Final answer:
When aircraft wing fuel temperature surpasses -20°C at engine start, the plane's altitude must be kept below 10,000 feet until the fuel temperature reduces—this is due to altitude's influence on air density and a fluid's boiling point.
Step-by-step explanation:
In this situation concerning the wing fuel temp of a plane, you need to follow certain guidelines to maintain airplane safety and efficiency. If the wing fuel temperature exceeds -20°C at engine start, the altitude must be limited to below 10,000 feet until the fuel temperature decreases.
This is because the air density at high altitudes can drastically affect the temperature and boiling point of fuels. As the altitude increases, the air density decreases as indicated in Figure 12.4.5 and Table A3. It's known that the boiling point of water (and other fluids like aviation fuel) decreases when the air pressure decreases, which is the case as you go higher in altitude.
Therefore, regulating your aircraft's altitude accordingly during conditions of higher fuel temperature is crucial for safe aircraft operation. Once the fuel temperature decreases (due to the increasing air density and pressure at lower altitudes, which raises the fuel's boiling point), it is then safe to climb to a higher altitude.
Learn more about Wing Fuel Temperature