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Output Number
R20060020
Approval Date
Organisation
Airservices Australia
Published Date Time
Recommendation type
Recommendation
Status
Closed - Action Taken
Mode
Aviation
Date released

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.

Organisation Response
Date Received
Organisation
Airservices Australia
Response 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.

ATSB Response date
Date Received
Organisation
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.

ATSB Response date