Definition
An operation under 14 CFR 91.176(b) in which a pilot uses an Enhanced Flight Vision System in lieu of natural vision to continue an instrument approach below the published Decision Altitude, Decision Height, or Minimum Descent Altitude, down to 100 feet above the touchdown zone elevation. Below 100 feet above the TDZE, the pilot must have the runway environment in sight using natural vision to continue the approach and land.
Plain English
A rule that lets a pilot use a special camera-and-display system to keep descending on an approach in low visibility, but only down to 100 feet above the runway. Below that height, the pilot must be able to see the runway with their own eyes to land.
Context Anchor
Seen in EFVS instrument approach rules, training, and operating approvals that explain how low a pilot may descend using enhanced vision before switching to natural outside vision.
Derivation
TDZE stands for Touchdown Zone Elevation, the highest elevation in the first 3,000 feet of the landing runway. "In lieu of" is Latin-rooted (literally "in the place of"), meaning the EFVS image substitutes for natural sight down to this point — but only down to it.
Why Pilots Care
It lowers the approach minimums, raising the probability of completing a safe landing when visibility is limited.
Grounding Statement
Picture using the EFVS image during the final part of an instrument approach, then reaching a 100-foot checkpoint above the runway touchdown zone where normal outside vision must be good enough to continue.
Intuition Check
Do not read “to 100 feet above the TDZE” as permission to land using EFVS alone. It means EFVS may support the descent only down to that 100-foot point; below that, required visual cues must be seen naturally.
Example Sentence 1
We briefed the EFVS operation to 100 feet above the TDZE and confirmed the missed approach plan if we couldn't acquire the runway visually at that height.
Example Sentence 2
Regulations allow an EFVS operation to 100 feet above the TDZE only after the pilot verifies system certification and current weather meets the published criteria.