SAFRAN - La maintenance d'un train d'atterrissage

Main ideas / lessons from the video

• The video is the third (final) episode in a Safran Landing Systems series explaining the life cycle of a landing gear: design/modeling → production/assembly → maintenance and repair.

• It shows a typical landing gear overhaul workflow, including:

  1. Receiving and disassembling components
  2. Expert inspection and sorting parts
  3. Repair / surface treatments (chrome-related work, coatings, machining, grinding)
  4. Non-destructive testing (NDT) to find internal/hidden defects
  5. Reassembly, including conditioning tests for shock absorbers
  6. Final acceptance / return-to-service approval with the required certification documents
• A recurring theme is standards-driven work: the process follows manuals/specs, uses calibrated tools, and complies with regulatory/traceability requirements.
• Parts are repeatedly classified as:
  • Rejected (red)
  • Accepted as-is (green)
  • Sent for repair/remediation (yellow) (often requiring NDT)

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Methodology / process (detailed)

1) Setup: workshop overview and disassembly workflow (received landing gear)

• The landing gear is received at the end of its service cycle and undergoes complete disassembly (“stripping it, and restoring it from scratch”).
• Disassembly stages include:
  • Pure disassembly
  • Misalignment / temperature-difference assembly concepts for separating parts mounted together
  • Stripping
  • Leveling/inspection for corrosion and surface damage (e.g., chrome wear/scratches)

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2) Shock absorber handling during disassembly (critical, time-consuming step)

• The shock absorber is deflated and drained first because it “takes the most time.”
• Inside shock absorbers:
  • Hydraulic oil
  • Nitrogen
• A safety approach is used so the shock absorber does not pop out unexpectedly.

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3) Temperature-difference assembly concept (to remove shafts/spindles)

• Principle:
  • Heat one component in an oven (example: 110°C) so it expands.
  • Cool the other component in liquid nitrogen so it contracts.
  • When both return to ambient temperature, parts “solidify,” making removal/fit easier.
• Materials noted:
  • Aluminum (e.g., rocker arm/housing) expands more
  • Steel (e.g., shafts) contracts more / expands less
• The technique is applied similarly across multiple shafts.

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4) Stripping step: removing chrome and preparing for corrosion evaluation

• Chrome removal/cleanup:
  • Sanding to remove worn chrome.
  • Protect chrome during sandblasting to prevent sparks/contamination (“chrome needs protection”).
• Sandblasting and micro-inspection:
  • Sandblast to reveal corrosion underneath.
  • Use “micro-cap”/magnification to inspect corrosion spots.
• Key rejection rule:
  • If the broaching hole is corroded, the part is not repairable and is rejected immediately.

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5) Post-stripping inspection and dimensional verification

• After preliminary checks, experts verify:
  • Outside corrosion presence
  • Surface condition
  • Dimensions within specification
• Dimensional measurement workflow:
  • Record part serial number in official paperwork.
  • Use calibrated instruments.
  • Measure multiple locations and cross-check to detect:
    • Ovalization
    • Effects of excessive chrome wear
  • Measurements are recorded with tool identity and validation in traceable databases.

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6) Parts sorting system (color-coded bins)

After initial inspection/stripping:

• Red box
  • “Everything that’s rejected,” especially parts corroded such that repair isn’t possible or is outside CMM repair scope.
  • Often includes parts sent for reorder/replacement and customer evidence via photos.
• Green box
  • Parts that are good and require no expert repair cycle.
• Yellow box
  • Parts needing remediation/regeneration or additional expert processing.
  • Example: an axle sent to NDT.

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7) Expert inspection steps (beyond initial stripping)

For parts in the yellow bin, the expert performs:

• Visual inspection under magnification/lighting:
  • Inspect key areas carefully (especially the broaching hole)
  • Circle/mark defects
• Dimensional measurement:
  • Decide the next step in the repair cycle

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8) Example of decisions: plating suitability and rejection logic

• The video contrasts:
  • Parts with usable coating characteristics
  • Versus parts with severe corrosion (described as rough like a “nail file”)
• If outside the chrome plating repair scope, the part is discarded because:
  • Severe corrosion likely exists in holes/passages too
  • Assembly contamination risk may occur (cross-contamination between parts)

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Surface treatment department workflow (coatings, grinding, plating, sacrificial metal)

9) Grinding and preparation before plating

• Surface treatment prepares parts that were machined outside spec.
• Grinding purposes:
  • Restore dimensions
  • Improve friction between interacting surfaces
• Example sequence:
  • Remove chrome and grind in steel to eliminate corrosion points.
  • Shot blasting: project steel particles to stress the surface and increase resistance.
  • Chrome plating:
    • Electrolytic deposition in baths (“deposited onto the steel”).
    • May require thick chrome, then grinding back to final dimension because:
      • Chrome is granular
      • Grinding alone can cause concavities unless thickness is built then finished smooth.

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10) Cage plating (sacrificial metal coating)

• After chrome plating and grinding:
  • Cage plating is applied.
• The sacrificial metal concept helps provide corrosion protection.

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Machine tool / grinding department workflow (chrome can’t be machined except by grinding)

11) Grinding process for chromed/re-chromed parts

• Key rule:
  • Chrome cannot be machined except by grinding because it is too hard.
• Grinding setup:
  • Parts held between centers (perfect roundness required).
  • Grinding wheel rotates while the part rotates in opposite direction.
  • Coolant/lubricant is used to prevent burns.
• Roughing vs finishing (mentioned):
  • Roughing: about 5 microns per pass
  • Finishing: about 2.5 microns per pass
• Grinding outputs:
  • Diameter restored to correct size (including post-rechroming workflow)

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12) Measurement during grinding

• Operators monitor:
  • Thickness differences
  • Progress in micrometers / controlled increments
• Checks include micrometers and confirmation of dimensions/cylindricity.
• Cylindricity adjustment is described via tilting/rotating.

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13) CNC grinding (diamond-cutting wheel concept)

• Newer CNC machines:
  • Use programs including bearing surfaces.
  • Use diamond sharpening to keep the grinding wheel effective.
• High-level sequence:
  • Coolant starts
  • Roughing dives
  • Diamond-cutting / finishing passes
• Challenge mentioned:
  • Chrome can form paste and clog grinding wheels (diamond-wheel helps mitigate removal issues).

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Non-destructive testing (NDT) and acceptance checks

14) NDT inspector’s mission

• NDT looks for indications that could weaken parts.
• Techniques mentioned (used in aeronautics):
  • Magnetic particle inspection
  • Magnetic flux density (MFD) testing
  • Electric current testing
  • Radiography
  • Ultrasound
• Dinard site specifically mentioned:
  • MFD
  • Electric current testing
• Other developing/less common techniques mentioned:
  • “Barcosone” testing (as transcribed)
  • Acid etching for metal corrosion

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15) Magnetic Particle Inspection (MFD) principle

• Magnetize the part so magnetic domains align.
• Defects disrupt field lines.
• Apply ferromagnetic particles/solution so particles collect where defects disturb the field.
• Defects are identified visually via their patterns.

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16) Dye penetrant / “electric current testing” confusion note (core penetrant logic)

• A penetrant with strong wetting (high capillary action) is used:
  • Penetrant seeps into defects
  • Excess is removed
  • Developer is applied; humidity/inspection helps pull penetrant back out for visibility
• Capillary effect is described as about 10× water.

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17) Electric current testing demonstration (bench)

• Current passed near/through a part generates a magnetic field (via a copper conductor).
• Field value bounds are compared against a maximum permissible value.
• Developer/ferromagnetic powder reveals defects (left intentionally visible for demonstration).
• Additional step:
  • Change direction to detect defects from all orientations (crossed field concept).
• After inspection:
  • Demagnetize using an alternating current solenoid method and a “sizing cycle” down to low field strength.

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18) Penetrant testing booth: checking chrome cracks (“crazing”)

• Goal:
  • Detect “crazing” (small natural cracks in chrome).
• Acceptance logic:
  • Some crazing can be necessary for thick chrome.
  • Too much crazing can allow corrosion to enter.
  • Avoid/verify:
    • Very deep cracks
    • Grinding cracks
• Confirming a suspicious defect:
  • Wipe with solvent on cotton ball to reveal a very fine line.
  • Visual confirmation indicates a crack.

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Reassembly workflow (shock absorber conditioning + overall reassembly)

19) Reassembly starting point: kitting and staged assembly

• Incoming parts are “kitted” (new or refurbished components).
• For each part, checks/verification occur before use (mentions NDT painting and “cadmium machining” in the process flow).

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20) Temperature-difference reassembly for shock absorber internal components

• Longest assembly involves slide/spindle components:
  • Spindle heated in nitrogen at about -150°C to -180°C
  • Mating part heated in oven around 150°C
• Time note:
  • Cooling/assembly can take about a day.

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21) Shock absorber conditioning tests (mandatory before service)

• A large industrial press performs:
  • Compression and rebound tests
• Programs are pre-recorded and run automatically.
• After testing:
  • Values must match the curve within minimum/maximum tolerances
• If out of tolerance, possible causes:
  • Too much/too little oil
  • Too much/too little nitrogen

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22) Shock absorber “conditioning” procedure described

• Assemble fully first.
• Condition with air (“3520 air” as transcribed) and regulate:
  • Inject oil via air pressure using valves
• Reset to zero to define oil clearance.
• Add nitrogen per specification (example range mentioned: 19 to 23 bars).
• Readouts are checked on fittings to confirm pressures.

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23) Final assembly steps for the landing gear unit

After conditioning and press testing:

• Mount cover, switches, hydraulic connections
• Route hoses
• Apply grease on fittings
• Connect electrical harness and ground braid
• Use greasepaper/protective wraps:
  • Protect chrome surfaces
  • Store on shelves (protection > 10 years mentioned)
• Apply protective sealant “PR” to sensitive areas to prevent corrosion and loosening, especially around switches and top regions.

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Return-to-service approval / certification workflow

24) Benjamin’s role in approval (release to service)

• Approval department checks:
  • Disassembly steps
  • Documentation used
  • Processes followed
  • Compliance with standards/regulations and personnel requirements
• Output:
  • Issuance of a release certificate
• Regulatory frameworks mentioned (examples):
  • NOASA (European part, as transcribed)
  • FA (U.S.)
  • TCCA (Canada)
  • UK uses CAC
  • China uses CAC
• Service categories described (four):
  • Repair (simple repair)
  • Overall service (complete overhaul)
  • Bench test (inspection/test)
  • Modification
• Documentation package:
  • The release certificate goes with a shop report (detailed record with photos)
• Purpose:
  • Allows aircraft manufacturer installation and certifies the equipment is airworthy.

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Speakers / sources featured (identified people)

• Narrator / main presenter (also introduced as a methods engineer at Safran; Elodie appears as an interviewer)
• Alexis (workshop colleague; disassembly stages and shock absorber disassembly prep)
• Elodie (interviewer; appears alongside multiple colleagues)
• Adie (brief appearance in greeting lines; co-host/interlocutor likely)
• Alain (expert; dimensional measurement and inspection from the yellow bin)
• Baptiste (methods department; mission of methods office; technical questions)
• Samuel (mentioned by Baptiste as a design engineer to consult)
• Gilda (mentioned as someone to meet in the machine tool room; dialogue not fully present)
• Gill (grinder; grinding of chromed parts and grinding machine operation)
• Régis (NDT inspector and expert; NDT techniques and demonstrations)
• Yvon (reassembly lead; reassembling landing gear and shock absorber conditioning/press tests)
• Benjamin (approval department; release certificate and shop report; return-to-service certification)
• Safran Landing Systems / Safran Landing Systems Services site at Dinard Airport (organizational source/context)