CONVECTIVE WEATHER DISPLAYS AND INDICATORS ARP7528

Issuing Committee: S-7 Flight Deck Handling Qualities Stds For Trans Aircraft

Rationale: Inadvertent encounters with convective weather have led to several accidents, numerous inflight injuries and aircraft damage. Using the most recent research into the nature of convective weather, an opportunity exists to improve the displays and indicators to mitigate this risk. Pilots need to • Exercise tactical avoidance of hazardous weather to maintain best safety margins and comfort . • This is based on correct color coding and displayed-weather to aid in appropriate avoidance of active weather. Good performance to allow early avoidance planning to incorporate route changes into ATM structure • Potential route or mission abort or diversion following the identification of hazardous weather • Management of pax, galleys, cabin and crew ahead of weather Some current systems do not provide available information depicting convective weather that exists, or, in other cases, can portray benign low-altitude rain as a threat, resulting in unnecessary deviations. These factors have been exacerbated by climate change, with a combination of more moisture in the atmosphere as well as warmer ocean temperatures. The standard model in aviation training depicts thunderstorms as virtually always lifting liquid water (Vertical Integrated Liquid, or VIL) to the 25,000 foot level. The guidance for pilots is to scan at the 25,000 foot level to ascertain if a storm is convective. Some automated systems are programmed to use this same model, so in cruise flight they depict storms that do not have VIL at the 25,000 foot level as “off path weather,” often displayed in cross-hatched areas, rather than solid weather returns. A separate factor exists for climbs and descents, where typically the guidance for pilots is to align the radar beam to be roughly along the flight path, perhaps just a few degrees higher to eliminate ground returns. Many automated radar systems follow a similar approach. Although this might seem to be ideal, it can lead to situations where the radar is depicting benign low-altitude rain. As an example, since a convective storm will have some vertical development, heavy rain that only goes to 12,000 feet over Florida is unlikely to be convective, as the local conditions create an ideal environment for water to be lifted to very high levels quickly. Although this may appear to be the conservative approach, there is a risk that pilots will sometimes find themselves in areas where their radar is depicting heavy rain but (because it is only low altitude rain and not convective) there is no turbulence. This can result in the same problem of false alarms or warnings where pilots ignore a real problem due to attenuating their response. This scenario might be different in the winter time, or high latitudes, where the storm is most likely not to have as much vertical development. Although thunderstorms are portrayed as being somewhat uniform in aviation training, there are significant differences in the VIL in storms that occur in different regions as well as different climates and seasons. These differences fall into three primary categories, although there are more: 1. Thunderstorms occurring over maritime regions, particularly areas of relatively warmer water. In many cases, these storms will “rain out,” such that any liquid water in the storm does not rise above around 19,000 feet. Above that level the water will freeze and drift upwards, reenergizing above 30,000 feet, containing significant turbulence and often graupel. This is particularly prevalent at night, and in some cases these storms appear not to contain significant lightning. The use of traditional algorithms during cruise flight might create a scenario where these are depicted as off-path weather, resulting in pilots flying into a storm believing that they are over low-altitude precipitation. 2. Storms that occur in desert areas which might not contain significant liquid water relative to their strength. 3. Storms that occur in wintertime or high latitudes, as previously described. Ground-based uplinked weather displays often do not include a profile view, so pilots are unable to determine if the weather depicted is low altitude or actually convective thunderstorms. This, again, has the same potential problem of false alarms. Finally, the committee notes that some automated radar systems, while removing ground clutter automatically, do not depict cases where the radar return is attenuated due to strong storms, potentially luring pilots into flying towards areas that appear to be thinner or clear when the actual storm is hidden due to the attenuation. NOTE: Although all of the preceding could represent training issues, these areas are often not included in training. In an ideal worlds pilots would receive the training but automated systems can be designed to capture them as well. The guidance in this ARP includes aspects that the committee believes are critical to include in newer automated systems to mitigate severe weather encounters.