Takeoff Thrust Setting

Transcription

1 Operational Liaison Meeting Fly-By-Wire Aircraft 2004 Takeoff Thrust Setting Customer Services

2 Contents Introduction Rolling Takeoff Engine-Related Issues during Takeoff Power Check FADEC Logics during Takeoff (KOZ and MEASTO) Engine Thrust Loss ECAM Message on A340 CFM 56 Conclusion Takeoff Thrust Setting Page 2

3 Introduction The Takeoff Thrust Setting Procedure May differ, depending on engine type: This is defined by Airbus and engine manufacturers Is a certified procedure, contained in the Aircraft Flight Manual (AFM) And is associated with specific certified performance May differ, depending on wind conditions: To minimize the risk of engine stall/surge Normally completed in two steps: To avoid asymmetry due to different engine response Takeoff Thrust Setting Page 3

4 Contents Introduction Rolling Takeoff Engine-Related Issues during Takeoff Power Check FADEC Logics during Takeoff (KOZ and MEASTO) Engine Thrust Loss ECAM Message on A340 CFM 56 Conclusion Takeoff Thrust Setting Page 4

5 Rolling Takeoff Definition of a Rolling Takeoff Takeoff for which the thrust setting sequence is initiated while the aircraft is moving. Thrust is not set under the brakes. What is considered to be a Rolling Takeoff? The aircraft does not stop, when it enters the runway When the aircraft is aligned, the brakes released and the thrust setting sequences are initiated. Takeoff Thrust Setting Page 5

6 Rolling Takeoff Advantages Less risk of FOD (less risk of ingestion) Takeoff can be conducted earlier Less risk of high power setting at low speeds (stall prevention) Less brake wear Smoother for passengers Disadvantages Engine response can differ (small dissymmetry) Alignment on the runway axis may be longer Performance-wise, if the rolling takeoff technique is applied correctly, there will be no difference between a rolling takeoff and static takeoff. Takeoff Thrust Setting Page 6

7 Rolling Takeoff Airbus recommended Rolling Takeoff In the Standard Operating Procedures (SOP) -FCOM Rolling takeoff is recommended, when possible However: This recommendation was sometimes considered too strong. Some operators felt obliged to perform it systematically. Rolling takeoff requires crew familiarization with the rolling takeoff piloting technique In some situations, the rolling takeoff technique is not recommended (Engine Intermix operations). Therefore, the SOP (FCOM ) will now reflect: Rolling takeoff is permitted Left up to the crew to decide whether or not to perform a rolling takeoff Takeoff Thrust Setting Page 7

8 Contents Introduction Rolling Takeoff Engine-Related Issues during Takeoff Power Check FADEC Logics during Takeoff (KOZ and MEASTO) Engine Thrust Loss ECAM Message on A340 CFM 56 Conclusion Takeoff Thrust Setting Page 8

9 Engine-Related Issues during Takeoff Engine Instability Phenomenon Stall/Surge caused by: Reduced margin due to wear Crosswind or tailwind Flutter caused by: Resonance frequencies generated in under certain conditions (N1, EPR) Application of adequate procedure: Insufficiently accurate Increase crew workload FADEC Logis automatically: Respect certain parameters Avoid Resonance Zones Takeoff Thrust Setting Page 9

10 Contents Introduction Rolling Takeoff Engine-Related Issues during Takeoff Power Check FADEC Logics during Takeoff (KOZ and MEASTO) Engine Thrust Loss ECAM Message on A340 CFM 56 Conclusion Takeoff Thrust Setting Page 10

11 Power Check Engines must reach the takeoff rating limit, established for the takeoff conditions: Engines N1 or EPR must be equal to the rating limit value: If one engine does not reach it, the takeoff should be rejected. In case of engine failure, takeoff performance is not guaranteed. Monitoring of engine parameters is done during takeoff: N1/EPR, and EGT In particular, the power check callout is done before 80 knots. What is the criteria/tolerance for aborting a takeoff: For performance reasons, all engines should reach the rating limit As a guideline, it is accepted that if a difference lower than: 1% N EPR It is the crew s decision It is always the crew s responsibility to check that the thrust is satisfactory for takeoff Takeoff Thrust Setting Page 11

12 Contents Introduction Rolling Takeoff Engine-Related Issues during Takeoff Power Check FADEC Logics during Takeoff (KOZ and MEASTO) Engine Thrust Loss ECAM Message on A340 CFM 56 Conclusion Takeoff Thrust Setting Page 12

13 FADEC Logics during Takeoff (MEASTO) MEASTO A330 Rolls Royce (Trent 700) Modified Engine Acceleration Schedule for TakeOff High crosswind, tailwind or intake turbulence: Increase risk of fan stall The Fan stall risk zone is more significant at low speed. Engines automatically react against fan stall. If a stall occurs: Engine power is reduced. Automatic and progressive thrust setting during takeoff: Engine acceleration is controlled by a predefined EPR/second rate. Function only active during the low speed phase of takeoff (speed < 50 knots). For RR T700 engines not fitted with this function, this acceleration law had to be reproduced by the crew. It takes about 10 additional seconds to reach takeoff power. For all flight conditions, takeoff thrust is achieved before 80 knots. This function is only available on ground, and with forward thrust: Also available for ground maintenance tasks. Takeoff Thrust Setting Page 13

14 FADEC Logics during Takeoff (MEASTO) The engine acceleration rate for the fan stall margin, compared to the engine acceleration rate with the MEASTO function. EPR Increased risk of fan stall Acceleration Rate of 0.04 EPR/second I 0 I 5 I 10 Acceleration Rate of 0.02 EPR/second I 15 Normal Acceleration Takeoff Thrust Setting Page 14 I 20 I 25 I 30 With the MEASTO Function Time

15 FADEC Logics during Takeoff (MEASTO) The thrust achieved progressively... Full takeoff thrust is reached: Within approximately 15 seconds Before reaching 80 knots Reduced acceleration rate with altitude, to compensate for the stall margin loss. EPR feet 0 feet 4000ft 12500ft and above Time from thrust lever movement Takeoff Thrust Setting Page 15

16 FADEC Logics during Takeoff (MEASTO) MEASTO is: Basically installed in production, an Retrofit worldwide Simplification of the Takeoff Procedure, in the event of high crosswind or tailwind: Rolling Takeoff no longer required Step at 1.1 EPR is not required Reduced engine stall risk during takeoff Specific performance has been developed for aircraft fitted with the MEASTO function Crew task reduction and simplification with this logic Takeoff Thrust Setting Page 16

17 FADEC Logics during Takeoff (KOZ) The KOZ (Keep Out Zone) implemented on: A330 Rolls Royce (Trent 700) A320/A319/A321 IAE (V2500 A5 series) A /600 Rolls Royce (Trent 500) To avoid fan flutter, the FADEC prevents stabilization in a certain EPR (N1) zone, depending on the engine type. For example, the KOZ for RR Trent 700 is between: 1.16 to 1.28 EPR The N1 interval changes, based on the temperature of the day. The max upper and min lower limit are: 51.4% and 73.6% The KOZ is active when: Aircraft on ground, and Low aircraft speed (M<0.15 or <80 knots), and Forward thrust. Takeoff Thrust Setting Page 17

18 FADEC Logics during Takeoff (KOZ) During Engine Acceleration. When the thrust lever is advanced through the KOZ, there is a pause in the EPR command at the lower EPR command limit. The EPR command will remain at the lower command limit, until the thrust lever is advanced such that the corresponding EPR command exceeds the upper EPR command limit. Then, engine power will continue to increase with the thrust lever position. KOZ is fully automatic for the crew STABILIZATION Takeoff Thrust Setting Page 18

19 FADEC Logics during Takeoff (KOZ IAE V2500 A5) To avoid cracking the fan blade root due to fan flutter, the FADEC prevents stabilization in a certain EPR (N1) zone. This automatic KOZ replaces the manual KOZ, applied by crews, to avoid operation in a specific fan speed range. In EPR mode, KOZ changes are based on the daily temperature. In N1, the Keep Out Zone is between 61% to approx. 74% KOZ is transparent to the crew: Not felt in the takeoff procedure Low probability to reach this value during taxi With the exception of the Ice Shedding Procedure Takeoff Thrust Setting Page 19

20 FADEC Logics during Takeoff (KOZ IAE V2500 A5) Modification of the Takeoff Procedure for tailwind, or high crosswind: Deletion of the 70% N1 step, which falls within the KOZ. Simplified Takeoff Procedure If tailwind or high crosswind: The performance impact is 25 meters in the takeoff distances PRE-SCN17 STEP SUPPRESSED SCN17 IDLE 1.05 EPR 1.15 EPR TO power IDLE 1.05 EPR TO power Takeoff Thrust Setting Page 20

21 FADEC Logics during Takeoff (KOZ IAE V2500 A5) IAE has considered the risk of fan flutter (for the pre-scn17 procedure) to be acceptable, since the aircraft is already moving and there is no stabilization. The main risk occurs during stabilization at low, or zero, aircraft speed: For the Ice Shedding Procedure For maintenance run-ups It is covered in the Airbus SOP. The engines are automatically protected, and the crew workload is reduced. This feature is available with the SCN 17 Software Airbus recommends embodiment of the SCN17 FADEC Software This software is basically installed on the production line. Takeoff Thrust Setting Page 21

22 Contents Introduction Rolling Takeoff Engine-Related Issues during Takeoff Power Check FADEC Logics during Takeoff (KOZ and MEASTO) Engine Thrust Loss ECAM Message on A340 CFM 56 Conclusion Takeoff Thrust Setting Page 22

23 Engine Thrust Loss ECAM Message on A340 CFM 56-5C A. ICE ENG X VALVE OPEN is triggered when: There is a disagreement between the anti-ice valve, and the pushbutton position: The engine anti-ice has not been selected open, and The anti-ice valve is open. COMPARISON PUSHBUTTON POSITION IF DISAGREE FWC A.ICE ENG X VALVE OPEN ENG ANTI-ICE VALVE POSITION Takeoff Thrust Setting Page 23

24 Engine Thrust Loss ECAM Message on A340 CFM 56-5C Also, the current FADEC does not provide adequate thrust for takeoff: Because takeoff thrust is computed by taking into account the position of engine anti-ice valve (N1 decrement applied). Therefore, ENG THRUST LOSS triggers during takeoff. COMPARISON PUSHBUTTON POSITION If DISAGREE ENG THRUST LOSS ENG ANTI-ICE VALVE POSITION Takeoff Thrust Setting Page 24 F A D E C

25 Engine Thrust Loss ECAM Message on A340 CFM 56-5C To avoid this scenario, the FADEC C3J will compute takeoff thrust, based on the engine anti-ice pushbutton position. Therefore, ENG THRUST LOSS will not trigger during takeoff. PUSH BUTTON POSITION IF DISAGREE ENG ANTI-ICE VALVE POSITION Takeoff Thrust Setting Page 25 F A D E C No N1 decrement applied

26 Engine Thrust Loss ECAM Message on A340 CFM 56-5C With the FADEC C3J Standard -- If the crew selection disagrees with the actual position of the valve: The FADEC provides adequate thrust, and increases the EGT to compensate for the effect of engine anti-ice extraction. Only for engines with a low EGT margin, and for temperatures higher than the corner-point, will it lead to an EGT overlimit. Airbus recommends retrofitting the FADEC C3J Software on A340 aircraft with CFM 56-5C Engines: To avoid rejected takeoffs FADEC C3J Software Takeoff Thrust Setting Page 26

27 Conclusion Rolling takeoffs may be advantageous in certain circumstances. However, it is up to the crew to apply this technique. The Takeoff Thrust Setting Procedure is standard for Airbus aircraft. However, it may vary slightly from one engine to another, and depends on wind conditions. Airbus is actively working on reducing crew workload during the Takeoff Setting Procedure: MEASTO KOZ Avoidance of ECAM messages that lead to aborting a takeoff. Airbus recommends retrofitting the latest FADEC Software Standards in order to: Further ensure safety Ease the crew workload Reduce maintenance costs. Takeoff Thrust Setting Page 27

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29 This document and all information contained herein is the sole property of AIRBUS S.A.S. No intellectual property rights are granted by the delivery of this document or the disclosure of its content. This document shall not be reproduced or disclosed to a third party without the express written consent of AIRBUS S.A.S. This document and its content shall not be used for any purpose other than that for which it is supplied. The statements made herein do not constitute an offer. They are based on the mentioned assumptions and are expressed in good faith. Where the supporting grounds for these statements are not shown, AIRBUS S.A.S. will be pleased to explain the basis thereof. AN EADS JOINT COMPANY WITH BAE SYSTEMS Takeoff Thrust Setting Page 29