What condition necessitates trimming an FCU?

Trimming a Fuel Control Unit (FCU) is typically dictated by the necessity to adjust the fuel flow to the engine to maintain optimal performance under changing operating conditions. In the context of the question, the presence of intake icing can disrupt airflow and affect engine performance, requiring adjustments to the fuel-air mixture for efficient engine operation. Icing in the intake can cause a reduction in airflow, which can lead to a rich fuel mixture affecting combustion efficiency and performance. Therefore, trimming the FCU helps compensate for the altered intake conditions by adjusting the fuel delivery in response to the reduced airflow, ensuring the engine continues to operate smoothly and efficiently despite the icing condition.

The other conditions listed do not directly necessitate trimming the FCU in the same way. High fuel pressure is often within acceptable operating limits and does not typically require adjustment of the FCU unless there's a specific concern about fuel metering. Excessive oil consumption is related more to lubrication issues and does not directly call for an adjustment in fuel control. Low engine temperature is generally a normal operational concern, but it doesn't inherently necessitate trimming the FCU unless it's impacting performance to a significant degree. Thus, the condition that specifically relates to the need for adjusting the FCU is the presence of intake icing.