Big Engines and Directional Control

1. FTSW 2008 – Melbourne, FL Big Engines and Directional Control Paul Bolds-Moorehead 777 Stability & Control Lead Engineer Boeing Commercial Airplanes WARNING: Export Controlled This document contains technical data whose export is restricted by the Export Administration Act of 1979, as amended, Title 50, U.S.C.; App. 2401, et seq. Violators of these export laws are subject to severe criminal penalties. Diversion contrary to U.S. law is prohibited. Controlled by ECCN: 9E991 Date: 11January2008

2. Welcome ………… to big engines

3. BIG engine… without directional control issues

4. But this one might have a problem shortly……

5. Overview • Preparation for a flight test program can be as important as the test program itself • Proper preparation delves into the corners of the envelope and remote probabilities of operation • Boeing uses extensive simulation activities for stability & control flight test preparation • Desktop standalone analysis • Generates Predicted Flight Characteristics document • Highlights areas of concern • Pilot-in-the-loop evaluations in engineering cab • Handling qualities assessments • Safety assessments

6. Overview (continued) • Key points: • Spurious data may not be in error • Sometimes have to trust that the data is trying to communicate a problem • VMCA/L reminder: • Takeoff or Landing configuration • Full thrust asymmetry • 5 degrees of favorable bank angle • Constant heading • Resulting airspeed is VMCA/L

7. Overview (continued) • Boeing found an issue during 2004-2005 flight test preparation analysis for the 777-200LR program • high thrust asymmetry and directional control issue not uncovered during our routine preparation work • Beyond area where we’d normally test • This specific issue is not model dependent however • BUT………….. it’s important to note: Boeing has not had any flight test issues in this area; this is an analysis discovery only

8. Overview (concluded) • What follows is the results of the analysis of this issue and is adapted from a presentation currently being made to our airline customers

9. Agenda • Concept • Situation • Effect • Plan • Summary • Concept • Situation • Effect • Plan • Summary

10. The Concept (continued) • Thrust on twin-engine airplanes tends to grow significantly over the life of the fleet • Rarely do vertical tail and rudder sizes grow with this thrust growth (sized initially for some growth) • High thrust asymmetry (engine failure) challenges directional control b Yawing moment due to thrust asymmetry Failed Engine Large thrust commanded from operating engine Yawing moment due to aerodynamic directional stability and controls

11. The Concept (continued) • Loss of directional control at a given airspeed in this environment is defined by: • Inability to reliably fly to specific bank angle • Inability to precisely control heading angle • Large displacements of control wheel and rudder pedals will be noticeable to the flight crew as this speed is approached • The certified minimum control speeds (VMCA/VMCL) are always greater than the airspeed for loss of directional control • Operational airspeeds (V2/VREF) are always greater than or equal to minimum control speeds • “Stretched” airplanes are less susceptible to this phenomenon (longer tail moment arm)

12. Airspeed Weight The Concept (continued) However, higher thrust asymmetry may cause a loss of directional control at airspeeds greater than that for stall warning VMCA Loss of Directional Control (now) Stall Warning (stick shaker) Thrust growth Loss of Directional Control (then)

13. The Concept: Takeoff Procedure Review Takeoff Thrust Setting Method

14. The Concept: Go-Around Procedure Review • Pilot initiates go-around with TOGA push (single or double push) • Single push gives thrust for ~2000 fpm climb • Double push gives full GA rated thrust • Pilot changes flap setting to go-around flap (typically flaps 20) • On achieving positive rate-of-climb, pilot raises landing gear • Should engine failure occur during go-around, continue normal procedures • Maintain VREF speed as minimum during the go-around • Follow Flight Director guidance to maintain recommended airspeed

15. Agenda • Concept • Situation • Effect • Plan • Summary • Concept • Situation • Effect • Plan • Summary

16. Reduced Directional Control Example - 777 • The 777 airplane family meets all certification regulations (including minimum control speeds, VMC) • There have been no reported 777 directional control incidents in Boeing flight test or airline revenue service • Decelerating enough to reach engine-out loss of directional control airspeeds is an extremely improbable event for 777 airplanes • Flying at approved operating airspeeds and following recommended procedures will maintain directional control

17. But if the airplane does encounter this phenomenon during a takeoff………….. Abused condition for the purpose of illustration only

18. Prompt recovery of lost airspeed results in a safe climb…………..

19. And if the airplane encounters this phenomenon during a go-around……… Abused condition for the purpose of illustration only

20. Again, prompt recovery of lost airspeed results in a safe missed approach…………..

21. Defining “Loss of Directional Control” • Recall: The airspeed at which it is no longer possible to reliably control bank angle and heading defines a loss of directional control airspeed Note: For all Boeing models, this speedis always less than VMCA • For example, with the 777 family: • On some of the minor models for lighter weight operations only, the speed for loss of directional control is greater than stall warning speed • While meeting all VMC regulations, decided to examine enhancing operational speed margins • Operations near ground in high thrust asymmetry conditions(single-engine go-arounds and single-engine takeoffs) are the areas of primary interest • Again, flying at approved operating airspeeds and following recommended procedures will maintain directional control

22. Agenda • Concept • Situation • Effect • Plan • Summary • Concept • Situation • Effect • Plan • Summary

23. Determination procedure: Fail one engine and command full thrust on operating engine(against Standard Operating Procedure for Fixed Derate or Fixed Derate/ATM takeoffs) Decelerate while maintaining constant heading using rudder and wheel deflections Airspeed at which bank/heading is no longer controllable is labeled the “loss of directional control” airspeed Large wheel and rudder displacements are readily apparent, even though crew proximity to this regimeis not specifically annunciated Determining “Loss of Directional Control” Airspeeds VMCA Airspeed Loss of Directional Control (high-thrust engines) Stall Warning Thrust Growth Loss of Directional Control (ideal) Weight

24. What is the desired margin between V2 and the loss of directional control? Minimum V2 speeds obtained assuming largest fixed derates where thrust lever push is not allowed (not an issue for full-thrust or assumed temperature takeoffs) Establishing guidelines for the margin between Minimum V2and the loss of directional control airspeed for all models For the takeoff scenario: May result in a V2 airspeed floor being implemented Margin Airspeed Margins (Takeoff) Note: Only an issue if pilot pushes thrust levers past fixed derate level disregarding training V2 (full thrust) Minimum V2 (fixed derate) V2 floor VMCA (full thrust) Airspeed Loss of Directional Control (full thrust) Stall Warning Weight

25. Airspeed Margins (Takeoff) – Proper Technique V2 (full thrust) Minimum V2 (fixed derate) Adequate margin VMCA (full thrust) Airspeed Loss of Directional Control (full thrust) Adequate margin VMCA (fixed derate) Stall Warning Loss of Directional Control (fixed derate) Stall Warning Weight Weight

26. What is the acceptable margin between VREF and the loss of directional control? Establishing guidelines for the margin between VREF and the loss of directional control airspeed for all models For the landing/go-around scenario: May result in a VREF airspeed floor being implemented Margin Airspeed Margins (Landing/Go-Around) Stall-Based VREF VREF floor VMCL Airspeed Loss of Directional Control Stall Warning Weight

27. 777-200LR flight test VMCG video GE90-115B engines (115,300 lb thrust) Another Big Engine Example …….

28. Agenda • Concept • Situation • Effect • Plan • Summary • Concept • Situation • Effect • Plan • Summary

29. The Plan • Simulation study across all Boeing models in process • Establishing margin guidelines for all Boeing models • Reviewing all Flight Crew training manuals for clarity • Communicating this analysis to all affected customers • Make modifications to the operational airspeeds (V2 and/or VREF) as warranted

30. Agenda • Concept • Situation • Effect • Plan • Summary • Concept • Situation • Effect • Plan • Summary

31. Summary • Providing heightened operator awareness of the affect of increased asymmetric thrust • On some of the minor models for lighter weight operations only, the speed for loss of directional control is greater than stall warning speed • Emphasizing the importance of following published procedures • Flying at Boeing-recommended airspeeds and followingBoeing-recommended procedures maintains directional control • Manage thrust as recommended (respect derated takeoffs) • Evaluating entire Boeing fleet to establish appropriate V2 / VREF margins to loss of directional control airspeed

32. Summary • Preparing for flight test needs to delve into extreme envelope corners • “Strange” data can be trying to tell you something • Remote probabilities can’t be ignored if the result is bad enough • Finding problems during pre-flight analysis is infinitely better than finding them during a test program

33. Big Engines and Directional Control Questions ?