When should fuel heaters be operated to avoid engine flame-out?

Fuel heaters should be operated during taxiing, takeoff, or landing to prevent engine flame-out. This is crucial because these phases of flight are particularly sensitive to fuel temperature fluctuations. When the aircraft is on the ground, during ascent, or while descending close to the runway, the fuel may not be circulated as effectively, and lower temperatures can lead to increased viscosity. This can result in fuel not reaching the engine in a usable state, thereby causing incomplete combustion or flame-out.

Operating the fuel heaters in these critical phases ensures that the fuel remains at an optimal temperature, thus maintaining proper flow and preventing any potential issues that could lead to engine failure. In contrast, some other phases, like climb and cruise, typically see more consistent fuel temperatures due to engine operation and better circulation, making it less necessary to actively heat the fuel during these times. Pre-flight inspections do not typically involve engine operations that would directly impact fuel temperature management during critical flight stages.