Recommendation R20070005

Recommendation issued to: Civil Aviation Safety Authority

Recommendation details
Output No: R20070005
Date issued: 04 April 2007
Safety action status: Closed - Action Taken
Background: Why this Recommendation was developed

Output text

Safety Issue

CASA's process for accepting an instrument approach did not involve a systematic risk assessment of pilot workload and other potential hazards, including activation of a ground proximity warning system.

Safety Recommendation

The ATSB recommends that the Civil Aviation Safety Authority address this safety issue.

Initial response
Date issued: 23 March 2007
Response from: Civil Aviation Safety Authority
Action status: Open
Response text:

CASA's current processes for periodic revalidation of instrument approaches specifically address pilot workload and other potential hazards. 

The approach design and validation methodology adopted in Australia is ICAO compliant (see Doc 8071 - in which Australia participated in the
development) and uses GPS United States Federal Aviation Administration TSO receivers. These standards have all been subject to international (risk
assessment) review and acceptance during their development, and are therefore not included in the approach validation process.

The validation requirements do necessitate the consideration of other potential hazards (refer Doc 8071 and MOS). This process is part of the
overall procedure design and implementation methodology as defined by ICAO.

ATSB response:

The ATSB acknowledges that although CASA may consider pilot workload and potential hazards during instrument approach revalidation, it does not intend to include such assessments in the original validation process. In addition, hazards currently assessed in the flight validation are very limited. In particular, the flight validation process does not systematically consider hazards such as GPWS activation, potential influence of turbulence, the nature of terrain information provided on the approach chart, and the nature of terrain close to the approach path.

Further correspondence
Date issued: 01 June 2007
Response from: Civil Aviation Safety Authority
Response status: Monitor
Response text:

In accordance with CASR Part 173, CASA issues procedure design authorisations and, procedure design certificates. Such authorisations have been provided to officers of Airservices Australia. CASA may also determine an instrument approach procedure under CAR 178(6). CASA validates new approaches by confirming that they meet the PANS - OPS criteria and test flying.

In the case of revalidation of an approach, CASA also test flies the approach concentrating on the identification of changes in physical obstacles, airspace, or traffic which may affect the approach.

CASA has developed a draft Advisory Circular (AC) which contains guidance, procedures and checklists to validate instrument approaches. This draft AC also covers issues such as approach fly-ability, and pilot workload (based on the standard of a recently rated pilot).

The draft AC is being used as the basis for the revalidation of a number of approaches. This project commenced in February, and to date CASA has completed approximately 100 approaches.

A final version of the AC will be settled once the revalidation project is completed and is expected to be made available to industry at the end of 2008.

ATSB comment:

The ATSB notes the actions being taken by CASA to address this safety issue and has amended the status of this recommendation to ' Monitor'.

Further correspondence
Date issued: 30 September 2008
Response from: Civil Aviation Safety Authority
Response status: Closed - Partially Accepted
Response text:

On 11 August 2008, CASA and Airservices staff flew the Runway 12 RNAV GNSS approach with an aircraft fitted with a Garmin 430w GPS and TAWS-B. The first approach was flown using the 3.49 degree profile on autopilot. No terrain or 'pull-up' warnings were received. After flying the approach on profile, two lower than profile approaches were flown, below the cloud base (around 2500') along the laterally guided flight path. On each occasion the terrain warning and pull up functions of the TAWS sounded well before the significant ridges. It was also noted by the operating pilot that the approach was no more difficult to fly than any other he had experienced.


I have also attached, for your information, a more detailed report with recommendations for further CASA action. I understand that these outcomes have been communicated to your staff and that it has been agreed that TAWS A warnings could be experienced on a range of approaches besides RNAV GNSS depending on the aircraft configuration and the nature of terrain in the vicinity and was affected by any pilot decision to not fly the optimum profile as published. This is not a circumstance unique to Lockhart River or RNAV (GNSS) approaches.




4. Consideration be given to a CASA funded TAWS A to be fitted to the Radiola (VH) conquest for CASA for project development applications and CASA staff training.

ATSB comment:

The ATSB is concerned that the flight test did not provide a true validation test as the TAWS Class B (TAWS-B) as fitted to the test aircraft is a reduced capability system aimed at reducing the cost of the equipment for use in general aviation. The primary difference between TAWS-A and TAWS-B is that TAWS-B does not include the basic GPWS components, which are dependent upon a height input from a radio altimeter. As such, it is our understanding that the aircraft was not appropriately equipped to conduct flying to validate (or otherwise) the activation of the ground proximity warning system mode 2A warnings that was the subject of ATSB recommendations R20070005 and R20070008.

The ATSB agrees with the observation 'TAWS A warnings could be experienced on a range of approaches besides RNAV GNSS depending on the aircraft configuration and the nature of terrain in the vicinity ... This is not a circumstance unique to Lockhart River or RNAV (GNSS) approaches.'

The ATSB agrees with the recommendation attached to the CASA letter of 30 September 2008 with the aim that the TAWS A system be used as part of the systematic validation of approach designs as per ATSB recommendation R20070005.

Last update 05 April 2012