Accidents involving area navigation system approaches prompt agency review
The Australian Transport Safety Bureau (ATSB) has made a number of recommendations designed to enhance the safety of area navigation (RNAV) global navigation satellite system (GNSS) approaches following what is believed to be the first study of the perceived pilot workload and safety of such approaches.
The bureau recommends that Australia's air traffic service provider, Airservices Australia, conducts a study to determine whether distance information on RNAV (GNSS) approach charts is presented in the most effective way.
In addition, it recommends that Airservices reviews: the 21.5% of approaches with segment lengths different from the 5nm (9km) optimum waypoint naming conventions to improve readability and situational awareness and training for air traffic controllers to ensure that clearances for RNAV (GNSS) approaches are granted in a timely manner.
The ATSB has also called on the country's air safety regulator, the Civil Aviation Safety Authority, to conduct further research to better understand factors affecting pilot workload and situational awareness during RNAV (GNSS) approaches.
The bureau's research was prompted by two recent accidents in Australia involving RNAV (GNSS) approaches - a Piper PA-31T Cheyenne crash in Victoria in July 2004, and the May 2005 Lockhart River, Queensland, crash of a Fairchild Metro 23.
The objective of the study was to understand pilot perceptions of pilot workload during an RNAV (GNSS) approach, the ability to maintain situational awareness, ease of approach chart use, how safe RNAV (GNSS) approaches are, and which aspects of RNAV (GNSS) approach and chart design contribute to these perceptions.
The ATSB sent the survey to all Australian pilots with a civilian licence and a command instrument rating endorsed for RNAV (GNSS) approaches and had a 22% response rate, with 748 surveys completed.
The bureau found pilot workload was perceived as being higher, and the reported losses of situational awareness were more common for RNAV (GNSS) approaches than any other approach, except the non-directional beacon (NDB) approach. The RNAV (GNSS) approach was perceived as being safer than an NDB approach, but less safe than all others.
Of particular concern to respondents was that RNAV (GNSS) approaches do not use a reference for distance to the missed approach point throughout the approach on the GPS or flight management system display and limited distance references on the approach charts were inadequate. One in 15 of the respondents had been involved in an incident involving RNAV (GNSS) approaches, the most common being commencement of descent too early due to a misinterpretation of position.
The 21.5% of Australian RNAV (GNSS) approaches with short and irregular segment distances and/or multiple segment altitude steps were also identified as a major concern for many pilots.
Approach chart interpretability was assessed as more difficult for RNAV (GNSS) approaches than any other, while the use of five capital letters for waypoint names was seen as increasing the chance of a pilot misinterpreting a waypoint.
Source: Flight International
