B2-7D #1 Upload

Knowledge Levels

• Basic knowledge levels for aircraft maintenance licenses A, B1, and B2 are indicated by knowledge level indicators 1, 2, or 3.
• Category C applicants need to meet either category B1 or B2 basic knowledge levels.

Knowledge Level Indicators

• Level 1: Familiarity with basic elements, simple descriptions using common terms, and use of typical terms.
• Level 2: General theoretical and practical knowledge with the ability to apply it, including understanding fundamentals, giving general descriptions with examples, using mathematical formulae, understanding sketches, and applying knowledge practically with procedures.
• Level 3: Detailed theoretical and practical knowledge with the capacity to combine and apply elements logically, including knowing theory, giving detailed descriptions, understanding formulae, preparing sketches, applying knowledge using instructions and interpreting results to apply corrective actions.

Aircraft Defects

• Aircraft defects are defined as events or occurrences that reduce an aircraft's serviceability.
• Maintenance schedules specify inspection areas and expected faults.
• Inspectors look for indications of abnormality.

General Defects

• Metal parts are inspected for cleanliness, damage, leaks, overheating, fluid ingress, obstructions, seating, distortion, missing fasteners, cracks, adhesive bonding separation, weld failures, deterioration, and attachment security.
• Rubber, fabric, glass fibre, and plastic parts are inspected for cleanliness, cracks, chafing, kinking, deterioration, overheating, fluid soakage, and attachment security.
• Control system components like cables, chains, pulleys, rods, and tubes are checked for alignment, movement, distortion, scores, wear, cracks, electrical bonding, and attachment security.
• Electrical components such as actuators, alternators, generators, motors, relays, solenoids and contactors. are inspected for cleanliness, overheating, corrosion, scoring, fluid ingress burning, and pitting of contacts.

External Damage

• Airframe damage is most commonly caused by ground equipment or severe hail.
• Contact with vehicles during ground servicing can cause dents or punctures.

Inlets and Exhausts

• Inlets and exhausts could be nesting sites for wildlife.
• Blocked ducts can cause overheating or engine damage.
• Careful inspections should ensure inlets and exhausts are not blocked.

Liquid Systems

• Liquid systems use gauges for quantity assessment, with physical checks to supplement.
• Systems include engine oil tanks, APUs, integrated drive generators, hydraulics, fuel, and potable water tanks.
• Lower-than-expected levels require immediate investigation.
• Consumption rates must be calculated before troubleshooting.
• A low hydraulic system should not be replenished before investigating any leaks.
• External leaks in oil and fuel systems are easy to locate and fix with component replacement and tests.
• Internal leaks require thorough inspection due to difficult to find problems.
• Symptoms of internal leaks includes slower or erratic movement of services.

Gaseous Systems

• Gaseous systems include oxygen, nitrogen, and air, and flight checks can be hard to confirm without a physical check.
• Leaks of oxygen is dangerous and can lead to explosions with presence of oil or grease.
• Recharge and leak test the system after fixing the leak.
• Pneumatic systems maintain stated air pressure, and compressor or ducting/pipe leaks may be suspected if pressure drops lower at the end of flight.
• Use leak-detecting fluids if the pressure is falling between flights and storage is probably the source.

Visual Inspection Techniques

• It possible to assess serviceability by simply measuring a component.
• Landing gear oleo shock struts measure correct inflation using measuring their extension.
• Further checks are required if the dimension is less than quoted in the manual.

Tyres

• Tyre serviceability relies on the groove depth of the tread.
• Defects to look out for includes cuts, blisters, creep, and low pressure.
• Tyres can be re-treaded only if the tyre isn't badly damaged.
• Creep is tyre movement around the rim usually due to heavy braking and dangerous for a tube as it can tear the charging valve out resulting in loss of pressure.
• Small white marks are indicators across the wheel rim and the tyre side wall so that if creep takes place, the marks will move in opposite directions.

Wheels

• Defects are usually due to impact damage.
• Other problems may arise from corrosion as a result of impact damage and shearing of wheel bolts.
• Wheels are thoroughly inspected during tyre replacement.

Brakes

• Brake units are attached to the axle of an undercarriage leg.
• They absorb large amounts of energy as heat resulting in wearing rotors and stators, and at extreme heat the stator material may break up.
• Inspection of brake units between flights is essential to check for excessive heating beyond limitations.
• Wear reduces the total thickness of the brake pack with the thickness of the pack measure to monitor wear.
• Wear reaches a set figure the brake pack requires overhaul.
• Damaged debris, debris or powder and case scoring require immediate replacement of the complete brake unit.

Landing Gear Locks

• Landing gear locks are safety devices to prevent unintended landing gear collapse.
• The flags are designed to attract attention to ensure they are not left in position when the aircraft departs.

Indicators

• The most common indicator is the blow-out disc used in fire extinguishing and oxygen systems.
• It uses high-pressure bottle indicating discharge for extinguishers releasing due to excessive pressure.

External Probes

• Several probe types send airflow information to the flight deck.
• Can contain pitot/static and angle-of-attack (AOA) probes.
• Probes projecting outwards from the aircraft skin make them prone to potential physical damage from regular inspection for signs of physical damage, discoloration, or obstruction.

Handles and Latches

• Handles and latches usually wear through constant use.
• Cargo bays and baggage holds are more prone to wear since they are used every time the aircraft lands.
• Panel fasteners wear and must be secured.
• Fasteners use a positive form of closing or locking mechanism.
• Worn fasteners must be repaired or replaced, as this can damage the panels and cause destruction of the parts.

Panels and Doors

• Panels and doors are are prone to potential damage.
• Damaged frames can happen with excessive used with baggage hold doors for instance.
• Check the inside of other doors and panels when they are removed.
• Corrosion is usually present at the fastener holes.
• Remove corrosion discovered along the seams of doors and panels, to determine its extent.

Emergency System Indication

• Protective covers helps prevent inadvertent switch operation.
• They are held closed by a frangible device.
• A broken thin copper wire indicates that the cover has been lifted and the system may have been operated, and this requires investigation.

Pressurised Structure

• Factors to consider include cyclic loading, hoop stress, and serviceability of blow-out panels, doors, windows, and seals.
• Check the surrounding area for damage to underlying structures that might not be apparent.
• Instead of looking, feel for possible deformation such as wrinkles or buckling and make measurements to ensure airframe symmetry.
• Removal of skin panels require investigation for corrosion.

Other Inspections

• Moving parts require proper lubrication, security of attachment, adjustment, cracked fittings, cleanliness, and sealing and tension.
• Fluid lines and hoses need the proper material, fittings, torque, and security, and to be free of leaks, tears, corrosion, and obstructions.
• Wiring needs to have security, proper insulation, and terminals, and no chafing, burning, heat deterioration, and corrosion.
• Bolts require correct torque, proper paste, and no elongation, deformation, damage or corrosion.
• Rivets with corrosion need to be drilled out and reinstalled according to the maintenance manual with no gap beneath the rivet head.
• Filters, screens, and fluids require cleanliness, contamination checks, replacement as prompted, and proper installation.
• Powerplant elements need proper engine mount security, accessory security, and exhaust flow.
• Propellers require nicks, dents, cracks, lubrication, gouges, the proper blade angles and governor function.
• Nicks on the leading edge produce stress concentrations, and should be removed upon discovery.
• Ground runs for engine analysis need to be within the correct parameters.
• Lifed items need to be replaced during maintenance and will have a finite fatigue life.

Locations of Corrosion in Aircraft

• Various sections of the aircraft require inspections and are open to corrosion than others:
• Magnesium and aluminium alloys are more sensitive to corrosion.
• The rate of deterioration can depend on aircraft design, build, operational use and environment.
• Fairings located in gas turbine and piston engine exhaust paths are subject to highly corrosive influences, examination.
• The protective finish on engine frontal areas is abraded with dust, air and eroded by rain on heat-exchanger cores and cooling fins are abraded.
• Landing gear bays are exposed to flying debris and cleaning must be made of crevices, ribs and lower-skin surfaces where debris can lodge.
• Drains can become blocked, and inspection of drains must happen frequently.
• Under galley and toilets should be very carefully inspected for corrosion.
• Hinges show potential corrosion areas are found where water and dirt may collect.
• Corrosive agents may become trapped between metal layers of spot-welded skins.
• Sealing, venting and protective paint cannot wholly obviate the corrosion in battery compartments.

Control Cables

• Loss of protective coatings on carbon steel control cables can, over time, lead to mechanical problems and system failure, which corrosive-resistant cables can also similarly be affected.
• Cables that have external corrosion require thorough inspection of the internal strands and the cable should be rejected if any damage is found.
• It's important to carefully inspect cables that are in the vicinity of bell cranks, as there is a greater chance for corrosion getting inside the cables when the strands are moving.

Prevention of Corrosion

• Preventative maintenance is corrosion control.
• This includes adequate and regular aircraft cleaning.
• Some steps may be to inspect, lubricate clean surfaces, treat and touch-up damaged paints.
• There is also need for drainage of fuel cell sumps and to seal during heavy weather and to use protective covers/blanks.

Corrosion Removal

• In general, for corrosion removal, perform the following:
• Clean the corroded area and strip the protective coating
• Get rid of corrosion product and neutralize the remaining residue, restore protective surface films, and apply coatings or paint.

Paint Removal

• Look out for corrosion under a film of paint.
• Prior to applying a paint remover, mask any areas not to be stripped should be masked with heavy aluminium foil.
• Water-rinseable paint remover of a syrupy consistency apply with dabbing rather than bushing, and stand until the paint swells and wrinkles.
• Reapply the remover to areas which have not been stripped, scrape away paint with a plastic/aluminium scraper, then apply the second coat of remover.
• Use hot water or steam when rinsing the surface, a stiff nylon brush is require for removal in stubborn places.
• Handle remover with caution, as solvent products attack rubber tyres and synthetic rubber products.
• Ensure personal protection and skin care by wearing equipment, immediate rinse for skin, and mask vulnerable plastic/resin parts.

Aluminium and Aluminium Alloys

• The products that appear on corrosion aluminum surfaces are white and voluminous.
• General surface attack penetrates slowly, but accelerates in the presence of dissolved salts.

Three seriously attacking forms of attack

• Pit-type corrosion through the walls of tubing.
• Stress corrosion cracking under with alloys that have incorrectly treated with heat.
• Treatment involves mechanical/chemical removal of the corrosion products.

Alclad

• It is a trademarked term with a generic use, used to describe corrosion-resistant aluminum sheet with high-purity on both sides.
• The cladding thickness is around 5%.
• Don't take away or remove so much of the protective aluminum layer with mechanical removal, corrosion in it is removed mostly by chemical removal.
• For maintenance, mask off areas, mask off areas that are corrosion free.
• Use a phosphoric- acid based fluid and then rinse and flood w/ water until traces of acid are removed.
• Checking aluminum is done by diluted caustic soda to the cleaned area, or the aluminum alloy core will show as black stain, unless you neutralize it with water.

Assessment for Serviceability

• Measure maximum depth with dial test indicator with guidance of structure repair manual for maximum thickness.

Re-Protection

• For Alocrom 12800, brush is supplied with it, and applied with Parts A and B. Mix sufficient volume is plastic container within 24 hours and then degrease.
• Apply with solution of nylon brush.
• Clothe must be worn, or discarded so they don't create a fire hazard.
• Rinse with clean water for 2 hours, finally apply epoxy primer to finish within 48hrs, do not etch over alocrom

Aluminium Alloy Castings/Forgings, Milled Skin Panels, Etc.

• Remove corrosion with mechanical methods after degreasing paint finish.
• One may want to use nylon/scotch brite pads.
• Aluminum wool/ wire brush.
• Abrasive paper/ abrasive blasting methods is possible.
• When complete, examine for traces of corrosion, use wire brush/wool only to avoid severe steel corrosion.
• Remove the corrosion, use alloy grinders/rotary files to grind out the damage. finish by sanding, cleaning and neutralizing with an inhibitor.
• Treat all traces of corrosion and use SRM service bulletin with 5% chromic acid to neutralize salts for at least 5 mins before rinsing with water.
• Transform pits into relief concentrations after power driving as the manual gives proportions for blended areas.

Assessment for Serviceability

• Limit metal to limits specified within the SRM/service bulletins and Initial after loose corrosion is removed to determine if salvaging.
• No pitting is usually allowed.
• Corrosion removal must not weaken a part to the degree that it endangers aircraft and the depth of a blended area has a measured way of knowing.

Ferrous Metals

• Ferrous oxide rusts some base metals with moisture, rust promotes metal to be removed, and rust will show on parts needing service checks with most practical corrosion for its products.

High-Stressed Steel Components

• Corrosion may be dangerous, must be mild with abrasives after greasing and paint removal with SRM/service bulletin.
• Steels in aircraft structures are plated with only min amount as plating for corrosion removal.
• With means that are mechanical, if it is especially for highly stressed parts, the corrosion is withing acceptable limits.
• Dusts, cadmium are considered toxic, wash clothes bags, and are marked that way and should be removed accordingly.
• Corrosion must be removed not in the chemical situated as per manufacturer.

Magnesium Alloys

• When magnesium corrodes, the products occupy more space between joints if applicable after removing paints.
• Do not use the anodic tool and methods include nonmetallic (IE nylon), using pads etc, so as to not remove a chromate film.

Acid Spillage

• Acids cause damage.
• Correct safety habits to have in place during these issues with lead acid.
• With a battery bay to have ventilation, anti-acid paint.

To counteract acid spillage:

• Mop water until there is no spreading w/ rags, wash ,test for acidity w/ litmus, dry it and remove corrosion to finish and restore surface.

Alkali Spillage

• There will be spillage with aluminum cadmium and there is health and safety.
• To be able to take alkali spillage then you alkaline with chromic acid.

Metallic Mercury Corrosion on Aluminium Alloys

• Clean spilled mercury as possible as mercury causes and is hard to control by amalgam causing liquid metal embrittlement.
• And x-ray may help as an effective method to find small parts.

Mercury Spills and Corrosion Damage

• The presence of the salts is a definite possiblity, and can cause the structure to leak.
• The steps must be isolation if possible and structural components must be able to embrittle at levels of:
• Stainless stee
• Cable turn Buckle barrels
• Penetration in the finish ( anonic film) with mercury.
• Mercury attacking is corrosion attack.
• The mercury may be heated to haste if process done in 3/4 mins