05-51-13
 ALL  ú ú 01 Page 201 ú Jun 18/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 G.  Airplane components made of ferromagnetic material may become strongly magnetized when subjected to lightning currents. Large current flow from the lightning strike in the airplane structure can cause this magnetization.
 H.  A lightning strike usually attaches to the airplane in Zone 1 (Fig. 201) and goes out a different location in Zone 1. 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

 (5)
Elevators

 (6)
Vertical Fin Tips

 (7)
Ends of the Leading Edge Flaps

 (8)
Trailing Edge Flap Track Fairings

 (9)
Landing Gear

 (10)
 Water Waste Masts

 (11)
 Pitot Probes

 I.  Zone 2 (Fig. 201) is where an initial entry or exit point is not usual, but where a lightning channel may be pushed back from an initial entry or exit point. As an example, the nose radome may be the area of an initial entry point, but the lightning channel may be pushed back along the fuselage aft of the radome by the forward motion of the airplane.
 J.  Lightning strikes can cause problems to the electrical power systems and the external light wiring. The electrical system is designed to be resistant to lightning strikes. But, a strike of unusually high intensity can possibly damage the electrical system components below:
 (1)
Fuel Valves

 (2)
Generators

 (3)
Power Feeders

 (4)
Electrical Distribution Systems

 K.  Frequently, a lightning strike is referred to as a static discharge. This is incorrect and may cause you to think that the static dischargers found on the external surfaces of the airplane prevent lightning strikes. These static dischargers are for bleeding off static charge only; they provide no lightning protection function. As the airplane flies through the air, it can pick up a static electrical charge from the air (or dust/water particles in the air). This static charge can become large enough to bleed off the airplane on its own. If the charge does not bleed off on its own, it will usually result in noise on the VHF or HF radios. The static dischargers help to bleed the static charge off in a way that prevents radio noise.
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 05-51-13
 ALL  ú ú 01 Page 202 ú Jun 18/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 L.  The static dischargers are frequently hit by lightning. The dischargers have the capacity to carry only a few micro-Amps of current from the collected static energy. The approximate 200,000 Amps from a lightning strike will cause damage to the discharger or make it fully unserviceable.
 TASK 05-51-13-052-072
 2.  Examine External Surfaces for Lightning Strike Damage
_____________________________________________________
 A.  References
 (1)  
AMM 23-61-00/201, Static Dischargers

 (2)  
AMM 28-11-00/201, Fuel Tanks

 (3)  
AMM 28-11-03/401, Door - Access, Wing Surge Tanks

 (4)  
AMM 23-11-00/501 HF, Communications System

 (5)  
AMM 23-12-00/001, VHF, Communications System

 (6)  
AMM 27-11-00/501, Ailerons

 (7)  
AMM 27-21-00/501, Rudder

 (8)  
AMM 27-31-00/501, Elevators

 (9)  
AMM 28-41-00/501, Fuel Quantity Indicating System

 (10)
 AMM 34-31-00/501, ILS Navigation System

 (11)
 AMM 34-32-00/501, Marker Beacon System

 (12)
 AMM 34-33-00/501, Radio Altimeter System

 (13)
 AMM 34-43-00/501, Weather Radar System
　
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