1_ Zone 1A:
- area where there is a high probability of initial attachment
and low probability of arc hang on, such as the
forward-mounted pitot probes, the radome diverter strips and
the nacelle leading edges.
2 Zone 1B:
_
-area where there is a high probability of initial attachment and high probability of arc hang on, such as the wing, stabilizers and fin tips and some trailing edge areas.
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Lightning Strike Inspection Areas Figure 601/TASK 05-51-18-991-001
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3_ Zone 2A:
- a swept stroke zone with low probability of arc hang on,
such as mid-chord regions of the wing surface, aft of an
engine and the total fuselage surface.
4_ Zone 2B:
- a swept stroke zone with high probability of arc hang on,
such as the wing trailing edge aft of Zone 2A.
(3) Effects on the aircraft structure and systems. There are two types of possible risks to the aircraft:
-indirect effects
-direct effects.
(a) Indirect effects.
1 Electromagnetic fields:
_
-the electromagnetic fields related to the lightning attachment can cause unwanted transient voltages and currents in the aircraft wiring and systems. In some conditions (low intensity strike, high protection), the effect on the systems can be temporary and the systems can operate correctly again after the strike. In other conditions (low protection, no circuit protection devices), the damage can be permanent and it will be necessary to replace parts.
(b) Direct effects The direct effects are the physical damage related to signs such as:
1 Pitting/meltthrough:
_
-this is the action of the electrical arc formed when a lightning stroke attaches to the aircraft (arc root damage at the attachment points or damage caused by current flow which can appear also far from the attachment points).
-signs of a lightning attachment are pitting and scorch marks and paint discoloration. On composite components, in addition to paint discoloration and skin puncturing, some delamination of the fibers can occur. If there is skin puncturing, there can be damage to the grounded equipment below composite material fairings.
-you must always compare the damage you find with the limits given in the Structural Repair Manual (SRM).
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2_ Magnetic force:
- the damage usually occurs where a small area causes the
density of the current to be high (e.g. a bonding lead
installed at a control surface hinge).
3_ Resistive heating:
- when lightning currents flow through an aircraft structure,
energy is changed to heat along its path.
- resistive heating usually causes marks of the weld type,
specially where the lightning current flows for some time.
4_ Acoustic shock wave:
- When a lightning strike occurs, there is an acoustic shock
wave. If the intensity of this shock wave is high, it can
cause deformation of thin metal skins or rupture of thin
composite skins.
(4) Inspection requirements:
(a)
Aircraft are designed to keep the effects of lightning to a minimum and make sure it can continue its flight and land safely after a lightning attachment.
(b)
It is not possible to accurately know where the attachment will occur but Zone 1 and Zone 2 show the most probable areas of lightning attachment.
(c)
Lightning strikes do not always give the same quantity of damage. The quantity of damage comes from the intensity of the lightning strike.
(d)
Therefore, it is necessary to do a full inspection after a lightning strike to make an estimate of the damage and make sure that the aircraft can, as a minimum, continue service in a Master Minimum Equipment List (MMEL) condition. The inspection after a lightning strike refers to:
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