What action must a pilot take if total cabin pressurization is lost during cruise at FL 270?

When total cabin pressurization is lost at cruise altitude, the primary concern for a pilot is the safety and well-being of everyone on board. Descending to the lowest practical altitude, ideally below 18,000 feet, is critical because the atmospheric pressure at lower altitudes is higher, which helps mitigate the effects of hypoxia due to reduced oxygen availability at high altitudes.

At 18,000 feet and below, pilots can breathe without supplemental oxygen, which is essential in a situation where cabin pressurization has failed. This descent allows the aircraft to provide a safer environment as the cabin pressure stabilizes and reduces the risk of hypoxemia, which can occur quickly at cruising altitudes such as FL 270.

Maintaining altitude may lead to dangerous conditions, especially if passengers are not trained or prepared for rapid decompression. Additionally, ascending to a higher altitude or returning to the departure airport without descending would not address the immediate risk posed by depressurization and hypoxia, and may exacerbate the situation due to the lack of breathable air at higher altitudes.