Tuesday, January 7, 2014

Module 5.14 Electromagnetic Environment

I am consolidating the modules in one blog. This is done to enable easier searching by readers...

I had prepare 18 slides for the topic shared below:


MODULE 5  SLIDES

CHAPTER 12 – ELECTROMAGNETIC ENVIRONMENT


Slide 1 - Syllabus as Per Part 66

Electromagnetic Environment Syllabus (part 66) (Level – 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  

Slide 2 WHY 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.

Slide 3. ADVERSED EXPERIENCES
The experiences had proven the need consider the threat seriously.
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.

4. 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.
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.

5. The purpose of electromagnetic compatibility (EMC) is to keep all those side effects under reasonable control
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.

6. EMI SOURCES (electromagnetic interference)
EMI IN AIRCRAFT
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

7. 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.

8. 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.

9. 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.

10. PROTECTION AGAINST LIGHTNING
Aircraft skin
Voltage and current protector at the equipment
Wire shielding

11 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.

12. The cautions were founded as some of the sensitive electronic wires run in close proximity to passengers.  
EXAMPLE OF HIRF CHECK




TYPICAL INSPECTION (P166)

13 REVIEW and QUESTIONING