1. at Lewis Field Glenn Research Center Controls and Dynamics Branch Engine Performance Deterioration Mitigation Control - A retrofit approach Dr. Sanjay Garg Branch Chief Ph: (216) 433-2685 FAX: (216) 433-8990 email: sanjay.garg@nasa.gov http://www.lerc.nasa.gov/WWW/cdtb Presented at: Aerospace Guidance and Control System Committee Meeting Boulder, CO, March 1, 2007 Research Performed by: Jonathan Litt – Army Research Lab Shane Sowers – Analex

2. at Lewis Field Glenn Research Center Controls and Dynamics Branch Overview Motivation Architecture Description Steady State Evaluation Transient Evaluation Piloted Simulation Conclusions

3. at Lewis Field Glenn Research Center Controls and Dynamics Branch Source: AIA PC 342 Committee on Continued Airworthiness Assessment Methodology Initial Report on Propulsion System and APU Related Aircraft Safety Hazards 1982 Through 1991 Propulsion Related Accidents & Incidents 1982 - 1991 Includes all Part 25 Category Transports Aircraft Data - Turboprop, Low Bypass, High Bypass Turbofans. (Does not include data from former Soviet Union and satellite countries’ products.) Uncontained Propulsion System Malfunction + Inappropriate Crew Response (PSM+ICR)

4. at Lewis Field Glenn Research Center Controls and Dynamics Branch Example PSM+ICR Turbofan Accidents Rejected Takeoff Events at or above V1 (30 Turbofan Events, 5 Hull Losses, 1 Fatal) 13 June 1996; Garuda Indonesian Airways DC10-30; Fukuoka, Japan (Contributing event: fracture of a HPT stage 1 blade) 19 October 1995; Canadian Airlines DC10-30ER; Vancouver, Canada (Contributing event: progressive HPC blade failures) Shutdown / Throttle Wrong Engine (27 Turbofan Events, 2 Hull Losses, 1 Fatal) 8 January 1989; British Midland Airways 737-400; near East Midlands Airport, UK (Contributing event: fan blade failure) Loss of Control (14 Turbofan Events, 11 Hull Losses, 7 Fatal) 24 November 1992; China Southern Airlines 737-300; Guangzhou, China (asymmetric thrust - stuck throttle) 31 March 1995; Tarom Romanian Airlines A310; near Balotesti, Romania (asymmetric thrust - stuck throttle)

5. Autonomous Propulsion System Technology Autonomous Propulsion System Technology - Reduce PSM+ICR incidents Reduce/Eliminate human dependency in the control and operation of the propulsion system Diagnostics/Prognostics Algorithms Are Being Developed Demonstrate Technology in a relevant environment Vehicle Management System Self-Diagnostic Adaptive Engine Control System Performs autonomous propulsion system monitoring, diagnosing, and adapting functions Combines information from multiple disparate sources using state-of-the-art data fusion technology Communicates with vehicle management system and flight control to optimize overall system performance Engine Condition/Capability Performance Requirement Model-Based Fault Detection Fuzzy Belief Network Data Fusion

6. at Lewis Field Glenn Research Center Controls and Dynamics Branch PILOT WORKSHOP at GRC - 2002 OBJECTIVE: Get direct input from pilots that will be used to help define the APST project plan GOALS: Under all flight regimes, identify what processes or procedures associated with propulsion system management could be candidates for autonomous operation Identify what propulsion system information or control features will be helpful in managing the integration of propulsion with flight control for normal and abnormal operations Identify what “sensory” information, other than the engine instruments, is used by the pilots in operation and control of the propulsion system for all flight regimes

7. at Lewis Field Glenn Research Center Controls and Dynamics Branch The conclusions of 2002 NASA Glenn Pilot Workshop fell into three main categories –Control Thrust asymmetry control Thrust response rate variation between engines Propulsion Controlled Aircraft Operating envelope expansion for emergency operation –Diagnostics Fault detection and isolation for vibration and potential engine shutdowns Health and usage monitoring –Indications to pilots Fault signals Vehicle status under autopilot, especially concerning throttle movement and split throttles Results from PILOT WORKSHOP

8. Engine Control Logic Is Developed Using A “Nominal” Engine Model…But “Nominal” Engine Does Not Exist Time PLA Thrust Nominal Engine with Fixed Control Normal Variation Normal Variation Degraded Engine with Fixed Control Measure of Performance Typical Current Engine Control Control Logic Limit Logic Engine Fan Speed Schedule PLAN2c N2 eN2WFcWFy FADEC – Full Authority Digital Engine Control + - Since Thrust cannot be measured, another parameter such as Fan Speed (N2), which correlates to Thrust, is regulated

9. Asymmetric Thrust Accident Information Aircraft asymmetric thrust accidents have been identified as a concern in the AIA/AECMA study on PSM+ICR [1]: “ A further area of concern was power asymmetry resulting from a slow power loss, stuck throttle, or no response to throttle coupled with automatic controls. Flying aids, such as the auto-pilot and auto-throttle, can mask significant power asymmetry until a control limit is reached. At this point, the flight crew has to intervene, understand the malfunction, and assume control of an airplane which may be in an upset condition. Better indications and/or annunciations of power asymmetry could warn crews in advance and allow them time to identify the problem and apply the appropriate procedures.” The following description of past asymmetric thrust accident is taken from an FAA Policy Statement on aircraft thrust management systems (TMS) [2]: 1.Sallee, G.P., and Gibbons, D.M., “AIA/AECMA Project Report on Propulsion System Malfunction Plus Inappropriate Crew Response (PSM+ICR), Volume I,” (Aerospace Industries Association and The European Association of Aerospace Industries, November 1, 1998). 2.FAA Policy Statement, “FAA Policy on Type Certification Assessment of Thrust Management Systems,” FAA Policy Statement Number ANM-01-02, March 2002. http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/0f670523ec44af9f86256ce9004c4539 http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/0f670523ec44af9f86256ce9004c4539 March 31, 1995, Tarom Airbus Model A310-300, Bucharest, Hungary: The airplane crashed shortly after takeoff. The Romanian investigating team indicated that the probable cause of the accident was the combination of an autothrottle failure that generated asymmetric thrust and the pilot's apparent failure to react quickly enough to the developing emergency. Report Conclusion: Data from these accident investigations have provided evidence that it is incorrect to assume that the flightcrew will always detect and address potentially adverse TMS effects strictly from inherent operational cues.

10. at Lewis Field Glenn Research Center Controls and Dynamics Branch Model-Based Controls and Diagnostics Ground Level Engine Instrumentation Pressures Fuel flow Temperatures Rotor Speeds Actuator Commands Fuel Flow Variable Geometry Bleeds Ground-Based Diagnostics Fault Codes Maintenance/Inspection Advisories On-Board Model & Tracking Filter Efficiencies Flow capacities Stability margin Thrust Selected Sensors On Board Sensor Validation & Fault Detection Component Performance Estimates Sensor Estimates Sensor Measurements Actuator Positions Adaptive Engine Control Applicable only to future systems Still in research mode with many technical changes to overcome

11. at Lewis Field Glenn Research Center Controls and Dynamics Branch THE NEED There is a need to develop a “simplified” approach to maintaining throttle to thrust relationship in the presence of engine degradation, and detecting thrust asymmetry situations. The approach “shall”: Be retrofitable to existing FADEC systems Leverage the extensive investment in existing FADEC control logic – specially in terms of limits imposed for operational life and safety Be mostly software/logic additions – not require any new sensors or actuation hardware Have “reasonable” development, verification and implementation costs

12. Control Logic Limit Logic Engine Fan Speed Schedule PLA T_des N2 eN2WFcWFy FADEC – Retrofit Thrust Model Thrust Estimator + - N2c Modifier delN2c N2cmod+ + - T_est Addition to Existing FADEC Logic Engine Performance Deterioration Mitigation Control (EPDMC) Mitigation Control (EPDMC) The proposed retrofit architecture: Adds the following “logic” elements to existing FADEC: A model of the nominal throttle to desired thrust (T_des) response An estimator for engine thrust (T_est) based on available measurements A modifier to the Fan Speed Command (delN2c) based on the error between desired and estimated thrust Since the modifier appears prior to the limit logic, the operational safety and life remains unchanged

13. EPDMC Testbed Architecture Engine –Full envelope, nonlinear Component Level Model –Represents a large commercial turbofan engine

14. Parts of EPDMC Testbed Architecture Engine Control –Typical Full Authority Digital Engine Control (FADEC) type controller –PLA in, fuel flow out –Fan speed is controlled

15. Parts of EPDMC Testbed Architecture Nominal Engine Model –Piecewise linear model –Scheduled on percent corrected fan speed

16. Parts of EPDMC Testbed Architecture Thrust Estimator –Piecewise linear Kalman filter –Based on Nominal Engine Model –Provides optimal estimation of variables in a least squares sense subject to sensors selected

17. Parts of EPDMC Testbed Architecture PI Control with Integrator Windup Protection –Performs outer loop PLA adjustment –Stops integrating error when PLA limit is reached

18. at Lewis Field Glenn Research Center Controls and Dynamics Branch EPDMC Evaluation The purpose of the evaluation is to determine –The steady state accuracy of the thrust estimator at many operating points and degradation levels with various types of uncertainty (model mismatch, nonlinearities, noise) –How well the outer loop control is able bring the thrust back to the nominal level in steady state –How well the outer loop control is able to maintain a nominal thrust response over a typical flight trajectory with a deteriorated engine

19. at Lewis Field Glenn Research Center Controls and Dynamics Branch Evaluation was performed in two phases –Steady State –Transient Assumptions –10 health parameters, two each (efficiency and flow capacity) for each of the five major components –Worst case degradation 5% in each health parameter –Health parameters degrade at their own pace, pretty much independent of each other  no restrictions placed on simulated deterioration except upper limit of 5% EPDMC Evaluation

20. Outer Loop Control off Steady State Evaluation Thrust performance deterioration with engine degradation Thrust estimation error is << Thrust deterioration => Thrust estimate can be used effectively for performance recovery

21. Outer Loop Control on Steady State Evaluation Outer Loop Control off EPDMC maintains “close” to nominal thrust performance - even with high levels of engine degradation

22. at Lewis Field Glenn Research Center Controls and Dynamics Branch Transient Evaluation Trajectory is takeoff/climb/cruise It passes through or near the linearization points No airframe is included, the engine is operating as if it were in a wind tunnel

23. at Lewis Field Glenn Research Center Controls and Dynamics Branch Transient Evaluation Nominal Engine with and without Outer Loop Control

24. at Lewis Field Glenn Research Center Controls and Dynamics Branch Transient Evaluation Degraded Engine with and without Outer Loop Control

25. at Lewis Field Glenn Research Center Controls and Dynamics Branch Flight Simulator THROTTLE STICK PEDALS INSTRUMENTATION DISPLAY HEADS UP DISPLAY SCREEN

26. “Piloted” Evaluation of Architecture Segment12345 Fan Speed86%90%88%82%86% Indicated Airspeed 290 knots Heading270º Altitude32,000 feet Climb33,000 feet descend32,000 feet Duration3 minutes- - Pilot-in-the-loop in a fixed-base simulator Maintain airspeed and heading while following profile - Three cases: Nominal, 1 engine degraded – OLC Off/On

27. at Lewis Field Glenn Research Center Controls and Dynamics Branch Pilot Workload During Transient Flight Very Clear Increase in Workload With Outer Loop Control Off

28. at Lewis Field Glenn Research Center Controls and Dynamics Branch Conclusions Developed a controls architecture that would maintain throttle to thrust relationship as the engine degrades –Addresses one of the major issues of propulsion related workload identified during a pilot workshop –Requires “minor” additions to existing FADEC logic –Preliminary simplified simulation results encouraging Current research focusing on implementing the architecture on the fan speed correction over the whole engine operating envelope and performing more detailed evaluations Need to address some of the potential challenges for implementation: –Pilots are used to relating throttle setting to fan speed –Acoustics issues related to two engines running at different but very close fan speeds (Beat frequency)