium, titanium and zirconium. The greatest hazard in these materials, is when they are either in liquid (molten) form, or in finely divided forms such as dust, chippings, turnings or shavings.
The ‘Fire Triangle’ Fig. 1
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
2.1.3 Fire Extinguishants and their Uses
The methods of extinguishing fires have led to the development of several types of extinguishants to cater for different types of fire. These methods include:
Cooling the fuel
Excluding the oxygen
Separating the fuel from the oxygen
The materials, used as general ‘domestic and commercial’ extinguishants, differ from those used in aircraft Fire Protection systems and, while the aircraft systems are discussed in other Modules of this course, consideration is given here only to the extinguishants and extinguishers which conform to the EN3 Standard fire extinguisher code. The materials used in these extinguishers are:
Water (Water/Gas)
Aqueous Film-Forming Foam (AFFF)
Carbon Dioxide (CO2)
Dry Powder
Applying the incorrect extinguishant to a fire can do more harm than good and may, actually, be dangerous. It is, therefore, important that extinguishers are well marked for quick identification in an emergency. It is also vital that all personnel are aware of the markings, which appear on extinguishers, so that the correct one is chosen to deal with a specific fire.
Table 2 shows how the EN3 Standard fire extinguisher code has replaced the older Standard, whereby the extinguisher containers were colour-coded all over to signify their contents. The EN3 Standard has the bodies of every fire extinguisher coloured red all over, with an identifying band of colour, separated by white lines, identifying the extinguishant contained in the extinguisher.
Table 2
FIRE EXTINGUISHER IDENTIFICATION AND USES EN3 Standard Extinguishers (All-red Container)
Extinguishant Band Colour Types of Fire
Water (Water/Gas)
Red Solids only, but NOT Electrical NOR Flammable Liquids
Aqueous Film-Forming Foam (AFFF)
Cream Oil, Fats, Paint, Petrol, and Solids, but NOT safe on Electrical fires Carbon Dioxide
(CO2)
Black Gases, Electrical, Flammable Liquids and Solids but NOT Burning Metals Dry Powder Blue Burning Metals, Flammable Liquids, and Electrical (<1000 V, >1 m) fires
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
From Table 2 it can be seen that Water or Water/Gas extinguishers are ONLY to be used on fires involving burning solids (Class A fires). Water could also cause liquid fires to spread and, obviously, using water on electrical equipment could have lethal results, so these extinguishers must NOT be used on Class B NOR on Class C fires. Water should, also, NOT be used on burning metal (Class D) fires, as the oxygen, in the water, will cause the fires to burn more fiercely and its use could lead to violent explosions.
Aqueous Film-Forming Foam (AFFF) is best suited for Class B fires, due to its smothering and cooling action and to the fact that its finer particles will not cause the fire to spread. AFFF extinguishers can also be used on Class A fires (though its cooling action is not as effective as the water extinguishers), but, because Foam does contain water, AFFF extinguishers are considered to be NOT safe on electrical fires where high voltages are encountered.
Carbon Dioxide (CO2) is the ‘universal’ fire extinguisher and, being non-corrosive,
non-conductive, and leaving no residue, it is suitable for almost all types of fire. CO2 extinguishers must NOT, however, be used on Class D fires, as the
extinguishant reduces the temperature very quickly, which (in a similar way to the use of water extinguishers) could cause serious explosions.
Due to the fact that CO2 gas tends to dissipate quickly, the extinguisher is
provided with a horn device, which helps to concentrate the CO2 at the site of the
fire. This horn must NOT be held with bare hands, as the intense cold of the released CO2 will freeze the skin to the horn, resulting in severe injury to the
hands. A rubber, insulated coating is provided on the discharge tube and the CO2
must be directed towards the fire by grasping and manipulating the insulated tube.
Dry Powder is another extinguishant which is suitable for most classes of fire, and, in particular, those involving burning metals (aircraft wheel brake fires). It is, however, limited in its use on electrical fires, as the powder particles are capable of conducting high voltages (in excess of 1000 V) and, possibly, lesser voltages if they are used at distances of less than 1 metre from electrical fires. Dry Powder (in a similar way to Foam), leaves a messy residue after its use, which could present a problem to electrical contacts and circuitry.
Note: It is possible that the older Standard ‘Halon’ fire extinguishants (in green-coloured containers) may be found at many indoor locations. Unfortunately, while Halons (Halogenated Hydrocarbons) are extremely effective as extinguishants of virtually every class of fire, it is felt that they contribute to the depletion of the ozone layer surrounding Earth and, so, they are being phased out of use. Buckets of dry sand may also be placed at the FIRE POINT in workshops (and especially in hangars) as an additional aid to fire fighting.
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2.2 FIRST AIDIt has been previously discussed that, when working indoors, whether it is in an office, a workshop or a hangar, there will be fixed points where fire-fighting equipment is available. Similarly, there will be First Aid points where emergency kits, eye washing equipment and call bells are installed and there will be trained First Aid personnel to assist in the treatment of injuries. It is the responsibility of every person at work to know:
The location of the First Aid Points
The methods of calling for help
The locations of alarm bells, and the siting of appropriate telephones which may be used to summon help in an emergency
The identity of the trained First Aid personnel in their vicinity
In the event of an injury (however slight), it is important that the injured person, or the attending First Aider, should complete an entry in the Accident Book, which is usually kept near the First Aid Point.
2.3 WORKSHOP AND HANGAR SAFETY
When working in a workshop or in any hangar, there are a number of safety precautions that must be followed, if injury (or death) is to be avoided.
2.3.1 Machinery
A machine can be defined as an ‘apparatus for applying power, having fixed and moving parts, each having a definite function’. In particular, machines embrace:
Operational Parts - performing the principal output function (Chucks or Bits)
Non-Operational Parts - conveying power or motion (Motor Drives).
The wide range of machinery, available in workshops and hangars, precludes giving specific rules and regulations for each machine. The basic drilling, grinding and milling types of machine, all require the use of eye protection, attachment of guards, secure holding of work and, most importantly, correct training before being operated.
Possible accidents from machinery, in general, include personnel:
Coming into contact with the machinery
Being trapped between machinery and material
Being struck by machinery or being entangled in its motion
Being struck by ejected parts or material
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2.3.2 ElectricityThe human body conducts electricity. Furthermore, electrical current, passing through the body, disrupts the nervous system and causes burns at the entry and exit points. The current, used in domestic 220-240 volt, 50Hz ac electricity, is particularly dangerous because it affects nerves in such a way that a person, holding a current-carrying conductor, is unable to release it. Table 2 shows some typical harmful values and effects of both ac and dc electricity supplies.
Table 2
HARMFUL VALUES OF ELECTRICITY Voltage/Current Possible Outcome
50V ac or 100V dc May give rise to dangerous shocks
1 mA Harmless tingle
1 – 12 mA Painful, but can be released 12 – 20 mA Very painful, cannot be released 20 – 50 mA Paralysis of respiration
> 50 mA Heart stoppage
Since water also conducts electricity, great care must be taken to avoid handling electrical equipment of all kinds when standing on a wet surface or when wearing wet shoes. The water provides a path to earth and heightens the possibility of electric shock. To ensure that equipment is safe, the minimum requirement is through the use of three-core cable (which includes an earth lead) and, possibly, a safety cut-out device.
In conjunction, more often than not, with ignorance or carelessness, electrical hazards generally arise due to one or more of the following factors:
Inadequate or non-existent earthing
Worn or damaged wiring, insulation, plugs, sockets and other installations
Bad wiring systems and the misuse of good systems
Incorrect use of fuses
Inadequate inspection and maintenance of power tools and equipment All electrical equipment must be regularly checked and tested for correct operation and electrical safety. To show that this has been done, a dated label should be attached, showing when the equipment was last tested and when the next inspection is due.
Any new item of equipment must have a test label attached. The presence of a test label does not, however, absolve the user from checking the equipment for any external signs of damage, such as a frayed power cord (or missing safety devices) before use.
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Shout for help and ensure there is no danger of also becoming a victim
Switch off the electrical current or remove the victim from the supply by means of insulated material
If the victim has ceased breathing, initiate resuscitation
Call for professional medical help
If the victim is suffering from burns, exclude air from wounds
Treat for shock by keeping the victim warm
The approved methods of artificial resuscitation must, by law, be displayed on wall charts in workplaces.
2.3.3 Noise
Workshops, hangars and flight lines can be very noisy places of work, so it is essential that ear defenders, or some other protection such as ear plugs, are used at all times that noise is perceived to be a risk. Loss of hearing, leading to deafness, can be the result of operating in a noisy environment without adequate ear protection. Ear protection is optional where noise levels are less than 85 dB, but is mandatory when greater than 90 dB.
2.3.4 High-Pressure Gases
Compressed gases are frequently used in the maintenance and servicing of aircraft. The use of compressed gases requires a special set of safety measures. The following rules apply for the use of compressed gases:
Cylinders of compressed gas must be handled in the same way as any high-energy (and therefore potentially explosive) sources
Eye protection must always be worn when handling compressed gases
Never use a cylinder that cannot be positively identified
When storing or moving a cylinder, have the cap securely in place to protect the valve stem
When large cylinders are moved, ensure that they are securely attached to the correct trolley or vehicle
Use the appropriate regulator on each gas cylinder
Never direct high-pressure gases at a person
Do not use compressed gas or compressed air to blow away dust and dirt, as the resulting flying particles are dangerous
Release compressed gas slowly. The rapid release of a compressed gas will cause an unsecured gas hose to whip about and even build up a static charge, which could ignite a combustible gas
Keep gas cylinders clean. Oil or grease on an oxygen cylinder can cause spontaneous combustion and explosions
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2.3.5 Gas Bottle Identification
High-pressure gas cylinders contain various types of gas, the most common used on commercial aircraft being nitrogen and oxygen. To ensure correct identification of these containers, they are colour coded and the name of the gas is stencilled on the side.
In the UK, gas containers use BS 381C as the standard to determine the correct colour and shade for each gas type. Nitrogen bottles are painted grey on the body with a black neck, whilst oxygen bottles are black with a white neck. Be aware that bottles of US manufacture use an alternative system, the main difference being oxygen bottles are painted green all over.
2.3.6 High-Pressure Gas Replenishing
When replenishing aircraft services such as tyres and hydraulic accumulators with high-pressure gas, care must be taken to ensure that only the required pressure enters the container. When full, a gas storage bottle can hold as much as 200 bar (3000 psi) whilst an aircraft tyre pressure may only require 7 bar (100 psi).
To safely control the gas, two pressure regulating valves are used, one at the storage bottle end and one at the delivery end of the system. If one valve fails the other will prevent the receiving vessel from taking the full bottle pressure with the consequence of an explosion.
For added safety the gas bottle valve opening key should be left in the valve whilst decanting operations are completed. If problems occur then the high-pressure bottle can be quickly isolated before the situation becomes dangerous. The transfer of high-pressure gases from a large storage bottle to the aircraft component is often called decanting and must be done at a very slow rate. If the gas is decanted rapidly the temperature of the receiving component will increase in accordance with the gas laws.
Again using the same gas laws the temperature of the gas in the container will drop to ambient, and the pressure in that vessel will reduce. The component pressure will now be incorrect and require the decanting process to be repeated.
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In workshops, compressed air is, sometimes, produced by a compressor (which is housed in a remote building), and fed, via galleries, to work stations. Care must be taken to ensure that no damage occurs to the piping whilst in use.
If a concentrated stream of compressed air is blown across a cut in a person’s skin, then air can enter the blood stream and cause injury or death. For this reason, air-dusting guns are restricted to about 2000 kPa (30 psi).
Aircraft tyres can require very high pressures and must be inflated inside a strong cage. This cage would protect the personnel working on the wheels in the event of a tyre or wheel bursting.
2.3.7 Oxygen Systems
Modern aircraft fly at altitudes where life support systems are needed. Even though most of these aircraft are pressurised, emergency oxygen must be carried in the event that the pressurisation system fails. Smaller aircraft can carry oxygen in cylinders whilst the larger, civil aircraft have individual oxygen generator units. These units are stowed in the overhead cargo bins, above the passenger seats, and are known as the passenger service units or PSUs. A PSU produces oxygen, by means of a chemical reaction, and is activated when its mask (which drops from the overhead bin in an emergency) is pulled by a passenger.
Note: When PSUs reach their life expiry and have to be returned to their manufacturer, it is vital that all precautions are followed to make the units ‘safe’ for transit. PSUs get very hot when working and have caused the destruction, due to fire, of an aircraft, which was carrying these units as cargo.
The main oxygen systems are serviced from trolleys or vehicles that carry a number of high-pressure bottles of oxygen, which can be at 140 bar (2000 psi) or more. Some trolleys may also have a bottle of nitrogen, to allow the replenishment of hydraulic accumulators and landing gears. The two types of bottles must be separated, in order to prevent the accidental mixing of the gases. It is extremely important that oxygen cylinders be treated with special care, because, in addition to having all the dangers inherent with all other high-pressure gases, oxygen always possesses the risk of combustion and explosion. As previously stated, oxygen must never be allowed to come into contact with petroleum products such as oil and grease, since oxygen causes these materials to ignite spontaneously and to burn. Furthermore, an oil-soaked rag, or tools that are oily or greasy (or badly oil-stained overalls), must never be used when installing an adapter or a regulator on an oxygen cylinder.
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Due to the risk of fire and explosion, replenishing trolleys must never be parked close to hydraulic oil replenishing rigs, or in any area where petroleum products are likely to come into contact with the oxygen servicing equipment. Similarly only specially approved thread lubricants can be used when assembling oxygen components.
2.3.8 Aviation Oils and Fuels
Aviation oils, generally, are a fairly low-risk material when compared with the more volatile, higher distillates of petroleum such as the aviation fuels - petrol (gasoline) and paraffin (kerosene). Most lubricating oils are flammable, if enough heat is generated but, when the materials are kept away from excessive heat sources, they are (comparatively) quite benign.
Synthetic lubricating oils, methanol and some hydraulic oils may be harmful or even toxic if their vapours are inhaled. Also, if they come into contact with the skin or eyes, they can cause injury or blindness. Particular note should be taken of any warnings of dangers to health that may be contained in the relevant maintenance manuals and the recommended procedures for the handling of these liquids should always be observed.
Oils and fuels also have an adverse effect on paintwork, adhesives and sealants and, thus, may inhibit corrosion-prevention schemes. Care should, therefore, be taken not to spill any of these liquids but, if a spillage should occur, it must be cleaned up immediately.
Note: Sweeping up gasoline spillage with a dry broom can cause a build up of static electricity, with the accompanying risk of explosion.
With gasoline and kerosene there is a much greater chance of fire, so more thorough precautions are required. These start with the basic rules, such as not wearing footwear with nails or studs (to prevent sparks), not carrying matches or cigarette lighters and ensuring that ALL replenishing equipment is fully serviceable.
Note: All references to refuelling, normally, also include the action of de-fuelling and both are considered under the common term of fuelling.
During any fuelling operation, in a workshop, a hangar or on the flight line, the relevant fire extinguishers must be in place.
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2.3.9 Chemical and Physiological Hazards
Many chemical compounds, both liquid and solid, are used in aircraft maintenance and these may need specific precautions. Any precautions can be found in the relevant maintenance manuals and in the Control of Substances Hazardous to Health (COSHH) leaflets applicable to those materials.
The range of adhesives used for repair and sealing during the maintenance of aircraft is vast. A large number of these produce vapours which, generally, can be dangerous in any enclosed space, both from the results of inhalation of narcotic fumes and from the fire risk associated with those which give off volatile, flammable, vapours.
Surface finishes present another area where the various types of material used (etchants, celluloses, acrylics, enamels, polyurethanes etc.), dictate specific precautions. The solvents used, before the actual painting and afterwards, need safety precautions with regards to ventilation, reaction with other materials and, most importantly, their possible corrosive, toxic, irritant and addictive effects on personnel.
Some materials have a mildly radioactive property, although they emit little ionising radiation in normal circumstances. These materials are sometimes referred to as ‘heavy metals’ and can be found in balance-weights as well as in smoke detectors, luminescent ‘EXIT’ signs and instruments.
This radiation differs from that used for non-destructive testing (NDT) procedures, where high levels of radiation are employed, by specially trained personnel, and which, therefore, require many safety precautions to avoid personal injury. The safety precautions for NDT procedures will be found within the manuals applicable to their employment.
2.3.10 Lifting and Shoring
Aircraft must often be raised from the hangar floor for weighing, maintenance or repair. There are several methods of doing this, however, and the maintenance manuals must be followed, during whichever method is used.
It is often necessary to lift only one wheel from the floor, to change a wheel or to service a wheel assembly or brake unit. For this type of jacking, some manufacturers have made provision on the undercarriage leg for the placement of a short hydraulic jack. When using this method, never place the jack under the brake housing or in any location that is not approved by the manufacturer.
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When jacking an aircraft asymmetrically, there is usually some movement by the other legs. Care must be shown, when jacking a single leg, that the aircraft is raised strictly in accordance with the maintenance manual.
Other places where a larger jack may be connected to the airframe might be:
Under the wings, at the main spar position
Under the nose
Under the tail assembly
On the side of the front fuselage (in place of the nose jack)
The location and operation of ALL jacks must be carried out both with great care and with the correct number of personnel, who must be well briefed.
Most of the larger jacks have a screw-type, safety locking collar, to prevent the jack collapsing in the event of a sudden leak. The jack operator must ensure that these safety collars are gradually screwed down, as the aircraft is being raised, so that they are very close to the jack body at all times.
As an additional precaution, especially if the aircraft is to be worked on for an extended period, trestles or ‘steadies’ can be installed under the wings and fuselage to augment the jacks and also to provide an additional means of shoring (supporting) the aircraft.
2.3.11 Slinging
It can be necessary, on occasions, to lift either the major components of an aircraft, such as wing or tail assemblies or the complete aircraft (refer to Fig. 2). For example, when recovering an aircraft from an ‘overrun’, it may be easier, and safer, to lift the entire aircraft and place it onto a hard standing, than to try and pull it out of soft ground, using a tug or similar vehicle.
When lifting either major components or an entire aircraft, the slings must be produced or approved by the manufacturer of the aircraft. The manufacturer’s slings ensure that the centre of gravity of the component, is always directly beneath the lifting hook of the sling.
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2.4 FLIGHT-LINE SAFETY
Many sources of accidents on the flight line are involved with propellers and rotor blades. They are difficult to see when they are turning, and personnel (despite being familiar with the hazards of propellers and rotors), sometimes become distracted and forget about the danger. The main difference between these, and other flight-line accidents, is that they are almost always fatal.
Most blades have high-visibility markings, to ensure that they can be seen when they are turning. These markings vary from a yellow blade tip marking, to black and white alternate stripes along the full blade length.
To reduce the risk of propeller and rotor blade strikes, it is best to follow strict rules as to the correct way to approach and leave the vicinity of an aircraft or helicopter whilst it is under power. For example (and allowing for the fact that there are specific rules laid down for each aircraft), installing and removing chocks should normally be done from the wing-tip direction. Boarding and leaving a helicopter should always be done from the side.
When dealing with running jet engines there are similar dangers. These come not only from the noise risk, which can result in deafness, but also from the risk of intake suction, which has resulted in ramp personnel being sucked into the engine and being killed. At the rear of the aircraft, there is the risk of jet blast, which, at maximum thrust is quite capable of overturning a vehicle if it passes too close behind the aircraft. (refer to Fig. 3). Piston-powered aircraft (depending on their size) will have similar danger areas.
Lifting an Aircraft with Slings Fig. 2
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2.4.1 Towing and Taxying
If an aircraft requires moving and no pilot is available, then a tug and towing arm must be used. This task will require a qualified tug driver, a supervisor, a ‘brake man’ and other personnel to keep a lookout. A qualified pilot always does the taxiing of larger aircraft, although engineers sometimes taxi light aircraft.
Each aircraft and its operator will have laid down rules regarding the way in which each aircraft will be towed. These rules will include the number of people needed, the type of tug, the radio calls if the aircraft is on the manoeuvring area, the maximum towing speed and many other details. These must always be followed if accidents are to be avoided.
Aircraft, when moving, either under power or whilst being towed, are sources of numerous risk areas. An airliner can be over 60 metres long and have a wing span greater than 60 metres. This means that when manoeuvring in restricted spaces, there is always the risk of part of the aircraft striking another object, due to a phenomenon known as ‘Swept Wing Growth’ (refer to Fig. 4).
It must be borne in mind that, when turning, the wing tips and tail of a large aircraft can move considerable distances in the opposite direction to that of the nose. This is why, whenever an aircraft is approaching its parking spot, there must be personnel available to watch out for any potential conflicts.
Driving in the vicinity of a parked aircraft must always be done with care, especially if the driver is alone or visibility from the cab of the vehicle is limited.
Typical Aircraft Danger Areas Fig. 3 50 40 30 20 10 0 Distance (metres)
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2.4.2 ParkingWhen an aircraft has to be parked for a period of time, especially overnight and in inclement weather conditions, there are a number of precautions that must be observed:
A chock must be placed at the front and rear of a number of wheels, depending on the aircraft type
The engine intakes and exhausts may need to be covered with special blanks
The control surfaces may have to be locked in place with integral control or gust locks or, if these are not installed, external locks may be attached to all of the surfaces that could be damaged in high winds
Other devices required could include blanks for the pitot tubes and static vents.
Wing Tip Sweep Area
Tail Sweep Area
Path of Wing Tip
Path of Tail Aircraft
Turning To Left
Swept Wing Growth Fig. 4
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2.4.3 MarshallingWhen marshalling an aircraft, it is essential that personnel are fully conversant with all the marshalling signals (refer to Fig. 5). It is also useful to know extra details such as:
The need for additional, ‘lookout’ men on the wing tips or tail
The correct place to stand to enable the aircraft’s crew to have sight of the marshaller
The point at which the aircraft is required to stop.
Some Basic Marshalling Signals for Fixed-Wing Aircraft Fig. 5
Come Ahead Stop Emergency Stop
Right Turn Left Turn All Clear (OK)
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2.4.4 FuellingWhile the topic of fuelling is covered more fully in Module 11 and in the relevant Chapter (28) of the Maintenance Manual, brief consideration of some of the general safety precautions is given here.
The first, obvious precaution, is the identification of the type of fuel in the fuel tanker (or bowser), ensuring it is of the type and grade required for the aircraft. There have been many times when petrol-powered aircraft have been filled with turbine fuel and, on occasions, the reverse has occurred.
The type and grade of fuel should always be stencilled or painted, adjacent to the fuelling point, but it is wise if a responsible person is consulted before starting fuelling. This is because there may be a requirement for some special fuel, or simply that the aircraft is only to be part-filled, due to a weight limitation.
The fuel tanker must be parked as far as possible from the aircraft, limited by the hose length, and parallel or facing away from it. This reduces the risk of fire passing from the aircraft to the tanker or vice versa, and also allows a clear path for the tanker to vacate the area quickly, should the need arise.
The fuel tanker, the fuelling hose, the aircraft and the ground must all be electrically bonded together, to allow the static electricity (generated during the fuel flow) to run to earth.
A safety zone of 6m (20 ft) should be established from the filling and venting points of the aircraft and attendant fuelling equipment. This area should be free from naked lights, smoking and the operation of electrical switches of any kind. There can also be a risk from the operation of radio and radar equipment, so these should also be switched off before fuelling commences.
Also, during the fuelling of aircraft, Auxiliary Power Units (APU) and Ground Power Units, (GPU), must be made safe, by checking that their exhausts and intakes are clear of any fuel vapours, and that GPU’s, are located as far as practical from the fuelling point(s).
NO switching of power from APU’s or GPU’s will be made during fuelling procedures.
There are many precautions involved when defuelling, due to the tanks being left empty of fuel, leaving potentially explosive vapours in its place.
ALL necessary safety precautions must be followed during aircraft fuelling procedures.
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2.4.5 Weather RadarThe heating and radiation effects of weather radar can be hazardous to life. Personnel should remain a safe distance from the radar if it is in operation. There are published figures and charts in the maintenance manual of each aircraft, showing the safe distances for personnel, depending on the power of the radar in use.
As an example, the aerial in the nose of the aircraft should have an unobstructed ‘view’ of something like 30 metres, with the aerial tilted upwards. There should also be a barrier erected about 3 metres or so from the nose of the aircraft, to prevent personnel getting too close.
Finally, there should be no fuelling operations in progress during the testing of weather radar.
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3
WORKSHOP PRACTICES
Despite the enormous advances in the mechanisation and computerisation of the engineering industry in general, there remains the requirement for a high degree of hand skills on the part of technicians who are engaged in the day-to-day maintenance of aircraft and their associated components.
While the majority of aerospace components are manufactured under stringent standards, in factory (and laboratory) conditions, it is necessary to remove many items of equipment for cleaning, inspection, overhaul and, if needed, repair before they are, subsequently, re-installed in their appointed locations.
These actions may entail the use of many specialist tools and materials, which are used while following written procedures, while it is quite possible that some, comparatively simple, repairs may call upon such basic hand skills as the cutting, filing, drilling, riveting and painting of metals or other materials.
No matter whether there are specialist or basic skills required, all will demand a certain quality of the work practices (and of the work-force) involved.
3.1 CARE OF TOOLS
Engineers are responsible for the maintenance of their personal tools, whilst other personnel, in designated Tool Stores, must care for all the different, specialist tools for which they have the responsibility. It is also the responsibility of engineers to ensure that any tools, or other items of equipment they use, are not left in an aircraft or associated components.
The care required for different tools can vary. Ordinary hand tools may merely require racking or locating within sturdy tool boxes, with careful, daily, maintenance restricted to little more than a visual check.
Precision instruments however, require great care both in storage and in use. They may need to be kept in special, soft-lined, boxes within other storage facilities. Prior to use they should have a ‘zero’ check or calibration. Some tools require that they have a light coating of machine oil, to prevent the onset of corrosion.
Each tool (whether it be a hammer or a micrometer), will require some special care, to ensure its optimum performance for, without this care, even the most expensive tools very quickly become second rate and useless.
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3.2 CONTROL OF TOOLSControl of tools is important to good engineering practices and is also vital to flight safety. A variety of systems can be used to control tools but, whichever system is used, it must allow a 100% check of the tools in use before it can be considered as acceptable.
One form of control is the ‘shadow board’ and ‘tool tag’ system, (refer to Fig. 6). Each tool is positioned over its silhouette, on the tool board. Technicians are issued with identification tokens (numbered ‘tags’) which are exchanged for the tool and, usually, a tag is hung above the silhouette, to be reclaimed, in exchange for the tool, when it is returned to the board. The shadow board/tool tag system works equally well when the tools are held within a designated Tool Store arrangement.
In workshops and bays it is normal for a toolkit to be held by the department in addition to its engineers holding personal sets of tools. The tools held by the department are often referred to as ‘special tools’, meaning that they are only for maintenance work on the items being serviced in that workshop.
A wheel bay, for example, may have sets of special spanners, levers, seal applicators and pre-set torque wrenches, which are used primarily for the servicing of particular types of aircraft wheels. This dedicated tool kit makes tool control much simpler and safer, with the tools all being clearly marked as belonging to that specific bay.
Shadow Board and Tool Tag Fig. 1
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No matter where tools are being used, it is the responsibility of each technician to keep track of ALL of the tools used during a particular task. The most important check of all is the final, ‘End of Work’ tool check, when all tools must be collected and checked off against personal inventories, ensuring all borrowed tools (from the Tool Store for example), are returned and any personal tool tags collected.
3.3 CALIBRATION OF TOOLS AND EQUIPMENT
Requirements within the relevant airworthiness codes, applicable to the United Kingdom Civil Aviation Industry, such as the British Civil Aviation Requirements (BCARs), Joint Aviation Requirements (JARs), and Air Operators Certificates, prescribe that, where necessary, tools, equipment and, in particular, test equipment are all calibrated to acceptable standards.
This topic provides an overall picture of the types of requirements and tests required in establishing and maintaining an effective calibration system. It takes into account factors such as the degree of accuracy required, frequency of use and the reliability of the equipment.
The key factor is the need to establish confidence in the accuracy of the equipment when it is required for use. The required calibration frequency for any particular piece of test equipment is that which will ensure it is in compliance with the standards applicable to its intended use. In all cases, standards used are attributed upon the need for ultimate traceability to one of the following:
The standard specified by the equipment manufacturer/design organisation
The appropriate National/International Standards. 3.3.1 General Notes on Calibration
The appropriate standards are used to achieve consistency between measurements made in different locations, possibly using alternate measuring techniques. The calibration of test equipment is best achieved by the operation of a methodical system of control.
This system should be traceable by an unbroken chain of comparisons, through measurement standards of successively better accuracy up to the appropriate standard. Where recommendations for calibration standards are not published, or where they are not specified, calibration should be carried out, in the UK, in accordance with British Standard EN 30012-1: Quality Assurance Requirements for Measuring Equipment.
As an alternative to operating an internal Measurement and Calibration System, an Approved Organisation or an Approved/Licensed Engineer may enter into a sub-contracting arrangement to use an Appliance Calibration Service. This arrangement does not absolve the contractors of the service from maintaining standards as if they were carrying out the work themselves.
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In all instances, it is the responsibility of the user to be satisfied that the unbroken traceability chain is in place. External organisations, which supply an external Calibration Service, should be those holding accreditation of the National Accreditation of Measurement and Sampling, (NAMAS).
3.3.2 Procedures
The definition of appliances requiring calibration are those items which are necessary to perform measurements or tests of an aircraft, a system or a component, to defined limits, as specified in the technical documentation of the Type Certificate holder.
Procedures, controlling regular inspection, servicing and, where appropriate, calibration of such items, are to indicate to the users that the item is within any inspection time limit. These ‘Next Inspection’ labels must clearly state when, and, if necessary, where the next calibration is due.
There should be a programme that plans the periodic inspection, service or calibration within the defined time limit, which ensures that the item remains in calibration. It is common sense to stagger the calibration of items, so that the largest number are available for use at all times. It is also important, that a register of all items requiring calibration is held, so that cross-checking can be simply carried out. Where a small number of particular items are held, then contract loan of equipment is permitted.
The intervals at which calibration is required, can vary with the nature of the equipment, the conditions under which it is used and the consequences of incorrect results. The frequency will be in accordance with the manufacturer or supplier’s instructions, unless the organisation can show that a different interval is warranted in a particular case. This would normally require a system of continuous analysis of calibration results to be established, to support the variation to the recommended calibration intervals.
Any appliance, the serviceability of which is in doubt, should be removed from service and clearly labelled accordingly. The appliance must not be returned to service unless the reason for its unserviceability has been eliminated and its continued calibration re-validated. Action must be taken, if an item of equipment is found, during calibration, to have a significant error. This must include re-checking of measurements made prior to finding the fault.
The scope of the records maintained, are dependent upon the standards required and the nature of the equipment. The record system can also provide a valuable reference in case of dispute or warranty claims. These records can also indicate ‘drift’ and can help in reassessing calibration intervals.
JAR 66 CATEGORY B1 MODULE 7 MAINTENANCE PRACTICES (MECHANICAL)
uk
engineering
Calibration records or certificates should, as a minimum, contain the following information for each appliance calibrated:
Identification of equipment
Limits of permissible error
Standard used
Authority under which the document was issued
Results obtained
Any limitation of use of equipment
Uncertainty of measurement
Date when each calibration was conducted
Assigned calibration interval.
Where calibration services are provided by outside organisations, it is acceptable that the accuracy of the equipment is attested by a release document in the name of the Calibration Company.
Any measurement is affected, to some degree, by the environment in which it is made. The equipment will need to be calibrated, transported and stored under conditions compatible with the type of equipment, to ensure its accuracy is not impaired.
To provide valid and repeatable test results, the facilities used for calibration must have a controlled environment. It is necessary to control the temperature, humidity, vibration, dust, cleanliness, electromagnetic interference, lighting and other factors that may affect the standard of the results. If any of these requirements cannot be met, then compensation corrections must be applied to the calibration standard to ensure continued accuracy.
A measurement Checking Standard can be applied, at the work place, to check the accuracy of an appliance and to ensure its continued correct functioning. The Checking Standard will be robust and its accuracy will not match that of a full calibration check, but it will give confidence between checks that the equipment is functioning correctly.
The company Quality System has the responsibility of ensuring the continued accuracy, not only of the items of equipment, but also of the actual testing facilities.
