INTEGRATED APPROACH TO HUMAN FACTORS AND SAFETY

INTEGRATED APPROACH TO HUMAN FACTORS AND SAFETY

 Integrated Approach

(a)      Human factors initiatives will be more effective if they are integrated within existing

company processes, and not treated as something additional or separate or short-term. Human factors initiatives have sometimes failed in the past because they have been marginalized and regarded as a temporary ‘fashion’. Much of human factors, in the context of maintenance organizations and JAR145 requirements, are common sense, professionalism, quality management, safety management – i.e. what organizations should already have been doing all along.

(b)     The “human factors” initiatives in the context of JAR145 are really “safety and airworthiness” initiatives, the aim being to ensure that maintenance is conducted in a way that ensures that aircraft are released to service in a safe condition. The organization should have a safety management system in place, many of the elements of which will need to take into account human factors in order to be effective.

(c)      Ideally, human factors best practice should be seamlessly and invisibly integrated within existing company processes, such as training, quality management, occurrence reporting and investigation, etc. Sometimes it is a good idea to re-invent an initiative under a new name if it has failed in the past, but we should be cautious about unnecessarily duplicating functions which may already exist (e.g. occurrence reporting schemes / quality discrepancy reporting/ etc.). It may only be necessary to slightly modify existing processes to meet the JAR 145 human factors requirements.

(d)      Human factors training is probably an exception to the advice given above, in that it is usually so new and different to any existing training that it warrants being treated as a separate entity, at least for initial training. Recurrent training, however, is probably better integrated within existing recurrent training. 

NEED TO ACCOUNT FOR HUMAN FACTORS PROBLEM IN WORKPLACE

 NEED TO ACCOUNT FOR HUMAN FACTORS PROBLEM IN WORKPLACE

(a)      Humans have performance limitations - therefore they make errors. Principles of HF establishes that policy of zero error tolerance is unlikely to be an effective safeguard against errors. Therefore, it is needed that effective program must be there to account for human factors problem in workplace – to established a policy of error management to create a safety net to trap human errors, to establish such  practices and procedures that human mind naturally follows and thus improve quality and safety. It is the human factors program that caters for this need.

(b)     An Effective Human Factors Programs train staff and put systems in place to pick up those errors – therefore, those errors don't result in delays, incidents or accidents.

(c)      Fewer errors by engineers mean reduced delays, incidents, and accidents. Therefore, the company is safer and more cost efficient.

(d)      A safer, more cost efficient, company means:

-    Fewer delays

-    Fewer injuries

-    Better company performance

-    And, therefore, better job security for its workers.

(e)      The study of human factors model establishes that humans are in the center of the working environment interacting with other elements. To have proper matching with peripheral components, proper practices and procedures are essentially needed, otherwise humans will not be able to perform in best way, rather there will be higher rates of error resulting in accidents and incidents, endangering aviation safety.

(f)      History of aviation accidents and incidents established already that it is the human factors chapter that needs to be studied, improved and practiced in aviation industry because accidents/incidents still happen in almost the same trend of statistics as those happened previously in spite of huge technological improvement in aviation. It implies that accidents don’t happen merely for technical failure, but those do happen mostly due to the failure of the human mind and management in working environment.

(g)      In 1940, it was calculated that approximately 70% of all aircraft accidents were the results of human errors.

(h)      International Air Transport Association (IATA) reviewed the situation 35 years later,  they found that there had been no reduction in the human error component of accident statistics. (Figure 1.4). 

Figure 1.4: The dominant role played by human performance in civil aircraft accidents Source: IATA, 1975

(i)       A study was carried out in 1986, in the by Sears, looking at significant accident causes in 93 aircraft accidents. These were as follows:

Causes/major contributory factors                                          %

of accidents in which this was a contributing factor

•        Pilot deviated from basic operational procedures            33

•        Inadequate cross-check by second crew member           26

•        Design faults                                                            13

•        Maintenance and inspection deficiencies                        12

•        Absence of approach guidance                                    10

•        Captain ignored crew inputs                                        10

•        Air traffic control failures or errors                                9

•        Improper crew response during abnormal conditions       9

•        Insufficient or incorrect weather information                  8

•        Runways hazards                                                      7

•        Air traffic control/crew communication deficiencies                    6

•        Improper decision to land                                          6

(j)      As can be seen from the list, maintenance and inspection deficiencies are one of the major contributory factors to accidents.

(k)      The UK CAA carried out a similar exercise in 1998 looking at causes of 621 global fatal accidents between 1980 and 1996. Again, the HF error in “maintenance or repair” area was found among the top 10 primary causal factors to accidents/incidents.

(l)       It is clear from such studies that human factors problems in aircraft maintenance engineering are a significant issue to be taken into serious consideration.

The SCHELL Model

The SCHELL Model

(a)      In 1994, Professor Graham Hunt from Massey University in New Zealand proposed that all of these interactions take place within a cultural context. While many commentators see this aspect as part of the environment, Professor Hunt believes that the organisational, national and ethnic backgrounds of individuals play a profound part in the interactions of the SHELL model and are currently not addressed satisfactorily in most cases. He has proposed the   SCHELL (pronounced skell) model. This is still a debatable point. (Figure 1.3)

Figure 1.3: SCHELL Model

The SHELL Model

The SHELL Model

(a)   In 1984, Frank Hawkins proposed that the interactions between people are also a significantarena for error generation. He proposed the addition of another Liveware to the model to take into account the interactions between people forming the interface Liveware-Liveware. This made the SHELL Model. (Figure 1.2)

Figure 1.2: SHELL Model

(b)     Liveware–Liveware: This is the interface between people.

In aviation, maintenance and aircrew training and proficiency testing have traditionally been conducted on individual basis. If each individual engineer/air crewmember is proficient, then it is normally assumed that the team of maintenance/operation team comprising those individuals is also be effective. But this is not always the case.  Interactions among team members play an important role in determining team performance.

In this L-L interface, Human Factors concentrates on errors caused by miscommunication between individuals, poor teamwork in small group situations, ineffective leadership by supervisors and managers that generate errors on the workshop floor. Staff management relationships are also within the scope of this interface.

HUMAN FACTORS MODELS

(a)              Fundamentals of human factors are better understood by different models postulated by experts.

(b)              In this section, some models of human factors will be highlighted as a beginning of the basic elements of the subject.

 The SHEL Model

(a)      Perhaps the most common way of expressing complex systems is to use simple models to illustrate the ideas. In aviation, Elwyn Edwards (1972) proposed the SHEL model to identify the components and interactions within our complex industry (see Figure 1.1).

 

Figure 1.1: Shel Model

(b)     The acronym identifies the components with the following meanings:

Software: manuals, rules, procedures, spoken words, etc., which are part and parcel of standard operating procedures in an organization;

Hardware: aircraft, machinery, tools, control and display systems;

Environment: physical, social and economic climate in which the organization and individuals operate; and

Liveware: the human beings i.e. engineers, flight crew, cabin crew, ground crew, management and administration people - in the system.

(a)              Interactions between components are represented in the model by interfaces. There are 3 interfaces in SHEL model: Liveware-software, liveware-hardware, and liveware-environment (see Figure 1.1), Human factors concentrates on theses interfaces and - from a safety viewpoint, on the elements that can be deficient, e.g.:

Deficiency in S: likelihood of misinterpretation of procedures, badly written manuals, poorly designed checklists, untested or difficult-to-use computer software etc.

Deficiency in H: not enough tools, inappropriate equipment, poor aircraft design for maintainability etc.

Deficiency in E: Uncomfortable workplace, inadequate hangar space, extreme temperatures, excessive noise, poor lighting etc.

Deficiency in L (the central component): Shortage of manpower, lack of knowledge or skill, lack of supervision, lack of support from managers, general nature of human fallibility and so on.

Note: Practical deficiencies may be identified/listed by participants that they experience in their own working environment and their impact on performance may be highlighted for realization.

(a)              Notably, Liveware is at the hub of the SHEL model. Liveware has to interact with other elements in the model forming the interfaces: Liveware-Hardware, Liveware-Software, Liveware-Environment. Suitable design and matching of the interfacings is very important to have optimum level in the performance output in the working system. 

Although modern aircraft are now designed to embody the latest self-test and diagnostic routines that modern computing power can provide, one aspect of aviation maintenance has not changed: maintenance tasks are still being done by human beings. However, man has limitations. Re-designing of aircraft with modern manufacturing techniques are making the aircraft more and more reliable but it is not possible to re-design the human being: we have to accept the fact that the human being (liveware) is intrinsically unreliable due to its natural tendency of fallibility. However, we can guard against this unreliability of human by careful design and suitable matching in the interfaces to assist his performance and respect his limitations. If these two aspects are ignored, the human - in this case the maintenance engineer - will not perform to the best of his abilities, may make errors, and may jeopardize safety.

          Liveware-Hardware: This interface is most commonly known as the human-machine systems e.g. the design of seats to fit the sitting characteristics of the human body; design of displays to match the sensory and information-processing characteristics of the user; design of controls with proper movement, force and location.

Deficiency in this interface (L-H deficiency) is to be removed to reduce the error rate. Controls that require extreme physical strength, displays that are easy to misread and hours of boring monitoring contribute to high error rates in this interface.

User-friendly controls and displays and a better understanding of the relative strengths of humans and machines provide a platform for reducing error rates considerably.

Human Factors ergonomically deals with issues arising from this interface.

Liveware-Software: This encompasses the interface between humans and the non-physical aspects of the system such as procedures, manual and checklist layout, symbology, and computer programs. The problems may be less tangible than those involving the L-H interface and consequently more difficult to detect and resolve (e.g. misinterpretation/misunderstanding of technical literature or symbology). Many of the manuals engineers were expected to use were not user friendly, policies were interpreted differently by different supervisors and rules were often ignored because they conflicted with common sense.

Liveware-Environment In the maintenance of aircraft, environment ranges from physical environment (e.g. noise, light, temperature, humidity etc) of working place to broad managerial, political, and economic constraints of the organization. These aspects of the environment interact with the human via this interface. Although modifications to some of these factors may fall beyond the function of Human Factors practitioners, they should be considered and addressed by those in management with the ability to do so.

MEANING OF HUMAN FACTORS

What is Human Factors?

(a)      Human Factors as a term and as a subject has to be clearly defined. But no single definition seems to meet all of the needs.

(b)     As a term, it refers to any factor related to humans when a human being is in a working environment.

(c)      Human element is treated as a central component of any working system. It is the most flexible, adaptable and valuable part;but it is also prone to various influences giving adverse affect to its performance. To understand this nature and reveal predictable capabilities and limitations of humans and to apply this understanding in real-life working situations, there has been research and investigations on Human Factors and it has evolved as a complete subject of study. The subject has been progressively developed, refined and institutionalized since the end of the last century and today, the subject has been backed by a vast store of knowledge which can be applied to enhance the safety of the complex system as well as increase the efficiency of the workman.

HUMAN FACTORS

The subject “Human Factors and Error Management” is most commonly termed as “Human Factors”.

(b)     The principles behind this subject area reflect the fact that as humans we all make errors. If we can accept that we all make errors, then a policy of zero error tolerance is unlikely to be an effective safeguard against errors. Therefore, a policy of error management is much more likely to result in safe operations.

(c)      This subject tells us to recognize various factors, commonly called “Human Factors” that affect us as humans, both positively and negatively, affecting our work performance and imposing limitations on our capabilities.

(d)       Research and study revealed today much about human capabilities and limitations. An understanding of these predictable human capabilities and limitations and the application of this understanding in working environment are the primary objectives of Human Factors. The result will be twin: safety and efficiency, although the major focus is on SAFETY; safety has always been the primary rationale for HF programs.

(e)      The elements of Human Factors are not new, although the subject as a matter of study is new; in most cases, human factors are application of “common sense” in working situation. The spirit of applying these common senses aim at utilization of all available resources - equipment, procedures and people - to promote safety and enhance the efficiency of flight operations as well as promote/improve quality of performance. In cockpit environment, this is called Crew Resource Management (CRM), while in maintenance, this is Maintenance Resource Management (MRM).

(d)      The CRM or MRM is concerned not so much with the technical knowledge and skills required to fly/operate an aircraft but rather with the cognitive and interpersonal skills needed to manage the flight/maintenance operations within an organized aviation system.

AIRCRAFT BONDED TYPE CONSTRUCTION

BONDED TYPE CONSTRUCTION

A bonded structure is a construction that is produced by chemical bonding of two or more layers of material with the application of a bonding agent (e.g thermosetting resin) between the layers.

Aircraft bonded structure is a form of LAMINATED CONSTRUCTION or a SANDWICH CONSTRUCTION.

A LAMINATED CONSTRUCTION is defined as a construction composed of laminations or layers of material firmly united by bonding.

A SANDWICH CONSTRUCTION is a laminated construction of three laminations: two facing sheets and a core sandwiched between the facing sheets.

Examples of bonded structure:

a)     A cricket bat or a wooden propeller: Laminated wood structure made of plank of    wood ( e.g birch)

b)     A honeycomb panel in a modern airplane: Sandwich structure with a cellular core (like honey cell) sandwiched between two facing sheets by bonding.

Varieties of bonded structures: There are wide variations of bonded structure, such as:

a)                 Laminated wood structure

b)                 Laminated metal structure or Metal bonded structure

c)                  Laminated fiberglass structure

d)                 Metal bonded honeycomb structure (sandwich construction)

e)                 Fiberglass honeycomb structure and so on.

Honeycomb sandwich structure in modern aircraft: Introduction of bonded structure, specially the sandwich construction (honeycomb)  in airframe design came as a major breakthrough in the search for a more efficient type of structure because bonded honeycomb structures are manufactured and used to perform their jobs in a manner different from the conventional structures.

Compared to the conventional structures, bonded structure has many excellent combinations of advantages like:

a)                 Much higher strength/weight ratio

b)                 Rigidity/Pliability as desired

c)                  Metallic or non-metallic or combination

d)                 Less or absolutely no corrosion problem

e)                 Better surface finish and aerodynamic smoothness

f)                   May be manufactured in a variety of shapes and sizes

Sandwiched constructed assemblies are used for such areas as bulkheads, control surfaces, fuselage panels, wing panels, and empennage skins, radomes or shear webs.

Figure 2.12 illustrates a section of bonded honeycomb. The honeycomb stands on end and separates facings, which are bonded to the core by means of an adhesive or resin. This type of construction as a superior strength/weight ratio over that of conventional structure. Also it is better able to withstand sonic vibration, as relatively low cost when compared with fastener cost and installation of conventional structures reduces the number of parts needed and greatly reduces sealing problems while increasing aerodynamic smoothness.

Special applications of metal bonded honeycomb may employ Stainless Steel, Titanium, Magnesium, and Plywood, Resin-impregnated paper, Glass, Nylon or Cotton cloth in various combinations.

Figure 2.12: Bonded honeycomb structure

AIRCRAFT WINDOWS & WIND SCREEN CONSTRUCTION

WINDOWS & WIND SCREEN CONSTRUCTION

Windows: The windows for the passenger compartment of a large airplane must be designed and installed so there is no possibility that they will blow out when the compartment is pressurized. They must be able to withstand the continuous and cyclic pressurization loading without undergoing a progressive loss of strength.

An understanding of the installation of cabin windows for pressurized airliners can be obtained from a study of Figure 2.9, which shows the details for the installation of a window in the Boeing 720 airliner. One passenger window consists of outer, center, and inner panes. The inner pane is nonstructural and is mounted in the cabin sidewalk lining. (It is not shown in Figure 2.9). The outer and center panes are each capable of taking the full cabin pressurization load. Fail-safe structure is ensured by the center pane, which can take shock loading subsequent to outer pane failure. All three panes are of acrylic plastic with the structural panes being stretched and formed to improve resistance to crazing and increase the strength.

Another example of the window installation for a jet airliner is shown in Figure 2.10. This window installation is utilized in the Douglas DC-10 airplane.

1. The passenger compartment window shown in Figure 2.10 consists of two acrylic panes, a silicone seal, eight clips, and a window ring pan. The inner pane is approximately 0.20 in (5mm)  thick, and the outer pane is approximately 0.40 in (10mm) thick. The two acrylic panes are installed in the seal and are separated by an air space. The outer pane takes the pressure load that exists when the compartment is pressurized. If the outer pane should fail, the inner pane is designed with the strength to withstand the pressure load, thus providing a fail-safe performance. A small hole at the top of the inner pane and a slit in the bottom of the seal permit conditioned air to circulate between the panes to prevent condensation.

Figure 2.9: Installation of window for a pressurized aircraft

Figure 2.10: Installation of  passenger compartment window 

Windscreen/windshield: Windscreen or windshield is the fixed windows in the flight compartment. Normally there are two windshields: captain’s windshield and the first officer’s windshield. Besides, the flight compartment has other windows: sliding clearview windows, and aft fixed windows.

The two windshields are to be installed from outside the airplane on either side of the flight compartment centerline and are heated for anti-icing and defogging.

Removal and installation procedures for the left and right windshield panels are normally identical.  The windshield panels are removed from outside the flight compartment after all electrical terminal blocks have been disconnected.

When a windshield panel is changed because of an overheat condition, the electrical system must be functionally checked. Figure 2.11 illustrates removal of a windshield.

Figure 2.11: Removal of windshield panel 

AIRCRAFT STRUCTURE IN THE EMPENNAGE

STRUCTURE IN THE EMPENNAGE

The stabilizers and the control surfaces of an airplane are constructed in a manner similar to the wings but wings but on a much smaller scale. They usually include one or more main longitudinal members (spare) and ribs attached the fuselage or may be a separate member which is both adjustable and removable.

The horizontal stabilizers often appear as the forward part of a wing, with the elevator serving as the rear part. Usually the airfoil section is that is, it has the same degree of chamber for both top and bottom.

STABILIZERS STRUCTURE

The internal structure consists of two main spars which extend the full length of the span. At the rear is an auxiliary spar to which four hinges are riveted to provide for installation of the elevators.

The principal structural members of the unit are rear spars and the ribs. The outside of the unit is covered with sheet-aluminum alloy, which adds considerably to the strength/the center section, which is within the fuselage. See Figure 2.9

 

Figure 2.9: Structures in empennage 

CONTROL SURFACE CONSTRUCTION

Control surfaces are:

a)                 Ailerons

b)                 Elevators

c)                  Rudders

d)                 Flaps & Slats

e)                 Spoilers

Construction structures of the control surfaces are basically same as the wings having attachment fittings to the main planes or tail planes or fins as applicable.

2.9   DOOR CONSTRUCTION

The doors for aircraft are usually constructed of the same materials used for the other major components.

Typically, the main framework of a door consists of:

a)                 A doorframe which is a strong and rigid sheet-metal structure

b)                 A sheet-metal outer skin which is riveted to the doorframe

The doors for a pressurized airliner must be much stronger and much more complex than the door for a light airplane. Typical of a door for the main cabin of a jet airliner is that the door consists of a strong framework of aluminum alloy to which is riveted a heavy outer skin formed to the contour of the fuselage. At the top and the bottom edges of the door are hinged gates that make it possible, in effect, to decrease the height of the door so it can be swung outward through the door opening.

The hinging and controlling mechanism of the door is rather complex in order to provide for the necessary maneuvering to move the door outside the airplane when loading and unloading passengers. For safety in a pressurized airplane, the door is designed to act as a plug fir the door opening and the pressure in the cabin seats the door firmly in place. To accomplish this, the door must be larger than its opening and must be inside the airplane with pressure pushing outward. This prevents the rapid decompression of the cabin that could occur if the door should be closed from the outside and the securing mechanism should become unlatched.

The doors and special exits for passenger carrying aircraft must conform to certain regulations designed to provide for the safety and well being of passengers. The FAA establishes these regulations, and they must be followed in the design and manufacture of all certificated aircraft for passengers.

The requirements for emergency exits for transport category airplanes are classified according to size and arrangement. The classifications are as follows:

Type 1 : A rectangular opening not less than 24 in wide by 48 in high with corner radii not less that one third the width of the exit. On each side of the fuselage must be located in the aft portion of passenger compartment unless the configuration of the airplane is such that some other location could afford a more effective means of passenger evacuation. All type-1 exits are floor level exits.

Type II :  A rectangular opening not less than 20 in (50.8 cm) wide by 44 in (112 cm) high with corner radii not greater than one-third the width of the exit. Unless type-I exits are required. one type-II exit on each side of the fuselage must be located in the aft portion of the passenger compartment except where the configuration of the airplane  is such that some other location would afford a more effective means of passenger evacuation. Type-II exit must be floor-level exits unless located over the wing, in which case they must have a step-up  inside the airplane of not more than 10 in (25.4 cm) and a step-down outside the airplane of not more than 17 in (42.18 cm).

Type-III : A rectangular opening not less than 20 in (50.8 cm) wide by 36 in (91.44 cm) high, with corner radii not greater than one-third the width of the exit, located over the wing a step-up inside the airplane of not more than 20 in (50.8 cm) and  a step-down outside the airplane of not more than 27 in (68.58 cm).

Type-IV : A rectangular opening not less than 19 in (48.26 cm) wide by 26 in (66.04 cm)high with corner radii not greater than one-third the width of the exit, located over the wing with a step up inside the airplane of not more than 29 in (72.66 cm) and a step-down outside the airplane of not more than 36 in (91.44 cm).