~~ I - . , -- ,Paper - 261 6 - \ November 1986 Ground-Based Time-Guidance , Algorithm for Control of A$planes in a Time-Metered Air Traffic Control Environment A Piloted Simulation Study Charles E. Knox and Nicole Imbert o) GbCUbC-EASEL !lI??i-GUidANCE bid7- l0%4 CCKTfiCL AlrEIAhZS A I- B CF IN AI5 ThAFEIC CCNTFCL .. A EILOTZCC SIMULAIlCh STUdY UUcl d s P CSCL 019 31/06 431177 G NASA NASA Technica I Paper 261 6 1986 Gro znd-BasLd Time-G Algorithm for Control of Airplanes in a Time-Metered Air Traffic Control Environment A Piloted Simulation Study Charles E. Knox Langley Research Center Hampt o n, Virginia Nicole Imbert ONERAICERT Toulouse, France NASA National Aeronautics and Space Administration Scientific and Technical Information Branch Summary necessary to develop more efficient ways to operate individual airplanes and to control air traffic for ar- A piloted simulation experiment was used to rival and departures to the terminal area. Airborne study and evaluate a time-guidance algorithm con- flight management systems have been designed and cept designed to provide guidance for an airplane to implemented that can result in an individual airplane cross a metering fix at a designated time. The guid- fuel savings of 2 to 6 percent (ref. 1). Advanced air ance provided to the pilot during these tests con- traffic control (ATC) procedures and systems are be- sisted of two airspeed commands and one heading ing designed to reduce traffic delays in the terminal command that were based upon time errors at three area by metering and sequencing arrival and depar- intermediate fixes on a nominal flight path to the air- ture airplanes. Two of these air traffic control sys- port. Eight different test conditions were evaluated tems (one is being designed for Eurocontrol (ref. 2) to determine initial time-error effects, airspeed-limit and one is on an operational basis in the United effects, and the wind-modeling unknown effect upon States (ref. 3)) utilize time control to meter arriv- the capability of the time-guidance algorithm to null ing traffic. In the time-based ATC systems, a time the time error at the final metering fix. These cases is assigned for each airplane inbound to the terminal were compared to a set of baseline tests in which no area to cross a metering fix. This time is computed errors were artificially induced. such that when airplanes cross the metering fix at The Federal Aviation Administration’s 250-knot their assigned times, they may continue along a nom- airspeed limit for flight at an altitude less than inal path to the runway without conflicts from other 10000 ft mean sea level can reduce the time control- arrival traffic. lability of the algorithm when higher airspeeds are In the United States airports at Dallas-Ft. Worth, required to null the time error. The severity of the Texas, and Denver, Colorado, time-based-metering reduction of time controllability of the algorithm is operational procedures require the ATC controller to variable and is a function of the path design. provide radar vectors and airspeed commands so that The effects of mismodeled winds were examined each airplane will cross the metering fix (typically by adding a 10-knot bias to the wind for all altitudes located 35 to 50 flying miles from the runway) at during two test scenarios, one with a prevailing head the assigned time. These vectors and commands are wind and the other with a tail wind. The test results determined by the controller and, depending upon his with these scenarios showed that most of the time skill, result in metering-fix crossing-time accuracies error at the metering fix was accrued on the last path of between 1 and 2 min (ref. 4). segment after the final heading command was issued. If this time error can be reduced at the meter- The magnitude of the error accumulated on the last ing fix or nulled along a nominal path prior to the path segment would be dependent upon the length point at which all airplanes are merged, the extra of this segment, the magnitude of the wind modeling flight time required for final sequencing and spacing error, and the time exposed to the wind modeling for landing can be reduced. This reduction of extra error. flight time can potentially save a significant quan- An initial time error of f60 sec was induced in tity of fuel. Flight tests have shown that airborne three more test scenarios. Final mean time errors electronically computed guidance may be used to fly of 8.4 sec or less resulted when both airspeed and fuel-conservative trajectories while maintaining a de- heading command corrections were computed by the sired time schedule (refs. 5 and 6). However, airborne time-guidance algorithm. However, in the scenario electronically computed time guidance is not read- in which the 250-knot airspeed limit precluded an ily available on the current generation of commercial increase in airspeed to null the time error, the initial transport airplanes. 60-sec time error was reduced to 21.3 sec through use As an alternative to airborne computations, time of only the heading command correction. guidance could be computed on the ground and pro- The subject pilots reported that the airspeed and vided to each arriving airplane. The ONERA/CERT heading commands generated by the time-guidance a time-guidance algorithm were easy to follow and did not increase of Toulouse, France, has developed algorithm concept in which heading and speed com- their work load above normal levels. Airspeed and mand corrections are computed for a pilot to follow heading errors recorded during each of the test runs in order to cross a metering fix at a designated time. were within normal operating tolerances. Once a time has been assigned for an airplane to cross a metering fix, command corrections may be Introduction radioed to the pilot as he approaches the metering The rapidly increasing cost of flight operations fix. The command corrections are computed based and the necessity for fuel conservation have made it on the difference between desired and actual times in crossing intermediate time checkpoints that lie on time required to fly between a nominal path to the metering fix. A fast- time checkpoints and t.ime compuber simulat>ionstudy (ref. 7) using the metering fix, sec ONERA/CERT guidance with three ATC correc- time to fly between time tions (two airspeed and one heading) to a metering checkpoint 2 and metering fix located about 10 n.mi. from the runway resulted fix at an off-nominal cali- in a mean crossing-time error of 8.5 sec (late) with a brated airspeed, sec standard deviation of 9 sec. Software of the ONERA/CERT time-guidance al- nominal time to fly between gorithm was then integrated into a real-time piloted time checkpoint 1 and simulation by NASA to study and evaluate the op- metering fix at 250 knots, erational concepts and to determine the effects that SeC various operational constraints had on time control- time to fly between time lability of the algorithm. In this study, the guidance checkpoint 2 and metering algorithm was applied to a path that began fly- 53.5 fix at a nominal calibrated ing miles from the runway. A final metering fix was airspeed, sec established at the outer marker of an Instrument Landing System (ILS) approach 5.7 n.mi. from the difference in time to fly the runway threshold. As the pilot flew along a nominal path at nominal and off- path toward the airport, he was given heading and nominal calibrated airspeeds calibrated-airspeed command corrections required to and/or headings, sec satisfy a time objective for crossing the metering fix. difference in time to fly This report will summarize the computations of the between time checkpoint 2 time-metering guidance algorithm, describe the pi- and metering fix at nominal loted simulation tests and facilities, and present the and off-nominal calibrated results of this study. A summation of the test condi- airspeeds, sec tions and results is presented in tables I and 11. calibrated airspeed, knots Symbols and Abbreviations commanded airspeed, knots air traffic control nominal calibrated airspeed along path segment 1, knots coefficients for quadratic equation to evaluate air- nominal calibrated airspeed speed changes at time along path segment 2, knots checkpoint 1 airspeed commands for pilot to follow based on time 1,k b2, k b3,k coefficients for quadratic equation to evaluate air- error at time checkpoints 1 speed changes at time and 2, respectively checkpoint 2 AV change in airspeed com- CRT cathode ray tube puted at first and second time checkpoints, knots coefficients for quadratic cl,k 1 c2,k c3,k AVi difference in nominal and equation to evaluate head- off-nominal calibrated air- ing changes at time check- speeds along path seg- point 3 ment 1, knots Instrument Landing System difference in nominal and mean sea level off-nominal calibrated air- speeds along path seg- standard deviation ment 2, knots time error at time check- WAL identification letters for the points 1, 2, and 3, respec- VORTAC navigation facility tively, sec located on the airport 2 I 9 heading command for pilot of using the algorithm to control airplanes or affect to follow based on time the final time error at the metering fix. error at time checkpoint 3 The second function of the time-guidance algo- rithm is to compute the coefficients of a quadratic off-nominal heading along curve fit of the time-difference data stored in the data path segment 3, deg tables.