What is meant by a “float” in the context of VNAV?

In the context of VNAV, the term "float" specifically refers to an unintended increase in altitude during a VNAV approach. This phenomenon can occur when an aircraft fails to descend as planned, often despite following the VNAV instructions. The term highlights the situation where the aircraft remains at a higher altitude than expected, potentially resulting in deviations from the desired vertical profile or approach path.

Understanding this concept is crucial for pilots, as it directly impacts approach procedures and can lead to issues such as unstable approaches if not managed properly. Effective management of descent rates and adherence to the VNAV path is essential in aviation to ensure safety and compliance with air traffic control instructions during the approach phase.