This program meets the requirements as set forth in 14 CFR 139.321 and is required every 24 consecutive calendar months. The most current addendum to AC 150/5230-4C indicates that this course is approved by the FAA Administrator as the initial and recurrent training required to meet the standard.  The 150/5230-4C Advisory Circular outlines these requirements in detail and a copy can be found on the Forms and Brochures page.  Additionally, the Supervisor and Line Service training sign off forms, Diesel Exhaust Fluid frequently asked questions, NTSB DEF Safety Alert and the FAAs DEF Safety Alert for Operators documents are also provided in PDF format for download. This program consists of 18 lessons and a final assessment. It is a self-paced program and should take between 9-10 hours to complete.