What effect do higher-than-standard temperatures have on crossing altitudes prior to the PFAF?

• A. It has no effect on crossing altitudes.
• B. It raises the minimum crossing altitudes above standard.
• C. It may cause crossing altitudes to be below minimum prior to the PFAF.
• D. It causes the aircraft to cross altitude earlier than standard.

Answer: (C)

Higher-than-standard temperatures alter the relationship between indicated altitude and the aircraft’s true altitude. The minimum crossing altitudes shown on approach plates are computed assuming ISA conditions. When it’s hotter than ISA, the true altitude at a given indicated altitude can differ from what the plate assumes, and if temperature corrections aren’t applied to the pre-FAF segment, you can end up crossing a fix at an indicated altitude that effectively falls below the published minimum. That’s why, in hot conditions, crossing altitudes before the Final Approach Fix may be at or below the minimums if temperature effects aren’t accounted for.