13.3 Lightning Protection, Bonding and Static Dischargers
Key Takeaways
- Typical industry teaching (SAE ARP5414 / EUROCAE ED-91) divides the airframe into lightning zones for first-return-stroke extremities, swept-stroke surfaces and conduction paths; use the type-specific drawing, not a universal map.
- Bonding jumpers provide the designed current path across moving joints, doors, control surfaces and composite-to-metal interfaces and must remain short, clean and unpainted.
- Static dischargers (wicks) bleed precipitation-static charge to reduce corona noise on radios; they are not a substitute for lightning bonding but often sit at likely exit or hang-on edges and are damaged in strikes.
- Composite repairs must restore designed conductivity (mesh, foil, diverters, fastener bonds); isolated metal fittings can spark if left unbonded.
- After a reported or suspected strike, follow the AMM inspection of likely entry and exit damage, jumpers, wicks, radomes, composites and systems; do not invent unpublished strike-current kiloamperes as EASA Module 5 facts.
13.3 Lightning Protection, Bonding and Static Dischargers
Topic 5.14 still sits at Level 2 for B1 and B2/B2L, Level 1 for B3, and not required for Category A. Lightning is a different electromagnetic environment from HIRF: a high-current, short-duration attachment and dwell on the airframe, with possible reattachment as the flash is swept aft. The influence on maintenance practices is the zoning concept (as typical industry teaching), bonding jumpers, static dischargers, composite conductivity, and inspection after a strike.
How lightning involves the aeroplane
Aircraft often trigger lightning when they fly through a charged cloud, rather than simply being hit at random. A leader attaches at a likely extremity; current flows through the structure; the flash may dwell and then sweep aft as the aeroplane moves, creating further attachment spots. Energy also couples into wiring (indirect effects): induced voltages and currents that can upset or damage avionics even when the skin is not holed.
Design organisations use standardised current components (first return stroke, intermediate current, continuing current, subsequent strokes, multiple bursts) published in industry lightning-environment documents such as SAE ARP5412 / EUROCAE ED-84. Those waveforms are certification design environments. They are not a set of kiloampere figures in EASA Part-66 Appendix I. Do not treat a peak current as a Module 5 fact, do not invent unpublished strike-current numbers, and do not try to “measure the strike” on the ramp with a clamp meter. The technician’s job is configuration and inspection, not reconstructing the waveform.
Zoning as typical teaching
Industry lightning zoning (typically SAE ARP5414 / EUROCAE ED-91) divides the outside of the aeroplane according to the probability of attachment and the type of current expected there. Exact zone drawings are type-specific (in the AMM or lightning-protection drawings). The teaching pattern is:
| Typical zone idea | What it means for teaching | Hangar implication |
|---|---|---|
| First-return-stroke extremities (often taught as Zone 1A and related 1-series surfaces) | Nose, wing tips, empennage tips, engine-inlet lips, propeller blades and similar projections are likely initial attachment regions | Look here first for pits, holes, burnt paint, damaged pitot/static probes and antennas |
| Swept-stroke surfaces (often taught as Zone 2-series) | After initial attachment the flash is dragged aft along skins, flaps and fairings | Search aft of the nose and tips for a trail of marks, fastener sparking and composite puncture |
| Hang-on trailing edges (often taught as 1B/2B-style edges) | The flash may remain attached at a trailing edge while current continues | Trailing-edge structure, static dischargers and control-surface bonds |
| Conduction / low-attachment regions (often taught as Zone 3) | Direct attachment is less likely, but current still flows between entry and exit through structure and designated bonds | Hidden damage: bonding jumpers, hinges, pipe bonds, fuel-tank fastener interfaces |
Do not invent a universal millimetre map of zones for every type. Use the aircraft lightning-zone diagram in the maintenance data when inspecting. Zoning is a search pattern, not a licence to skip a jumper that happens to sit in a “quiet” painted area on a training sketch.
Bonding jumpers and structural current paths
The metal (or protected composite) airframe is intended to carry lightning current in a controlled path so that the interior is not the preferred route. Bonding jumpers close gaps that the structure cannot: control-surface hinges, engine-cowl doors, landing-gear doors, spoilers, flaps, moving radomes, and composite-to-metal joints.
Rules that follow from section 13.1 and become critical in a strike:
- Jumpers must be the specified part, short, and landed on clean conducting structure.
- A painted or corroded lug forces current into fasteners, sealant or fuel-tank interfaces where sparking is unacceptable.
- Isolated metal fittings in composite (latches, hinges, plumbing) must have the designed bond or they can spark to the nearest fibre or mesh.
- Do not add unofficial extra straps that create a new path through a tank or a wiring bundle.
Fuel-tank ignition prevention (continuing-airworthiness programmes that grew from fuel-tank safety work) depends on known electrical paths and fastener design. Unofficial bonding “improvements” are a safety failure, not initiative. After any structural or composite repair that disturbs a jumper land, restore the bond and perform the milliohmmeter check the AMM requires.
Static dischargers (static wicks)
Precipitation static (P-static) charges the airframe as ice, rain or dust strikes the surface. Charge bleeds by corona, which produces broadband radio noise on HF and VHF. Static dischargers (wicks, typically on trailing edges of wings, ailerons, elevators and rudder) provide sharp points so that corona occurs off the trailing edge at a controlled location, reducing coupling into antennas.
Static dischargers are not a substitute for lightning bonding and are not the primary down-conductor of the airframe. They do, however, sit on trailing edges that are likely lightning exit or hang-on points, so they are frequently melted, shortened or missing after a strike. Inspect them for that reason and for radio-noise complaints. Resistance and mechanical-condition limits come from the AMM, not from a single Module 5 megohm figure. Do not fly with a set of missing wicks just because the aeroplane is metal: the radio-noise and lightning-exit inspections still apply as written.
Composite conductivity
Carbon laminates need the designed conductive layer to spread lightning current and to keep HIRF skin currents on the outside. Maintenance implications:
- Follow the structural repair manual electrical steps (mesh overlap, conductive adhesive, surface ply, fastener bonding).
- After paint, restore diverter strips on radomes and any unpainted bonding lands.
- Check that metal mesh is not wrenched into an isolated island by a poorly scarfed repair.
- Treat a composite puncture or fibre bloom after a strike as structural and electrical damage.
A fair aerodynamic repair that omits conductivity can leave a puncture path into a tank boundary or a wiring run on the next strike, and it can reopen the HIRF aperture discussed in section 13.2.
Inspection after lightning
Crews may report a flash, a bang, transient instruments, a burnt smell, or nothing but a mark found on walk-round. Treat a reported or suspected strike as an AMM lightning-strike inspection, not as a polish-out.
Typical teaching sequence (always overridden by the type AMM):
- External search of likely entry and exit: nose, tips, radome, engine inlets, wing and tail trailing edges, static dischargers, antennas, lights, pitot probes.
- Marks: pits, burn marks, punctures, delamination, missing paint, exploded fasteners, damaged bonding jumpers.
- Systems: popped breakers, spurious warnings, compass or inertial-reference behaviour, radio performance, fuel-quantity anomalies.
- Progressive inspection as the AMM requires if damage is found (deeper non-destructive testing, tank areas, hidden bonds).
- Do not release the aeroplane until the required inspection and any repairs are complete.
[!WARNING] Do not invent the current. A small surface pit does not tell you the peak kiloamperes, and a spectacular exit hole does not authorise skipping hidden-bond and tank-interface inspections. Use the AMM criteria. Unpublished strike-current numbers are not EASA Module 5 facts.
B1/B2 Level 2 means you can apply zoning as a search pattern, explain bonding and wicks, and carry out (or call for) a lightning-strike inspection. B3 Level 1 means you recognise that lightning-protection hardware and post-strike inspection are airworthiness tasks.
How should a certifying technician use the lightning-zoning concept taught for topic 5.14?
What is the primary function of static dischargers (static wicks) on trailing edges?
After a crew reports a lightning strike, which action matches topic 5.14 maintenance practice?
Which statement about lightning bonding jumpers and composite conductivity is correct?