Narrative:

On a return VFR flight from spinks, tx, to thomson airport, a colored, I think colored, biplane broke off doing aerobatics and flew up behind my RV6A on my right side within 30 ft of my aircraft. This formation was not briefed and no contact was established prior or during.

Google
 

Original NASA ASRS Text

Title: NMAC BTWN AN RV6 SMA SEL NEARING TFC PATTERN FOR LNDG AT AN UNCTLED ARPT AND A SEL BIPLANE FLYING UP ALONG THE R SIDE OF HIM, 30 FT AWAY, WITHOUT ANY PRIOR ARRANGEMENT OR WARNING. IT STARTLED THE RPTR SINCE HE HAD NOT MADE ANY PRIOR ARRANGEMENT TO DO FORMATION FLT AND THE OTHER ACFT WAS UNKNOWN TO HIM.

Narrative: ON A RETURN VFR FLT FROM SPINKS, TX, TO THOMSON ARPT, A COLORED, I THINK COLORED, BIPLANE BROKE OFF DOING AEROBATICS AND FLEW UP BEHIND MY RV6A ON MY R SIDE WITHIN 30 FT OF MY ACFT. THIS FORMATION WAS NOT BRIEFED AND NO CONTACT WAS ESTABLISHED PRIOR OR DURING.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.