EFFECTIVITY
ALL
L70861
External Lightning Strike Areas 500
5-51-151 Figure 201 May 01/01
Page 202
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
EFFECTIVITY
ALL
G. A lightning strike usually attaches to the airplane in a Zone 1 (Fig. 201) area 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 usual areas for lightning to make an entrance or exit point are the nose radome, the wing tips, the engine nacelle lip, the horizontal stabilizer tips, and the vertical stabilizer tips. Less regularly, lightning entrance and exit points are found on trailing edge flap track fairings, external lights, landing gear, landing gear doors, waste water masts, and pitot probes. But it is important to know that lightning can make an entrance or exit from any area of the aircraft, even from Zone 3 areas where lightning strikes do not usually occur.
H. Zone 2 areas (Fig. 201) are areas 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.
I. 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 and can get a lightning strike without damage. But, a strike of unusually high intensity can possibly cause damage to the electrical system components.
J. 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 have no lightning protection function. As the airplane flies through the air, it can pick up a static 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 interference to the VHF or HF radios. The static dischargers help to bleed the static charge off in a way that prevents radio noise.
K. The static dischargers are frequently hit by lightning. Because of this, some personnel think static dischargers are for lightning protection. This is incorrect; the static dischargers have no lightning protection function. The dischargers have the capacity to carry only a few micro-Amps of current from the collected static energy. The 200,000 Amps from a lightning strike will cause damage to the discharger or make it fully unserviceable.
May 01/01 5-51-151 Page 203
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
EFFECTIVITY
ALL
2. Examine External Surfaces for Lightning Strike Damage
A. References
(1)
AMM 23-11-0, HF Communications System
(2)
AMM 23-21-0, VHF Communications System
(3)
AMM 23-61-0, Static Dischargers
(4)
AMM 28-11-0, Fuel Tanks
(5)
AMM 28-11-11, Door - Access, Wing Surge Tanks
(6)
AMM 27-11-0, Ailerons
(7)
AMM 27-21-0, Rudder
(8)
AMM 27-31-0, Elevators
(9)
AMM 28-41-0, Fuel Quantity Indicating System
(10)
AMM 34-24-0, Standby Magnetic Compass
(11)
AMM 34-31-01, ILS Navigation System
(12)
AMM 34-35-0, Marker Beacon System
(13)
AMM 34-48-0, Radio Altimeter System
(14)
AMM 34-41-0, Weather Radar System
(15)
AMM 34-31-01, VOR System
(16)
AMM 34-53-0, ATC System
(17)
AMM 34-55-01, DME System
(18)
AMM 34-57-01, Automatic Direction Finder (ADF)
(19)
AMM 53-52-0, Nose Radome
(20)
SRM 51-40-9, Allowable Damage and Repair of Flame Sprayed Aluminum Coatings
(21)
D637239, Nondestructive Test Manual
B. Examine the Airplane External Surface
(1) Examine the Zone 1 (Figure 201) surface areas for signs of lightning strike damage.
(a) Do the examinations that follow: 1) Examine the external surfaces carefully to find the entrance and exit points of lightning strike. 2) Make sure to look in the areas where one surface stops and another surface starts. 3) Examine the internal and external surfaces of the nose radome for burns, punctures, and pin holes in the composite honeycomb sandwich structure. 4) Examine the metallic structure for holes or pits, burned or discolored skin and rivets.
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