A Pilot-centered Turbulence Assessment and Monitoring System (tams)

Airborne encounters with clear air turbulence (CAT) continue to significantly affect the safety and efficiency of commercial aviation. Fatalities, injuries and the additional costs associated with both encountering and avoiding turbulence are serious problems. Turbulence-induced injuries are airlines’ most frequent source of insurance and workers’ compensation claims. This paper will discuss the preliminary results of a NASA sponsored Phase 2 SBIR contract to develop a system to improve the detection, assessment, categorization and reporting of in-flight encounters with clear air turbulence. Additionally, the design for an aircraft-based system that will inform both aircraft operators and airspace managers in a timely and appropriate manner of the location and severity of various forms of turbulence is presented. The goal of this research is to give flight crews, air traffic controllers, flight planning/dispatch organizations and weather forecasters more timely and accurate information on the extent and severity of turbulence that may impact their operations. TAMS (Turbulence Assessment and Monitoring System) uses an innovative approach to the problem. The merits and challenges of developing a standardized, human-centered scale to accurately quantify the energy state of the atmosphere are discussed. By integrating data already available from the flight deck avionics with potentially new software and/or hardware designs, the goal of this research is to develop a standardized rating system of turbulence that would provide meaningful information to all users of the airspace, allowing better short-term operational decisions and improved longer-term forecasting models. PROBLEMS ASSOCIATED WITH TURBULENCE While data about in-flight turbulence encounters are not systematically gathered and reported, the Federal Aviation Administration (FAA), the National Transportation Safety Board (NTSB), and Transport Canada all consider turbulence to be an extremely serious problem. These sources report the costs of turbulence-induced injuries to be the airlines’ most frequent source of insurance and workers’ compensation claims, asserting that “turbulence injuries to passengers and flight attendants are a highcost item in terms of dollars as well as human suffering” (FAA, 1994 p.9). NASA has identified turbulence as a significant contributor to non-fatal accidents in transport category aircraft (Huettner & Lewis, 1997 p.5). There are two primary concerns relating to operations involving CAT: passenger and crew injuries and increased operating costs. Passenger and Crew Injuries: An FAA Office of Integrated Safety Analysis study of accidents on U.S. scheduled passenger flights identified in-flight turbulence as the leading cause of serious injuries to passengers and crew members in non-fatal accidents (FAA, 1994 p.1). In the fourteen-year period from 1984 through 1997, 90 accidents involving turbulence-related serious injury on scheduled domestic passenger carriers were reported to the FAA and NTSB, accounting for 68 serious flight attendant injuries and 55 serious passenger injuries. During the same period, 142 incidents involving minor injuries were also reported. These accidents and incidents incurred 270 minor flight attendant injuries and 707 minor passenger injuries (FAA, 1999). Increased Operating Costs: Compensating for areas of anticipated or encountered turbulence yields disruptions in planned altitudes and/or routing, which significantly decreases aircraft efficiency, therefore increasing operating costs. Three areas in which turbulence significantly increases operating costs are: 1. Avoiding areas of forecasted turbulence that actually would not adversely affect the flight. Because turbulence is a poorly understood and modeled atmospheric phenomenon, forecasting it is even more difficult. Further complicating this situation is that different aircraft experience the same turbulence conditions differently. What may be “moderate” for one aircraft type may only be felt as “occasional light” by a heavier or slower aircraft. Reports and forecasts should account for the specifics of the particular aircraft type, but this information may not always be available. Despite oftentimes inaccurate forecasts, it is the responsibility of the Pilot-in-Command and Flight Dispatcher (for airline operations) to assess the planned route of flight and make adjustments as necessary in an attempt to avoid “significant” turbulence. These adjustments often mean flying several flight levels above or below the optimum, or they may require flying a circuitous route around the area of forecast turbulence. These preflight planning adjustments to altitudes or routes may require increased fuel loads, longer flight times, or, in extreme cases, removing revenue cargo or passengers. All of these adjustments are expensive because they either add to the operating costs of the flight, or lower the revenues from it. 2. Prematurely vacating an optimum altitude or course based on reports of turbulence ahead. Once a flight encounters unexpected turbulence, particularly clear air turbulence (CAT), the captain must assess the severity, solicit additional route and altitude turbulence information from air traffic control (ATC), ascertain where the flight attendants are in their cabin service, and calculate fuel reserves and time constraints to determine the best course of action. Because reports of turbulence are subjective -based on the type of aircraft and the experience and priorities of the crew making the report -the variability of the reports are considerable. Pilots have little or no concrete data on which to base a decision. They often err on the conservative side and request a change in altitude or course. While this may be prudent from a safety perspective, it is also expensive, especially if the change was actually unnecessary. 3. Remaining at an altitude or on a course for too long, given the turbulent conditions. Because pilots only have subjective assessments of turbulence conditions to consider enroute, some may ride out the turbulence encounter. However, if these pilots were to make a more timely decision to avoid the area of turbulence (based on more precise turbulence data), their fuel and time resources would be used more effectively than when spent seeking smoother conditions after or during an encounter. Typically, though, due to the discomfort experienced by passengers and the disruption of cabin service (as well as the direct and indirect costs mentioned above), most flight crews aggressively seek to avoid turbulence encounters. To summarize, there are significant costs associated with turbulence encounters, especially for airliner operations. Many of these problems are exacerbated by the subjective and imprecise way in which turbulence is currently measured and reported. PROBLEMS ASSOCIATED WITH THE CURRENT TURBULENCE REPORTING SYSTEM Currently, turbulence is categorized and reported by using a subjective system that requires the crew to assess the aircraft and occupant reaction to it. This subjective system suffers from several shortcomings that limit its usefulness in both forecasting and reporting turbulence. Among these shortcomings are: Forecast and reports are not aircraft specific. Different types of aircraft have different sensitivities to turbulence. These sensitivities vary from 0.015 to 0.046 g’s/ft/sec and are due to various airplane characteristics, including: weight, wing surface area, wing sweep angle, typical operating altitudes, and typical operating airspeeds. For example, a Boeing 747 has a sensitivity of 0.034, whereas a Boeing 727’s is 0.031, and a DC-10’s is 0.026 (Lee, Stull & Irvine, 1984 pp. 69-70). (Based upon the general notion that a heavier airplane is less sensitive to turbulence, one would expect the 747 to be the least sensitive of these three airplanes, not the most.) Thus, a report of “moderate” turbulence by one aircraft type may not actually cause the same reaction in another aircraft flying through the same area. Turbulence also affects different parts of the same aircraft differently. The Boeing 767ER and DC-8 are “famous” among flight attendants for how difficult it is to even stand in the aft galley when the aircraft encounters what many pilots in the front of the aircraft consider to be “light chop.” It is often this subjectivity and the resulting disparity of assessment between the aircraft’s occupants that leads to injuries. Occupant reaction is subjective. Assessment is a subjective measure -defined by the experience of the reporting aircraft. The three categories of turbulence (extreme/severe, moderate and light) roughly match the concerns of the three major constituencies aboard an aircraft. Extreme/severe turbulence, which seriously affects the controllability of the aircraft, is of the greatest concern, particularly to the cockpit crew. The second level (moderate) often prevents the flight attendants from providing cabin service and attending to passenger needs; or the flight attendants risk injury to themselves and others if they attempt a service. The third level (light) does not prevent the flight crewmembers from completing their respective duties safely, but often creates such a raised level of discomfort and apprehension among many passengers that the flight experience is considered “poor” or “uncomfortable.” In a competitive service industry, such as air travel, pilots may wish to avoid this unfavorable customer impression at almost any economic cost. Thus, many airline pilots adjust their characterization of encountered turbulence based on what they believe is in the best interest of their particular flight at the time of the encounter. This subjectivity can lead other aircraft to make adjustments to their own operations that may not have been necessary if reports were more standardized, more accurately interpreted, and more easily transmitted among airspace users. Measurement is imprecise. One pilot’s “rhythmic bumpiness” may be another’s “rapid jolts.” Terms such as slight, momentary, erratic, large, and abrupt are not well defined and are not part of current pilot training programs. Therefore, interpretations by pilots are based on individual experiences, tolerance level, and concerns for cabin service and passenger comfort. Additionally, the density, frequency and resolution capability of the present upper-air observation network is incompatible with the microscale nature of turbulence. Observations are taken at 12-hour intervals at stations averaging several hundred miles apart, with a vertical resolution of about 2,000 feet (Lee, et al., 1984 p.8). Sparse data sampling requires the forecasters’ computer algorithms to further reduce accuracy by smoothing the prediction models in both the vertical and horizontal planes to achieve a computational answer in a reasonable amount of time. TAMS – TURBULENCE ASSESSMENT AND MONITORING SYSTEM Solving the problems enumerated above requires beginning with a standardized, objective way to measure turbulence, so that forecasts will be more accurate, so that encounters will be more avoidable, and so that any remaining encounters will be less costly. An innovative turbulence assessment and monitoring system (TAMS) that provides pilots, dispatchers, air traffic controllers/managers and forecasters with objective information about turbulence could greatly improve the safety and efficiency of airline operations. TAMS is envisioned as a tactical weather information system. NASA has identified systems relating to the tactical assessment and display of turbulence as currently having minimal or no current capacity and minimal or no R&D efforts underway or funded. (Huettner & Lewis, 1997 p.7). TAMS’s development effort is directed in this area. Atmospheric turbulence can be viewed as an energy state, much like an earthquake. Using an earthquake as a metaphor for turbulence is useful in understanding the innovation of TAMS. In an earthquake, a fixed amount of energy is released, but its effects vary considerably. Structures such as buildings and roads, designed to different tolerance levels, react differently. Additionally, persons in the quake area often categorize the severity of the quake differently, based on their prior experience and particular tolerance level. Thus, the same quake may damage one type of structure and not seriously affect another built next to it. The temblor also might be reported by the local population as “mild” but seriously scare a newcomer who has never experienced one. To overcome this variability in assessment and reporting earthquakes, the Richter scale has become widely used. This scale quantifies the quake and gives architects, engineers, city planners, the news media, and many others a simple standardized number that is very useful in describing the energy released during the quake. The current state of turbulence assessment and reporting suffers many of the limitations that earthquake assessment did until the development of the Richter scale. We believe it may be possible to use existing aircraft technology, interpreted in an innovative fashion, to overcome this limitation. It should prove useful to consider describing turbulence similarly as an energy state with a standardized, precise value. We have undertaken a research program to use aircraft sensors to provide data to a software module that converts the effects of the turbulence on the aircraft into a normalized energy state value and scales it such that it is useful to flight crews, ATC controllers, flight dispatchers and weather forecasters. TAMS then displays the information in the cockpit, records it for future analysis, and transmits it to other users. The users of the airspace could then use these values to assess the impact of turbulent air fields on their operations, and to monitor turbulence location and severity. Another aspect of TAMS is to provide pilot-centered displays of turbulence information. The turbulence information: 1. Provides an index that maps to the pilot’s key decision criteria (i.e., when to turn-on the fasten seat belt signs, when to sit down flight attendants, when to avoid an area like the plague) 2. Is customized to key differences between aircraft types, such that what is displayed reflects an objective energy state of the atmosphere is independent of an airframe’s or occupant’s reaction to that state. and 3. Is displayed in a format that is easy to monitor