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Recommendation issued to: Airservices Australia

Recommendation details
Output No: R20060020
Date issued: 16 December 2006
Safety action status: Closed - Action Taken
Background: Why this Recommendation was developed

Output text

Safety issue: RNAV (GNSS) approach chart design and interpretability

The most common concern identified by respondents about the design of RNAV (GNSS) approaches was that the charts did not use references for distance to the missed approach point throughout the approach on the global positioning system (GPS) or flight management system (FMS) displays, and distance references on the approach charts were inadequate. Approach chart interpretability was assessed as more difficult for the RNAV (GNSS) approach than all other approaches by respondents from all aircraft performance categories. Respondents considered that the information presented on RNAV (GNSS) approach charts, including distance information, may not be presented in the most usable way, and consequently may lead to loss of situational awareness.

Safety Recommendation

The Australian Transport Safety Bureau recommends that Airservices Australia address this safety issue.

Initial response
Date issued: 08 March 2007
Response from: Airservices Australia
Action status: Monitor
Response text:

This recommendation is borne of three findings:

  1. No ranging to Missed Approach Point (MAPt) throughout the approach on GPS or FMS displays:
    The matter of distance to the MAPt being shown by the navigation equipment is outside the scope of Airservices Australia's responsibility and should be directed to equipment manufacturers and database coders.
  2. Distance references on charts inadequate:
    All Australian DAP RNAV (GNSS) instrument approach charts produced by Airservices Australia have distance to the MAPt reference from the Initial Approach Fix (IAF) to the MAPt below the profile view of the procedure (see Fig 1 below).  The distances shown below the profile are in a similar format to existing conventional procedures.

    Fig 1 - Merimbula, Rwy 03 RNAV (GNSS) approach plate profile - Distance-to-go highlighted below the profile

    Merimbula, Rwy 03 RNAV (GNSS) approach plate profile - Distance-to-go highlighted below the profile
  3. Data on charts not presented in the most usable way:

    The charts are produced to agreed international standards in a format that is similar to other States that have RNAV procedures.

    One factor that that could be addressed to facilitate interpretation of the charts is to realign the waypoint named as the Missed Approach waypoint, with the runway threshold.  Historically, for coding purposes, the MAPt could not be at the threshold as there would then be one geographical point with two different functions.  This is no longer an issue and all procedures could be redesigned to have the MAPt at the threshold.  However, whilst removing one possible cause of confusion for some pilots, all pilots would require further training/notification as the 'standard' had changed.  There would also need to be some research on the effect of procedures that require the MAPt to be sited prior to the threshold for obstacles located in the Missed Approach segment and how to correctly design the procedure and chart it accordingly.

    The recommendation is partly not accepted (1 and 2 above).  In relation to the other aspect of the recommendation, the issue of the positioning of the MAPt, Airservices Australia will liaise with CASA to determine to what extent the pilot community will need re-education.  Regarding the design considerations, Airservices Australia, in conjunction with CASA, will consult the ICAO Obstacle Clearance Panel, sponsors of ICAO Doc 8168 PANS-OPS, which describes the design criteria that Airservices must adhere to under our Civil Aviation Safety Regulations Part 173 certification (173.085).
ATSB response:

Our assessment is that the RNAV approach presents new challenges for the presentation of distance information that has not existed for other types of non-precision approach. The RNAV approach is unique in that it presents distance information between waypoints, which is different from traditional approaches using ground-based aids. While the chart design conforms with the style of charts for other approach types, we think that the special characteristics of the RNAV approach would benefit from some additional design elements.

In particular, we are concerned that the distance information to waypoints and the distance to run information is not sufficiently well linked to provide pilots with the level of situational awareness that is desirable. Hence, our recommendation requested Airservices Australia consider options for a different presentation, whereby the pilot is able to see the relationship between distance to run and the distance to the next waypoint more clearly. A task-needs analysis to understand how pilots use RNAV (GNSS) approach charts would be one method that could examine how chart readability might be enhanced. That is, what information they take from the charts, how charts are scanned, and how information is assimilated. It was not our suggestion to change the position of the missed approach point relative to the runway threshold, but rather, to consider chart design improvements that would improve readability and aid situational awareness.

Further correspondence
Date issued: 27 May 2007
Response from: Airservices Australia
Response status: Monitor
Response text:

[The ATSB] raised the issue of improved charting standards to enhance pilot situational awareness with respect to the relationship between distance to run and distance to the next waypoint. The suggested task-needs analysis to understand how pilots use RNAV (GNSS) approach charts is related to Human Factors associated with operational flying and pilot behaviour. As this aspect of chart design is not wholly within our competency, Airservices will consult with CASA to determine how an appropriate analysis can be progressed for the most effective safety outcome.

ATSB response:

The ATSB notes the response from Airservices Australia and will monitor progress. The ATSB will review the status of this recommendation in approximately 6 months.

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Last update 05 April 2012