car 66 module 5.14 electromagnetic environment

7/31/2019 CAR 66 Module 5.14 Electromagnetic Environment

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5.14 ELECTROMAGNETIC

ENVIRONMENT


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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


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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 compositematerials.

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 greatersensitivities 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 toHIRF.

Ref: AC 20-158


4/17

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.


5/17

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.


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EMC Electromagnetic Compatibility

Electromagnetic compatibility, or EMC means that adevice is compatible with (i.e., no interference iscaused by its electromagnetic (EM) environment and itdoes not emit levels of EM energy that cause

electromagnetic interference (EMI) in other devices inthe vicinity.

All electric devices or installations influence each otherwhen interconnected or close to each other. Eg your TVset, 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


7/17

EMIELECTROMAGNETIC 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.
http://en.wikipedia.org/wiki/Electromagnetic_radiationhttp://en.wikipedia.org/wiki/Electromagnetic_radiation


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EMI SOURCES (electromagnetic interference)


9/17

EMI IN AIRCRAFT


10/17

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


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CONTROLLING THE INTERFERENCE

Well Located aerials

the interference to thecomm/nav systems like ADF and VHF

Electronic equipment to be grounded and therelated wires to be shielded and grounded.

The lighting current flows through the outer skinand discharge to the extremity.

Bonding all equipments to be bonded together,min R = 0.05 ohms.

Static Discharger provide the low resistancepath to the admosphere.


12/17

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.


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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.


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PROTECTION AGAINST LIGHTNING

Aircraft skin

Voltage and current protector at the

equipment

Wire shielding

Static discharger


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PERSONAL ELECTRONIC DEVICES (PED)

Personal Electronic equipments can producesignals that affect electronic equipments.

However there was no definitive proof of

individual cases. Symptoms and failures wentoff when passengers were asked to switchPED.

The cautions were founded as some of thesensitive electronic wires run in closeproximity to passengers.


16/17

EXAMPLE OF HIRF CHECK


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TYPICAL INSPECTION (P166)

car 66 module 5.14 electromagnetic environment

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