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Project OS 11/17 - Proposed amendments to CAO 20.18 - Computer navigation databases (subsection 9A)

Topic code: 
Flight Operations
Project status: 

Consultation documents


This project is now closed.

2 Feb 2012

Project OS 11/17 - Proposed amendments to CAO 20.18 - Computer navigation databases (subsection 9A)

This project is now closed.

Refer to the project closure Notes for further information.

18 Nov 2011

Consultation Draft - Proposed Changes to CAO 20.18 - Aircraft Equipment - Basic Operational Requirements

All comments should be sent to the Project Leader, Mal Read (Mal.Read@casa.gov.au), by close of business Thursday 1 December 2011.

3 Jun 2011

Project OS 11/17 - Proposed amendments to CAO 20.18 - Computer navigation databases (subsection 9A)

Project approved.

Closure notes

Project closed 2 February 2012.

CAO amendment No 1 was signed on 21 December and registered on 4 January 2012.


Subsection of the CAOs applies in relation to computers fitted in an aircraft for use with GPS and sets out CASA's directions for the purposes of regulation 232A of the Civil Aviation Regulations 1988. However, regulation 232A does not limit CASA giving directions in relation to GPS computers only. It enables CASA to give directions in relation to computers fitted to an aircraft for use in navigation, aircraft performance and automatic pilot systems. Consequently, the limited scope of subsection 9A means that other computer systems fitted to an aircraft for the purposes of navigation but which do not incorporate GPS, are not captured by 9A. From a safety standards perspective this is unsatisfactory.

Additionally, paragraph 9A.4 of CAO 20.18 requires that a GPS computer's database must be current and provided by a person who is an approved supplier for the purposes of paragraph 233 (1) (h) of the Regulations. However, this strict requirement conflicts with the operational policies of national aviation authorities (NAA) responsible for the approval of aircraft type design and manufacture in their particular State. Respective NAAs provide master minimum equipment list (MMEL) relief for navigation databases integral to flight management systems (FMS). The FAA policy (PL-98, Navigation Databases, MMEL Code 34) states that where a navigation database has expired that it should not preclude the use of the FMS provided that other acceptable alternative sources of navigation information are available.

Further, subsection 9A requires that a GPS computer database fitted to an aircraft and being used for navigation be current for the duration of the flight. This is not possible in all instances because the AIRAC cycle, on which the database depends to be current, may change whilst the aircraft is in flight. Most FMSs have the capacity to store the next AIRAC cycle, however, that update can only be selected prior to the aircraft being dispatched when on the ground.

Therefore, to provide CASA the means of applying conditions generally in the use of computers fitted to an aircraft for the purpose of navigation, it is proposed that subsection 9A be broadened, which will give regulation 232A greater effect. Also, it is proposed to amend paragraph 9A.4 to allow an aircraft to dispatch in accordance with its approved MEL, for a period no greater than 72 hours after the expiration of its navigation database. This will allow the aircraft to return to a maintenance facility where the update can be undertaken by an approved supplier. The amendment will also address the AIRAC cycle changing whilst aircraft are still in flight and the crew need to continue using the FMS. Use of computer navigation databases whether, current or not, will be subject to specified mitigating conditions.

This proposed legislative change will legitimise current non-compliant aircraft and also result in enhanced aviation safety. It will also avert the need for Exemption issue, with the attendant workload and costs.

Project Objective

  • Modernise subsection 9A of CAO 20.18 to ensure that it considers navigation computer systems that are typically in use today, i.e. that incorporate computer navigation systems; and
  • Provide appropriate provisions that facilitate use of modern navigation systems whilst ensuring aviation safety is maintained.

As a result of this project CASA Operations may need to update the Air Operator Certification Manual (AOCM). In addition, Standards Development will need to amend draft CASR Part 91 to the extent of any differences.


This project was approved by Peter Boyd, EM Standards Development & Future Technology on 1 June 2011.

Rules affected

CAO 20.18

Project management

Project Leader: Mal Read, Standards Officer Large Aeroplanes, Standards Development

Project Sponsors: Greg Hood, EM CASA Operations

Standards Development Project Manager: Peter Robbins, Senior Standards Officer Large Aeroplanes, Standards Development

Project Priority


Project OS 11/17