Published date: 29 September 2023


This Advisory Circular (AC) describes an acceptable means of compliance with standards for operators when calculating the piston engine time between overhaul (TBO) for aircraft on mixed agricultural and non-agricultural operations and changing to, or from, agricultural and non-agricultural operations.

Related rules

This AC relates specifically to Civil Aviation Rule Part 91 and Part 43.

Change notice

Revision 1 makes minor stylistic and format changes in line with other ACs and adds a version history.

We have also made a marked-up copy of AC91-19 [PDF 362 KB], so changes can be easily checked. As with other ACs, text in yellow highlight denotes insertions and text in strikethrough denotes deletions.