Which action is recommended if detonation is suspected in an aircraft?

When detonation is suspected in an aircraft engine, opening the cow flaps (if the aircraft is equipped with them) can help dissipate heat from the engine. Detonation is caused by the unplanned ignition of the fuel-air mixture in the cylinder, which can lead to engine damage. Opening the cow flaps increases airflow over the engine, promoting cooling and lowering the overall temperature. This can mitigate the conditions that lead to detonation, as high temperatures can exacerbate the problem.

Maintaining proper engine temperatures is crucial, as overheating can also increase the likelihood of detonation. In contrast, ensuring the fuel is of a lower grade would not be ideal if detonation is occurring, as lower-octane fuel is even more susceptible to pre-ignition and detonation. Leaning the mixture for climbing could lead to increased engine temperatures and the risk of detonation, rather than alleviating it. Lastly, maintaining a high power setting during detonation would likely increase engine stresses and heat, further contributing to the issue. Therefore, the most effective immediate action is to open the cow flaps to aid cooling.