Flight crew and aircraft performance during RNAV approaches: studying the effects of throwing new technology at an old problem

Non-precision approaches (without vertical guidance) are known to expose aircraft to greater risk of CFIT (controlled flight into terrain). One solution consists of RNAV (area navigation) approaches with a computer-generated lateral and vertical path, which use the aircraft's flight management computer to fly an approach without any conventional ground-based radio facilities. We studied 22 pilots who flew 66 real RNAV approaches. Of special interest to us were the human factors and safety implications of using this new technology for an old problem. The high level of automation used for RNAV approaches brings with it a new potential for automation surprise (e.g. unexpected level-offs at go-around altitude) and extra monitoring requirements, especially for the pilot-not-flying. There is also an effect of low temperature that makes for shallower approaches as compared to ILS (instrument landing system). Pilot acceptance of RNAV approaches as measured in this study is high, and perceived mental workload for both pilot flying and pilot not-flying is low. This can be explained in large part by the shift from double-checking height against distance in traditional non-precision approaches, to pattern matching (aircraft symbol/reference) during RNAV approaches.