Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Maintenance Lapse Identified as Initial Problem Leading to Lion Air Crash

Tech Log The very best in practical technical discussion on the web

Maintenance Lapse Identified as Initial Problem Leading to Lion Air Crash

Old 25th Dec 2018, 14:16
  #1 (permalink)  
Thread Starter
 
Join Date: Jun 2014
Location: Chocolatetown
Age: 58
Posts: 83
Maintenance Lapse Identified as Initial Problem Leading to Lion Air Crash

Maintenance Lapse Identified as Initial Problem Leading to Lion Air Crash

Crash investigators have concluded preliminarily that improper calibration of an airspeed (AoA?) sensor during maintenance touched off the sequence of events that led to October’s fatal Lion Air jetliner crash in Indonesia, according to people familiar with the details.

The conclusion is subject to further analysis, these people said, but it is the firmest indication so far that a suspected maintenance lapse was the initial misstep that ended with the months-old Boeing Co. 737 MAX aircraft plunging into the Java Sea, killing all 189 people on board.

Two days before Lion Air Flight 610’s early morning takeoff from Jakarta on Oct. 29, according to these people, mechanics installed but failed to properly calibrate a replacement airspeed sensor called an angle-of-attack indicator.

Based on information downloaded from the flight-data recorder, last month’s interim report revealed a constant 20-degree difference between signals from the angle-of attack sensor on the captain’s side—which had been replaced—and those from the co-pilot’s-side sensor.

Until now, the precise cause of the improper signals from the captain’s-side sensor hasn’t been clear.

People closely tracking the probe said that after U.S. air-safety experts re-enacted the tasks of installing, calibrating and verifying operation of the sensor, they deemed current maintenance instructions appropriate.

https://www.wsj.com/articles/mainten...39204?mod=e2tw

Last edited by climber314; 25th Dec 2018 at 15:31. Reason: Added additional text from WSJ re: MX Procedures
climber314 is offline  
Old 25th Dec 2018, 16:50
  #2 (permalink)  
 
Join Date: Feb 2013
Location: 60 north
Age: 55
Posts: 2
I, for one would deem the current procedure NOT appropriate , considering the result!

Now , I am sure they can pull out the old card : It hardly ever happens that someone gets it wrong!
Well that was OK until the Max as the misaligned AoA sensor was just a faulty indicator and did not lead to an uncontrollable aircraft via false trim input ( only needing one crew error to open up the last hole in the cheese.)

I am looking forward to see what was actually done, and it would be nice to know if this has been done before and if an aircraft has gotten airborne with same error.
BluSdUp is offline  
Old 25th Dec 2018, 17:27
  #3 (permalink)  
Thread Starter
 
Join Date: Jun 2014
Location: Chocolatetown
Age: 58
Posts: 83
Not sure why AoA display is an option on the 737 MAX if a critical flight control surface is controlled by a (single) AoA sensor.
Maybe Boeing should update the QRH for BOTH Runaway Stabilizer AND AoA Disagree?
Seems like Boeing rushed this "PATCH" and didn't think this through completely.
In Boeing's defense it took some poor maintenance and sketchy aviating for this issue to manifest.
climber314 is offline  
Old 25th Dec 2018, 17:52
  #4 (permalink)  
 
Join Date: Sep 2018
Location: Laredo, TX
Posts: 96
How many turns of the screw?

20 degrees seems like a lot to change, however it is done. Im sure well see the maintenance procedure from someone here.
jimtx is offline  
Old 25th Dec 2018, 19:29
  #5 (permalink)  
 
Join Date: Mar 2014
Location: WA STATE
Age: 74
Posts: 1
FWIW seems to be confusion in the above posts between AOA and Airspeed. AFIK the AOA ( Angle of attack ) indicator measures the angle of the plane to the mass of air flowing past the plane- and has little to do with airspeed ( the indicator FUNCTION is independent of airspeed) . Whil it is true that for stable flight, the PROPER angle of attack is a function of airspeed and weight and CG and . . . the measurement device is like a windvane whose angle is RELATIVE to the body-airframe .

Sure sounds like somehow, the AOA indicator was installed in the wrong set of holes ( clocked ) relative to the correct set. " If it doesn't FIT - FORCE IT ' assmbly method
CONSO is offline  
Old 25th Dec 2018, 21:07
  #6 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 10,790
Originally Posted by CONSO View Post
Sure sounds like somehow, the AOA indicator was installed in the wrong set of holes ( clocked ) relative to the correct set. " If it doesn't FIT - FORCE IT ' assmbly method
According to the Preliminary Report, the AoA values from the suspect sensor were 20 degrees adrift.

If you tried to fit the sensor offset by 20 degrees, none of the attachment screws would pick up on the captive nuts, so that sounds highly unlikely.
DaveReidUK is online now  
Old 25th Dec 2018, 21:54
  #7 (permalink)  
 
Join Date: Jul 2013
Location: Everett, WA
Age: 64
Posts: 2,418
Originally Posted by BluSdUp View Post
I, for one would deem the current procedure NOT appropriate , considering the result!
BluSd, they are saying there is nothing wrong with the existing procedure - IF IT'S FOLLOWED!!!

The best AMM procedure in the world is worthless if it isn't followed.

DR - I'll be very curious to find out how they messed up the installation, but Murphy's Law says that people can be extraordinarily inventive when it comes to messing things up. I remember us getting back parts that had indexing keys to prevent improper installation where the indexing keys had been very professionally machined off...
tdracer is online now  
Old 25th Dec 2018, 22:00
  #8 (permalink)  
 
Join Date: Apr 2010
Location: IRS NAV ONLY
Posts: 835
Originally Posted by climber314 View Post
Not sure why AoA display is an option on the 737 MAX if a critical flight control surface is controlled by a (single) AoA sensor.
Maybe Boeing should update the QRH for BOTH Runaway Stabilizer AND AoA Disagree?
Seems like Boeing rushed this "PATCH" and didn't think this through completely.
In Boeing's defense it took some poor maintenance and sketchy aviating for this issue to manifest.
A lot of FBW aircraft have much more flight control surface movements (including completely limiting pilot authority) based on AoA without flight deck indication of the AoA and seem to be flying around safely. Also, it would be very hard to design an aircraft that will be still very safe with "some poor maintenance and sketchy aviating".

Hopefully they find the CVR and we see in final report what really happened.
FlyingStone is offline  
Old 25th Dec 2018, 23:09
  #9 (permalink)  
 
Join Date: Oct 2013
Location: McHales Island
Age: 64
Posts: 139
Looking from another angle (no pun intended) a question for the Engineers/Mechanics out there.... Is the AOA sensor calibrated at the factory BEFORE the operator receives it into his spares stock inventory so as to enable a quick sensor change out on the line. For example, disconnect cannon plug, remove old AOA sensor / Install new AOA sensor, reconnect cannon plug, do test (bite check?) and on your way OR install new AOA sensor and then carry out calibration of said sensor.

Rgds McHale.
Capt Quentin McHale is offline  
Old 25th Dec 2018, 23:30
  #10 (permalink)  
 
Join Date: Sep 2018
Location: Laredo, TX
Posts: 96
Maybe left and right use the same unit and you have to adjust the unit for the correct side?
jimtx is offline  
Old 26th Dec 2018, 04:01
  #11 (permalink)  
 
Join Date: Sep 2001
Location: Toronto
Posts: 2,209
The sensor is mounted on the fuselage; so in the case of a sensor that can be mounted on either side, perhaps needs to calibrated to the angle of incidence between local flow at the fuselage location and wing which will be positive or negative. However being 20 off implies a 10 difference between local flow and AoA

That kind of difference implies a misalignment when mounting.

Are the sensors generic units with various calibration values for different aircraft and sides?
RatherBeFlying is offline  
Old 26th Dec 2018, 12:29
  #12 (permalink)  
 
Join Date: Feb 2013
Location: 60 north
Age: 55
Posts: 2
tdracer
I am all with You on that.
I am wondering how many times , if any, an 737 AOA unit has been installed wrong to this extent, and were it was found out, ie on ground or airborne?
If never, then procedure is good.
The fact that a miss-installed AOA on my 737- 800 is not doing much more then making a lot of rattle and making me work hard for some minutes on the QRH as opposed to the MAX that will demand me to take prompt action on that semi- runaway trim , if not A/c becomes uncontrollable as so tragically demonstrated, SHOULD demand of the Maint Procedure even more rigid adherence and double checking!

I wager the procedure was the same, even with the potential for dramatically worse outcome on a different aircraft.
I have seen this on the Dornier 328 Turboprop when they certified the D328 Jet: Same airframe, lots of cut and paste, small details not applicable ( Propheat ciquitbraker being the nobrainer in QRH)

Anyway
I am looking forward to fly the MAX next year.
BluSdUp is offline  
Old 26th Dec 2018, 13:30
  #13 (permalink)  
 
Join Date: Dec 2018
Location: Dundee
Posts: 1
Originally Posted by jimtx View Post
Maybe left and right use the same unit and you have to adjust the unit for the correct side?
Yes.You just turn it inside out.

Last edited by weemonkey; 26th Dec 2018 at 13:31. Reason: In case you don't get it this is SARCASM.
weemonkey is offline  
Old 26th Dec 2018, 13:44
  #14 (permalink)  
 
Join Date: May 2018
Location: London/Fort Worth
Posts: 0
Originally Posted by Capt Quentin McHale View Post
Looking from another angle (no pun intended) a question for the Engineers/Mechanics out there.... Is the AOA sensor calibrated at the factory BEFORE the operator receives it into his spares stock inventory so as to enable a quick sensor change out on the line. For example, disconnect cannon plug, remove old AOA sensor / Install new AOA sensor, reconnect cannon plug, do test (bite check?) and on your way OR install new AOA sensor and then carry out calibration of said sensor.

Rgds McHale.
On the 737NG you just have to swap the sensor and thats it job done. It is recommended that you you do the calibration but not mandatory.
BAengineer is offline  
Old 26th Dec 2018, 13:59
  #15 (permalink)  
Thread Starter
 
Join Date: Jun 2014
Location: Chocolatetown
Age: 58
Posts: 83
The NY Times has some fancy new graphic images and a step by step narrative this morning.
It doesn't seem to add anything to the conversation at hand.
https://www.nytimes.com/interactive/...ml?mtrref=t.co
climber314 is offline  
Old 26th Dec 2018, 20:02
  #16 (permalink)  
 
Join Date: Sep 2018
Location: Laredo, TX
Posts: 96
Originally Posted by weemonkey View Post
Yes.You just turn it inside out.
What Ametek says about it: " Port and Starboard AOA Transducers Are Interchangeable"
jimtx is offline  
Old 26th Dec 2018, 21:44
  #17 (permalink)  
Thread Starter
 
Join Date: Jun 2014
Location: Chocolatetown
Age: 58
Posts: 83
FWIW I found the following online regarding MCAS:
"This is from a maintenance training manual for technicians/mechanics.
Pilots do not see this. Maintenance do a two week difference course, pilots get a handout."


climber314 is offline  
Old 26th Dec 2018, 22:32
  #18 (permalink)  
 
Join Date: May 2016
Location: Sunshine Coast
Posts: 4
Originally Posted by climber314 View Post
FWIW I found the following online regarding MCAS:
"This is from a maintenance training manual for technicians/mechanics.
Pilots do not see this. Maintenance do a two week difference course, pilots get a handout."


Only the F/Os column cutout switch module is affected because it is the only module that interfaces with the FCCs.
What the hell does that mean? Could that have anything to do with the apparent ineffectiveness of the ANU trim commands after control was handed over to the FO?

Separately, with regards to focus on the calibration (or alleged lack thereof) of the replaced left AOA sensor, that aircraft had a history of left-side invalid air data and AOA data problems that preceded the fitting of the replacement sensor. My money has been on a developing problem with the left ADIRU; a Sunwing MAX 8 delivered 6 weeks before PK-LQP had a left ADIRU problem two weeks after the JT610 crash.
MickG0105 is offline  
Old 26th Dec 2018, 22:33
  #19 (permalink)  
 
Join Date: Mar 2014
Location: WA STATE
Age: 74
Posts: 1
Originally Posted by jimtx View Post
What Ametek says about it: " Port and Starboard AOA Transducers Are Interchangeable"
Hmmmm- normally the transducer is the device that TRANSforms motion- movement or pressure/vacuum into a electrical signal . But the ' windvane' or aoa ' vane' and mounting brackets would have to be reversible when mounting on opposite sides of aircraft. left side would be O---! versus !---O for right side ( O being transducer mounted on --- axle and ! being vane ( up being forward )
CONSO is offline  
Old 27th Dec 2018, 01:46
  #20 (permalink)  
 
Join Date: May 2018
Location: London/Fort Worth
Posts: 0
I seem to remember that the position (port or stbd) is indicated by pin programming.
BAengineer is offline  

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.