Warning and alerting systems

The most important aspect of evaluating warning and alerting systems is to determine the effectiveness of the system in capturing the attention of the crew in a timely and appropriate manner. An effective warning will posses adequate attention-getting qualities so that it can gain the crew’s attention even during high workload situations where there may be little surplus mental capacity to register new information. In rotorcraft the main means of providing warnings is by lights usually on a centralized warning panel (CWP). The effectiveness of these illuminated warnings depends on factors such as the intensity of illumination, the position of the CWP in relation to the pilot’s normal field of regard, and the size of the light. Often separate lights known as ‘attention getters’ are used to increase the chances of capturing the crew’s attention and causing them to look at the CWP. Warning lights may be placed on the instrument of interest as is the case of the Aerospatiale Gazelle overtorque warning. To test the effectiveness of warning lights the aircraft is operated under a range of lighting conditions and, in particular, with bright sunlight on the instrument panel. The conversion of some aircraft to NVG compatibility has caused problems with filters being placed over CWPs resulting in poor daylight readability. Testing the suitability of the position of warning lights ideally involves unannounced illuminations during high workload tasks.

All warnings should be appropriate to the emergency or malfunction that they indicate. Major warnings requiring immediate intervention by the pilot are normally coloured red and are often supplemented with audio tones while lesser warnings are indicated by an amber colour. Advisory lights are usually coloured blue or green. Where warnings are used to indicate the approach of a limit it should activate sufficiently early to aid the pilot in respecting the limit. Audio warnings are checked to ensure that they can be heard even when radio calls are being received and crew members are talking over the intercom. If multiple audio warnings are fitted then the system of allocating priority is checked.

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