Tom Bishop, PE
Senior Technical Support Specialist
Electrical Apparatus Service Association
St. Louis, MO
The paper "A “How To Guide” for Root Cause Failure Analysis" by Tom Bishop, presented at the EASA Convention 2013, provides a comprehensive methodology for conducting a Root Cause Failure Analysis (RCFA) of failed electric motors or generators. The guide emphasizes the importance of systematically identifying the fundamental issues that lead to failures, rather than settling for superficial explanations.
The process begins with preparation, where the failed motor should be quarantined and not disturbed until the investigation starts. Essential tools for the analysis include a digital camera, flashlight, magnifying glass, shop microscope, and a notebook. The investigator must remain objective, distinguishing between facts and opinions, and should prepare a list of relevant questions to gather information about the failure.
The next step is to visually inspect the motor, ideally at its operating location, but usually in the service center before any disassembly or testing. The inspection should be thorough, using tools like flashlights and microscopes to examine components closely. It is crucial to photograph the motor and its components from multiple angles and levels of detail to maintain perspective and orientation.
Interviews with customer personnel and service center employees who have firsthand knowledge of the motor's operation are vital. These interviews should be fact-finding, not fault-finding, and the same lead questions should be asked to each interviewee to ensure consistency. Documentation such as operating logs, maintenance records, and repair histories should be reviewed and organized chronologically.
Checklists from the EASA’s Root Cause Failure Analysis methodology section, or equivalent, should be used to ensure all relevant information is gathered. These checklists evolve as more information is collected, helping to create a detailed picture of the failure.
Evaluating findings involves thoroughly reviewing all collected data, including physical evidence, recorded evidence, and personal testimony. Hypotheses about possible causes should be developed and tested against the evidence. It is essential to consider all potential causes, even those that seem unlikely, to avoid erroneous conclusions.
Drawing conclusions requires analyzing the motor and its surrounding system, including the power supply, mounting, coupling, driven equipment, and environment. A Failure Mode Effect Analysis (FMEA) can help identify how different failure modes impact the system. The goal is to identify the root cause(s) of the failure, which may involve eliminating secondary causes and focusing on the primary issues.
In conclusion, the RCFA process is about preventing future failures by identifying and addressing the root causes. Even if a single root cause cannot be determined, identifying multiple probable causes can help prevent recurrence and improve overall reliability.
Key Points Covered:
- Importance of preparation and objectivity in RCFA
- Visual inspection and photographic documentation of the motor
- Conducting interviews with personnel who have firsthand knowledge
- Reviewing and organizing relevant documentation
- Using checklists to gather comprehensive information
- Evaluating findings and developing hypotheses
- Drawing conclusions by analyzing the motor and its system
Key Takeaways:
- Systematic preparation and objective analysis are crucial for effective RCFA.
- Thorough visual inspection and detailed photographic documentation help maintain perspective.
- Consistent interviews and comprehensive documentation review provide valuable insights.
- Checklists ensure all relevant information is gathered and analyzed.
- Evaluating findings and testing hypotheses lead to accurate identification of root causes.
- Understanding the motor's system and environment is essential for drawing correct conclusions.
- Preventing future failures involves addressing multiple probable causes and improving reliability.
