Module 7.19 Abnormal events: lightning, HIRF, heavy landing, turbulence

An abnormal event is any occurrence outside normal operation that may have damaged the aircraft. The AMM (ATA 05-50 "unscheduled maintenance checks") gives the required inspections. This is a classic essay topic.

Knowledge levels

Item	A	B1 / B3	B2 / B2L
7.19(a) Inspections following lightning strikes and HIRF penetration	2	2	2
7.19(b) Inspections following heavy landings and flight through turbulence	2	2	—

Lightning strikes

What happens

• Lightning typically attaches at an extremity (nose/radome, wing tips, engine nacelles, propeller or rotor tips, tail) and exits at another extremity; as the aircraft moves, the arc can "sweep" along the surface, leaving a series of marks (swept stroke zone).
• Currents can reach about 200 kA for very short durations, producing burning, pitting, melting of metal, delamination of composites and induced voltages in wiring.
• Lightning zones (1, 2, 3) define areas of likely initial attachment, swept stroke and conducted current.

Inspection after a lightning strike

1. Obtain the crew report (location of strike, any system malfunctions) and record it.
2. Inspect entry and exit points: small pits or burn holes in skins, often in lines along the airflow; burnt or missing static dischargers; damaged radome (punctures, burnt diverter strips); tip lights, antennas, fairings.
3. Composite surfaces: burns, delamination, puncture, damaged lightning protection mesh/foil - may need tap test or ultrasonic inspection.
4. Bonding straps and jumpers across hinges and control surfaces: burnt or broken; check control surface hinge bearings for arcing (pitting, roughness) - may require bearing replacement.
5. Fuel system: fuel tank access panels, vent outlets, fuel quantity indications.
6. Systems check: compass/magnetic heading systems (lightning can magnetise structure - compass swing may be required), radio and navigation systems, instruments, electrical generation, engine indications; functional tests per AMM.
7. Engines: if struck near the intake or propeller, engine and propeller inspections (blade erosion/burn marks, magneto/ignition effects on piston engines).
8. Damage outside limits is repaired according to the SRM; record all findings and return-to-service actions.

Key fact: Lightning damage is usually found at the extremities and may continue along the swept stroke path; always check both entry and exit points and the bonding across movable surfaces.