4 Risk Analysis Considerations

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Aircraft maintenance and repair are topics that have been extensively researched for over 110 years. The Wright Brothers’ first flight at Kitty Hawk, NC in 1903 was actually four flights, the first of which resulted in a bent forward elevator. It was only after repairing the damage that the Wright Brothers proved that powered flight was possible.

Aircraft maintenance is essential to the safety of flight crews, passengers, and bystanders. For this reason, all systems, particularly mission-critical systems, are subject to extensive maintenance procedures.

Risk analysis is a way for aircraft maintenance to identify potential adverse events and quantify the probability those events will occur. With a system such as a Sikorsky UH 60 Black Hawk, conditions change constantly and failure is catastrophic. Although risk analysis is statistical and does not account for the actual conditions of Sikorsky UH 60 Black Hawk parts, it can still be used to set inspection and maintenance schedules.

Here are four links between risk analysis and maintenance:

Which parts fail?

In the long run, all parts will fail. With a maximum speed of 183 mph, Black Hawk helicopters endure enormous stress. Knowing that all Sikorsky UH 60 Black Hawk parts will eventually fail, risk analysis begins by identifying the consequences of the failure of helicopter parts or systems and focuses on those with serious consequences. For example, the failure of a screw holding a switch cover might be dangerous, but the screw and switch cover will not cause the helicopter to crash or suffer any serious consequences.

On the other hand, failure of the switch itself might be accompanied by many serious consequences. Therefore, the switch cover might be categorized much lower in the risk analysis than the switch.

When will it fail?

This is not intended to provide an exact date and time of that Sikorsky Black Hawk parts will fail. Rather, it is intended to prompt an analysis of the process by which failure occurs to determine a metric for determining the likelihood of failure.

For example, some Sikorsky UH 60 Black Hawk parts, such as landing gear, are under the greatest stress during take off and landing. For these parts, the answer to the question “when will it fail?” is “after a certain number of take offs and landings.” The remaining steps of the risk analysis process are intended to try to figure out what that number is.

On the other hand, other Sikorsky UH 60 Black Hawk parts, such as electrical relays, are under constant use during a flight. For these parts, the answer to the question “when will it fail?” is “after a certain number of flight hours.” Thus, for these parts, risk analysis is intended to try to figure out the number of flight hours to failure.

Why does it fail?

This step begins the quantification of risk. Knowing why parts fail tells you the inspections and testing that can help you to predict failure. For example, an inspection may reveal that landing gear fasteners or windshield bolts fail due to corrosion and fastener fatigue. In other words, inspection reveals that corrosion creates pits in fastener threads and vibration causes those pits to propagate into cracks.

This gives us our first empirical data point that can be tested. Knowing why Sikorsky parts fail allows us to test parts to determine the probability of that failure mode occurring at various times. For example, it could be found that pits form in threaded fasteners after 10,000 hours, and that those pits propagate into cracks after an additional 3,000 hours under vibration.

How does it fail?

This step is intended to determine the failure mode. For example, for cracked fasteners, the failure mode may be fracture, that is, the cracks in the fastener cause it to break into pieces. This gives us an additional empirical data point that can be tested. Once it is determined how long it takes for a pitted faster to crack, it is possible to test how long it takes to fracture. Typically, fracture occurs quickly after crack propagation commences.

Risk analysis is intended to aid the maintenance of aircraft. When you need to invest in new parts, don’t hesitate to rely on the experienced professionals at Rotair for help.