Troubleshooting Strategies
Two methods of reasoning are used predominantly when troubleshooting complex equipment. They are functional analysis, and differential diagnosis – and the two methods complement each other.
“Functional Analysis” is a method of systematically evaluating the function of system components in order to determine which is not performing its function correctly. If you ask design engineers to describe troubleshooting, most will describe functional analysis. It is also the method that expert technicians will use when they encounter a problem that they have never seen before. Its success requires a deep understanding of the structure and function of the equipment, and skill in devising an effective test strategy.
“Differential Diagnosis” is a method of recognizing the cause of a problem by its symptoms. This is the method used by your family doctor, and it is also the method used first by expert troubleshooters. When presented with a complaint, your doctor will first recall problems that could possibly cause the reported complaint. He (she) will ask intelligent questions and perform selective tests whose results serve to support or refute those candidates, progressively differentiating among the possible causes until one stands out from the others. Its success relies upon the individual’s knowledge of potential causes and their symptoms.
These two strategies are complementary in the following way. Functional Analysis is often used in solving the original occurrence of a problem, and Differential Diagnosis is used to recognize subsequent instances of that problem.
- The first time that a new problem (failure mode) is encountered, someone needs to find the cause. That person is likely to use the Functional Analysis method. Once solved, that experience is added to the problem-solver’s personal knowledge – and he (she) is one step closer to becoming an expert.
- Now, if the following week he encounters a similar complaint, he will be able to think of several possible causes of that complaint, including the cause he identified just last week. He will ask questions and conduct tests to verify the sets symptoms that confirm or refute each of the possible causes he has in mind. If it is one of these causes, he finds the answer very quickly. This is Differential Diagnosis in action.
- However, if the root cause of today’s problem happens to be unknown to him, he soon realizes that and he will revert to the lengthier functional analysis method in order to resolve the problem.
©2008 CaseBank Technologies Inc.
In February 2000, an unusual brake problem grounded a British Airways Concorde flight from London to New York at a total cost to BA operations of over $800,000. The fault turned out to be a simple sensor failure. It took a whole day to troubleshoot, but the fix was simple and fast once they found the cause. Later, when a case history was forwarded to BA's commercial partner, Air France, BA was astonished by their reply: "We know - the same thing happened to us last year - we sent you a report on it".
The costly delay would have been avoided if the British Airways technician in London had been shown the story about Air France's experience when the problem symptoms first appeared. That's what the ADDS Service does.
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