Definition
A reference chart, typically published on instrument approach plates, that converts one set of values into another — most commonly converting Runway Visual Range (RVR) values in feet to ground visibility in statute miles, used when the required RVR equipment is inoperative or unavailable.
Plain English
A small table on an approach chart that lets you swap one type of visibility measurement for another when you can't use the original one.
Context Anchor
Seen when reading instrument approach landing minimums, especially where visibility values are listed in different forms.
Derivation
Conversion comes from Latin words meaning “to turn around” or “change.” Table comes from an old word for a flat board or written list. Together, the phrase points to a written list that changes one value into its matching value in another system.
Why Pilots Care
Accurate use prevents misjudging whether actual conditions meet the published minimums for an approach.
Intuition Check
Do not assume a conversion table is just a rough estimate. In this context, it is a published reference used to match one approved measurement value to another.
Example Sentence 1
When the tower reported the touchdown RVR equipment was out of service, the pilot used the conversion table on the approach plate to determine the equivalent ground visibility minimum.
Example Sentence 2
Before the approach the crew checked the conversion table for cold-weather altitude corrections.