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737-500 missing in Indonesia

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737-500 missing in Indonesia

Old 17th Apr 2021, 14:27
  #801 (permalink)  
 
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ok, if it is mandatory to scroll back your logs for maintenance actions, how far do you have to scroll back? One flight, two flights, a week?
What I am triggered on is that you call others “derelict in their duties” for something that is good practice but not required.
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Old 17th Apr 2021, 15:22
  #802 (permalink)  
 
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I wouldn't even go so far as to call it "good practice". More like ... vaguely interesting. Open defects are enough - I would only look through previous history if I had a problem myself and wanted to see if it looked like a recurring problem.
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Old 17th Apr 2021, 18:36
  #803 (permalink)  
 
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Originally Posted by safetypee View Post
tdracer, re AT clutch / cable description #792.
Is it possible, depending on design, for both thrust levers to move together - AT clutch control in flight deck area, but with cable friction etc, for one engine to lag or freeze resulting in asymmetric thrust.
If I understand your question correctly, not really. There is some cable stretch and lost motion in the connections between the throttle and the fuel control, but we're talking the equivalent of maybe a half knob of throttle movement - so while one engine may lag a bit, it shouldn't be enough to cause a serious issue.
With cable engines, there is normally some throttle stagger between the engines - in addition to what I noted above, there are differences in the fuel controls and their 'trim' settings, and (IIRC) on the CFM56-3 engine, the fuel control controls to N2 - not N1 - so to align N1s might require slightly different throttle positions (there is also an analog electronic supervisory control that trims the fuel control to attempt to keep N1 constant as the conditions change). However even with all that, there should be less than a knob of throttle stagger with equal N1s (and maintenance action taken if it gets that large).
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Old 18th Apr 2021, 15:00
  #804 (permalink)  
 
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td. Thank you; my thoughts relate to the need for meaningful instrument displays re thrust asymmetry, and crews prioritising these over thrust lever position.
Also, considering a range of scenarios, indications, analysis, and action:-
- AT clutch slip could involve two cues; instruments and TL. ~ AT malfunction; disengage AT.
- Engine/FCU fault; probably only instruments. ~ Engine malfunction; review other engine instruments and related systems.

Presumably modern FADEC controlled engines have the capability for cross monitoring and alerting displays; e.g. similar to air data instruments ‘disagree’.
Are there any aircraft which have such a system?

Associated refs;
https://www.faa.gov/aircraft/air_cer...ne_psm_icr.pdf
“Although the vast majority of propulsion system malfunctions are recognized and handled appropriately, there is sufficient evidence to suggest that many pilots have difficulty identifying certain propulsion system malfunctions and reacting appropriately”.

https://www.aia-aerospace.org/wp-con...ITT_Report.pdf
Powerplant Indications Task Team Report;
‘… opportunities for safety improvements’, para 1.4 onwards.

Investigation of (Automatic) Asymmetric Thrust Detection
https://core.ac.uk/download/pdf/42702866.pdf
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Old 18th Apr 2021, 15:31
  #805 (permalink)  

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Further to td's explanation, there's a controlling circuitry in the Classic called PMC, I seem to recall. It's job is to fine-tune everything controlling the N1s and if operational the engines behave very gracefully.

BananaJoe somewhere near?

I.e. most likely in your scenario the PMC would feed inputs to A/T for matching N1 first, resulting in the stagger described and not the other way around. The governing input is the N1, not throttle angle.
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Old 18th Apr 2021, 19:43
  #806 (permalink)  
 
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safetypee

It was found that flight crew would often start troubleshooting things like low oil pressure or an IDG dropping offline when the actual problem was the engine had quit. So starting with the 747-400, Boeing implemented an "ENG X FAIL" message on EICAS - the logic was pretty basic (N2/N3 well below idle) - Similar ENG FAIL logic was included in the 767 EICAS but for reasons I never understood it was never turned on...
777 took it a step further - partly due to the implementation of TAC (Thrust Asymmetry Compensation) which could hide a thrust asymmetry caused yaw, they implemented L/R ENG THRUST which indicated an engine was producing less than commanded thrust (by at least 10% IIRC) and not recovering. I think the ENG THRUST logic was in the FADEC but I wouldn't swear to it. The 777 also has L/R ENG FAIL with somewhat more sophisticated logic than the 747-400.
The 787 and 747-8 have the ENG FAIL and ENG THRUST messages.
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Old 19th Apr 2021, 00:07
  #807 (permalink)  
 
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There's always the case where the engine doesn't annunciated a failure condition at high altitude or at low power during approach, yet over time the drag asymmetry can lead to an unstable aircraft mode (pitch and/or roll) which can manifest itself and confuse the crew if they fail to note such changes.

So just how far to you go with engine controls or instruments, either in design or annunciating to the crew?
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Old 20th Apr 2021, 14:38
  #808 (permalink)  
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That is a great question.
Case in point and a very subtle failure that happened to a friend. When leaving FL360, on descent, the thrust levers were at idle and the number 2 engine flamed out. At that time the only caution that the crew saw was the engine generator message indicating an "off line" condition.
If the descent had an intermediate level off, then that would have been interesting.
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Old 20th Apr 2021, 22:09
  #809 (permalink)  
 
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Originally Posted by Joejosh999 View Post
I’m not a pilot (my Dad was) but, if I’m flying an aircraft w misbehaving auto-throttles, would I not at minimum 1) watch the throttles closely during climb and/or 2) have my hand on the throttle quad at all times such that even if I was looking elsewhere I would feel the split?
I know it’s easy for a non-pilot like me to say, but....any comments?
Yes ! Well, I certainly would anyway. (Sometimes you want both hands on the yoke for finer control, but you can always see the engine gauges).

Some pilots say that non moving Airbus FBW thrust levers are a bad thing, yet there have been several accidents in recent years with Boeing thrust levers that didn't move when they should have, but the situation was not noticed by the pilots.

The Airbus system requires the pilots to look at the N1/EPR gauges every instrument scan to confirm what the engines are doing. This is a very GOOD thing, and avoids getting caught out.
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Old 21st Apr 2021, 06:21
  #810 (permalink)  
 
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You are of course required to monitor the engine instruments in a Boeing as well, thrust lever movement is not the primary engine indication. They add an element to the monitoring. It is very easy to get lazy when it comes to engine monitoring in an Airbus.
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Old 21st Apr 2021, 06:57
  #811 (permalink)  
 
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Yes, my point was that several recent Boeing crashes have been a direct result of pilots NOT looking at the engine instruments, but assuming - from the proxy of the thrust lever position(s) - what the engines were doing. But even then, the wrong thrust lever position - for example an asymmetry - has not been noticed. In particular, a common theme seems to be not noticing when the thrust lever(s) don't move, but should have moved.

The danger is that some use the moving thrust levers as their engine monitoring and get out of the vital habit of checking the engine instruments in every scan,

In Airbus FBW, pilots must look at the engine instruments to know what the engines have been commanded to do and are doing, (apart from large accelerations felt through the body).
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Old 21st Apr 2021, 07:28
  #812 (permalink)  
 
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Are you trying to sell the lack of tactile feedback in Airbus FBW design (both thrust levers and sidestick) as positive?

It's not. The fact that you have to stare inside the flightdeck to monitor what automation is doing, instead of being able to look outside and feel with hands on controls that the autopilot is starting to do something silly, isn't a positive in my book.
​​​​​
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Old 21st Apr 2021, 07:29
  #813 (permalink)  
 
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The danger in an Airbus is that engine instruments are not included in the scan. You can use BIG letters as much as you want, but movable levers are not dangerous.
If thrust is assymetric, thrust levers split, aircraft in a yaw/roll and the pilots fail to notice, they are not doing their job.
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Old 21st Apr 2021, 07:51
  #814 (permalink)  
 
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It's two different planes with different operating philosophies... Stop arguing whether one of them is better. In either of them you should be trained for and know about the traps you can fall into, and in either of them you are not doing your job properly if a major thrust asymmetry goes unnoticed. Whether you don't pay attention to thrust levers that have moved or to engine instruments, you are not doing your job. If anything, autothrust is the danger as it brings out the lazy part in any pilot. Bring back manual thrust only, wohoo! /sarcasm
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Old 21st Apr 2021, 13:41
  #815 (permalink)  
 
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Following through the history of this crash up to present date, it looks increasingly like the scene in the 737 simulator described by Centaurus at Post 309 date 18 January 2021, is uncomfortably close to that of what really happened.
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Old 21st Apr 2021, 14:09
  #816 (permalink)  
 
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Sheppy, totally agree! Cockpit gradient is some countries is staggering and zero CRM . Add to that complacency, lack of skill and the holes line up quickly.
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Old 21st Apr 2021, 14:28
  #817 (permalink)  
 
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Originally Posted by golfyankeesierra View Post
ok, if it is mandatory to scroll back your logs for maintenance actions, how far do you have to scroll back? One flight, two flights, a week?
What I am triggered on is that you call others “derelict in their duties” for something that is good practice but not required.
It was required in Naval Aviation and in the airline where I worked.

It is also covered under FAR 91.103 in the US:
§91.103 Preflight action.
Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that
flight.
Recent maintenance history and recurrent maintenance problems certainly are relevant to the flight!
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Old 21st Apr 2021, 16:04
  #818 (permalink)  
 
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Any open defect, no mater how far back , was and is the captain's responsibility. No excuses for not knowing what you are signing for.
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Old 21st Apr 2021, 16:04
  #819 (permalink)  
 
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Intruder

"Recent maintenance history and recurrent maintenance problems certainly are relevant to the flight!"

So how many previous sectors' log entries should a crew expect to have to trawl through when accepting an aircraft ?
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Old 21st Apr 2021, 16:22
  #820 (permalink)  
 
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You nailed it Intrance. The convenience of autothrottle may have tipped the balance in the wrong direction where control of the airplane is concerned. Too much automation has disengaged the pilot.
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