[IEEE 17th DASC. AIAA/IEEE/SAE Digital Avionics Systems Conference. Proceedings - Bellevue, WA, USA (31 Oct.-7 Nov. 1998)] 17th DASC. AIAA/IEEE/SAE. Digital Avionics Systems Conference. Proceedings (Cat. No.98CH36267) - An integral flight director and surveillance system for helicopters in metropolitan service

17TH DASG PAPER SYSTEM FOR HELICOPTERS IN METROPOLITAN SERVICE (Conceptual Design and Preliminary Test) Chin E. Lin S. J. Hong K.L. Chiu C. Y. Tsai Department of Aeronautics and Astronautics National Cheng Kung University Tainan, Taiwan, R. 0. China AN INTEGRAL FLIGHT DI GTOR AND SURVEILLANCE Abstract High density helicopter flights in metropolitan area arises conflict threat and challenges flight safety due to the absence of strict ATC surveillance. An integral system for flight director and surveillance (FDS) for helicopter operations in low altitude flights is proposed with feasibility study. The proposed FDS combines GIs with GPS data based on ADS concept to meet helicopter operation with collision avoidance. Both pilot and ground ATC are aware of conflict situation from the proposed FDS. System configuration with operation concept is presented with simulated tests using remote-piloted helicopters to verify FDS performance. Introduction Helicopter to be used as a general transport in Taiwan will increase air traffic control (ATC) load and challenge flight safety. Method to offer an effective means for helicopter ATC is moat desired to reduce risk of flight collision in low altitudes. Within the scope of CNS/ATM developments, GPS data as well as Geodetic Information System (GIS) are applied together to receive geographic background to pronounce air traffic conditions to all aircraft. An Integral Flight Director and Surveillance System (FDS) proposes a idea for both airborne flight director, as an avionics, and ground surveillance, as ground ATC facilities. The main loop of FDS contains automatic dependence surveillance system for local area broadcasting (ADS-LB), a communication network, CIS mapping- transform system, and ATC surveillance and collision avoidance. A metropolitan surveillance CIS display is designed for ground ATC with complete presence of flight conditions. ATC functions of separation, terrain and warnings are implemented for operation. In addition to ATC, an airborne flight director with dynamic GIS display is created to assist pilot of traffic alert for helicopters. In this paper, methods to develop traffic collision avoidance for the proposed FDS are discussed by definitions of advisories [ 1,2] with computer software implementation on both the airborne segments and ground segment. Two remote-piloted helicopters are used for simulated tests to examine GPS accuracy and FDS Derformance with feasibility [3]. Traffic Alert and Conflict Resolution for Helicopters The helicopter flights are permitted as general transport under VFR in Taipei FIR. All light aircraft operating in VFR 0-7803-5086-3 /98/$10.00 01998 IEEE F42-1 except authoiized flights shall follow the established VFR corridors and flight rules. Pilots flying in VFR corridors shall follow altitude, speed, operation constraints and voice report procedures [ 11. Since helicopters may be used as a prompt transport among special industrial sites, this demand stimulates the increase of helicopter flights near metropolitan areas. Traffic alert and conflict resolution become important to helicopter flights. Threat Advisloiy and Conflict Resolution The basic concept for collision avoidance arises that the pilot should be alerted to a threat in time for his remedial action to operate the aircraft to escape by changing its speed or altitude. Indeed, if possible, ATC controller should also be aware of such situations before and after a traffic alert happens. The development of FDS should follow ICAO standards. FDS functions include: (a) threat detection, (b) generation of Proximity Advisory (PA), Traffic Advj sory (TA), and Resolution Advisory (&I), (c) coordination to ground ATC station, (d) effective system performance. Different levels of advisories represent different threat of aircraft approach in terms of collision time [1,2]. Threat detection: Conflict detection and hazard criteria are based on the relative motion of multiple moving aircraft for either fix-wing or rotor-wing. Time and position of aircraft to the point of closest approach (PCA) in 3-D are calculated. Protected Zone: Consider pilot’s sensuous reaction to t3elay helicopter maneuver, a protected zone, called “bubble”, is created for each aircraft. On the screen, the bubble can constantly remind the pilot of threats. This also includes the instant intrusion of other helicopters with proper vertical separation. A r e q U i r e d v e r t i c a l s e p a r a t i o n s h o u l d b e o v e r 5 t i m e s o f m a i n r o t o r d i a m e t e r , when one h e l i c o p t e r i s r i g h t b e l o w o r above a n o t h e r . F o r e x a m p l e o f B e l l - 2 1 2 , t h e v e r t i c a l s e p a r a t i o n s h o u l d b e 240 f e e t . The b u b b l e i s t h e n d e f i n e d as a c o l u m n o f 2 ,050 f e e t r a d i u s w i t h 240 f e e t h e i g h t above and b e l o w . T h i s a l s o c o n c e r n s w i t h t h e l i m i t o f m i s s d i s t a n c e i n 3- D s p a c e and p r o v i d e s enough v e r t i c a l s e p a r a t i o n when P C A i s a c c o u n t e d [ 2 1 . Generation o f Advisories Conflict resolution comprises two actions: (a) to alert the pilot to potential conflicts including terrain; (b) to present the conflict resolution from ATC. When threats or potential threats are detected, the proximate traffic within certain range and certain altitude, if altitude is reported, should be displayed and distinguished by color or symbol. Recommend maneuver is sent to the pilot as part of resolution. PA, TA, and RA are displayed in terms of estimated collision time. Both pilot and ATC receive all the same information. The requirements of helicopter to identify a threat include 3-D position; relative velocity vector; and sensitivity state of helicopter. Sensitivity state: According to the aircraft performance, the sensitivity state is defined. (1) S=l, a “ S T A N D B Y ” mode i n w h i c h TA and RA a r e i n h i b i t e d ; ( 2 ) S=2, a “ T A o n l y “ mode i n w h i c h RA i s i n h i b i t e d ; ( 3 ) S=3-7, further states that enable to issue TA and RA to provide alert time. Alter time: Referring ICAO standards of ACAS, a nominal RA before closest 0-7803-5086-3 /98/$10.00 01998 IEEE F42-2 approach varies from 15 to 35 seconds, depending on the relative velocity vector of two aircraft. TA is generally issued around 5 to 20 seconds in advance to RA. Alert time depends on the sensitivity state. Considering Bell-212 at cruise speed 80- 100 knots, S=3, TA=5 and RA= 15 seconds for example. Resolution constraints: Ignoring the strategic maneuvers, the tactical resolution analysis is focused on safety constraint. Three maneuver patterns are taken into account as Altitude Maneuver to climb or descend 300 feet, which is above minimum vertical separation, Heading Maneuver to make a right turn in a 500 feet radius circle to make-ways, and Speed Change Maneuvers to accelerate or decelerate 10 knots, above “dead zone”. Coordination The FDS coordination of Collision Avoidance logic is built into the ground ATC station with priority control to decide the resolution as shown in Fig. 1. For compatibility, a set of resolutions should be decided for all helicopters in a multi- aircraft conflict event simultaneously, and the resolution maneuver or traffic warning could be performed after confirmation between pilot and ATC. This implies that the coordination of airborne to ground uses the same configuration. About priority control, assume that A, B, C and D aircraft are in a multiple conflict event. The Collision Avoidance logic issues one suite of resolutions for A, B, C and D in which the resolution between A and B is concerned first, then others. Three maneuvers are applied to let the highest priority aircraft “escape” from conflict threat. In operation, any fixed- wing aircraft can always get the highest priority. PDS Architecture In Fig. 1, the proposed FDS is mainly composed of three segments: (1) the airborne segment for all participating helicopters, (2) the ground segment for local ATC ground station, and (3) the software segment €or performance requirements. Through radio transceiver and radio modem, each helicopter down- links its airborne data to the local ATC ground center. ADS-LB is defined following the ADS definition for local area application only. According to the airborne data, the ground station sends ATC commands, including collision avoidance resolutions, to the helicopters within its safety bubble, or broadcasts aircraft’s relative position in time sharing mode. Aircraft’s positions are projected on the GIS maps of both the airborne segment and the ground segment. Coordination is also displayed on each segment as well, with symbols and abbreviation. Such information in GIS background will clearly assist pilots or controllers to be aware of environments. The GIs supports necessary background of local map for flight director. Each local area is defined as a 25 miles by 25 miles area. All participating helicopters and ground station will generate the same GIS database during ATC monitoring. Airborne Segment The airborne segment is an avionics for helicopters. The main feature of the airborne segment is shown in Fig. 2-a. All fixed wing aircraft are not concerned. Ground Segment The ground segment is an ATC station to perform helicopter surveillance and control within the defined local area. The main feature of the ground segment is shown in Fig. 2.b. 0-7803-5086-3 /98/$10.00 01998 IEEE F42-3 Software Segment The sofi.ware segment contains GIS access, threat advisories generation logic, conflict resolution logic, and display generation logic. The proposed FDS chooses MapInfo as the core software for it’s compatihle with Microsoft Windows 95 and Office 97. Under such environment, the desktop mapping with Graphic User Interface (GUI) can easily be handled, and its MapBasic language can be used to integrate MapInfo functionality into applications using Visual Basic, MapBasic, Microsoft Excel and Visual Basic are the main software of concerns. The main function of the MapBasic is to receive GPS data and GIS map database:. At the same time, this geo- information can be shown on the cells of Excel. While the program is running, a loop is crcated to check the flight conditions to send ATC commands to the cells on Excel. Visual Basic processes the geo-information and ATC commands in broadcasting using its format as: I GPS data I Encode I ATC command 1 Fig. 3 show the coordination flow of software. The software segment converts the collision avoidance advisories and algorithm into execution software as shown in Fi,g. 4. During the flight, both airborne segment and ground segment are running the same software program to generate conflict warnings onto displays. Communication Radio inodem is used to down-link GPS data, and two-way VHF radio transceiver is used to exchange flight data and ATC commands in the FDS. Their effective rarge covers about 25 miles. It determines the defined local area of 25 miles by 25 miles in width. The ADS-LB is performed to have access airborne data down-link to ground ATC. System Performance Test The concept of FDS is composed of software engineering and hardware facilities. Most part of FDS is promoted by software integration to improve its function capability. Since helicopter test is very expensive, the FDS test used two remote-piloted helicopters for simulation, as shown in Fig. 5. Three vans are used, one plays as the ground segment, and the others operate as airborne segments. The remote control helicopters transmit flight data to these three vans. The simulated test verifies the FDS with the following performance. (1) Data transmission for both radio modem and radio transceiver is capable deliver data within the local area. (2 ) As airborne GPS is calibrated initially, the new GPS data can be regarded as a shift from the calibrated position. It maintains repeatable error under 100 feet. For a helicopter of 80 knots, 100 feet error means about 1 second flight. Multipath exists during the simulated tests since the vans are running on the streets, but can be ignored while in real flights. (3) The FDS provides increased awareness to both ATC controllers and helicopter pilots. The ground station up-links the ATC command and flight director information to the airborne segments. The FDS provides the terrain with helicopter data on the moving map monitor via radio data-link. (4) The simulated tests examine the validity of GIS and GPS integration. Both airborne segments and ground segment are capable to display necessary flight information. (5) Collision avoidance logic is supported to alert to both pilots and ATC for threats. A simulated test for four helicopters in demonstrated as shown in Fig. 6. The ground ATC station monitors helicopter flight in the local area. Airborne A and 0-7803-5086-3 /98/$10.00 01998 EEE F42-4 Airborne B are approaching to cause a conflict warning. RA is firstly announced. At time t, both airborne segments and ground segment alert the conflict. Scenario assumes that Airborne A obtains higher priority, Airborne B has to make ways to make a 500 feet radius circular flight. (R5r) is pronounced on the airborne segment of Airborne B. Airborne A receives a (M) director to get the highest priority of flight. Airborne B receives a (R5r) director to make a right turn. At time t+4, Airborne A is “escaped” from collision. At time t+5, the alarm of Airborne A is dismissed. The participating helicopters C and D are not affected at this very moment, but vertical separation is pronounced by ATC to Airborne C to climb 300 feet and leave more vertical space. (uH+3) is pronounced to Airborne C. Since Airborne A is making a 500 feet circular flight, Airborne D may intrude its airspace by a RA. A reducing speed of 10 knots as (US-1) is pronounced. In this figure, the solid line means the past trajectory and the dashed line indicates the expected trajectory. Airborne A and -B are two remote-piloted helicopters. In Fig. 6, there are five monitor displays. The central one shows the ground ATC station to watch all four helicopters in this local area. Each corner shows the airborne display with conflict warnings after RA being issued. Each helicopter shows its flight direction with heading with intruders into RA. The flight paths of all helicopters in this local area are marked and extrapolated to show their performance. In Fig. 6, darker circle (green) means TA=5 sec., lighter circle (blue) means RA=15 sec., ”star” means each sample point of helicopter position. Each window of Fig. 6 shows the concerned relative positions of intruders, such as A and B; while helicopter is flying without conflict threat will show a clear 0-7803-5086-3 /98/$10.00 01998 EEE F42-5 one, such as C and D. Conclusion A configuration of an integrated flight director and surveillance system (FDS) is proposed in this paper based on CNS/ATM concept. The FDS contains GIS mapping with GPS data and ATC collision avoidance with early-warning and conflict resolution. The proposed FDS integrates the airborne avionics to direct pilot flight and the ground ATC facility to maintain helicopter separation in low altitude. Both hardware and software are implemented for the FBS with simulated tests. Further studies on cellular phone for communication, wider multiple local area operation, traffic alert, conflict resolution are concerned. The proposed FDS is a feasibility study for helicopter applications. Conceptual design of the proposed FDS is demonstrated. The simulated test results encourage the motivation for advanced studies. References [1] T. Willianson, N. A. Spencer, “Development and Operation of the Traffic Alert and Collision Avoidance System (TCAS)”, Proc. of EEE, Vol. t n 77, NO. 11, NOV. 1989, pp.1735-1744. [2] J. E. Rogers, "Terminal Area Surveillance System", IEEE Int'l Radar Conf., 1995, pp. 501-503, 0- [3] J. Y. Gilkey, R. C. Galijan, "The Army GPS Truth Data Acquisition, Recording,, and Display System at the White Sands Missile Range", EEE Int'l Radar Conf., 1994, pp. 134-144, 7803-2 120-0-95. 0-7803- 14.35-2/94. Fig. 1. FDS Concept and Operation. Fig. 5. Simulated Tests. Fig. 4. Flow Chart of Software Segment. Fig. 2. The Proposed FDS Airborne icBsl n I...-1 A U Segment and Ground Segment. 1ATC Commands Airborne Segment o"dstntlon Fig. 3. Software coordination Flow. Output A Input A (Position Information of helicopters1 Input B lhlrbolne Datal6 I Ground segment 0-7803-5086-3 /98/$10.00 01998 EEE F42-6