Crew errors

In the lawsuits following the 1995 B757 Cali accident, American Airlines was held liable for the crash based on the Colombian investigators blaming crew error entirely for the accident. The official accident investigation report cited the following four causes for the loss [2] ... 

Argue that the crew are empowered to cope wth unsafe system operating condtions and / that the probabiily of crew errors are / minimised 9S2Sl1309(i /... 

Step lb is therefore based on the application of a lessons learned checklist, an example of which is contained in Table 6.1. Its purpose is to identify potential sources of systemic errors (which could lead to systematic failures). It considers the possibility of requirement, design and implementation errors (as weU as reasonably anticipated crew errors after the failure occurrence of a failure condition). The checklist may be applied to consider system architecture vulnerabilities as well as physical installation vnlnerabilities in the ZSA (see Chapter 8). 

Human errors continue to dominate as a contributing factor in aircraft accidents (see Annex A to this chapter). A Boeing study (2001) found that flight crew errors are listed as the primary cause in 66% of accidents and that despite the introduction of protective devices or systans, this percentage has remained relatively unchanged in recent years. An FAA study (2002) into Aeroplane Safety Assurance Processes concluded that the processes used to determine and vahdate human responses to failure and methods to include human responses in safety assessments need to be improved and that the industry challenge is to develop aeroplanes and procedures that are less likely to result in operator error and that are more tolerant to operator error when they do occur . 

Propose a simple methodology to consider flight crew error as another failure mode in the SSA process. 

The scope of this chapter is limited to considering flight crew errors/mistakes only for the purposes of completing a typical CS25.1309 Safety Assessment. 

System Safety Assessment process to mitigate crew errors... 

Within the scope of this chapter then, let us consider the regulatory requirements which drive the integration of crew errors into the Safety Assessment process. 

Information concerning unsafe system operating conditions must be provided to the crew to enable them to take appropriate corrective action. A warning indication must be provided if immediate corrective action is required. Systems and controls, including indications and annunciations must be designed to minimise crew errors, which could create additional hazards . 

There are various ways to approach this complicated task, and the illustration in Fig. 10.1 attempts to simplify the basic approach of how to mitigate crew errors as part of the system development life cycle. Most of these steps fall within the remit of the design team (with input from the HF specialist). The System Safety Engineer s key input is at Step 3, but each step will be explained below as any neglect upstream will make downstream certification efforts increasingly more difficult. 

Right crew errors typically occur when the crew does not perceive a problem and fails to correct the error in time to prevent the situation from deteriorating. A report by the FAA, The Interfaces between Rightcrews and Modem Right Deck Systems found... 

Design (taking us back to Step 1) to make the system more forgiving of crew errors and revocable (i.e. provide time/opportunity to recognise and correct errors). 

Add probability of crew error to any qualitalive and or quantitative probability analyses (e.g. Human Hazard ETA, see Chapter 4), noting that the probability of crew error is likely to increase (see Fig. 10.5) in a stress environment. ... 

Figure 10.5 Crew error in a stress environment (Bell, as contained in Jacob s presentation 2002). 

An Event Tree Analysis (ETA), which explores aU possible outcomes of an undesired event (i.e. the specific crew error of concern), because it is only when there is a derived architecture that the exact role of humans in the system becomes clear. By using ETA the potential role of critical Human Error is evident, as are the combinations of Failures and errors necessary to create Hazardous or Catastrophic systems states. 

Recommendations for flight crew training (see Step 6), specificafly those scenarios which may induce catastrophic and hazardous crew errors. 

In Section 2.3 we defined a safety strategy for a modification progranune where an aircraft attitnde and altitude system (see Section 1.3) are upgraded. Below is an example of where crew error, in using such a system, caused an accident ... 

Systems and controls, including indications and annunciations must be designed to minimise crew errors, which could create additional hazards. 

Argue that systems and controls (ind. indicators annunciators) are designed to minimise crew errors... 

Step 3c, where the aU sources of crew errors are mitigated,... 

Table 10.2 Example crew error assessment summary...

Aldiough the probability in this column uses the same definitions as in Table 3.3, it is tlie additional probability of tlie crew error only. See Chapter 11 where this probability is added to the technical failure probability to provide for a risk which the operator needs to manage ion service (i.e. total s tem performance is a function of the H/W and S/W functioning correclly and the user p forming the task correctly). 

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