International audience; TCAS resolution advisories generation process during level-off situation is overviewed and illustrated on a real situation captured through mode S radar with RA downlink service. It underlines that one common type of resolution advisories is that which is issued when aircraft are expected to level-off 1000 feet apart, and are converging at the same time. These resolution advisories, often subsequently classed as ?operationally unnecessary? from an air traffic control standpoint, can be perceived as disturbing by controllers and by pilots. This issue has been tackled in this paper by proposing a method to prevent RA triggering during level off situation. This method is based on the setting of the altitude at which the autopilot switches towards the altitude capture mode and on an intrinsic parameter of the autopilot altitude capture mode, namely its natural frequency. It is shown that applying the proposed method to the illustrative example prevents the issuance of resolution advisories when aircraft are expected to level-off 1000 feet apart. The method which is presented is one of the simplest options, and allows altitude capture without triggering resolution advisories for vertical speeds up to 3000 feet/min. Nevertheless, the time needed by the aircraft to capture the cleared flight level is increased. Consequently, future work will focus on improving the time needed to capture the cleared flight level under the constraint to keep positive the distance between the autopilot altitude capture dynamic and the boundary of the RA zone.
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