Convective Weather Detection by General Aviation Pilots with Conventional and Data-linked Graphical Weather Information Sources

This study compares how well general aviation (GA) pilots detect convective weather in flight with different weather information sources. A flight test was conducted in which GA pilot test subjects were given different in-flight weather information cues and flown toward convective weather of moderate or greater intensity. The test subjects were not actually flying the aircraft, but were given pilot tasks representative of the workload and position awareness requirements of the en route portion of a cross country GA flight. On each flight, one test subject received weather cues typical of a flight in visual meteorological conditions (VMC), another received cues typical of flight in instrument meteorological conditions (IMC), and a third received cues typical of flight in IMC but augmented with a graphical weather information system (GWIS). The GWIS provided the subject with near real time data-linked weather products, including a weather radar mosaic superimposed on a moving map with a symbol depicting the aircraft’s present position and direction of track. At several points during each flight, the test subjects completed short questionnaires which included items addressing their weather situation awareness and flight decisions. In particular, test subjects were asked to identify the location of the nearest convective cells. After the point of nearest approach to convective weather, the test subjects were asked to draw the location of convective weather on an aeronautical chart, along with the aircraft’s present position. This paper reports preliminary results on how accurately test subjects provided with these different weather sources could identify the nearest cell of moderate or greater intensity along their route of flight. Additional flight tests are currently being conducted to complete the data set. Introduction Eighty-five percent of the aviation accidents that occurred from 1990-1996, and nearly eightyfive percent of the accident fatalities, involved small general aviation (GA) airplanes. Weather is a factor or cause in nearly a third of these accidents, which equates to approximately eleven weatherrelated GA accidents per week, with four of the eleven involving fatalities. The Aviation Weather Information (AWIN) program element, which is part of the NASA Aviation Safety program, aims to improve these accident statistics by improving weather information available to aviation users. A particular focus of the AWIN element is to develop technologies and design/use guidelines that provide improved cockpit weather information via graphical displays of data-linked weather products. Goals of this technology and guideline development are to improve pilots’ in-flight weather situation awareness and decision quality, ultimately leading to safer flights. General aviation is particularly affected by convective weather. A survey of GA accidents from 1982 to 1993 revealed that while only 3.5% of these accidents are directly attributed to thunderstorms, a large percentage of these accidents, 66%, resulted in fatalities [1]. Convective weather is challenging because it can be characterized by rapidly changing weather conditions, heavy rain, severe to extreme turbulence, high winds and gusts, hail, icing, lightning, severe downdrafts and microbursts, reduced ceiling and visibility, and instrument meteorological conditions (IMC). Such concomitant weather phenomena were analyzed separately in the aforementioned accident analysis and contribute to many additional accidents. Therefore the incidence of GA accidents attributed to convective activity, and the fatalities resulting Submitted to 20 Digital Avionics Systems Conference October 2001 2 from such weather systems, is likely underrepresented by the percentages cited for only thunderstorm effects. Currently, pilots of small GA aircraft have limited in-flight information on convective weather activ ity, especially when compared to that available on larger aircraft. Unlike larger aircraft, most small GA aircraft are not equipped with onboard weather detection equipment such as weather radar or lightning detection systems (e.g., Stormscope, Strikefinder) that can indicate convective activity. In addition, the onboard weather radar systems that are available for small GA aircraft are typically expensive, and limited in performance by size and power constraints. When available, these systems can provide improved weather awareness for severe weather hazards, but are limited in range and accuracy [2]. Onboard weather radar systems are workload-intensive to use accurately [3], are subject to attenuation, have a limited range, and provide information that is primarily forward of the aircraft and at the aircraft's altitude [4]. While these systems show severe local weather to avoid, they do not provide the more comprehensive weather picture required to fully support strategic planning or avoidance maneuvers. Pilots of small GA aircraft today rely principally on aural sources and external, or "outthe-window," weather cues for weather information. Aural sources can include direct queries to Flight Service Station (FSS), En Route Flight Advisory Service (EFAS, or "Flight Watch"), and Air Traffic Control (ATC) personnel, as well as monitoring frequencies to hear other pilots' comments, queries, and the information supplied to them. Pilots can also tune in automated weather information services such as HIWAS, AWOS/ASOS, and ATIS to obtain a broadcast of conditions over a large area or at specific reporting stations. Unfortunately, the information available from these aural sources is limited and, when weather becomes a problem, the frequencies used to obtain this information become saturated, making this information inaccessible at exactly the time it is most needed. More accessible, complete, and usable weather information would benefit pilots' situation awareness, decision-making, and safety. Graphical weather is a more appropriate representation [5], can more effectively be integrated with other such information (e.g., terrain) and can be extended using symbology. Accordingly, pilots using prototype graphical weather information systems (GWIS) in static and dynamic desktop simulation experiments were more likely to acquire trend data, have a more comprehensive awareness [6], make better go/ no-go decisions, rate hazard levels higher, have more confidence in weather-related decisions, make fewer calls to ground aviation weather personnel [7][8], and make more correct decisions with graphical, than with verbal or text alerts [9][10]. One early implementation of an uplinked radar mosaic GWIS, developed at MIT Lincoln Labs with funding from the FAA Datalink Operational Requirements Team (DLORT), had a 15-minute update rate, 6km-square resolution and employed a "lossy" algorithm (resulting in less well-defined precipitation areas) to compensate for lower available bandwidth (250bps) [11][12]. In desktop usability assessments, all subjects found the high level of lossy compression unacceptable, and some found that the medium level lacked the functional equivalence of the uncompressed image [7][13]. When used in a GA flight test, accompanied by terminal forecasts and surface observations, and integrated with a traffic information service, subjects commented enthusiastically on the utility of this GWIS [14]. More than 82% of subjects had positive responses to the utility of precipitation maps, surface observations, and terminal forecasts individually [15]. All subjects had a positive overall impression of the system; 88% indicating that it would be important to make available to GA operations [15]. The FAA Flight Information Services Data Link (FISDL) program will soon make data-linked weather information systems widely available to GA pilots via commercial FISDL vendors. The FISDL vendors will provide, for no service charge, uplink of textual aviation weather products. These products include weather observations (METARS & SPECIs) and forecasts (TAFS) of terminal environments, as well as reports of severe weather conditions (SIGMETS, Convective SIGMETS, AIRMETS, and severe weather forecast alerts) and pilot reports (PIREPS). GA pilots may augment this basic information by purchasing services that will uplink graphical weather information, Submitted to 20 Digital Avionics Systems Conference October 2001 3 including a national weather radar mosaic (NEXRAD mosaic). This textual and graphical weather information will be broadcast via a network of VHF ground stations, and received and displayed via an onboard GWIS. NavRadio Corporation (now part of the Bendix-King Division of Honeywell International), in a cooperative agreement with NASA AWIN, developed such a prototype GWIS which was subsequently selected for the FISDL program. FAA FISDL and NASA AWIN jointly funded a simulation experiment at Research Triangle Institute (RTI) to evaluate pilot weather flying with and without a version of this GWIS. In this study, the flight simulator subjects were in IMC, had access to an autopilot, and were given a GWIS display that included a NEXRAD mosaic map but lacked an overlaid aircraft present position symbol. Results indicated that while this GWIS increased awareness of the general location of convective weather, it did not improve pilot diversion decisionmaking (subjects did not understand the location of weather with respect to their position), increased workload for at least half the subjects, and reduced reliance on ground-based weather professionals [16]. This simulation study suggested several features for GWIS's (e.g., aircraft present position symbol) and concluded that further experimentation is required to develop industry standards for appropriately designing GWIS interfaces and procedures for using these systems. The AWIN Convective Weather Sources (CoWS) experiment, described in this paper, also uses a variant of the NavRadio-developed prototype GWIS but does so in a flight environment. This particular GWIS variant, hereafter referred to in this paper as the “AWIN GWIS,” includes a symbol depicting the aircraft’s present position and direction of track overlaid on a NEXRAD mosaic map, which is displayed on a handheld, tethered unit. The CoWS experiment principally investigates how GA pilots’ use of various weather information sources – conventional aural, "out-the-window" visual, and GWIS-displayed cues – affects their inflight weather situation awareness and decisionmaking related to convective weather systems. In addition, this experiment allowed us to collect usability data for this GWIS implementation. An earlier publication [17] reported initial CoWS experiment flight test results of pilots’ relative confidence, information sufficiency, and workload ratings when using aural, out-window visual, and graphically represented weather information cues in flight near convective weather. This paper reports on the accuracy and consistency of the test subjects’ ability to identify convective weather relative to their aircraft location and flight track. Additional flight tests are currently being conducted to complete the data set.