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Ethiopian airliner down in Africa

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Ethiopian airliner down in Africa

Old 28th Mar 2019, 00:56
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Another AoA display 'thing"...
.how exactly would it have helped in either of these two 737 MAX accidents.
the crew barely knew whether they were on foot or horseback once MCAS kicked off. Pretty sure AoA display wouldn't have helped solve "the immediate control crisis'.

.again.. I'd welcome an AoA display being sn engineer/technophile.
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Old 28th Mar 2019, 01:07
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Originally Posted by Takwis
You could (and I have) pull the stick slowly back into your lap, full aft, and the plane would maintain a nose up attitude, but descend at greater than 12,000 fpm. That was fine at 30,000 feet, in a MOA, but not optimal on approach. So an AOA indicator was fitted, not on the instrument panel, but on top of the dash, right in your line of sight when looking at the runway. The data was simplified...on airspeed, a green donut. Too fast, a yellow chevron indicating you needed to slow down, too slow, a red chevron indicating you had better increase your airspeed, and mind your sink rate. The instrument was absolutely essential to flying the T-38 well
That's what airspeed indicators are for. In my previous life on fighters, we only used the "AOA" indicator (traffic light system) for manoeuvring limits. We used IAS for takeoff, approach and landing.

I agree with Harry. An AOA indicator may be useful in a UAS situation (provided of course you can verify it/which one is correct) but in the 737 Max crashes, would have been of limited or no value.
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Old 28th Mar 2019, 01:50
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Originally Posted by hans brinker
No, there was no comparison done between the left and right AOA. The left side incorrectly indicated a very high AOA, the right side indicated correct. The warnings generated (stall/UAS) were all from the left side, and the MCAS was using the left side too.
From earlier in the thread the ADIRUs disagreed because of the AoA disagree. I was pointing out that the aircraft systems had already sensed an AoA disagree otherwise they would not alert to a UAS.
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Old 28th Mar 2019, 02:34
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Originally Posted by Ian W
From earlier in the thread the ADIRUs disagreed because of the AoA disagree. I was pointing out that the aircraft systems had already sensed an AoA disagree otherwise they would not alert to a UAS.
The UAS on Lion Air resulted from the left and right airspeed signals not tracking each other. This was most likely caused by the the left /right sensed AOA difference, but declaring UAS did not involve a direct comparison of the two AOA signals. On 737 the difference between measured static pressure and actual static pressure is a function of AOA. In order to account for this, measured static pressure is compensated based on measured AOA to minimize the resulting static pressure error that would result from a change in AOA. This AOA compensation for static pressure is done independently by the two air data systems that use the sensors on the two sides of the airplane. As a result, if the left and right static pressure ports measure identical pressures but AOA as sensed by the vanes on the two sided of the airplane differ, the compensated static pressure signals will between left and right. This difference causes the left and right barometric altitudes to differ slightly and the computed left and right airspeeds to differ slightly. It is the difference in airspeeds left to right that leads to the system issuing its UAS indication.
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Old 28th Mar 2019, 02:58
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Originally Posted by HarryMann
Another AoA display 'thing"...
.how exactly would it have helped in either of these two 737 MAX accidents.
the crew barely knew whether they were on foot or horseback once MCAS kicked off. Pretty sure AoA display wouldn't have helped solve "the immediate control crisis'.

.again.. I'd welcome an AoA display being sn engineer/technophile.
So how to differentiate quickly whether it usual STS or insidious MCAS faster? Aoa display or MCAS activation alert,that may written in future AD.

Could Aoa display save the plane before airborne (in taxy) by detecting the differentiate two vane?

Aoa display is more like debugging. It will stress more pilot but it will helped understand the way Hal think.






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Old 28th Mar 2019, 03:19
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Originally Posted by Realbabilu
So how to differentiate quickly whether it usual STS or insidious MCAS faster? Aoa display or MCAS activation alert,that may written in future AD.

Could Aoa display save the plane before airborne (in taxy) by detecting the differentiate two vane?

Aoa display is more like debugging. It will stress more pilot but it will helped understand the way Hal think.
AOA vane position is not valid until up to an airspeed well above that for taxi. Revised MCAS logic keeps MCAS from acting at all if an AOAs signals differ by anywhere near as much as appears to have been the case with the Lion Air accident data. I don't think the MCAS changes do anything for stick shaker so the shaker on the side with AOA failed high would activate as it did on Lion Air, but no MCAS.
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Old 28th Mar 2019, 03:32
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Salute!

Gums and maybe PJ and others are advocating limited use of an AoA indication, and primarily for your approach phase. You guys that want only airspeed will one day have a heavy plane and use a wrong entry on the table. The AoA doesn't care about the weight. Using both AoA and a rough idea for speed ( +/- a few knots) from a table is the best way to go.

For those not used to the really low aspect wings, or the jets with variable leading edge devices and so forth, there is no sharp AoA for stall, if any. Deltas like I flew early and the Concorde, Mirage series, etc, simply mushed. No stall break, just increasing vertical descent rate and loads of drag. Knowing the right speed for those helped a lot, but knowing the AoA was vital to keep from getting behind the "curve".
______________________
U.S. Congress hearing today shoulda had Sully. He knows about AoA, leaing edge devices, underslung motors, crew coordination and such. Plus has unreal reputation, right up there with the Sioux City folks in that crippled DC-10.

Gums sends...
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Old 28th Mar 2019, 03:39
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Vertical winds?? Banked turns?? I suggest they would have no practical bearing on the AOA. If the aeroplane is balanced in a turn, I'd reckon the airflow around both sides of the nose would be, for all intents and purposes, exactly the same. As for "vertical winds", that's all AOA is; anybody who's flown these types of aeroplanes would notice the stick shaker zipper bouncing up and down in turbulence when you're slow, but to say they are "useless without algorithms" is going a bit overboard.
Read Boeings Aero-12. That is where this information comes from.

It has been here several times, but keep getting deleted, so you will have to look up the issues with AoA measurement, calibration, latency, and other issues on your own.
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Old 28th Mar 2019, 04:03
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Originally Posted by FCeng84
The UAS on Lion Air resulted from the left and right airspeed signals not tracking each other. This was most likely caused by the the left /right sensed AOA difference, but declaring UAS did not involve a direct comparison of the two AOA signals. On 737 the difference between measured static pressure and actual static pressure is a function of AOA. In order to account for this, measured static pressure is compensated based on measured AOA to minimize the resulting static pressure error that would result from a change in AOA. This AOA compensation for static pressure is done independently by the two air data systems that use the sensors on the two sides of the airplane. As a result, if the left and right static pressure ports measure identical pressures but AOA as sensed by the vanes on the two sided of the airplane differ, the compensated static pressure signals will between left and right. This difference causes the left and right barometric altitudes to differ slightly and the computed left and right airspeeds to differ slightly. It is the difference in airspeeds left to right that leads to the system issuing its UAS indication.
AOA sensors are standard on almost every transport category aircraft. They are the primary sensor for the stall warning system (along with indicated airspeed), and may (or may not, depending on model) be used as part of static source error compensation.

I am an AME, not a pilot, so cannot comment on the operational utility of having an AOA display in the cockpit. Two aircraft models I have worked on that do have such displays as “standard kit” are the Beech 400A - which uses a military-style lighted chevron indexer on top of the glareshield, and the Gulfstream GIV, which has an relative AOA index scale on the pilot and copilot PFD displays, immediately to the left of the airspeed tape.

On both models, I assume flight crews are trained in the proper use and interpretation of the AOA readings.

On every other model in my experience, AOA is “there” in the background, as part of the overall stall warning and air data system, but not displayed to the pilots directly.

On the GIV, the AOA correction to altitude and airspeed can be significant in certain flight configurations. It is something we test during the required 24-month re-certification of the air data system. In landing configuration, with full flaps and the AOA vane rotated to a specified high alpha setting, the correction to indicated altitude can be as much as 600 feet.

The only aircraft model I am familiar with where the AOA system can cause an automatic aircraft configuration change is the Falcon 900. If both AOA vanes sense an impending stall, and the leading edge slats are deployed, the inboard slats will automatically retract. I believe this is done to prevent instability in the roll axis from occurring when close to to a stall.

But unlike the 737-8 MCAS - the Falcon autoslat retraction is not a “hidden mystery”. Every Falcon pilot is trained in the existence and operation of the system, and there is are specific preflight tests performed prior to taxi to insure it is working properly. If either AOA vane fails in flight, the autoslat system becomes inoperative with a warning light displayed to alert the crew.

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Old 28th Mar 2019, 05:39
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Originally Posted by FCeng84


Please explain what you mean by “Stall ID”. Also please describe “737Ng Stall ID trimming”. I am very familiar with the term “Stall ID” as part of the regulations but not in this context.
infrequentflyer789 answered the question. Stall ID is Boeing speak for when the SYMD has identified an AoA above the stall threshold for a 737ng. This triggers Stick shaker, Increased stick force (four times) and a nose down trim to make it harder for the pilot to pull more aft yoke. As we have full stall ID, how does MCAS come into play. Does MCAS replace Stall ID trim or not? The Stall ID trim respects the Column cut-out switches, MCAS does not. What logic prevails and why?
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Old 28th Mar 2019, 06:38
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Originally Posted by JRBarrett


AOA sensors are standard on almost every transport category aircraft. They are the primary sensor for the stall warning system (along with indicated airspeed), and may (or may not, depending on model) be used as part of static source error compensation.

I am an AME, not a pilot, so cannot comment on the operational utility of having an AOA display in the cockpit. Two aircraft models I have worked on that do have such displays as “standard kit” are the Beech 400A - which uses a military-style lighted chevron indexer on top of the glareshield, and the Gulfstream GIV, which has an relative AOA index scale on the pilot and copilot PFD displays, immediately to the left of the airspeed tape.

On both models, I assume flight crews are trained in the proper use and interpretation of the AOA readings.

On every other model in my experience, AOA is “there” in the background, as part of the overall stall warning and air data system, but not displayed to the pilots directly.

On the GIV, the AOA correction to altitude and airspeed can be significant in certain flight configurations. It is something we test during the required 24-month re-certification of the air data system. In landing configuration, with full flaps and the AOA vane rotated to a specified high alpha setting, the correction to indicated altitude can be as much as 600 feet.

The only aircraft model I am familiar with where the AOA system can cause an automatic aircraft configuration change is the Falcon 900. If both AOA vanes sense an impending stall, and the leading edge slats are deployed, the inboard slats will automatically retract. I believe this is done to prevent instability in the roll axis from occurring when close to to a stall.

But unlike the 737-8 MCAS - the Falcon autoslat retraction is not a “hidden mystery”. Every Falcon pilot is trained in the existence and operation of the system, and there is are specific preflight tests performed prior to taxi to insure it is working properly. If either AOA vane fails in flight, the autoslat system becomes inoperative with a warning light displayed to alert the crew.
JR - your story about automatic retraction of the inboard leading edges at high AOA on the Falcon 900 reminds me of stall characteristics on the original 777. As an airplane approaches stall you would like to see two things happen. First the center of lift shifting aft will generate a nose down pitch break. Second the wing tips continuing to hold on (i.e., not stall first) will preserve roll control. Both of these objectives are achieved if the inboard portion of a swept wing can be made to stall before the outboard portion of the wing. On 777 the darn thing would not stall! It got up to 30+ degrees without a pitch break and the wing tips would sometimes go first leading to a rather exciting rolloff - beyond 90 degrees in some cases! The solution on 777 was to practically eliminate the leading edge gap on the inboard wing when the slat are extended. This caused the inboard wing to stall first at a much lower AOA and preserved roll control with the outboard ailerons. It sounds like the Falcon 900 by retracting the inboard leading edges at high AOA was probably accomplishing the same thing by forcing the inboard portion of the wing to stall first with the wing tips still flying well and thus preserving roll control.

Memory lane ...
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Old 28th Mar 2019, 06:41
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From a piece on Radio 4 Today programme just- refreshingly simple and succinct:
'the only mention of MCAS in the a/c manufacturer's manual is in the abbreviations- that was quite a surprise'
and this;
'Absolutely novel that a major system in the cockpit or a/c was not explained to the pilots'
Tilmann Gabriel. IPTA
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Old 28th Mar 2019, 07:57
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Originally Posted by parabatix
From a piece on Radio 4 Today programme just- refreshingly simple and succinct:
'the only mention of MCAS in the a/c manufacturer's manual is in the abbreviations- that was quite a surprise'
and this;
'Absolutely novel that a major system in the cockpit or a/c was not explained to the pilots'
BBC TV News showed the page in question from the FCOM:




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Old 28th Mar 2019, 08:44
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Originally Posted by HarryMann
Another AoA display 'thing"...
.how exactly would it have helped in either of these two 737 MAX accidents.
the crew barely knew whether they were on foot or horseback once MCAS kicked off. Pretty sure AoA display wouldn't have helped solve "the immediate control crisis'.

.again.. I'd welcome an AoA display being sn engineer/technophile.
Ref AOA
Harry. That is so right. Adding more confusion to confusion/ which AOA would have done in this instance was not going to help. The most important instrument in a confusing situation is the horizon- ADI. If you are flying level with power set you are flying level no matter what lights are flashing, horns blaring. Unless you have gone into deep stall.
And your ground speed is always there which equates closely to airspeed at lower levels.
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Old 28th Mar 2019, 08:50
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Originally Posted by yanrair

Ref AOA
Harry. That is so right. Adding more confusion to confusion/ which AOA would have done in this instance was not going to help. The most important instrument in a confusing situation is the horizon- ADI. If you are flying level with power set you are flying level no matter what lights are flashing, horns blaring. Unless you have gone into deep stall.
And your ground speed is always there which equates closely to airspeed at lower levels.
exactly! Revert to attitude + power = performance.

Cessna 172 flying.
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Old 28th Mar 2019, 08:57
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Originally Posted by DaveReidUK
BBC TV News showed the page in question from the FCOM:
The entry 'MCAS Maneuver Characteristics Augmentation System' started appearing in the Abbreviations section of the B737 NG FCOMs from around late 2016 but neither the term nor the acronym appeared anywhere else in the FCOM.

I don't know if it's significant or not but Boeing have been referring to the system fitted to the MAX as the 'Maneuvering Characteristics Augmentation System'.
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Old 28th Mar 2019, 09:11
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Boeing I believe have a "fix" for the problem. Strange how these things can be moved forward, when the fleet is grounded. Tombstone regulation?
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Old 28th Mar 2019, 09:39
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Originally Posted by JRBarrett


AOA sensors are standard on almost every transport category aircraft. They are the primary sensor for the stall warning system (along with indicated airspeed), and may (or may not, depending on model) be used as part of static source error compensation.

I am an AME, not a pilot, so cannot comment on the operational utility of having an AOA display in the cockpit. Two aircraft models I have worked on that do have such displays as “standard kit” are the Beech 400A - which uses a military-style lighted chevron indexer on top of the glareshield, and the Gulfstream GIV, which has an relative AOA index scale on the pilot and copilot PFD displays, immediately to the left of the airspeed tape.

On both models, I assume flight crews are trained in the proper use and interpretation of the AOA readings.

On every other model in my experience, AOA is “there” in the background, as part of the overall stall warning and air data system, but not displayed to the pilots directly.

On the GIV, the AOA correction to altitude and airspeed can be significant in certain flight configurations. It is something we test during the required 24-month re-certification of the air data system. In landing configuration, with full flaps and the AOA vane rotated to a specified high alpha setting, the correction to indicated altitude can be as much as 600 feet.

The only aircraft model I am familiar with where the AOA system can cause an automatic aircraft configuration change is the Falcon 900. If both AOA vanes sense an impending stall, and the leading edge slats are deployed, the inboard slats will automatically retract. I believe this is done to prevent instability in the roll axis from occurring when close to to a stall.

But unlike the 737-8 MCAS - the Falcon autoslat retraction is not a “hidden mystery”. Every Falcon pilot is trained in the existence and operation of the system, and there is are specific preflight tests performed prior to taxi to insure it is working properly. If either AOA vane fails in flight, the autoslat system becomes inoperative with a warning light displayed to alert the crew.
That's a pretty relevant post Thanks and puts it in a nutshell!
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Old 28th Mar 2019, 10:38
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I’m still really confused as to why the MCAS is being held totally responsible for this crash.
Didn’t this flight and the Lion Air flight both have unreliable airspeed problems immediately after takeoff?
Can somebody please explain how the MCAS system can cause an unreliable airspeed indication after takeoff?
I still don’t understand why a blocked pitot isn’t even being discussed.
It’s my understanding that this was a morning flight (local time).
Could the pitot covers have been left on, or possibly a mud wasp got in there overnight?
At the end of the day, if the engines and the hydraulics were working, why weren’t two qualified pilots able to “fly” the aeroplane in apparently fine weather back to Addis Ababa?
I’m honestly confused as to why everybody seems to be jumping on the MCAS bandwagon!
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Old 28th Mar 2019, 10:51
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Because if it was a case of only a blocked pitot, the plane would have sat trimmed with a nose up bias and very few control inputs would have been required in order for the aircraft to fly away from the ground. It is thought by many ( waiting on report) that the MCAS system trimmed the stab nose down with no command from the pilots to do so, which would necessitate
1/ making more control inputs of greater magnitude in order to allow the aircraft to fly away from the ground
2/ recognising that the trim was running uncommanded
3/ preventing the trim from running uncommanded.

Two different scenarios really.
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