Aviation turbine fuel — paramount specification: The single most important property that governs safe high-altitude operability of jet fuel is its:

Introduction / Context:
Jet fuel must function in extreme cold during cruise. While many properties matter (flash point for handling safety, viscosity for atomization, calorific value for range), freezing point is the key limit preventing fuel solidification at altitude.

Given Data / Assumptions:

• Aircraft wing tanks experience cold-soak temperatures well below 0°C.
• Fuel system reliability depends on remaining single-phase liquid.
• Standard commercial jet fuel specifications apply.

Concept / Approach:
Freezing point defines the onset of significant crystal formation; staying below this temperature ensures flow through filters, pumps, and injectors. Other properties, though important, are not typically the governing cold-limit constraint in flight.

Step-by-Step Solution:

Verification / Alternative check:
Jet A-1 specifications cap freezing point near -47°C, highlighting its criticality for airworthiness.

Why Other Options Are Wrong:

Common Pitfalls:
Prioritizing flash point (for storage safety) over freezing point (for in-flight safety).

Final Answer:
freezing point