For the Rolls Royce Allison powered SK-76 , engine topping/limiting check is performed to ensure that the engine will deliver 2.5 minute power without excessive droop. It is usually performed after a 150 hour inspection, engine installation , or FCU/governor maintenance. There are a couple of different limiting checks for the 76A, the one I prefer is found on page 2-5 of the Flight Check Procedures Manual(FCPM).
For example; referring to figure 2-1 of the FCPM, on a standard day 15 C @ SL the target NR would be 101.5%. With the engine to be checked set to 107% NR and the other engine at idle the collective is raised to achieve 111% torque or 826 C. T5 and maintained until NR stabilizes , usually 5 s. Nr is then recorded and compared to the target value.
If the recorded NR is = or > than the target value of the chart, in this case 101.5 % then no further maintenance is required. If the NR is less than target, then maintenance is required. Usually the engineers will then tweak the FCU or governor.
Important note, in cold climates; make sure that the aircraft is heavy so that it won’t hover on one engine.