7.18 Inspection & Repair Techniques Flashcards
What is the life span of an aircraft based on?
Based on the stresses it receives over time
What are the load carriers in a stressed skin philosophy?
- fuselage skin
- bulkheads
- frames
- beams and ribs
What is the purpose of an inspection system?
ensure the aircraft is maintained to the highest condition
What should be followed when establishing inspection intervals?
- airframe and engine manufacturers instructions
What two system scan be used when creating an aircraft inspection programme?
- flying hours
- calendar inspection system (for hourly operating limitations)
What does the term “damage” mean in the SRM?
A cross sectional area or a permanent distortion of a structural member
What is a defect?
Any event or condition which reduces the serviceability of the aircraft.
Who specifies areas that need to be inspected and the type of damage to be found?
Manufacturers
What is abrasion?
- damaged areas as a result of scuffing or rubbing
- Rough and irregular shape
What causes corrosion?
complex electro- chemical action
How is the depth of corrosion damage established?
determined by a clean-up or by a removal operation
What is usually the cause of cracks?
fatigue
What damage is considered equal to a crack?
A crease
What is delamination?
Separation of plies in a multi-laminate material which could be caused by impact or if the resin fails
What is the length and width of a dent?
- Length: Longest distance from one end to another
- Width: second longest distance across the dent, measured at 90° to the direction of the length.
What is disbond? What is its cause?
- separation of materials
- Occurs due to an adhesive failure
- Doesn’t have to occur across the full sentence
What two damages’ limits, given by the manufacturer, can be interchangeable?
If an allowable damage section or repair section does not give limits for disbonds, use the limits specified for delaminations and vice versa
What is a gouge?
- cross sectional change caused by a sharp object and gives a continuous, sharp, or smooth groove in the material.
What is a hole?
Complete penetration of the surface
What is a nick?
- A local gouge with sharp edges
- a series in a line can be considered equal to a gouge
What is a puncture?
damage that goes fully through a part thickness and has no regular shape
Does a scratch result in a cross- sectional change?
Yes
What is important to look for after shock or heavy landing?
any secondary damage
What are the three classifications of damage?
- Allowable damage (within limts)
- Non- allowable Damage (requiring a repair)
- Non- repairable Damage (requiring replacement)
What can provide background info on a defect and the aircrafts maintenance history?
Tech log
aircraft damage chart
What areas need to be considered when developing a checklist for general inspection of an aircraft?
- Fuselage and hull
- Systems and components
- Cabin and flight deck
- Engine and nacelle
- Landing gear
- Wing and centre section
- Empennage
- Propeller
- Communication and navigation
- Miscellaneous item (emergency and first aid equipment)
What should inspections provide about damage?
- an accurate assessment of the damage
- the type of repair to carry out
What should the assessment of the damage begin with?
an inspection of riveted joints and an inspection for corrosion.
What are some of the defects found by NDI?
- corrosion
- pitting
- heat/ stress cracks
- discontinuity of metals
What criteria can an engineer use to decide the type of repair required?
Type of damage
Type of original material
Location of the damage
Type of repair required
Tools and equipment available to make the repair
How is an inspection mirror mounted?
With universal joint so that it can be positioned at various angles
Inspection mirror: What is the magnification most commonly used?
2x
What is the magnification of a stereoscopic magnifying glass?
20x
What magnifying glass is used to view inside structures?
- hand instrument with 8x magnification
What is a boroscope?
optical instrument used for the inspection of the internal structure or components
How can boroscopes be inserted to examine internal parts in a turbine engine?
often designed with plugs at suitable locations in the casings, which can be removed to permit insertion of a borescopes and examination of the internal parts of the engine.
What are some corrosion preventative maintenance actions?
- daily draining of fuel sumps
- drain holes free of obstructions
How is corrosion apparent on a painted surface?
- A scaly or blistered surface
- A change of colour
- Blisters in the paint
How is corrosion apparent on a metallic surface?
- dull or darkened area
- pitted surface
- White, grey, or red dust, or particles can also be seen
What must be done to corrosion before a repair?
All of it must be removed by a trained personnel. Even a little bit left can start more corrosion.
What are the two methods of pain removal?
Mechanical: when corrosion is light and contained in a small area
Chemical: when corrosion is heavy and covers a large area, using strippers
What should be done to fasteners within the area of corrosion whilst corrosion is removed?
Must be removed to prevent cross contamination between dissimilar metals
What are the most common abrasive by hand methods used?
Abrasive cloths and abrasive pads
What areas is abrasion by hand suitable for?
Areas of light corrosion
What is wire brushing?
- mechanical abrasive operation
- removes heavy corrosion, embedded paint or dirt
- with a hand brush or motor- driven brush
What materials can wire brushing be used on?
- best suited to steel
- Not for aluminium, the scratches can open the base material to elements that are more susceptible to corrosion
What is used to carry out grinding?
Motorised grinding wheels
Finish with fine abrasive paper
What materials is grinding not suitable for?
-Aluminium alloys
- grinding wheels would just become clogged w soft aluminium
How is heavy corrosion removed?
use a rotary file or hand scraper
What materials can rotary files be used on?
Aluminium and steel alloys
What is a quick method of removing filiform corrosion and scale from metal surfaces?
Abrasive blasting
What is abrasive blasting ?
When a metal surface is bombarded with abrasive particles to clean or finish metal surfaces
What beads are used for general cleaning, peening and cosmetic finishing during an abrasive blasting procedure?
Glass beads
What magnifying glass is recommended for corrosion check after a removal?
10x
Where can neutralising agents not be used?
In areas where it can’t be washed off
How can deep corrosion on aluminium alloys be removed?
Neutralisation
What is the solution used for neutralisation?
90g Chromic acid (CrO3) to 1L of water
How long should a neutralisation agent be left to work?
5-20 mins
What is used to restore protective oxide coating on metal surfaces?
chromic acid inhibitor
What is a less active chemical mixture for surface treatment of aluminium?
Solution of sodium dichromate and chromic acid
What does aluminium corrosion look like?
White, more voluminous than the metal
What causes intergranular corrosion on aluminium?
Improperly heat treated
What does rust act as?
A catalyst for more corrosion
Whats the most common type of corrosion on carbon steel?
Rust
How can rust be mechanically removed?
- abrasive paper, wire brushing or steel wool
How is rust chemically removed?
Phosphoric acid
Makes the rest water- soluble
What two materials are used when corrosion resistance is important?
Stainless steel and nickel chromium alloys
How does corrosion appear on stainless steels?
Pitting, usually black in colour
How is titanium deterioration shown?
black or white coloured oxide
How is titanium cleaned?
alumiunium polish or mild abrasive w fibre brushes
What does pretreatment do?
- increases corrosion resistance
- good surface adhesion
How can anodising be done? (two ways)
- tank method
- selective method
What is film thickness dependent on?
- current per unit area
- process time
What is CAA treatment?
anodising using chromic acid as the electrolyte
What is eloxadising?
comparable to anodising but w sulphuric acid
What anodising does airbus use?
Sulphuric acid anodising
What properties does eloxation have?
- ceramic proerties
- means its inelastic so can crack if bent
When is anodising used?
- all integrally milled structural components
- on all bonded surfaces
- on the outer skin of the fuselage
What are phosphate coatings on steel used for?
- corrosion resistance
- lubricity
- foundation for other coatings
Three main types of phosphate coatings:
- Manganese
- Iron
- Zinc
What is chemical conversion coating (CCC)?
- Alodine, Iridite or Alodine coat aluminium
What does CCC provide?
- good contact for paint coatings
- aluminium- chromide- oxide cover formed for corrosion protection
When can CCC not be used?
Components that are subjected to operating temperatures of more than 70 °C
What is the thickness of chromium plating and phosphate plating?
chromium: 0.001 mm
Phosphate layers: 0.003 mm
What are paint finishes?
coatings that are manually painted or sprayed on
What are two properties of paint finishes?
- after drying the layer of thickness can be measured
- Paint can be be removed with corrosives
What are the two main reasons for paint finishes on aircraft and aircraft parts?
- A pleasant/decorative finish to the outside surface of the aircraft.
- protection
What 3 layers does airbus use?
- wash primer
- paint primer
- coating lacquer
What 2 layers does boeing use?
Primer
Top coat
What is done before priming on Boeing?
Pretreatment: CCC
What happens before priming on Airbus?
Pretreatment: CCC or CCA
When can fixing be done?
as long as they can be carried out with a paintbrush and appear to be optically justifiable
What is partial or total renewal?
- a paint finish that is aged or damaged.
- partially or totally sanded and repainted
When should FCR (Wash-Primer Filiform Corrosion Resistant) not be used?
Humidity higher than 75%
Temps below 15 degrees C
If use of FCR cannot be avoided where its not recommended, what should be done?
- decrease adhesion
- increase curing time
What should FDR primer never be used as?
Single layer primer
Where is coating lacquer applied?
- outer cabin parts subject to weather conditions
- interior structure in contact w aggressive fluids
What parts require electrically conductive paints?
All plastic components
How is sufficient conductivity achieved in composite components?
75% of countersinks must be covered with electrically conductive paint
Where must antistatic primers not be applied?
Antennae cover
Where are water dispalcing inhibitors used?
Where corrosion cant be removed
What are water displacing inhibitors effectiveness based on?
- good wetting ability
- penetrating properties
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