How Lightning Strikes Affect Aviation
Capt. Martin Brodbeck
Head of Flight Operations Engineering
Swiss International Air Lines Ltd.
SEREC, October 14, 2011
Content
− Examples of lightning strike events
− How aircraft are struck by lightning
− Protections on aircraft against lightning strikes
− Regulations for airport and flight operations
− Effect to the aircraft, structure and systems
− Behavior of new material like CFRP
− Checks required by maintenance after a lightning strike
− Summary
2
Examples of lightning strike events
Navigation system failure
FedEx MD-11 freighter, had departed from Hong Kong and was already enroute when
the crew recognized a navigation system failure, that the crew suspected had been
caused by an earlier lightning strike during departure. The crew returned to Hong Kong
for a safe landing.
(aviationherald.com)
Fuel dumping
Virgin Atlantic Airbus was climbing out of London Heathrow when a lightning struck the
airplane, the crew decided to return to Heathrow Airport but dumped fuel before land.
(aviationherald.com)
3
Examples of lightning strike events
Engine failure (temporarily)
A SWISS Airbus experienced lightning strike while on approach. One engine temporarily
failed. The crew decided to abort the landing and divert to an airport with maintenance
support.
An examination of the airplane revealed no damages. The airplane resumed journey,
about half of the passengers preferred to fly on another airplane.
(SWISS)
Effects on Material
A SWISS Avro RJ100 during approach encountered a heavy lightning strike on the
forward left side of the cockpit. The strike was noticed as a very loud bang with a heavy
flash. The aircraft was inspected and several burned spots were detected in forward left
zone.
(SWISS)
4
Content
− Examples of lightning strike events
− How aircraft are struck by lightning
− Protections on aircraft against lightning strikes
− Regulations for airport and pilot operations
− Effect to the aircraft, structure and systems
− Behavior of new material like CFRP
− Checks required by maintenance after a lightning strike
− Summary
5
How aircraft are struck by lightning
− In Cumulonimbus clouds static charges are build up
− An aircraft passing through this zone can initiate a discharge  Lightning Strike
− It mostly occurs within 5’000 feet of the freezing level
− Effects are: brilliant flash of light, smell of burning material and noise
− Physical damage to an aircraft is rare
− However, damage can occur to avionics and fuselage
 Safety not threatened!
6
Content
− Examples of lightning strike events
− How aircraft are struck by lightning
− Protections on aircraft against lightning strikes
− Regulations for airport and pilot operations
− Effect to the aircraft, structure and systems
− Behavior of new material like CFRP
− Checks required by maintenance after a lightning strike
− Summary
7
Protections on aircraft against lightning strike
Manufacturing regulations
Aircraft manufacturing regulations require proper protection against catastrophic effects
from lightning:
− Minimise accumulation of electrostatic charge
− All important metal parts have to be bonded to the main earth system
− Fuel system designed to prevent the ignition of fuel vapour in tanks by lightning strike
− Make sure that functions whose failure would affect a safe flight are not adversely
affected when aeroplane is exposed to lightning
8
Protections on aircraft against lightning strike
Fly by wire technology
Advantages against conventional flight controls:
− Easy handling, good stability
− Overspeed protection, stall, windshear protection
− Maintenance costs reduced
Problems:
− Signals to control surfaces via wires not cables
 Protection against lightning strike mandatory
Protection measures:
− Wires are twisted and in metal shields in the exposed areas
− Computer in- and outputs are protected against the most severe spikes
These protections + precautions in the software ensure good protection.
9
Protections on aircraft against lightning strike
Electrostatic discharger
Electrostatic discharger to reduce electrostatic load
1)
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2)
Protections on aircraft against lightning strike
Diversion straps
Diversion straps on keflar type radome
3)
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Content
− Examples of lightning strike events
− How aircraft are struck by lightning
− Protections on aircraft against lightning strikes
− Regulations for airport and flight operations
− Effect to the aircraft, structure and systems
− Behavior of new material like CFRP
− Checks required by maintenance after a lightning strike
− Summary
12
Regulations for airport and pilot operation
If lightning strike activity exists over the airport the following restrictions apply to the
servicing of an aircraft:
− Stop work outside the aircraft (loading, catering)
− No Start Up / Push Back of the aircraft
− No connections between airplane and ground (electrical supply, headset
communication)
− Entry and exit only via jetway (not by metallic stairs)
13
Regulations for airport and pilot operation
Flight Operations
Following rules from the operations manual apply, when aircraft is exposed to lightning:
− Airport ground personell should not communicate to cockpit via interphone system
− Avoid thunderstorms with lightning activity by a distance of 20 NM
 detected by weather radar
4)
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Regulations for airport and pilot operation
Pilot
− Switch on cockpit lights to full brightness
− Note actual gear position
− File an air safety report
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Regulations for airport and pilot operation
Air Safety Report (ASR)
5)
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Regulations for airport and pilot operations
St. Elmo’s fire
www.youtube.com
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Content
− Examples of lightning strike events
− How aircraft are struck by lightning
− Protections on aircraft against lightning strikes
− Regulations for airport and pilot operations
− Effect to the aircraft, structure and systems
− Behavior of new material like CFRP
− Checks required by maintenance after a lightning strike
− Summary
18
Effect to the aircraft, structure and systems
Areas where lightning strike is most probable
6)
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Effect to the aircraft, structure and systems
Possible damage
− Pitting/meltthrough
− Scorch marks, paint discoloration, skin puncturing, deformation of fibre
− Resistive heating
− When lightning currents flow through structure, the energy is changed into heat
 weld type marks
− Acoustic shock wave
− If intesity is high, deformation of thin metal skin
20
Effect to the aircraft, structure and systems
Possible damage
− Magnetic force
− Damage in small areas, were the density of the current is high e.g. a bonding
lead installed at a control surface hinge
− Electromagnetic fields
− Unwanted transient voltages and currents in aircraft wiring and systems
Crew and passengers are not in danger as the aircraft is a kind of Faraday Cage!
21
Effect to the aircraft, structure and systems
Damage examples to an aircraft (Avro RJ100)
7)
8)
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Effect to the aircraft, structure and systems
Damage examples to an aircraft (Airbus A300)
9)
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Content
− Examples of lightning strike events
− How aircraft are struck by lightning
− Protections on aircraft against lightning strikes
− Regulations for airport and pilot operations
− Effect to the aircraft, structure and systems
− Behavior of new material like CFRP
− Checks required by maintenance after a lightning strike
− Summary
24
Behavoir of new materials like CFRP
Carbon Fiber Reinforced Plastic benefits
…to the User
…to the Designer
Reduced
weight
Fatigue &
Corrosion
resistant
Design
flexibility
…to Manufacturing
Reduced fuel
consumption
Fewer & easier
inspection
Reduced
maintenance
cost
Longer
life
25
Fewer
parts
Reduced
production cost
Manufacturing
flexibilty
Behavoir of new materials like CFRP
Carbon Fibre Reinforced Plastic benefits
− New aircraft types like B787, A350 and CSeries are using CFRP
− Possibility and Severity of Lightning Strike to a CFRP airframe is equivalent to
metallic frame
− CFRP is 1’000 times less conductive than aluminium.
 Thin CFRP fuselage panels risk a delamination of the layers in addition to burn
marks
 More energetic pulses on the wiring
Solution:
Copper or bronze metallic foil on external face of the panel restore good conductance
26
Behavoir of new materials like CFRP
Protection test
− High current generator loaded under about 70kV
− Generator connected to an electrode
− Electrode installed 10 to 15 cm above the panel
− Panel is connected back to the other pole of generator
27
Behavoir of new materials like CFRP
Comparision
CFRP panel without protection
CFRP panel with bronze mesh
10)
28
11)
Behavoir of new materials like CFRP
Horizontal stabilizer solution
Structure
Lightning Strike Protection
Carbon monolithic
Bronze mesh
Carbon sandwhich
Aluminium straps
Aluminium part
Bonding braid
12)
29
Behavoir of new materials like CFRP
CFRP Fuselage part
13)
30
Content
− Examples of lightning strike events
− How aircraft are struck by lightning
− Protections on aircraft against lightning strikes
− Regulations for airport and pilot operations
− Effect to the aircraft, structure and systems
− Behavior of new material like CFRP
− Checks required by maintenance after a lightning strike
− Summary
31
Checks required by maintenance after lightning strike
Checks according to manufacturer maintenance manual:
− Inspection of aircraft surface to find strike areas
− Inspect strike areas, type and quantity of damage
− Repair of damage and perform system checks
Aircraft is only allowed to re-enter service, after all these procedures have been
performed.
32
Checks required by maintenance after lightning strike
Example of temporary repair of a burned whole with a rivet.
14)
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Content
− Examples of lightning strike events
− How aircraft are struck by lightning
− Protections on aircraft against lightning strikes
− Regulations for airport and pilot operations
− Effect to the aircraft, structure and systems
− Behavior of new material like CFRP
− Checks required by maintenance after a lightning strike
− Summary
34
Summary
Lightning strike in aviation is a regular event, however:
− Precautionary measures are imperativ
− It can be distressing to crew and passengers
− After encountering a lightning strike maintenace action is required
− It is not threatening flight safety
35
Thank you for your attention
QUESTIONS?
36
Picture Sources
1,4)
www.flightforum.ch
2)
www.wikipedia.org
3)
www.amevoice.com
5,7,8,14) SWISS
6,9-13)
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Airbus
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