Module 7.19 Flashcards
At what altitude do lightning strikes most likely occur?
8000ft to 14000ft
What does a lightning strike produce in aircraft skin?
A charge, which generates voltage
How is a spark produced?
When the current encounters a discontinuity on the aircraft skin, it jumps the gape creating a spark
What can happen if these gaps are near the fuel tanks?
The spark can ignite the fuel
How often do lightning strikes occur?
Approximately every 3000 flying hours
Do designers assume a lightning strike will be of a high or low intensity in there designs?
High intensity
How many strike points to lightning strikes cause, what are they?
2:
One at the entrance point
One at the exit point
What are the 2 types of lightning strike damage?
Direct damage
Indirect damage
What is direct damage described as?
- Metallic structures which are burned, melted, or show signs of metal distortion
- Non-metallic structures which are burned, punctured, or delaminated
What is indirect damage described as?
Damage to electrical systems, i.e. wires
What areas do lightning strikes normally occur?
- Nose section and radome
- Engine nacelles
- Wing tips
- Horizontal stabiliser tips and elevator tips
- Vertical fin tip and rudder tip
What areas do lightning strikes normally not occur?
- Drain masts
- Pitot probes
- Blade antennas
- Extended ends of leading-edge slats
- Trailing edges of flap track fairing tips
- Landing gear
Where must all flight crew report all lightning strikes?
Tech log
What are the possible sizes of direct damage?
1/8 inch (3mm) in diameter
1/4 inch (6mm) or greater if the intensity is high
What are 3 examples of direct damage?
- Burns
- Discoloured paint
- Delaminated
What type of testing techniques does delimitation require and why?
Non-destructive testing to determine extent of damage
What do lighting strike diverter strips do?
Divert lightning strikes
Where are diverter strips installed?
On composite radomes
What must all damage be repaired in accordance with?
SRM
What can be done to get the aircraft back into service quickly?
Temporary sealing (speed tape)
What can happen to ferous components after a lightning strike?
They can become magnetised
What is indirect damage caused by?
High-intensity lightning strikes
why are magnetised components bad?
They can affect magnetic instruments like a compass
How do we prevent instruments being affected by magnetised components?
We use non-ferrous fasteners in areas with sensitive equipment
What can a lightning strike do to a bearing?
Cause burning or melting
What do we use to stop the burning of bearings?
Bonding leads/cables, they provide a lower resistance path
What is a lightning strike often referred to as?
A static discharge
What is the function of stack discharger wicks?
To dissipate the static charge that builds up on the aircraft
What does HIRF stand for?
High Intensity Radiated Fields
When was HIRF requirements introduced?
1992
What is HIRF?
Electromagnetic radiation that can potentially affect an aircrafts electrical systems
What can high power circuits switching on and off cause?
HIRF and induce voltages in other circuits
What can HIRF also be caused by?
lightning
When does an aircraft undergo HIRF testing?
During its certification process
What are the 3 primary areas to be considered for HIRF protection?
- Aircraft structure (airframe skin and frame)
- Electrical wiring installation protection (solid or braided shielding connectors)
- Equipment protection (LRU case, electronics input-output protection)
What are the 4 HIRF penetration checks?
- Proper bonding of the aircraft
- Correct crimping
- Screens correctly terminated and earthed
- All bonding terminals correctly torque loaded
What will the aircraft also require after HIRF penetration?
- Degaussing (demagnetising)
- Calibration compass swing
What 2 things can cause structural stresses upon landing?
- Overweight landing
- Hard landings
What does the special inspection after a heavy landing determine?
If the aircraft exceeded the Maximum Design Landing Weight (MDLW)
What is the most easily detectable sign of a heavy landing?
Wrinkled or creased wing skin
When is a phase 1 inspection applicable?
When a hard landing or a high drag/side-load landing occurs
What is a touchdown limitation expressed as?
- A rate of decent
- As a āgā loading value
What are the 4 different conditions for a high drag/side load?
- The aircraft skidded or overran the prepared surface.
- The aircraft made a landing short of the prepared surface.
- The aircraft made a landing, and two or more tyres were blown.
- The aircraft skidded on the runway sufficiently to make you think damage occurred.
What happens during a phase 1 inspection?
A close visual inspection, kept as simple as possible
When would you carry out a phase 2 inspection?
When the phase 1 inspection indicates that damage has occurred
What inspection is carried out when an overweight landing occurs?
An aircraft overweight inspection
What is checked in an aircraft overweight inspection?
- Wrinkled Wing Skin
- Fuel Leakage
- Spar Webs, Bulkheads, Nacelle Skin, Firewall Skin, and Stringers
What can severe turbulence cause?
The wing to exceed the normal wing load
What must be performed after severe turbulence?
A special inspection covering all critical areas
As a general guide, what loads indicate damage to airframe and/or engines on transport aircraft?
2.5Gs to 5.0Gs
What can high heat do to heat-teated components?
Severely degrade the strength of the structure
What must be done to any parts completely submerged in water?
They must be completely disassembled, thoroughly cleaned, dried, and treated with a corrosion inhibitor
What must you do to water damaged seats, carpets, side panels, and instruments?
Replace them as water acting as an electrolyte can cause corrosion
When will the aircraft be considered airworthy after water damage?
When all traces of water are removed
