This document provides an overview of airframe maintenance and repair. It discusses the objectives of airframe repair which are to restore damaged parts to their original condition in terms of strength, contour, weight and shape. It also describes different types of damage classification and non-destructive inspection methods. Guidelines for rivet repair design and different types of welding, joints, and inert gas arc welding are explained. Maintenance of electric resistance welding equipment, composites inspection and rigging of aircraft and helicopter flight controls are also summarized.

1. AIRFRAME MAINTENANCE AND REPAIR
By
Sivasankar G A
Assistant Professor
Department of Aeronautical
KIT Kalaignar Karunanidhi Institute of Technology

2. OBJECTIVE OF AIRFRAME REPAIR:
THE PRIMARY OBJECTIVE OF AIRFRAME REPAIR IT TO RESTORE THE
DAMAGED PARTS TO THEIR ORIGINAL CONDITION.
IF DAMAGED PART CAN BE REPAIRED ITS PURPOSE OR FUNCTION MUST BE
FULLY UNDERSTOOD .
1.TO RESTORE TO ORIGINAL STRENGTH
2.ORIGINAL CONTOUR
3.MINIMUM WEIGHT
4.ORIGINAL SHAPE

3. DAMAGE CLASSIFICATION:
•NEGLIGIBLE DAMAGE
•PATCH REPAIRABLE DAMAGE
•DAMAGE REPAIR BY INSERTION
•DAMAGE REQUIRING REPLACEMENT

4. NON DESTRUCTIVE INSPECTION(NDI):
1.VISUAL INSPECTION
2.DYE PENETRANT INSPECTION
3.FLUORESCENT PENETRATION INSPECTION
4.MAGNETIC PARTICLE INSPECTION
5.RADIOLOGICAL (X RAY) INSPECTION
6.EDDY CURRENT INSPECTION

5. GUIDELINES FOR RIVET REPAIR DESIGN:
1.RIVET REPLACEMENT
2.RIVET DIAMETER
3.RIVET SPACING
4.REPAIR WIDTH
RIVET REPAIR DESIGN:(GENERAL,APPLIED,CALCULATED)
1.DETERMINATION OF THE RIVET DIAMETER
2.DETERMINATION OF NUMBER OF RIVETS
3.DETERMINATION OF RIVET SPACING AND LAYOUT

6. WELDING
WELDING IS A PROCESS USED FOR JOINING METAL PARTS BY
EITHER FUSION OR FORGING.
TYPES
FORGE WELDING
FUSION WEDING
TYPES OF FUSION WELDING:
•OXYACETYLENE WELDING
•ELECTRIC ARC WELDING
•ELECTRIC RESISTANCE WELDING
•INERT GAS ARC WELDING

7. INERT GAS ARC WELDING:
TYPES:
1.TUNGSTEN INERT GAS WELDING(TIG)
TIG USES TUNGSTEN ELECTRODE WHICH IS NON COSUMABLE
2.METAL INERT GAS WELDING(MIG)
MIG USES METAL ELECTRODE WHICH IS CONSUMABLE
3.PLASMA ARC WELDING
PLASMA ARC WELDING THE GAS GETS IONIZED AFTER THE
PASSAGE OF ELECTRIC CURRENT.THIS RESULTS IN HIGH
TEMPERATURE.

8. TYPES OF WELD JOINTS:
•BUTT JOINTS
•TEE JOINTS
•LAP JOINTS
•EDGE JOINT
•CORNER JOINTS
•FLANGE BUTT JOINTS

11. Welding Jigs.
Welding jigs are specialized devices which enable the
components to be easily and rapidly setup and held.
Jigs are stationery while fixtures rotate usually on trunions
about vertical and horizontal axis.
It should be
1. rigid and strong to stand without deforming.
2. simple to operate, yet it must be accurate.
3. Designed such that it is not possible
to put the work in it in the wrong way.
4. Faced with wear resistant material to stand continual wear.

12. Welding Fixtures
A welding fixture serves the same purposes as
welding jig, but in addition, it permits the changing
of the position during actual welding so as to place the welds in plane convenient
to the operator at all times. This increases welding speed
Characteristics
Supporting, clamping grounding, imparting movement
Fixture classification
Those that act on the work being welded
Those that act on the welding equipment

13. Maintenance of Electric resistance welding eqpt
Weekly
•Inspect electrical connections
•Clean electrode holders and exterior.
•Clean transformer with low pr hose
•If noisy stop operation &tighten bolts.
Monthly
•Flush cooling system to wash out dirt and rust particles
•Check air system for leaks and faults,valves
•Clean cables,sockets,swtiches
•Tighten loose electrical connections, replace worn wires and insulation

14. Three monthly/Quarterly
1.Check cooling hoses for rust and
damage
2.Run a test on sequencer timer using
oscilloscope
3.Inspect entire air system
Annually
1.Clean transformer with secondaries
2.Replace the hoses of air if reqd
3.Clean machining cabinet and paint if
necessary
4.Check excess wear in all moving parts.
5.Clean controls
Consult manufacturer in case of doubts

15. ELCETRIC ARC WELDING –DC
WEEKLY
MONTHLY
YEARLY
GAS WELDING
DAILY
MONTHLY

16. • The main source of synthetic plastics is
crude oil.
• Coal and natural gas are also used.
• Petrol, paraffin, lubricating oils and high
petroleum gases are bi-products,
produced during the refining of crude oil.
• These gases are broken down into
monomers. Monomers are chemical
substances consisting of a single
molecule.
• A process called Polymerisation occurs
when thousands of monomers are linked
together. The compounds formed as
called polymers.
• Combining the element carbon with one
or more other elements such as oxygen,
hydrogen, chlorine, fluorine and nitrogen
makes most polymers.

17. ADVANTAGE OF PLASTICS
1.PLASTICS ARE USED IN PLACE OF GLASS FOR WINDOWS BECAUSE
THEY ARE LIGHT IN WT AND NO REDUCTION IN CLARITY.
2.RESISTANT TO BREAKING THAN GLASS.
3.POOR CONDUCTOR OF HEAT AND PROVIDES SOME LEVEL OF
THERMAL INSULATION.

18. Thermosetting
Thermosetting plastics are plastic compounds that require application
Of heat to set up properly or harden.
Once these materials have set ,further appn of heat does not allow them
to be formed in a controllable manner. Any further heating normally
Results in deformation or structural weakening. It is permanently hardening.
It hardens permanently after one application of heat and presure.
The molecules of thermosetting plastics are heavily cross linked.They form a
Rigid molecular structure.
Ex.
Bakelite,melamine resign,polymer resign,epoxy resign

19. • The molecules of thermosetting plastics are heavily
cross-linked. They form a rigid molecular structure.
• The molecules in thermoplastics sit end-to-end and
side-by-side.
• Although they soften when heated the first time, which
allows them to be shaped they become permanently stiff
and solid and cannot be reshaped.
• Thermoplastics remain rigid and non-flexible even at
high temperatures. Polyester resin and urea
formaldehyde are examples of thermosetting plastics.
Cross-linked molecules

20. THERMOPLASTICS
IT HAS THE PROPERTY OF SOFTENING WHEN HEATED AND HARDENING
AND BECOMING RIGID AGAIN WHEN COOLED.THEMOPLASTIC CAN BE
REMELTED AND COOLED TIME AFTER TIME WITHOUT UNDERGOING ANY
APPRECIABLE CHEMICAL CHANGE.
1.WHEN HEATED MOLECULES MOVE APART WHICH INCREASES THE
DISTANCE BETWEEN THEM,BECOMING UNTANGLED.
THIS ALLOWS TO BECOME SOFT WHEN HEATED SO THAT THEY CAN BE
BENT TO ALL TYPE OF SHPES.
2.THE PROCESS OF HEATING,SHAPING,REHEATING AND REFORMING
CAN BE REPEATED MANY TIMES.
3.THERMOPLASTICS ARE THEREFORE RECYCLABE.
Eg TEFLON,POLYCARBONATE,POLYSTER,POLYETHYLENE,POLYVINYL
CHLORIDE.

21. • There are a wide range of
thermoplastics, some that are rigid and
some that are extremely flexible.
• The molecules of thermoplastics are in
lines or long chains with very few
entanglements. When heat is applied the
molecules move apart, which increases
the distance between them, causing
them to become untangled. This allows
them to become soft when heated so that
they can be bent into all sorts of shapes.
• When they are left to cool the chains of
molecules cool, take their former position
and the plastic becomes stiff and hard
again. The process of heating, shaping,
reheating and reforming can be repeated
many times.
Long chain molecules

22. • Plastic are easily formed materials.
• The advantage to the manufacturer is that plastic products can be
mass-produced and require less skilled staff.
• Plastics require little or no finishing, painting, polishing etc. Plastic is
referred to as a self-finishing material. Particular finishes can be
achieved at relatively low cost.
• Plastics can be easily printed, decorated or painted.
• Plastics are corrosion resistant, and generally waterproof although
certain types of plastics such as UPVC can become brittle and it is
possible for the sun’s rays to cause the colour of the plastic to fade. It
becomes bleached.
• Plastics are lighter than metals, giving deeper sections for a given
weight, and hence stronger sections.

23. • It was first used to
make aircraft
canopies. It is ten
times more impact
resistant than glass.
• Image: Perspex top of
a container

24. TYPES OF CLEAR PLASTICS:
1.ACRYLICS
2CELLULOSE ACETATES
CEMENTING OF PLASTICS:
MANY THERMOPLASTICS CAN BE FASTENED TOGETHER TO FORM
STRONG BONDS USING CHEMICAL ADHESIVES OR SOLVENTS.
ANNEALING OF PLASTICS:
PURPOSE:
1.IT RELIVES INTERNAL STRESSES.
2.PROVIDES GREATER DIMENSIONAL STABILITY
3.IT IMPROVES PLASTIC RESISTANCE TO CRAZING

25. COMPOSITE INSPECTION(NDI)
1. ACOUSTIC EMISSION
2. HOLOGRAPHY
3. ULTRASONICS
4. X AND N RAYS
5. THERMOGRAPHY
6. RING TESTS

26. RIGGING:
IT IS ALIGHNMENT OF AIRCRAFT PARTS OR SECTIONS TO OBTAIN
PROPER FLIGHT CHARACTERISTICS.A CERTAIN AMOUNT OF RIGGING
IS NECESSARY DURING THE ASSEMBLY OF AN AIRCRAFT AND AFTER
FINAL ASSEMBLY.THERE IS OVERLAP BETWEEN THE ASSEMBLY
OPERATION AND RIGGING OPERATION.

27. HELICOPTER FLIGHT CONTROLS
IT CONTROLS:
1.MOVEMENT ABOUT THE THREE AXES OF THE AIRCRAFT
2.THE ENGINE POWER
3.THE ROTOR SYSTEM LIFT.
THE CONTROL CONSISTS OF CYCLIC CONTROL,ANTITORQUE
CONTROLS,THROTTLE AND COLLECTIVE CONTROL

28. RIGGING OF HELICOPTERS
MAIN ROTOR IS CONTROLLED BY TWO PRINCIPAL SYSTEMS,
THE COLLECTIVE PITCH CONTROL AND CYCLIC PITCH CONTROL
THE COLLECTIVE PITCH CONTROL CHANGES PITCH ON ALL BLADES
OF THE MAIN ROTOR SIMUTANEOUSLY.COLLECTIVE PITCH IS ADJUSTED
BY RAISING OR LOWERING THE COLLECTIVE PITCH LEVER.
THE CYCLIC PITCH CONTROL IS EMPLOYED TO CHANGE THE PITCH
OR ANGLE OF THE PLANE OR DISK THROUGH WHICH THE MAIN ROTOR
BLADES ROTATE.
THE DIRECTION IN WHICH A HELICOPTER IS POINTED IS CONTROLLED
BY THE ANTITORQUE ROTOR(TAIL ROTOR)

29. TRACKING AND BALANCING THE MAIN ROTOR
TRACKING OF A HELICOPTER ROTOR MEANS DETERMINING IF ONE
BLADE FOLLOWS THE PATH OR TRACK OF THE OTHER BLADE OR BLADES
AS THEY ROTATE DURING OPERATION.TWO PRICIPAL METHODS OF
ROTOR TRACKING ARE
1.STROBOSCOPIC LIGHT TRACKING
2.FLAG TRACKING
THE ELECTRONIC EQUIPMENT USED IS VIBREX TRACK AND BALANCE
SYSTEM.IT IS USED TO CORRECT TRACK AND BALANCE BY DEVELOPING
DATA IN THE FLIGHT THROUGH THE USE OF ACCELEOMETERS AND
STROBOSCOPIC LIGHTS.THE SIGNALS FROM THESE DEVICES ARE
REFERED ROTOR POSITION BY MEANS OF MAGNETIC PICK UP
AND INTERRUPTER SYSTEM.

30. FLAG TRACKING METHOD:
IN THIS METHOD A TRACKING FLAG IS CONSTRUCTED FROM
ALUMINIUM OR STEEL TUBING. THE FLAG PORTION SHOULD
BE MADE OF STRONG,LIGHT WEIGHT FABRIC TAPE.
THE REINFORCING TAPE USED IN AIRCRAFT FABRIC WORK
IS A SUITABLE MATERIAL.THE MAIN ROTOR BLADE TIPS ARE COLORED
WITH GREASE PENCILS,USING A DIFFERENT COLOUR ON
EACH TRIP.

31. INSPECTION AND MAINTENACE OF LANDING GEAR
A THROUGH INSPECTION OF LANDING GEAR INVOLVES THE
CAREFUL EXAMINATION OF THE ENTIRE STRUCTURE OF THE
GEAR ,INCLUDING THE ATTACHMENTS TO THE FUSELAGE
OR WING,STRUT,WHEELS,BRAKES,ACTUATING ,MECHANISM,
FOR RETRACTABLE GEAR,GEAR HYDRAULIC SYSTEM AND
VALVES,GEAR DOORS,AND ALL ASSOCIATED PARTS.
1.FIXED GEAR INSPECTION
2.INSPECTION OF RETRACTABLE LANDING GEAR

32. INSTALLATION AND MAINTENANCE OF INSTRUMENTS
THE INSTALLTION OF INSTRUMNET REQUIRES THAT THEY BE MOUNTED
TO A METAL INSTRUMENT PANEL OR SUBPANEL.
REGARDLESS OF THE TYPE OF MOUNT ,THE INSTALLATION
SHOULD ALLOW THE PILOT OR CREW MEMBER TO CLEARLY VIEW
THE INSTRUMENT FROM A NORMAL FLIGHT POSITION.THE INSTALLATION
SHOULD CAUSE A MINIMUM OF OPERATIONAL INTERFERENCE WITH
CONTROL SYSTEMS AND OTHER INSTRUMENTS.
INSTRUMENT SHOULD BE CHECKED FOR PROPER OPERATION,CONDITON
AND PLACEMENT OF RANGE MARKINGS,CONDITION OF CASES,
CLEANLINESS OF CASE VENT FILTERS,
SECURITY OF MOUNTING,AND TIGHTNESS OF TUBE AND ELECTRICAL
CONNECTIONS.
GYRO INSTRUMNETS SHOULD BE CHECKED FOR GYRO ERECTION TIME
AND UNUSUAL NOISE DURING OPERATION.

33. INSPECTION AND MAINTENACE OF FIRE PROTECTION SYSTEMS
MECHANICAL PARTS ARE EXAMINED FOR THE DAMAGE,WEAR,
SECURITY OF MOUNTING AND COMPLIANCE WITH TECHNICAL AND
REGULATORY REQUIREMENTS.ELECTRICAL CONTROL SYSTEM
ARE INSPECTED IN ACCORDANCE APPROVED PRACTICES.
CONTINUITY OF ELECTRICAL CIRCUITS
MAY BE TESTED.

34. INSPECTION AND MAINTENANCE OF ICE PROTECTION SYSTEM
THE INSPECTION OF PNEUNATIC MECHANCIL DEICER SYSTEMS
REQUIRE AN EXAMINATION OF THE DEICER BOOTS FOR CONDITION,
ADHERENCE TO THE PROTECTED SURFACE AND CONDITION OF THE
SURFACE OF THE BOOTS.
DURING INSPECTION AND MAINTENACE THE TECHNICIAN
SHOULD DETERMINE WHETHER THE CONDUCTIVE COATING
IS INTACT AND EFFECTIVE.
OPERATIONAL TESTS ARE PERFORMED AS SPECIFIED IN
APPROPRIATE INSTRUCTIONS.THE INFLATION OF THE
TUBES IN THE BOOTS CAN BE EASILY BE OBSERVED.

35. TROUBLESHOOTING
TROUBLE SHOOTING IS THE PROCESS OF IDENTIFYING THE
CAUSE OF A MALFUNTION DETERMINING ITS SEVERITYH,ELIMINATING
THE CAUSE,REPLACING OR REPAIRING DISCREPANT
COMPONENTS,SYSTEMS ,OR STRUCTURES AND FINALLY
RETURNING THE AIRCRAFT TO SEVICE.
THE ULTIMATE OBJECT OF TROUBLESHOOTING IN
AVIATION IS TO RETURN AIRCRAFT TO AN AIRWORTHY
CONDITION OFFERING A HIGH PROBABILITY THAT THE MALFUNCTION
OR DISCREPANCY WILL NOT RECUR.
TROUBLE SHOOTGING IS MORE THAN JUST REPLACING
MALFUNCTIONING COMPONENT OR MAKING A REPAIR.
1.THE FIRST STEP IN TROUBLESHOOTING IS TO IDENTIFY THE TRUE
CAUSE OF THE DISCREPANCY.

36. 2.THE SECOND STEP IN THE TROUBLESHOOTING PROCESS IS
TO EVALUATE THE REPORTED DICREPANCY TO DETERMINE IF IT HAS
AN ADVERSE EFFECT UPON THE AIRCRAFT AIRWORTHINESS.
3.THE THIRD STEP CORRECTIVE ACTION MUST BE TAKEN BEFORE
ITS NEXT FLIGHT.
TROUBLE SHOOTING CHARTS DESIGNED TO HELP
THE TECHNICIAN IDENTIFY FAILED COMPONENTS.

37. VALIDATION OF TROUBLESHOOTING RESULTS.
THE FINAL STEP IN THE TROUBLESHOOTING PROCESS
IS THE VALIDATION THAT THE ANALYTICAL STEPS OF THE
TROUBLSHOOTING PROCESS WERE PROPERLY INTERPRETED.
THIS OFTEN RESULTS IN THE NECESSITY FOR SOME TYPE OF
OPERATIONAOL CHECK.THE PROCEDURES FOR SUCH A CHECK
SHOUOLD BE SPECIFIED IN
THE AIRCRAFT MAINTENANCE MANAUL.
WHEN OPERATIONALLY CHECKING INTERMITTENT DISCRPANCIES,
THE CHECK NEEDS TO INCLUDE THE SUPECTED CAUSES.

38. HAZARDOUS MATERIALS
THE AVIATION MAINTENANCE TECHNICIAN FREQUENTLY MUST
WORK IN POTENTIALLY DANGEROUS ENVIRONMENTS.
THE TECHNICIAN MAY NOT AWARE HE IS WORKING
WITH HAZARDOUS MATERIALS.
THREE CATEGORIES.
1.CHEMICAL AGENTS
2.PHYSICAL AGENTS
3.BIOLOGICAL HAZARDS.

39. CHEMICAL AGENTS
FACTOR STANDS FOR
FLAMMABLE
AND
CORROSIVE
TOXIC
OR
REACTIVE

40. FLAMMABLES AND COMBUSTIBLES
FLAMMABLES ARE MATERIAL THAT MAY EASILY
IGNITE IN THE PRESENCE OF CATALYST SUCH AS HEAT ,
SPARKS,OR FLAME.THEY MAY IN THE FORM SOLID,LIQUID,
OR GAS.COMBUSTIBLE LIQUIDS ARE VERY SIMILAR TO
FLAMMABLE LIQUIDS,BUT THEY ARE NOT AS EASY TO IGNITE.
THESE MATERIAL IN AVIATION INDUSTRY
INCLUDE FUELS,PAINT RELATED PRODUCTS,ALCOHOLS,
ACETONE,TOLUENE .

41. PERSONAL SAFETY EQUIPMENT
1.FIRE RETARDANT CLOTHING
2.FIRE EXTINGUISHER
HANDLING AND STORAGE
1.LIMIT ACCESS TO OPEN FLAMES,SPARKS,HOT SURFACES ETC
2.LIMIT QUANTITY REQUIRED TO THE MINIMUM
3.STORE IN THE APPROVED CONTRAINERS AND DESIGNATED AREAS
ONLY.
4.STORE FLAMMABLE TOXINS AND CORROSIVE TOXIC MATERIALS
SEPARATELY.

42. TOXINS
TOXINS ARE GENERALLY DEFINED AS ANY SUBSTANCE
THAT CAN CASUSE AN ILLNESS OR INJURY.
EIGHT CATEGORIES OF TOXINS.
1.SOVENTS AND THINNERS FOR PAINTS,KETONES AND ADHESIVES.
2.SOLIDS SUCH AS METAL DUST OR ASBESTOS.
3.MACHINE LUBRICANTS,CUTTING FLUIDS AND OILS
4.POLYMERS,EPOXIES AND PLASTICS
5.GASES SUCH AS CARBON DIOXIDE OR NITROGEN.
6.SENSITIZERS SUCH AS EPOXY SYSTEMS.
7.CARCINOGENS
8.REPRODUCTIVE HAZARDS

43. PHYSICAL HAZARDS
THESE HAZARDS INCLUDE X RAY,MICROWAVES,BETA OR GAMMA
RAYS,INVISIBLE LASER BEAMS AND HF SOUND WAVES
BIOLOGICAL HAZARDS
BIOLOGICAL HAZARDS ARE LIVING ORGANISMS THAT CAUSE
ILLNESS OR DISEASE.SPREAD THROUGH AIR DROPLETS OR SPORES
AND ENTER THE BODY THROUGH CONACT.eg cargo aircraft/baggage