ZENG YANGFAIDHIROHIT

SHOFIYAH

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Contents Page• Problem Statement• What are Human Factors?• What is SHEL? Or SHELL?• Elements of SHELL• What is Error Chain?• Murphy’s Law?• Human factors that led to the Incident• What the Investigators Found/ Conclusion• The End

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Problem Statement

• Your task today is to investigate the human factors issues that could have caused this incident.

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Human Factors In general, a human factor is a physical or cognitive property of an individual or social behaviour which is specific to humans and influences functioning of technological systems as well as human-environment equilibriums.

Rohit- http://www.usernomics.com/human-factors.html

http://en.wikipedia.org/wiki/Human_factors

http://www.mtr.com.hk/eng/sustainability/sustainrpt/2005rpt/sia-hfs.html 4

What is SHEL? Or SHELL?• This concept has originated from the ‘SHEL Model’ by

Edwards in 1972, which the name was derived from the initials of its components:

(Software, Hardware, Environment, and Liveware).

• The most different point between Edwards’s SHEL Model (1972) and Hawkins’s SHELL Model (1975) is that Hawkins urged for the necessity of another ‘Liveware’ (the person) and diagrammed to illustrate the interactions between the central Liveware and each of other four systems

(ZENG YANG) 5

http://wikiofscience.wikidot.com/science:shell-model-of-human-

factors

SHELL Diagram

http://lamoureux-cse.com/hf/ (ZENG YANG) 6

Elements of SHEL• SOFTWARE (procedures , documentation , symbology , etc )

• the Software comprehends all non-physical resources, which are for organically operation, like organizational policies/rules, procedures, manuals and placards.

• HARDWARE (machines and equipment )• Various equipments, tools, aircraft, workspace,

buildings and other physical resources without human elements in aviation constitute the Hardware.

(ZENG YANG) 7

http://wikiofscience.wikidot.com/science:shell-model-of-human-factors

Elements of SHEL(II)Environment (internal and external )

• The Environment includes not only the factors which influence where people are working such as climate, temperature, vibration and noise, but also socio-political and economic factors.

Liveware (Human Factors)• The Liveware includes factors like teamwork,

communication, leadership and norms.

(ZENG YANG) 8

http://wikiofscience.wikidot.com/science:shell-model-of-human-factors

Hawkins(Central Liveware)• The Liveware, which is in the centre of the SHELL

Model, can be defined as human elements such as knowledge, attitudes, cultures and stress. This Liveware is regarded as the core of the SHELL Model and other components match with the Liveware as the central figure .

(ZENG YANG) 9

http://wikiofscience.wikidot.com/science:shell-model-of-human-factors

Chain of event or Error chain• term referring to the concept that many contributing factors typically lead to an

accident, rather than one single event.• contributing actions typically stem from human factor related mistakes and pilot

error, rather than mechanical failure.

• For today problem, if the SMM to the work by the book following the step and not judging by himself which lead to the different size of bolt use for the windscreen. And why the procedures not requiring a pressure check or duplicated check. This lead to an accident waiting to occur.

• The SMM must ensure to perform each and every function safely and by the book, no shortcuts.

• If we can break just one link in the chain, the accident will not happen.

• And also, A study conducted by Boeing found that 55% of airline accidents between 1959 and 2005 were caused by such human related factors, while only 17% of accidents were caused by mechanical issues with the aircraft.

Faidhihttp://en.wikipedia.org/wiki/Chain_of_events_%28aviation%29

Murphy’s Law• “Murphy’s Law” can be regarded as the notion: “If

something can go wrong, it will.”

• The engineer replace the bolt without referencing to the maintenance documents

• He replaces it on a like for like basis as he thinks that it could not go wrong as it is the same type of bolt.

Human factors issues that had resulted to this incident.

• Shift Maintenance Manager (SMM), short-handed on a night shift, had decided to carry out the windscreen replacement himself. He consulted the Maintenance Manual (MM) and concluded that it was a straightforward job.

• He decided to replace the old bolts and, taking one of the bolts with him (a 7D), he looked for replacements. The store man advised him that the job required 8Ds, but since there were not enough 8Ds, the SMM decided that 7Ds would do (since these had been in place previously)

The problem start...

• However, he used sight and touch to match the bolts and, erroneously, selected 8Cs instead, which were longer but thinner.

• He failed to notice that the countersink was lower than it should be, once the bolts were in position.

• He completed the job himself and signed it off, the procedures not requiring a pressure check or duplicated check.

• Accident investigators found that a replacement windscreen had been installed 27 hours before the flight, and that the procedure had been approved by the Shift Maintenance Manager.

• However, 84 of the 90 windscreen retention bolts were 0.026 inches (0.66 mm) too small in diameter, while the remaining six were 0.1 inches (2.5 mm) too short.

• The investigation revealed that the previous windscreen had been fitted with incorrect bolts, which had been replaced on a "like for like" basis by the Shift Maintenance Manager without reference to the maintenance documentation.

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