Aircraft Metal Structure

Aircraft Metal StructureAircraft Metal Structure

Light Alloy RepairLight Alloy Repair

P10P10

Write a short report describing Write a short report describing the repair theory for a simple the repair theory for a simple light alloy riveted repair light alloy riveted repair carried out to national carried out to national standardstandard

Contents:Contents:

• Identification of damage.Identification of damage.

•Use of technical documentations.Use of technical documentations.

•Selection of materials and Rivets.Selection of materials and Rivets.

•Tools required.Tools required.

• Inspections of repair.Inspections of repair.

•Relevant legislations and guide Relevant legislations and guide lines.lines.

There are eight major zones for the aircraft. Each major zone is identified by the first digit of a three digits number.

The even numbers identify the zones on the right hand side of the aircraft, while odd numbers identify the zones on the left hand side of the aircraft.

The aircraft structure is divided according to the ATA 100 specifications.

WaterlineWaterline – – is the measurement of the is the measurement of the height perpendicular from a horizontal height perpendicular from a horizontal plane located below the bottom of plane located below the bottom of the aircraft fuselage.the aircraft fuselage.

Station Numbers:Station Numbers:Buttock line or Butt line (BL) Buttock line or Butt line (BL) - - is a is a width measurement left or right of, width measurement left or right of, and parallel to, the vertical centre and parallel to, the vertical centre line.line.

Aircraft Structure and Aircraft Structure and MaintenanceMaintenance

Each major part of the aircraft receives a section number.

The fuselage section base number is 10.

The fuselage is divided into various sections for manufacturing

Reasons.

Section Numbers:Section Numbers:

Aircraft Structure and Aircraft Structure and MaintenanceMaintenance

Sections 41 - 43 - 46 - 48Sections 41 - 43 - 46 - 48

Section Numbers:Section Numbers:

The station number is the distance in centimetres of a cross-section from a reference point.

Station Numbers:Station Numbers:

Station Numbers:Station Numbers:

Technical Documentation:Technical Documentation:

• Aircraft maintenance Manuals (AMM Aircraft maintenance Manuals (AMM or MM)or MM)

• Aircraft Structural Repair Manual Aircraft Structural Repair Manual (SRM)(SRM)

• Civil Aircraft inspection Procedures Civil Aircraft inspection Procedures (CAIP) and other guidance (CAIP) and other guidance documents.documents.

How to use an Aircraft Structural Repair Manual How to use an Aircraft Structural Repair Manual (SRM)(SRM)

• Find the location of the damage.Find the location of the damage.

• water line and station number.water line and station number.

• Nearest frame number and stringer Nearest frame number and stringer number.number.

• Extent of damage: negligible, repairable Extent of damage: negligible, repairable or discard.or discard.

• Method of repair.Method of repair.

Strip the paint away assumingStrip the paint away assuming the aircraft is paint.the aircraft is paint.

With the paint removed it could With the paint removed it could evident that the scratch mayevident that the scratch mayhave only been in the painthave only been in the paint

and not in the aircraft.and not in the aircraft.Use Dye Penetrant to Use Dye Penetrant to

confirm the damage, crackconfirm the damage, crackor scratch etc.or scratch etc.

Determine the Extent of the Damage:Determine the Extent of the Damage:


Measure the depth (DTI) Measure the depth (DTI) width and length width and length vernier calliper.vernier calliper.Check with the Check with the

Structural Repair Manual Structural Repair Manual (SRM)(SRM)

if the damage is if the damage is allowable allowable

or within tolerance.or within tolerance.NB a scratch will haveNB a scratch will have

to have its sharpto have its sharpedges removed prior toedges removed prior to

measuring.measuring.

Allowable Damage:Allowable Damage:

Example :Example :From B737-300From B737-300

Structural Repair Structural Repair ManualManual


If the damage is allowable or within tolerance according to the If the damage is allowable or within tolerance according to the Structural Repair Manual (SRM) annotate the Aircraft Structural Repair Manual (SRM) annotate the Aircraft

Technical Log Book damage chart stating.Technical Log Book damage chart stating.

Permanent Repair - Interim Repair - Time-Limited Permanent Repair - Interim Repair - Time-Limited RepairRepair

This will prevent the damage being continually being found by This will prevent the damage being continually being found by other people.other people.

All damage must be classified to determine what All damage must be classified to determine what repair action repair action

should be taken.should be taken.

Ultimately, all discrepancies will be placed into one of Ultimately, all discrepancies will be placed into one of three three

categories, negligible damage, non-repairable damage categories, negligible damage, non-repairable damage or or

repairable damage.repairable damage.

Damage Classification:Damage Classification:

Negligible damage is damage that can be Negligible damage is damage that can be permitted to exist permitted to exist

“ “as is,” or corrected by a single cosmetic as is,” or corrected by a single cosmetic refinishing procedure refinishing procedure

with no restrictions on flight operations.with no restrictions on flight operations.

This damage may also include some de-This damage may also include some de-lamination, disbonds lamination, disbonds

and voids. and voids.

Negligible Damage:Negligible Damage:

Non-repairable damage exceeds published criteria or limits.Non-repairable damage exceeds published criteria or limits.(Structural Repair Manual)(Structural Repair Manual)

Non-repairable damage may be reclassified as repairable, if Non-repairable damage may be reclassified as repairable, if

the manufacturer prescribes a repair on an individual basis.the manufacturer prescribes a repair on an individual basis.

Normally, non-repairable damage requires the changing Normally, non-repairable damage requires the changing of components.of components.

Non-repairable Damage:Non-repairable Damage:

Repairable damage is any damage to the skin or structure that Repairable damage is any damage to the skin or structure that

cannot be allowed to exist “as is” without placing performance cannot be allowed to exist “as is” without placing performance

restrictions on the airframe. restrictions on the airframe.

Repairable Damage:Repairable Damage:

Hail Storm Damage:Hail Storm Damage:

Replacement of Replacement of Leading Edge Panel?Leading Edge Panel?

It will take more then It will take more then speed-tape to fix this one.speed-tape to fix this one.

Lighting Strike:Lighting Strike:

Bird Strike:Bird Strike:

Aerodynamic Smoothness Requirements:Aerodynamic Smoothness Requirements:

Fuselage limitations on repairs inFuselage limitations on repairs in

region of static pressure ports, region of static pressure ports,

pitot-static probes, angle of pitot-static probes, angle of

airflow sensors.airflow sensors.

Wing, ailerons, stabilizers, Wing, ailerons, stabilizers,

elevators rudder, flats, leading elevators rudder, flats, leading

edge slats, spoilersedge slats, spoilers

Nacelle and PylonNacelle and Pylon

Patch RepairPatch Repair

Repairs:Repairs:

Insert RepairInsert Repair

Restore the structural integrity ofRestore the structural integrity of

the airframe. the airframe.

Typical Skin Repair:Typical Skin Repair:

It is permitted for some types It is permitted for some types of crack repair to drill a hole at of crack repair to drill a hole at

the end of each end of the crack the end of each end of the crack to prevent it from extending any to prevent it from extending any

Further.Further.

Crack Propagation:Crack Propagation:

Complex repair for a Boeing 737Complex repair for a Boeing 737door aperture crack in the bottom door aperture crack in the bottom

corner.corner.

This includes multi external repair This includes multi external repair plates and the crack is stop drilled.plates and the crack is stop drilled.

Repairs:Repairs:

Spacing and Edge Distance Rivet spacing, Spacing and Edge Distance Rivet spacing, also referred as rivet pitch, is the distance also referred as rivet pitch, is the distance between the rivets in the same row and is between the rivets in the same row and is measured from the rivet centre to the rivet measured from the rivet centre to the rivet

centre.centre.

Metallic Repairs on Aircraft Structure:Metallic Repairs on Aircraft Structure:

Riveting Terminology:Riveting Terminology:

Metallic Airframe Metallic Airframe StructuresStructures

‘‘A’A’Edge distance for all rivets, except Edge distance for all rivets, except those with a flush head, should not those with a flush head, should not be less than twice the diameter of be less than twice the diameter of the rivet shank or more than four the rivet shank or more than four

times the diameter of the rivet shank. times the diameter of the rivet shank.

Flush-head rivets require an edge Flush-head rivets require an edge distance of at least 2½ times the distance of at least 2½ times the

diameter.diameter.



‘‘B’B’Rivet pitch, is the distance Rivet pitch, is the distance

between the rivets in the same between the rivets in the same row and is measured from the rivet row and is measured from the rivet

centre to the rivet centre.centre to the rivet centre.



‘‘C’C’Transverse pitch is the distance Transverse pitch is the distance

between the rows of rivets and between the rows of rivets and

is measured from the rivet centre is measured from the rivet centre

to rivet centre.to rivet centre.



1 ½ x D + G = L 1 ½ x D + G = L

Where: Where: D = the rivet diameter D = the rivet diameter

G = grip (total thickness of G = grip (total thickness of material) material)

L = total length of the rivet. L = total length of the rivet.

The proper length of rivet is an important part of the repair. The proper length of rivet is an important part of the repair. If the rivet is too long, the formed head will be too large or the rivet may bend If the rivet is too long, the formed head will be too large or the rivet may bend

or be forced between the sheets being riveted.or be forced between the sheets being riveted.If the rivet is too short, the formed head will be too small or the riveted material If the rivet is too short, the formed head will be too small or the riveted material

will be damaged. will be damaged.



TABLE OF SIZESTABLE OF SIZES

Standard twist drills are used to drill rivet holes. Standard twist drills are used to drill rivet holes. Note that there is a slight clearance in each case. Note that there is a slight clearance in each case.

This prevents binding of the rivet in the hole.This prevents binding of the rivet in the hole.

Drilling Rivet Holes:Drilling Rivet Holes:

Riveting:Riveting:

• Type of rivet; Head shape, material & Type of rivet; Head shape, material & heat treatment.heat treatment.

• Rivet strength, length and diameter.Rivet strength, length and diameter.

• How many rivet, spacing and pitch How many rivet, spacing and pitch required.required.


Riveting Tools:Riveting Tools:

Rivet CuttersRivet Cutters

Rivet Forming ToolRivet Forming Tool

Rivet BlocksRivet BlocksRivet SnapRivet Snap Rivet GunRivet Gun


Pneumatic Rivet Forming Tool

Riveting Tools:Riveting Tools:

Reports:Reports:

• Damage classification.Damage classification.

• Finding limits (structural repair manual SRM).Finding limits (structural repair manual SRM).

• Prepare surface.Prepare surface.

• Rivet selection:-length, diameter & type.Rivet selection:-length, diameter & type.

• Rivets: Pitch, spacing & edge distance.Rivets: Pitch, spacing & edge distance.

• Materials.Materials.

• PPEPPE

• CAA and Manufacturer Recommendation. CAA and Manufacturer Recommendation.

Any QuestionsAny Questions

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Aircraft Metal Structure

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