Changes to publishing standards and calculation of visibility minima - (CD 1904AS)

Closed 2 Jun 2019

Opened 2 May 2019

Results updated 9 Dec 2019

The purpose of this review was to gain feedback on a proposal to amend the Part 173 Manual of Standards (MOS). This would permanently set in place a longstanding temporary exemption arrangement relating to instrument flight procedure publishing standards, and to clarify the requirements for calculating visibility minima.

There were nine completed responses in total. A summary of this feedback is included in the Summary of consulation on changes to publishing standards and calculation of visibility minima document below. 


Published responses

View submitted responses where consent has been given to publish the response.


Amendments to:  Part 173 Manual of Standards (MOS)

Part 173 of the Civil Aviation Safety Regulations 1998 (CASR) sets the Australian standards for instrument flight procedure design. The regulation and its associated MOS was introduced in 2003.

CASA is proposing to amend the Part 173 Manual of Standards (MOS) to permanently set in place a longstanding temporary exemption arrangement relating to instrument flight procedure publishing standards, and to clarify the requirements for calculating visibility minima.

Publishing standards

The MOS includes the publishing standards for flight instrument procedures. The standards include the text format - for example the way latitude and longitude values are depicted on an instrument approach chart, and the pictorial layout for instrument flight procedure charts. The MOS also contains the procedures and formula for calculating the visibility minima that appear on all Australian instrument approach procedures.

The MOS reflects publishing standards that were in use at the time it was first issued. Since then, there have been changes to the regulatory arrangements for publication of aeronautical data such as instrument flight procedure charts. Most significantly, Part 175 (Aeronautical information management) came into effect in 2014. Part 175 introduced a scheme for aeronautical information management whereby information (including instrument flight procedure charts) must comply with a data product specification (DPS).

Until recently, it has not been possible to amend the MOS to reflect the changed situation. Instead, and for several years, CASA has granted exemptions from the publishing requirements in the MOS to the small class of Part 173 certified designers. The terms of these exemptions reflect the current and ongoing arrangements according to Part 175.

However, instruments of exemption are time-limited. This means CASA has had to renew the exemptions from time to time; processes that have a time and cost impact.

CASA proposes to change the MOS to reflect the terms of the latest exemption. In effect, CASA intends to replace the whole of Section 8.9 (including the sample charts and publishing standards) with a broad requirement for procedures to be prepared in accordance with a DPS given to the designer under regulation 175.160 of CASR.

Calculation of instrument approach visibility minima

There has been an ongoing issue with the Section 8.1 standards for determining visibility minima. Due to the formatting of the requirements, the standards have sometimes been interpreted as requiring designers to adjust vertical minima to account for the visibility minima available for a particular situation. However, the intended policy requirement is that the visibility minima must be adjusted taking into account the vertical minima, and not vice versa. Further, the calculation standards have been found restrictive compared to international standards, specifically in terms of allowing an operational benefit (reduced visibility minima) for runways equipped with approach lighting systems that are shorter than the standard 900 m length.

To address these issues, CASA proposes to consolidate paragraphs, and subsection 9.1.1 into a single section. The new section will have standards to the effect that visibility minima calculations will be on the basis of runway alignment and length of approach lighting (if any) provided for the runway. The precise technical details can be found in the draft instrument for amending the MOS that is included on this webpage.

Consequential and editorial amendments

The proposed changes require some consequential amendments. CASA is also taking the opportunity to consolidate various definitions into a new definitions section and to make some minor editorial changes in the document.

Documents for review

A copy of the Summary of Proposed Change and the draft MOS amending instrument called ‘Manual of Standards (MOS) Part 173 Amendment Instrument 2019 (No. 1)’, are provided below in the ‘Related’ section.

Why your views matter

This consultation is seeking feedback on the proposal to amend Part 173 MOS for the purpose of finally setting in place the temporary exemption arrangements pertaining to publishing standards and to consolidate and simplify the standards pertaining to visibility minima calculations.

General comments and file upload option

There is a general comments box at the end of the consultation. You can add your comments on matters related to the regulatory amendment, which have not already been addressed in the consultation. This page also contains a file upload for an additional document should you wish to provide one.

Comments on the proposal to amend Part 173 MOS should be submitted through the online response form.

What happens next

Once the consultation has closed, we will register and review each submission received through the online response form. We will make all submissions publicly available on the Consultation Hub, unless you request that your submission remain confidential. We will also publish a Summary of Consultation which summarises the feedback received.

Information about how we consult and how to make a confidential submission is available on the CASA website.

To be notified of any future consultations, you can subscribe to our consultation and rulemaking mailing list.


  • CASA Staff
  • Aerodrome operator
  • Air operators
  • Pilots
  • Part 173 of CASR Certified/Authorised Instrument Flight Procedure Designer Aerodrome
  • Part 175 of CASR Aeronautical information service providers


  • Airspace and infrastructure
  • Operational standards