05-51-18
 ALL  ú ú 01 Page 204 ú May 28/01
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757
MAINTENANCE MANUAL

 LIGHTNING STRIKE CONDITION (CONDITIONAL INSPECTION) - MAINTENANCE PRACTICES
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 1.  General
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 A.  This procedure has these three tasks:
 (1)
Examine the External Surfaces for Lightning Strike

 (2)
Examine the Internal Components for Lightning Strike

 (3)
Inspection and Operational Check of the Radio and Navigation Systems

 B.  The airplane has all the necessary and known lightning strike protection measures. Most of the external parts of the airplane are metal structure with sufficient thickness to be resistant to a lightning strike. This metal assembly is its basic protection. The thickness of the metal surface is sufficient to protect the internal spaces from a lightning strike. The metal skin also gives protection from the entrance of electromagnetic energy into the electrical wires of the aircraft. The metal skin does not prevent all electromagnetic energy from going into the electrical wiring; however, it does keep the energy to a satisfactory level. If lightning strikes the airplane, you must fully examine all of the airplane to find the areas of the lightning strike entrance and exit points. When you look at the areas of entrance and exit, examine this structure carefully to find all of the damage that has occurred.
 C.  Lightning strike entrance and exit points are usually found in Zone 1 (Fig. 201), but also can occur in zones 2 and 3.
 D.  You can usually find signs of a lightning strike in Zone 1 (Fig. 201). However, lightning strikes can occur to any part of the airplane which includes the fuselage, wing skin trailing edge panels, wing-body fairing, antennas, vertical stabilizer, horizontal stabilizer, and along the wing trailing edge in Zone 2, (Fig. 201).
 E.  In metal structures, lightning damage usually shows as pits, burn marks or small circular holes. These holes can be grouped in one location or divided around a large area. Burned or discolored skin also shows lightning strike damage.
 F.  In composite (non-metallic) structures, solid laminate or honeycomb damage shows as discolored paint. It also shows as burned, punctured, or delaminated skin plies. Damage you can not see can also be there. This damage can extend around the area you can see. Signs of arcing and burning can also occur around the attachments to the supporting structure.
 G.  Airplane components made of ferromagnetic material may become strongly magnetized when subjected to lightning currents. Large current flowing from the lightning strike in the airplane structure can cause this magnetization.
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 05-51-19
 ALL  ú ú 01 Page 201 ú Sep 28/99
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757
MAINTENANCE MANUAL

SEE B SEE A
SEE A
SEE B
SEE A
SEE B
SEE A
SEE B
SEE A
SEE B
ZONE 1: HIGH PROBABILITY
ZONE 2: PROBABLE
ZONE 3: LOW PROBABILITY (AREA INCLUDES ALL STATIC
AREAS NOT IN ZONES DISCHARGER 1 AND 2)
SETSCREW
SETSCREW
RETAINER

STATIC DISCHARGER
RETAINER
TRAILING EDGE SURFACE INSTALLATION STABILIZER AND FIN CAP INSTALLATION (EXAMPLE) (EXAMPLE)
A B
External Lightning Strike Areas Figure 201
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 05-51-19
 ALL  ú ú 01 Page 202 ú May 28/99
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MAINTENANCE MANUAL

 H.  A lightning strike usually attaches to the airplane in Zone 1 (Fig. 201) and goes out a different Zone 1 area. Frequently a lightning strike can enter the nose radome and go out of the airplane at one of the horizontal stabilizer trailing edges. The external components most likely to be hit are listed below:
 (1)
Nose Radome

 (2)
Nacelles

 (3)
Wing Tips

 (4)
Horizontal Stabilizer Tips
　
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