What is APU torching?

APU torching refers to the phenomenon where there is a burst of flame expelled from the Auxiliary Power Unit (APU). This occurs during the operation of the APU when there is an incomplete combustion of fuel, leading to a visual display of fire and flames being ejected from the exhaust. This situation can happen due to various factors like fuel quality, operational conditions, or mechanical issues within the APU.

Understanding APU torching is crucial for safety procedures because it indicates that the APU is not functioning efficiently, potentially leading to more serious issues. Recognizing this condition allows crew members to assess the situation, take necessary precautions, and manage the APU effectively to prevent accidents or further mechanical failures.