A321neo Pitch Warning
Original design modified and then.....
A321neo operators alerted over 'excessive pitch' anomaly
Airbus has introduced a temporary revision to A321neo flight manuals intended to prevent the possibility of the aircraft reaching excessive pitch attitudes. The European Union Aviation Safety Agency has disclosed that the revision follows analysis of the re-engined type's elevator and aileron computer. It has not elaborated on the situation beyond stating that "excessive" pitch could occur under certain conditions and "during specific manoeuvres". EASA cautions that this could result in "reduced control" of the aircraft. Airbus has issued temporary revisions to the aircraft's flight manual incorporating operational limitations. EASA has ordered operators of the A321neo to amend the flight manuals accordingly, within 30 days. The order covers both the CFM International Leap-1A and Pratt & Whitney PW1100G versions of the aircraft. Airbus has issued seven relevant temporary revisions to the flight manual, on 21 June and 10 July. EASA says the safety measure is an interim action and could be followed by further requirements. |
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Would someone be able to advise what are the specific limitations in the AFM regarding this AD please.
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Does anyone have a definition of reduced control?
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Originally Posted by Onions
(Post 10521906)
Does anyone have a definition of reduced control?
Originally Posted by Longtimer
(Post 10520904)
"during specific manoeuvres".
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Originally Posted by TechnicalPilot
(Post 10521825)
Would someone be able to advise what are the specific limitations in the AFM regarding this AD please.
Excessive pitch attitude can occur with: CG aft of 34% and Flight controls "Flare Mode" activated and Flaps Full and Large pitch up sidestick inputs (during a GA for example) |
Originally Posted by Onions
(Post 10521906)
Does anyone have a definition of reduced control?
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Talked to a former Boeing 737-200 pilot who flew for Silk Air. He was cruising in IMC one night in that part of the world and due to a mix-up in radio frequencies was unaware he was trailing a Boeing 747 freighter about ten miles ahead. Suddenly his aircraft was affected initially by mild turbulence followed by an extremely sharp wing drop to 90 degrees angle of bank. The AP disconnected at the same time. He was able to unload and rapidly regain control and roll wings level. Discussed this incident with a current 737-800 pilot who had a similar experience when being vectored behind an A330 ahead. On this occasion the 737 rolled rapidly to more than 60 degrees angle of bank and the AP disengaged. Weather was VMC and the pilot rolled back to wings level.
When practicing unusual attitude recoveries in the simulator some instructors restrict UA manoeuvers to be within the legal definition of an unusual attitude which among other parameters includes bank angle more than 45 degrees. The perceived reason being fidelity is not assured beyond those figures. If real aircraft affected by wake turbulence behind a heavy aircraft have finished up at extreme bank angles well beyond official UA parameters, it strikes me as the ostrich head in the sand approach to pretend it will never happen and thus let the unfortunate crew and passengers wear it on the day. Prompt and ideally flawless recovery on instruments is the mark of the true professional pilot. There is no shortage of examples where unusual attitudes have resulted from a wake turbulence encounter. Yet because simulator fidelity may not be guaranteed, we choose not to equip the crew with the instrument flying skills to recover from an extreme wake turbulence encounter. I think that is wrong in principle. No doubt there are other points of view. Question: With Airbus aircraft, does the inbuilt protection prevent instant roll beyond a specified figure regardless if the aircraft is being manually flown or on autopilot at time of jet upset due wake turbulence? |
Originally Posted by sheppey
(Post 10522799)
Question: With Airbus aircraft, does the inbuilt protection prevent instant roll beyond a specified figure regardless if the aircraft is being manually flown or on autopilot at time of jet upset due wake turbulence?
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given sufficient aileron authority, the abnormal attitude will not be reached in an Airbus FBW system, as the envelope protection is trying to level the aircraft while the wing is being dropped. In a Boeing, the AP will disconnect as soon as the AP detects insufficient authority, similar to giving the control column a good yank with AP engaged. It'll disengage rapidly. A wing drop due to wake turbulence in an Airbus thus will be slowed down compared to a Boeing. Difference in philosophy.
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From the source cited by Longtimer: "It (Airbus) has not elaborated on the situation beyond stating that "excessive" pitch could occur under certain conditions and "during specific manoeuvres". Isn't that sort of pitch up problem why MCAS was developed by Boeing? What's going on here? Does the A321neo also have a problem with pitch instability?
This is the first I've heard of a possible pitch stability problem with the A-321neo. Let's hope that no lives are lost before the problem can be rectified. Cheers, Grog |
Trying to compare flight control systems between certain aircraft types is very flawed as some are trying to do.
Anyway, this AD affects L102 STD ELAC software only. Spoke to a Tech Services colleague and if you want to recover the full operating envelope ie not have to apply the AFM TR requirements then you can request approval for the L101 STD software to be reloaded (de-modding the aircraft), not a big deal on the software loadable ELACs which would likely be all that are installed on A321neo aircraft. |
Here is the goto: https://www.flightglobal.com/news/ar...ch-ano-459718/
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Originally Posted by Longtimer
(Post 10523718)
Here is the goto: https://www.flightglobal.com/news/ar...ch-ano-459718/
"halfofrho" elaborates somewhat in his Post #5; however, some of the acronyms he's cited, such as "ZFW/TO/LDG" are not meaningful to me. To my old, "back in the day" understanding, "TO" was short for TakeOff, and LDG was short for LanDinG. I'm embarrassed to admit that I have never encountered the acronym, "ZFW", and the only meaning I've found for it on the ol' interweb was "Zero Fuel Weight". I'm sure that's incorrect, since one would not sustain powered flight for very long at "Zero Fuel Weight". I'd appreciate some help on the meaning of these acronyms since I need all the help I can get ... in most circumstances. In his Post #11, Station Zero seems to imply that the alleged (by EASA) pitch up problems of the A321neo are due to a software glitch, not to an aerodynamic problem. Has that been confirmed by EASA/Airbus? Cheers, Grog |
I understand halfofrho's post that way the CG has to be below 34% for Zero Fuel Weight, takeoff and landing.
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ZFW does mean zero fuel weight. Although it is not normally a weight you’d be flying at it does still need to have a CofG within certain limits. |
I'd appreciate some help on the meaning of these acronyms since I need all the help I can get ... in most circumstances. |
Airbus response to Leeham enquiry:
https://leehamnews.com/2019/07/19/bj...itch-up-issue/ "The issue is an A321neo landing configuration at extreme aft CG conditions and below 100ft only issue, discovered by Airbus and reported to AESA. Violent maneuvers in for instance a go-around in these conditions can cause a pitch up which the pilots can counteract using their side-sticks. No FBW nose downs or similar is commanded, it’s just the FBW doesn’t neutralize the pitch-up (like FBW using the Airbus style flight laws are supposed to do), the pilots have to do it. Airbus has assisted AESA in issuing the AD which restricts the aft CG used in operational landings until the ELAC software is updated." |
the goto was posted so all could have access to the original plus any updates.....
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This is most certainly software rather than Aerodynamics, read the second page of the AD. Group 1 aircraft with L102 ELACs fitted the AFM TR has to be placed in the manual with 30 days. Group 2 aircraft without L102 ELACs fitted the AFM limitation is only applicable once the L102 is installed. This alone means it affects just one ELAC standard. I’ve not seen the TR but if is below 100ft it will be something to do with the landing aspect of the flight control software. The A321neo from my understanding doesn’t have flare law compared to a CEO, its been replaced with something more akin to direct law where the sidestick input is proportional to output during that flight phase. |
I wonder what the reason for the change in the flare mode/law and the takeoff law was on the NEO series? For over 30 years it has been working perfectly fine.
If it ain't broke, don't fix it... |
Heavier, stronger engines, higher MTOW?
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Originally Posted by Less Hair
(Post 10524094)
Heavier, stronger engines, higher MTOW?
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Originally Posted by Station Zero
(Post 10523872)
This is most certainly software rather than Aerodynamics, read the second page of the AD. Group 1 aircraft with L102 ELACs fitted the AFM TR has to be placed in the manual with 30 days. Group 2 aircraft without L102 ELACs fitted the AFM limitation is only applicable once the L102 is installed. This alone means it affects just one ELAC standard. I’ve not seen the TR but if is below 100ft it will be something to do with the landing aspect of the flight control software. The A321neo from my understanding doesn’t have flare law compared to a CEO, its been replaced with something more akin to direct law where the sidestick input is proportional to output during that flight phase. |
I've read an re-read the posts on this thread as well as EASA AD No. 2019-0171 and now believe I have a basic understanding of the situation. My understanding (such as it is) is thus:
Cheers, Grog |
Possibly repeating capngrog and b1lanc:
1) as mentioned, the A321neo apparently has a balance problem similar to what the 73M8 would have had with no MCAS - a tendency to overpitch-up in some rare scenarios. 2) the A321neo is tail-heavier than the A321, due to mass added behind the center of lift and the previous CG - larger sharklets, reinforced (heavier) main gear and wing, and in some configurations, additional (2-4) seat-rows/pax-weight extending further back (aft galley and toilets reduced in size/number), and some doors moved further aft (I make the assumption that doors with hinges and seals and frames and locking mx are more massive than standard fuselage frames). 3) Airbus did flight-testing and tweaked many things (including the control software) because of the changes - but apparently they have now discovered something overlooked. A patch is on the way, but until then, they are advising that steps be taken to avoid pushing the CG even further aft. And be careful with pitch-up control inputs. 4) Part of that is the "mystery phrase" which (to me) simply means - "Avoid a CG of 34% MAC or more when: calculating ZFW, or for TO and LDG." If the calculator spits out "CG >34% MAC" - move some weight forward. |
From the FCOM FLARE MODE A321 NEO When passing 100 ft RA, the THS is frozen and the normal flight mode changes to flare mode as the aircraft descends to land. The flare mode is essentially a direct stick-to-elevator law without auto trim, with some damping provided by load factor and pitch rate feedback. The flare law provides full elevator authority. The flare law has no compensation of the ground effect nor the thrust effect. FLARE MODE All the others When the aircraft passes 50 ft RA, the THS is frozen and the normal flight mode changes to flare mode as the aircraft descends to land. Flare mode is essentially a direct stick-to-elevator relationship (with some damping provided by the load factor and the pitch rate feedbacks). The system memorizes the aircraft's attitude at 50 ft, and it becomes the initial reference for pitch attitude control. As the aircraft descends through 30 ft, the system begins to reduce the pitch attitude to -2 °nose down over a period of 8 s. Consequently, to flare the aircraft, a gentle nose-up action by the pilot is required. |
pattern_is_full I have read the Flight Operations Telex (FOT FOT-999.0059/19) sent out by Airbus which prescribes the CG restriction to affected airlines. Their explanation is clear, n.b. the 1) 2) and 3) above are nowhere near the real thing.
Admittedly for the A320, this is the relevant AD https://ad.easa.europa.eu/blob/EASA_...AD_2019-0189_1. |
Originally Posted by I-NNAV
(Post 10536528)
From the FCOM FLARE MODE A321 NEO When passing 100 ft RA, the THS is frozen and the normal flight mode changes to flare mode as the aircraft descends to land. The flare mode is essentially a direct stick-to-elevator law without auto trim, with some damping provided by load factor and pitch rate feedback. The flare law provides full elevator authority. The flare law has no compensation of the ground effect nor the thrust effect. FLARE MODE All the others When the aircraft passes 50 ft RA, the THS is frozen and the normal flight mode changes to flare mode as the aircraft descends to land. Flare mode is essentially a direct stick-to-elevator relationship (with some damping provided by the load factor and the pitch rate feedbacks). The system memorizes the aircraft's attitude at 50 ft, and it becomes the initial reference for pitch attitude control. As the aircraft descends through 30 ft, the system begins to reduce the pitch attitude to -2 °nose down over a period of 8 s. Consequently, to flare the aircraft, a gentle nose-up action by the pilot is required. |
Rotation Mode
Originally Posted by S speed
(Post 10523933)
I wonder what the reason for the change in the flare mode/law and the takeoff law was on the NEO series? For over 30 years it has been working perfectly fine.
If it ain't broke, don't fix it... I'd suggest that while not 'broken', there was room for improvement.... Flare and Rotation incidents; especially on the 321 we not unheard of, and part of every PF before takeoff brief.... |
737 Pitch
Originally Posted by pattern_is_full
(Post 10524659)
Possibly repeating capngrog and b1lanc:
1) as mentioned, the A321neo apparently has a balance problem similar to what the 73M8 would have had with no MCAS - a tendency to overpitch-up in some rare scenarios. 2) the A321neo is tail-heavier than the A321, due to mass added behind the center of lift and the previous CG - larger sharklets, reinforced (heavier) main gear and wing, and in some configurations, additional (2-4) seat-rows/pax-weight extending further back (aft galley and toilets reduced in size/number), and some doors moved further aft (I make the assumption that doors with hinges and seals and frames and locking mx are more massive than standard fuselage frames). 3) Airbus did flight-testing and tweaked many things (including the control software) because of the changes - but apparently they have now discovered something overlooked. A patch is on the way, but until then, they are advising that steps be taken to avoid pushing the CG even further aft. And be careful with pitch-up control inputs. 4) Part of that is the "mystery phrase" which (to me) simply means - "Avoid a CG of 34% MAC or more when: calculating ZFW, or for TO and LDG." If the calculator spits out "CG >34% MAC" - move some weight forward. |
In simplified terms, Airbus has been analyzing the A320 NEO and discovered under analysis and testing of the NEO flight control laws there are conditions a pilot can experience increased pitch. Temporary revisions to the A320new flight manual have been made to address the situation. Changes in the CG envelope and loading recommendations. Both the Leap-1A and P&W versions are affeted. EASA has opted for a quick implementation of an AD requireing the changes within 30 days of 14 August. They follow the problem found on the A321neo elevator and aileron computer which affected AOA protection. Airbus is working on a software fix for the A321new to become available next year.
Like the MAX but no fatal crashes yet. |
a) it was discovered on a software test rig, no in-service events or complaints from SIM rides
b) pre-condition is a significant deceleration, e.g. from 160 to Vls -10 kt (which is down to Vapp -15 kt on a normal day) c) if at that point TOGA thrust would be applied . . d) the aircraft might pitch up and follow the thrust moment. Which is not supposed to happen in the normal control law, where uncommanded attitude changes should be attenuated and contained. The A/C will still, they insist, normally respond to a nose-down command on the stick to overcome the pitching tendency. In a sense, the AD is issued because it might behave like a conventional aircraft - and that is not supposed to happen. |
Originally Posted by neilki
(Post 10536710)
Homesick Angel mode wasn't limited to the 737 Max. Didn't Thompson get one down to 20 or 30 KIAS on qa go around per the AAIB?
Autothrottle disengaged but pilots didn't immediately notice - event masked by speeds being as expected in an approach with engines at idle. Speeds dropped below target on application of more flap. Captain initiated a go around but power/pitch couple gave a nose up pitch that exceeded elevator authority in a machine trimmed AND. Power/pitch couple is, AIUI, present in all aircraft - see DC10 at Sioux City. Difference with MAX8 is that nacelle aerodynamics can add nose up pitch over/above that associated with addition of thrust. |
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