Posted for Kevin Kossi <kevin@airforcemechanical.com>:

 Drew,
 
 According to EAA, “Undel Tri” ..
 
 http://www.eaa.org/communications/eaanews/060117_registration.html
 
 * Note: “Undel Tri” means - every three years (triennial period). The  FAA
mails notices to registered aircraft owners every three years to  either
update their information or to confirm what is posted to the  registry. Those
cards returned to FAA as “undeliverable” have the  “undel tri” entry - which
means this file is also “at risk.”
 
 
 Kevin