Instrument flight procedures (operational information) - Draft Advisory Circular - 91-27 v1.0

CASA sought feedback on draft advisory circular (AC) 91-27 v1.0 - Instrument Flight Procedures (Operational Information). It was developed to:

• provide information on the use of instrument flight procedures in Australia
• explain the reasons for and background to industry practices for instrument flight
• clarify safety precautions to be used with instrument flight procedures.

The consultation invited feedback on the suitability of the AC (Q1) and the layout including tables, figures, highlight boxes, examples, and appendices (Q2). Targeted feedback was also sought on several key technical topics, which included:

• instrument approach procedures (IAPs) requiring CASA approval (Q3a & Q3b)
• IAPs terminology and interrelationships (Q4)
• LNAV with advisory vertical guidance (LNAV+V) (Q5)
• temperature correction and temperature compensation (Q6a & Q6b)
• circling procedures and requirements (Q7a & Q7b)
• approach procedures with vertical guidance (APVs) (Q8a & Q8b)
• the effects of incorrect QNH settings on APVs and precision approaches (Q9).

There was also an opportunity for general feedback on any other issues.

About this consultation

The consultation opened on 18 February 2026 and closed 18 March 2026.

CASA received 22 responses of which:

• 14 respondents (63.6%) consented to publication of their responses.
• 8 respondents (36.4%) requested that their submissions remain confidential.

Of those 22 responses:

• 11 respondents (50%) submitted feedback on behalf of an organisation
• 11 respondents (50%) submitted personal responses.

Respondents represented a broad cross-section of industry including commercial and airline pilots, instructors and examiners, aircraft owners and operators, Part 173 instrument flight procedure designers and other aviation professionals.

Most of the feedback supported the draft AC, either as written or subject to clarification and editorial improvements. Feedback focused primarily on improving clarity and usability rather than changing policy intent or technical requirements.

Summary of feedback

Respondents generally welcomed the development of a dedicated AC covering instrument flight procedures.

Feedback indicated support for the:

• overall purpose of the AC being consolidated into a single guidance document
• coverage of key operational and safety-related topics
• explanations relating to safety critical information
• structure and layout of the document.

Suggestions for improvement

Respondents frequently selected 'Yes, but with changes' throughout the consultation. This response indicated support for the content while identifying opportunities for improvement to clarity, readability and operational usability.

Common themes included:

• distinguish more clearly between regulatory requirements and recommended practices
• expanding explanatory material and practical examples
• completion of reserved sections
• add more diagrams and worked examples
• reduced word count and simplify technical language.

Technical suggestions

Technical feedback focused largely on improving the understanding of:

• which IAPs require CASA approval
• LNAV with advisory vertical guidance (LNAV+V)
• circling procedures and requirements
• QNH errors, altitude awareness and terrain protection
• temperature correction and temperature compensation
• mixed IFR/VFR operations in Class G, Class E and non-controlled aerodromes.

The feedback generally sought additional clarification and guidance rather than changes to the underlying regulatory or operational framework.

Next steps

In response to the feedback received, CASA will review the draft AC and consider amendments to:

• improve clarity and readability
• refine technical explanations, examples, notes and explanatory material where appropriate
• address minor drafting, formatting and editorial issues.

CASA will then finalise AC 91-27 where appropriate improvements will be incorporated into the final version before publication.