# What does the letter in these ATC data blocks indicate?

Why do some have an F and others have a D?

• What is the source of the image? What else can you tell us about it (what airspace does it show, etc.)? Mar 18 at 18:24
• @TypeIA It is Sarasota airspace. It is from this Vasaviation video. youtu.be/Wsf6zzmzH8c Mar 18 at 18:33

Based on context—LFA, callsign "BUCKY," is a flight school and is unlikely to by flying "Upper Large" aircraft—the categorization being used in the video is probably the "Wake Turbulence Recategorization" (RECAT) rules, which is an older version of of the wake recategorization project (see FAA JO 7110.659C, the latest version of RECAT in use before its cancellation). The current standard is known as "Consolidated Wake Turbulence" (CWT) and procedures are defined in FAA JO 7110.126. The wake turbulence category of a particular aircraft type can be found in FAA JO 7360.1. If you had taken the screenshot at a slightly different time the datablock would have shown the aircraft type in the righthand side instead of the groundspeed.