2. SYLLABUS
5.14 Electromagnetic Environment – L2
• Influence of the following phenomena on
maintenance practices for electronic system:
– EMC-Electromagnetic Compatibility
– EMI-Electromagnetic Interference
– HIRF-High Intensity Radiated Field
– Lightning/lightning protection
3. THE INCREASED CONCERN IN RECENT
YEARS BECAUSE:
• Greater dependence on electrical and electronic systems for
continued safe flight.
• Reduced electromagnetic shielding due greater use of composite
materials.
• Increased susceptibility of electrical and electronic systems to
HIRF due to increased data bus and processor operating speeds,
higher density integrated circuits and cards, and greater
sensitivities of electronic equipment;
• Expanded frequency usage, especially above 1 gigahertz (GHz);
• Increased severity of the HIRF environment because of an
increase in the number and radiated power of radio frequency
(RF) transmitters; and
• Adverse effects experienced by some aircraft when exposed to
HIRF.
Ref: AC 20-158
4. ADVERSED EXPERIENCES
• Gross navigation error in a passenger aircraft
in USA (from Newark to San Maarten) caused
by a portable tv set used by a passenger.
• Lap top used by a passenger affected the
navigation equipment during aircraft take-off
and landing.
5. ELECTROMAGNETIC ENVIRONMENT
• Caused by transmission of electrical energy in
space, e.g from radar, radio or TV.
• Like current flowing in a wire, magnetic fields
are created.
6. EMC – Electromagnetic Compatibility
• Electromagnetic compatibility, or EMC means that a
device is compatible with (i.e., no interference is
caused by its electromagnetic (EM) environment and it
does not emit levels of EM energy that cause
electromagnetic interference (EMI) in other devices in
the vicinity.
• All electric devices or installations influence each other
when interconnected or close to each other. Eg your TV
set, your GSM handset, your radio and nearby washing
machine or electrical power lines.
• The purpose of electromagnetic compatibility (EMC) is
to keep all those side effects under reasonable control
7. EMI
ELECTROMAGNETIC INTERFERENCE
• Electromagnetic interference or EMI, also
called radio frequency interference or RFI. It is
the disturbance that affects an electrical
circuit due to either electromagnetic induction
or electromagnetic radiation emitted from an
external source.
• If avionics equipments are left unprotected,
may cause serious flight safety issues.
10. SOURCES OF EXTERNAL
INTERFERENCES (note P168)
• Two forms of interference
– Conducted interference
– Radiated interference
• Sources of interferences
– External Electrical Systems e.g brushes, switches
– Engines system – ignition system
– Inadequate bonding
– Faulty static discharger/wicks
11. CONTROLLING THE INTERFERENCE
• Well Located aerials – the interference to the
comm/nav systems like ADF and VHF
• Electronic equipment to be grounded and the
related wires to be shielded and grounded.
• The lighting current flows through the outer skin
and discharge to the extremity.
• Bonding – all equipments to be bonded together,
min R = 0.05 ohms.
• Static Discharger – provide the low resistance
path to the admosphere.
12. WHAT IS HIRF
• It is High Intensity Radiated Fields
(electromagnetic energy) external to the
aircraft, of a strength sufficient to have
adverse affect on aircraft safety.
• Note: The source of energy is external,
exclude onboard system and static sources.
13. LIGHTNING
• The high energy and high voltage can affect
the aircraft hardware as well as the data.
• The high transient discharge current can
damage the skin of the aircraft and the
bonding wires.
14. PROTECTION AGAINST LIGHTNING
• Aircraft skin
• Voltage and current protector at the
equipment
• Wire shielding
• Static discharger
15. PERSONAL ELECTRONIC DEVICES (PED)
• Personal Electronic equipments can produce
signals that affect electronic equipments.
• However there was no definitive proof of
individual cases. Symptoms and failures went
off when passengers were asked to switch
PED.
• The cautions were founded as some of the
sensitive electronic wires run in close
proximity to passengers.
