## 4 Case Study
### Risk Scenario Definition
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**FM** & **Failure Mode** & **Failure Causes** & **Failure Effects** \\ \hline \multirow{3}{*}{1} & Poor requirements & Inadequate access to stakeholders and other sources of requirements. & Increased development and sustainment costs; major schedule overturns. \\ \cline{2-4}  & Use of inappropriate constraints & Specification of unnecessary requirements & Prevents a better solution to the problem from being selected. \\ \hline \multirow{3}{*}{3} & & Requirements are not documented, difficulty in tracing large numbers of requirements & The impact of proposed and actual changes in requirements is not known \\ \cline{2-4}  & Missing requirements & Significant requirements are accidentally overlooked & Difficult and expensive to include the missing requirements. \\ \hline \multirow{3}{*}{5} & Uncontrolled requirements change & Excessive requirements volatility and unmanaged scope creep & Havoc with existing architectures, designs, implementations, and testing. \\ \hline \multirow{3}{*}{6} & & Failure to verify sufficiently early in the development process whether the requirements have sufficient quality or not & Requirements defects that are not identified during the requirements engineering process \\ \cline{2-4}  & & & \\ \cline{2-4}  & & Requirements stored in different media and by different teams without interconnection and feedback & Scattered requirements are hard to find, sort, query, and maintain. \\ \hline \multirow{3}{*}{8} & & Requirements method used is largely undocumented. It is often incomplete in terms of either missing or inadequately documented & Inconsistently specified requirements, which are difficult for architects, designers, implementers, and testers to use. \\ \cline{2-4}  & & & \\ \cline{2-4}  & & & \\ \cline{2-4}  & & & \\ \cline{2-4}  & & & \\ \hline \multirow{3}{*}{9} & & Lack of support tools, no use or inadequate use of support tools. & Increase in inconsistencies; documented requirements easily get out-of-date. \\ \cline{2-4}  & & & \\ \cline{2-4}  & & & \\ \hline \multirow{3}{*}{10} & Unprepared requirements engineers & Lack of specific technical experience and training & Inability to understand and follow good requirements methods; production of poor requirements. \\ \cline{2-4}  & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Most common failure modes found in requirements identification process [34; 35; 36]. From now on, the ten failure modes described in Table 3 will be considered here as the main causes of failure in user requirements elicitation and management, and are used in this case study to assess the risk of inadequate user identification in aircraft repair projects. This type of information is particularly important in portfolio selection, where evaluating business performance against a particular project is an important process in the go-no-go decision process for project selection. Qualitative Evaluation of the Failure Modes in the Elicitation of User Requirements  
In this section, the failure modes described in Table 3 are qualitatively assessed for each of the three repairs described in Section 4.2. The qualitative variables of severity, occurrence, detectability, reliability, availability, resilience, and robustness are used and rated using the 10-point scale described in Table 2. These ratings were obtained through interviews with MRO experts and entered in Tables 4-6. The experts selected for this type of interviews needed to have extensive experience in the field and a thorough knowledge (technical and human) of the capabilities and limitations of the company that would carry out the project. In situations where it was not possible to obtain statistical information about each risk variable, as in the case study presented, these experts used a scale from 1 to 10 to assign the value of each variable based on their experience and knowledge, as is the case with the traditional F  
and that there are tools and methods to overcome this subjectivity, but this issue is beyond the scope of this study.