Indonesian aircraft missing off Jakarta
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Would it be fair to say that the previous crew worked an issue whilst not understanding the nature of the issue? In other words, they thought they had a trim runaway and flicked the stab trim switches. Luck rather than judgement?
Given the CVR has not been recovered the only two people that definitively know exactly what transpired cannot defend themselves, is it not wiser to resist the arrogance afforded by 100% hindsight and wait for the CVR to be found?
Thank you Semreh, far more eloquently put.
What I noted from the reported is that the PIC of the flight from DPS-CGK picked up the automatic trim inputs nose down and also stated that by the third trim input the control column became too heavy for the SIC. Fortunately, a decision was made at that point to cut off the electric trim which probably saved the aircraft.
Could unfortunately the crew of the incident flight realised what they needed to do but by the fourth/fifth trim input, but it was already too late as the control forces were such that both had to compensate by holding on to the column with neither of them wanting to/or being able to let go of the column as that's all that was keeping the nose up to reach for the trim cut out switches.
I have been thinking further about what possibly caused the increase forces, as aerodynamic forces should not really be felt even on a 737 through the column unless the hyds are off, so could the Elevator Feel Shift that occurs when a stall is detected (I believe based on AOA input to the SMYD) be the cause of the increase of column forces, as this applies forces to the feel and centering unit to resist elevator up movement which could have effectively compounded the situation.
Could unfortunately the crew of the incident flight realised what they needed to do but by the fourth/fifth trim input, but it was already too late as the control forces were such that both had to compensate by holding on to the column with neither of them wanting to/or being able to let go of the column as that's all that was keeping the nose up to reach for the trim cut out switches.
I have been thinking further about what possibly caused the increase forces, as aerodynamic forces should not really be felt even on a 737 through the column unless the hyds are off, so could the Elevator Feel Shift that occurs when a stall is detected (I believe based on AOA input to the SMYD) be the cause of the increase of column forces, as this applies forces to the feel and centering unit to resist elevator up movement which could have effectively compounded the situation.
Last edited by Station Zero; 28th Nov 2018 at 09:59. Reason: Typo
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I have been thinking further about what possibly caused the increase forces, as aerodynamic forces should not really be felt even on a 737 through the column unless the hyds are off, so could the Elevator Feel Shift that occurs when a stall is detected (I believe based on AOA input to the SMYD) be the cause of the increase of column forces, as this applies forces to the feel and centering unit to resist elevator up movement which could have effectively compounded the situation.
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I'm long retired and I wouldn't dream of second guessing the inquiry but I can't help thinking that too many present day pilots are indoctrinated to fly the aircraft through the system. Fine as far as it goes but, if the system is malfunctioning, how long does it take to disconnect and use pitch/power to restore straight and level?
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The Preliminary Report (78 pages) linked to above is a very slow download this morning.
However, ASN have a copy at https://reports.aviation-safety.net/...RELIMINARY.pdf which seems to be responding fine.
Initial glance through suggests no new technical information on MCAS and no FDR info beyond what we've already seen from the press release.
There's no explicit mention of the flying spanner in the Preliminary Report, suggesting that he/she was not on the flight in any kind of pre-assigned troubleshooting role.
I have been thinking further about what possibly caused the increase forces, as aerodynamic forces should not really be felt even on a 737 through the column unless the hyds are off, so could the Elevator Feel Shift that occurs when a stall is detected (I believe based on AOA input to the SMYD) be the cause of the increase of column forces, as this applies forces to the feel and centering unit to resist elevator up movement which could have effectively compounded the situation.
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Would it be fair to say that the previous crew worked an issue whilst not understanding the nature of the issue? In other words, they thought they had a trim runaway and flicked the stab trim switches. Luck rather than judgement?
You see the tech log from the previous flight, it says:
"IAS and ALT Disagree shown after take off","Performed flushing Left Pitot Air Data Module (ADM) and static ADM. Operation test on ground found satisfied."
"feel diff press light illuminate","performed cleaned electrical connector plug of elevator feel computer carried out. test on ground found OK"
There is nothing said about a trim or stab runaway or STS issue (the comment about STS trimming wrong was made to an IT system that you did not have access to before the flight)
You are mentally prepared for an IAS and ALT disagree, but somehow you expect it had been fixed.
You are not mentally prepared for a trim system to push the nose down on its own.
You pull, stick shaker goes off on rotation.
You get IAS disagree.
You remember the tech log saying ALT DISAGREE, your co asks ATC. They tell you you are at 900 feet. This seems to be in line to what you see.
You are somehow comfortable with the speed, you retract the flaps at 2000 feet.
You see the trim wheels spinning nose down in increments. This is the unexpected. You are surprised.
You pull and from your NG experience you expect the trim to stop, it does not, it keeps trimming.
You think trim down makes sense somehow to fight the stick shaker. But you have not heard of a 737 system that does that.
You think it is better to set flaps again.
Stick shaker remains. Does not make sense to you. But trim stops.
You are fixed on speed. You are uncertain which is the correct speed, left or right or stby. (The report suggests from the ATC tape that all three speed indications were different).
You are confused, you order flaps up again, you are concerned about speed.
Trim spins down again in intervals, you never heard of a 737 doing that before.
You think it is not a runaway stab, it is not STS, it does not stop when I pull, it is something different. But what?
You are fixed on not becoming too slow and stall and not too fast and break the plane.
You trim up, the plane trims down ...
You do not trust any indication in front of you.
You ask PNF to ask ATC about ground speed.
ATC tells you are at 322 kts, you are at 5000 feet. You think that's damned fast and not far away from 320 KIAS, damned fast,
You are fixed it is an UAS issue.
You have never heard of an automatic trim down function in intervals.
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Sunwing 737 Max suffers spurious indication incident
Canadian investigators have disclosed that engineers replaced an air data computer on a Sunwing Airlines Boeing 737 Max 8 after the crew received spurious indications from the aircraft’s instruments.The aircraft (C-GMXB) is less than six months old, having been delivered to Sunwing at the end of May.
It had been operating to Toronto from Punta Cana, in the Dominican Republic, when the incident occurred on 14 November.
Transportation Safety Board of Canada says the aircraft had been cruising at 35,000ft when the crew received “erroneous” indications on the captain’s side.
The first officer’s instruments, and the standby indicators, were functioning normally and the first officer took control of the aircraft.
It descended to 25,000ft as a precaution, in order to clear instrument meteorological conditions, but – as it passed 28,000ft – the weather radar and collision-avoidance system both failed. The aircraft was some 50nm north-west of Washington DC at the time.
The crew transmitted a ‘pan pan’ urgency call. The safety board says a left-side inertial reference system fault light also illuminated.
Investigators state that the flight proceeded to Toronto and landed without further incident, with no injuries among the 182 occupants.
Sunwing’s maintenance service replaced the left-side air data inertial reference unit (ADIRU) before returning the aircraft to operation.
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re. the maint log, I see lots of busywork and resetting things, but nothing to actually trace and fix a problem. Is that unfair, or is that typical in aircraft maintenance?
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Here's the full quote:
"In Indonesia, an onboard mechanic/engineer is nothing related to an aircraft having problems from the previous flight. They're there to release the aircraft should the aircraft develop a problem that can be deferred, should that problem occur at an outstation. Placing engineers at outstations can be more expensive than the loss of revenue from 1 seat plus flight pay, because aviation in Indonesia is very Jakarta-centric. Place someone at an outstation and the company has to fork out money for his accommodation and outstation pay, plus transportation to go back and forth to Jakarta or nearest maintenance base, and get a back up person. And you can't just get any engineer certified/rated on the type at an outstation to do stuff for you, the guy has to be approved on the type AND approved by the DGCA to do work for your airline. Now, Outstation based 3rd party contractors can be very expensive because of that. The same happens with dispatchers, and loadsheeters, it's not uncommon in Indonesia to see an engineer and a dispatcher onboard to outstations. Moves by the industry to make the use of certified 3rd party contractors and to make such a thing cheaper was effectively blocked by the previous transport minister in the aftermath of the Air Asia crash in end of 2014, because he seems to believe that safety should be expensive. Heck, he banned the use of centralized dispatch and tried to ban the use of approved weather information in computerized flight plans and dispatch briefs 'because they're not from the national weather bureau', despite the national weather bureau were giving out the same exact information and source as those within the airline dispatch briefs!"
2nd flight they also had NCD on the Capt side but also picked up an issue with the AOA sensor. Again a reset was done fault cleared. Still faily common practice. Also perhaps a heads up was given to Bali to be ready for an AOA probe change.
3rd flight again NCD fault on on Capt side. Fault with AOA sensor reconfirmed and replaced. Following replacement aircraft released as tests passed. Still following fairly normal troubleshooting process.
4th flight IAS/ALT disagree reported, FIM/TSM consulted. Flush performed. Slightly different defect. Possibly engineer considered it unrelated to NCD on the previous flights.
Whats missing in these logs are stall warning reports going off and unknown trim commands. If its in the tech log the entries must be answered but telling engineers or putting it in a follow up report is no good. Doesn’t highlight the problem. Good example most airlines now don’t even have licensed engineers meet aircraft. So that message/conversation supposedly had by the crew on arrival of the fourth flight may have not even reached the engineer who did the work.
Simple, if it happens put it in the tech log... anywhere else there’s a risk it will get missed or forgotten. To flight crew from an engineer one of my pet hates is every once and a while you’ll get a post flight brief (when you get the chance to have one) and then find the defect discussed not in the log, should simply not happen.
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Quote:Would it be fair to say that the previous crew worked an issue whilst not understanding the nature of the issue? In other words, they thought they had a trim runaway and flicked the stab trim switches. Luck rather than judgement?
I would have thought that the response would be something along the lines of the successful previous flight. <<Thinks>> "Trim seems to have something wrong with it it keeps trying to trim down even though it stops when I trim nose up - CUT OFF trim switches OFF - that's better now to solve the other issues".
I didn't realize that parsing words was one of the memory items. <<thinks> "The trim keeps on trimming nose down, but if I trim nose up it stops. But that cannot be a trim runaway as runaway means continuous and it is stopping every now time I trim back - therefore I will ignore the nose down trim and just pull harder...
In other words the first reported issue occurred seven sectors prior to the accident flight.
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Even in the fly-by-wire A320 the flight control computers don't really care who makes the inputs. All computers evaluate inputs from both sticks and air data from all available sensors (indirectly via the ADIRUs).
The MCAS is also completely independent of pilot inputs (except trim inputs, but that only inhibits it for 5 seconds), and no system (except possibly force sensors at the control columns themselves) "knows" which pilot is making inputs. Sometimes both do, especially in cases of a badly mis-trimmed aircraft.
Bernd
