EWIS Reroute: Separation, Splices and a Pushed-Back Contact
During an avionics modification, a technician reroutes a 20 AWG signal bundle around a new rack. The bundle, insulated with 105 degrees C PVC, is now clamped every 600 mm, passes within 15 mm of a 115 V AC feeder, and bends sharply (about two bundle diameters) into a connector. Two wires were stripped with a knife and show nicks; three strands of one are cut. A crimp splice sits in the middle of the bundle, 80 mm from any support. On the connector, one socket contact is pushed back and does not click when inserted. The technician wants to seal the splice with tape, push the contact in with a screwdriver and sign it off, because the aircraft is due out tonight.
1. Sort each finding into: acceptable as is, rectifiable under standard practice, or requiring approved data. Explain the reasoning.
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Requires approved data (engineering)
- Routing within 15 mm of a 115 V AC feeder. EWIS separation distances are design data. A chafed feeder can arc onto the signal wires, with arc tracking and fire risk, and induced noise corrupts the signal. Changing the route is a modification, not a repair.
- Clamp spacing taken to 600 mm. Support spacing is specified data based on bundle mass, vibration and connector loads. If the specified spacing is shorter, the bundle will fret against structure and load the contacts.
Rectifiable under standard practice, done correctly
- Bend radius about two bundle diameters at the connector: too tight. It stresses the crimp and can crack insulation at the backshell; re-route for a straight approach and a service loop.
- Splice in mid-bundle, 80 mm from support: a splice must be the approved type, correctly crimped, supported so it carries no tension, and accessible for inspection.
- Nicked and cut strands: a nick reduces conductor cross-section, creating a hot spot and a fatigue crack site; three cut strands in 20 AWG is a significant loss of section - replace or re-terminate. Tape is never acceptable.
Not standard practice at all
- Pushing a contact in with a screwdriver damages the retention clip and the contact barrel.
2. Describe how the contact, the splice and the damaged wire should actually be rectified.
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Contact
- Remove it with the correct extraction tool, inspect the contact and cavity for damage, then reinsert until it clicks and cannot be pushed back.
- Verify with a visual depth gauge and a pull test at the specified force. Replace the contact if the retention clip or barrel is deformed.
Splice
- Remove the old splice, cut back, strip with a calibrated stripping tool (no nicks, no nicked strands), crimp an approved splice with the specified tool and die, and check it with a pull test or go/no-go gauge.
- Insulate per specification, support it, and place it where it can be inspected. Record the splice.
Nicked wire
- If strand damage exceeds the permitted limit, replace the wire run or cut back and re-terminate at an approved point. Do not tape over it - tape hides the defect from every future inspection.
Finally, restore clamping and separation to the drawing, add protective sleeving or conduit if the approved data calls for it, and remove all swarf.
3. What tests and documentation are required before this aircraft can be released?
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Tests
- Point-to-point continuity and correct pin-out (no crossed or swapped wires).
- Insulation resistance between wires and to ground, at the voltage limits of the installed equipment - do not over-voltage avionics.
- Voltage drop or current check where specified, plus bonding/grounding checks for the new rack.
- Physical inspection: bend radii, separation from power feeders, clamp spacing and condition, no tension on connectors, backshells torqued, no swarf or loose hardware.
Documentation
- The routing as installed must match approved data. If the actual route differs from the drawing, an undocumented change has been created - that must go through engineering, not be signed off.
- Splice, repair and test records entered; EWIS documentation updated.
- Return-to-service certification by authorised staff.
Schedule pressure is irrelevant to the decision: an untested splice, a damaged contact or an unapproved route is a potential in-flight fire or system failure, and the correct answer tonight is 'not released'.