Calibración del modelo

This thesis is presented in nine chapters as illustrated in Figure 1-2:

Chapter Title Synopsis

1 Introduction Describes the need and motivation of this

research and introduces the problem statement and research questions. This section provides an overview of the need for prognostics, current maintenance practices and issues in the area of maintenance, repair and overhaul.

2 Prognostic Techniques for

Avionics

Comprehensively reviews the prognostics and its application, also its advantages and drawbacks. This section provides the techniques currently used for prognostics in avionics.

3 Research Methodology Discusses the methodology proposed and

how they merge in this study.

4 Remaining Useful Life (RUL)

Prediction Methods in Line Replaceable Units (LRU)

Describes the fundamental theory behind research methodology that was chosen to be used in this research work.

5 Terrain Awareness and Warning

System

Describes the purpose, composition, functions, and specification related to TAWS/EGPWS.

6 Results Embeds the validation using field data into

the discussion of the results.

7 Discussion Discusses the findings that could be

potential solutions for industry problems.

8 Conclusion This chapter concludes the research work

and gives direction for further research.

CHAPTER 2

PROGNOSTICS TECHNIQUES FOR

2

AVIONICS

The aim of this chapter is to analyse evolutionary findings and techniques used in handling prognostics problems. Literature studies in pertinent to prognostics, prognostics methodology and prognostics effects in relation to aviation maintenance are studied and analysed for understanding. This chapter also provides a background study on how the problems are tackled by other researchers. In this chapter, prognostic studies will be identified by its classification and in accordance to the current trends and applications. Finally, this chapter will determine the research gap in the area of prognostic methodology for airborne avionics.

2.1 Introduction

In 2001, Federal Aviation Administration (FAA) amended a ruling on the operating rules which requires certain airplanes to be equipped with an FAA- approved terrain awareness and warning system (TAWS) or the enhanced ground proximity warning system (EGPWS). Such equipment was designed to prevent Controlled Flight into Terrain (CFIT). According to a paper by Airbus (2014) entitled “Commercial Aviation Accidents 1958-2013 – A Statistical Analysis”, CFIT, which refers to in-flight collision with terrain, water or obstacle without indication of loss of control, CFIT contributes about 23% of total number of accidents since 1994 under the fatal accidents category. A fatal accident in this case is an event in which at least one passenger or crewmember is fatally injured or later dies of his or her injury. Both the TAWS and the EGPWS, like other avionics system are quite a challenge to monitor. This is reflected by a

study done for electronics equipment where the wear-out time has been longer than the life cycle of the whole system (Sundström et al., 2008). At times also, electronics equipment fails without any definite measurable signs of fault. Therefore, it is important to establish a proper prognostic method and precursor of failure to be able to detect, isolate, and achieve prognostics outcome. Particularly important is the system level prognostics as compared to the single component level because, when faults or failure occur in airborne avionic system, technicians will simply remove an LRU rather than an electronic component such as a resistor or a memory card in the LRU. System level prognostics referred in this study is the prognostics levels of between level 4 and level 5 as summarised in Table 2-1.

Table 2-1: Failure site and prognostics level in electronics (Jie Gu et al., 2007)

Prognostic level Site

Level 0 chip and on-chip sites

Level 1 parts and components that cannot be disassembled and reassembled with the expectation that the item would still work

Level 2 circuit board and interconnects connecting the components to the circuit card

Level 3 enclosure, chassis, drawer and connections for circuit cards

Level 4 entire electronic system (LRU/ notebook)

Level 5 multi-electronic systems and external connections between different systems (LRU and cockpit display) As shown in the Table 2-1, each level is grouped according to similar electronic interaction where group level 0, being the lowest level that describes chips and on-chips sites. Regular electronic components like transistors and resistors alike fall under the grouping of ‘level 1’. Level 5 is the highest level considering the intergroup interaction among multi-electronic systems.

As with the electronics system in the aircraft, the LRUs (level 4) are removed to enable a component (level 2 or 3) to be removed, hence a quicker turn-around time for the aircraft. Many LRUs in Boeing 757/767, Airbus A300/A310

McDonnell Douglas DC-10 and Lockheed L-1011 used to have digital codes to display types of fault that was detected (Vachtsevanos, 2006). Over time, this became less effective as systems became increasingly integrated with each other.

Because of an increase in system complexity and component quality, it is useful to be using the results of a level 1, 2 or 3, as it contributes to the failure of a larger system. However, different prognostic methods are needed to cater each level as complexity accumulates as the levels increase. Intensity of factors affecting degradation may also be of different rates. For example, an increase in temperature at level 0 does increase the rate of degradation at level 5. This though may or may not be affected at the same rate. A hybrid approach to handling this issue maybe the way forward as industries are lacking in hybrid approaches in electronics (Tuchband, 2007).