What should you inspect when high impact is reported by a wheel impact detector but high impact is not found at the location?

When a high impact is reported by a wheel impact detector but is not subsequently found at the location, it is critical to conduct a thorough inspection to ensure that any potential issues are identified and addressed. Inspecting at least 20 axles is appropriate in this scenario for several reasons.

First, a higher number of axles helps to provide a more complete assessment of the train’s condition. A wheel impact detector may pick up transient or momentary impacts that could be related to various factors, such as track conditions, wheel defects, or other mechanical issues. By inspecting 20 axles, you ensure that any irregularities across multiple cars are detected and handled appropriately.

Additionally, inspecting a larger sample size allows for better identification of trends or patterns that might not be evident with fewer axles. This can help determine if the high impact is an isolated incident or part of a larger issue affecting the train's entire journey.

In summary, the recommendation to inspect at least 20 axles when high impact is indicated but not confirmed is grounded in the need for thoroughness and safety, ensuring that any problems are identified before they can lead to more significant issues in service.