Page 1 of 1

Lion Air crash from maintenance perpective

Posted: Mon Feb 11, 2019 5:14 am
by aerotech777
There was a lot of talk regarding Lion Air Crash especially about MCAS, pilots, AOA sensor, etc...
There was also talk about the poor safety record.

I would like to talk about aircraft maintenance, more importantly about the compliance with the procedures
in the AMM (Aircraft Maintenance Manual) and FIM (Fault Isolation Manual)
.
I noticed something that seems wrong (at least to me) in the Aircraft Flight and Maintenance Log (AFML) regarding
the flush of the pitot system and static system. It is mentioned in the AFML, that they performed the flushing of left pitot ADM and static ADM.
If I remember correctly (I am former AMT and I stand to be corrected), AMT (aircraft maintenance technician) flush the pitot
or static system and not ADMs because ADM should be disconnected from the system.If ADM is connected to the system
(pitot and static tubes and hoses), this system is not flushed. In addition if the ADM is connected to the system, the contaminants/debris
will go the ADM which negates the goal of flushing the pitot or static system.

Some persons may say this is just because of the English language (barrier language). If this is true, this also affects the aircraft maintenance because
the maintenance crew may not understand well the procedures in the AMM and the FIM.

Here the link of the preliminary report of the crash:
https://reports.aviation-safety.net/201 ... MINARY.pdf
Please look at pages 7,8, and 9 for the AFML (pitot and static flush is mentioned in page 9)

Based of what I noticed regarding the flush and ADM in the AFML, I am wondering if the maintenance crew complied with AMM and FIM regarding what they performed
not just for pitot and static but all the defects/problems mentioned in the AFML.

I would like to know your opinions (especially the persons who have access to the AMM and FIM) if the maintenance crew complied with AMM and FIM regarding
all the defects/problems mentioned in the AFML including the pitot and static flush flush.

Feedback appreciated.

Re: Lion Air crash from maintenance perpective

Posted: Mon Feb 11, 2019 5:45 am
by aerotech777
I forgot to mention that there is risk of damaging the ADM during the flush if the AMT exceeds certain pressure with the ADM connected to the system.

I am wondering if a leak check for pitot and static system is recommended for such defect (IAS and ALT disagree).

Re: Lion Air crash from maintenance perpective

Posted: Mon Feb 11, 2019 10:35 am
by WIederling
aerotech777 wrote:
I forgot to mention that there is risk of damaging the ADM during the flush if the AMT exceeds certain pressure with the ADM connected to the system.

I am wondering if a leak check for pitot and static system is recommended for such defect (IAS and ALT disagree).


Wouldn't you also drive some contaminant into the cul de sac to the pressure sensor?

( any values around how much leakage is acceptable in the pitot or static line?)

Re: Lion Air crash from maintenance perpective

Posted: Thu Feb 14, 2019 11:39 am
by akoma
aerotech777 wrote:
There was a lot of talk regarding Lion Air Crash especially about MCAS, pilots, AOA sensor, etc...
There was also talk about the poor safety record.

I would like to talk about aircraft maintenance, more importantly about the compliance with the procedures
in the AMM (Aircraft Maintenance Manual) and FIM (Fault Isolation Manual)
.
I noticed something that seems wrong (at least to me) in the Aircraft Flight and Maintenance Log (AFML) regarding
the flush of the pitot system and static system. It is mentioned in the AFML, that they performed the flushing of left pitot ADM and static ADM.
If I remember correctly (I am former AMT and I stand to be corrected), AMT (aircraft maintenance technician) flush the pitot
or static system and not ADMs because ADM should be disconnected from the system.If ADM is connected to the system
(pitot and static tubes and hoses), this system is not flushed. In addition if the ADM is connected to the system, the contaminants/debris
will go the ADM which negates the goal of flushing the pitot or static system.

Some persons may say this is just because of the English language (barrier language). If this is true, this also affects the aircraft maintenance because
the maintenance crew may not understand well the procedures in the AMM and the FIM.

Here the link of the preliminary report of the crash:
https://reports.aviation-safety.net/201 ... MINARY.pdf
Please look at pages 7,8, and 9 for the AFML (pitot and static flush is mentioned in page 9)

Based of what I noticed regarding the flush and ADM in the AFML, I am wondering if the maintenance crew complied with AMM and FIM regarding what they performed
not just for pitot and static but all the defects/problems mentioned in the AFML.

I would like to know your opinions (especially the persons who have access to the AMM and FIM) if the maintenance crew complied with AMM and FIM regarding
all the defects/problems mentioned in the AFML including the pitot and static flush flush.

Feedback appreciated.



The ADMs could possibly suffer damage if not removed during flushing of the pitot & static lines (if that was what was done). If flushing the lines, one of the first steps would be to isolate the ADMs from the lines being flushed, there is no need to even refer to the AMM for that, I would imagine?

However, I have just looked at the B737-8 AMM pitot / static flushing procedures and it is stated clearly "Disconnect the pneumatic connector from the Air Data Module (Task 34-21-004-000-801/802)..."

Reading further down the AMM procedures, there is this big caution "DO NOT APPLY PRESSURE TO THE SYSTEM WHEN AN AIR DATA MODULE IS CONNECTED TO THE SYSTEM. IF YOU DO, DAMAGE TO THE AIR DATA MODULE CAN OCCUR".

Re: Lion Air crash from maintenance perpective

Posted: Thu Feb 14, 2019 11:51 am
by akoma
WIederling wrote:
( any values around how much leakage is acceptable in the pitot or static line?)
[/quote]

During a maintenance low range static leak check, the system is brought to an altitude 5,000 feet above airfield elevation. After readings have stabilized, Boeing specifies a altitude reading decrease of less than 80 feet in one minute.

For the pitot leak check, the system is brought to a pressure of 300 knots. After stabilization, Boeing specifies a drop of less than 5 knots in one minute.

Re: Lion Air crash from maintenance perpective

Posted: Thu Feb 14, 2019 1:43 pm
by WIederling
akoma wrote:
<acceptable leakage information>.


So it is low leakage but not hermetic.
Thanks.

Re: Lion Air crash from maintenance perpective

Posted: Thu Feb 14, 2019 8:42 pm
by fr8mech
WIederling wrote:
So it is low leakage but not hermetic.
Thanks.


That’s just the acceptable leak rate. The system is designed to be tight, and I’ve tested many systems that didn’t lose a foot, or a knot, during a low range test.

Re: Lion Air crash from maintenance perpective

Posted: Thu Feb 14, 2019 9:16 pm
by fadecfault
aerotech777 wrote:
There was a lot of talk regarding Lion Air Crash especially about MCAS, pilots, AOA sensor, etc...
There was also talk about the poor safety record.

I would like to talk about aircraft maintenance, more importantly about the compliance with the procedures
in the AMM (Aircraft Maintenance Manual) and FIM (Fault Isolation Manual)
.
I noticed something that seems wrong (at least to me) in the Aircraft Flight and Maintenance Log (AFML) regarding
the flush of the pitot system and static system. It is mentioned in the AFML, that they performed the flushing of left pitot ADM and static ADM.
If I remember correctly (I am former AMT and I stand to be corrected), AMT (aircraft maintenance technician) flush the pitot
or static system and not ADMs because ADM should be disconnected from the system.If ADM is connected to the system
(pitot and static tubes and hoses), this system is not flushed. In addition if the ADM is connected to the system, the contaminants/debris
will go the ADM which negates the goal of flushing the pitot or static system.

Some persons may say this is just because of the English language (barrier language). If this is true, this also affects the aircraft maintenance because
the maintenance crew may not understand well the procedures in the AMM and the FIM.

Here the link of the preliminary report of the crash:
https://reports.aviation-safety.net/201 ... MINARY.pdf
Please look at pages 7,8, and 9 for the AFML (pitot and static flush is mentioned in page 9)

Based of what I noticed regarding the flush and ADM in the AFML, I am wondering if the maintenance crew complied with AMM and FIM regarding what they performed
not just for pitot and static but all the defects/problems mentioned in the AFML.

I would like to know your opinions (especially the persons who have access to the AMM and FIM) if the maintenance crew complied with AMM and FIM regarding
all the defects/problems mentioned in the AFML including the pitot and static flush flush.

Feedback appreciated.

It just might be poor english but they may have flushed the system correctly per the amm.
But each signoff from the logpages shown in the lion air report shows a maintenance team that is clueless or just used to whipping defects. IE: the first two write ups were for speed and altitude flags and yet the signed each one off with a SMYD ops check.
Fun Fact: Per my companies internal doc it shows Lion air averaged a 99.7% MAX mechanical dispatch reliability from sep 17 to nov 18. No other max carrier came close with each having normal drops in MDR that you would see with a new type a/c. Draw your own conclusion.

Re: Lion Air crash from maintenance perpective

Posted: Fri Feb 15, 2019 5:16 am
by akoma
fr8mech wrote:
WIederling wrote:
So it is low leakage but not hermetic.
Thanks.


That’s just the acceptable leak rate. The system is designed to be tight, and I’ve tested many systems that didn’t lose a foot, or a knot, during a low range test.


I have rarely seen a near perfect leak rate during testing. However, the leak rates were usually minor and nowhere near to the acceptable figures given by the aircraft manufacturers. Leaks were usually caused by the couplings (eg between static ports & equipment or pitot probes & equipment) rather than the aircraft systems.

Re: Lion Air crash from maintenance perpective

Posted: Fri Feb 15, 2019 5:19 am
by akoma
fadecfault wrote:
Fun Fact: Per my companies internal doc it shows Lion air averaged a 99.7% MAX mechanical dispatch reliability from sep 17 to nov 18. No other max carrier came close with each having normal drops in MDR that you would see with a new type a/c. Draw your own conclusion.


Interesting figure!

Re: Lion Air crash from maintenance perpective

Posted: Fri Feb 15, 2019 8:31 am
by WIederling
akoma wrote:
fadecfault wrote:
Fun Fact: Per my companies internal doc it shows Lion air averaged a 99.7% MAX mechanical dispatch reliability from sep 17 to nov 18. No other max carrier came close with each having normal drops in MDR that you would see with a new type a/c. Draw your own conclusion.


Interesting figure!

Interesting look at things!
Any numbers around for other MAX users ?

Re: Lion Air crash from maintenance perpective

Posted: Fri Feb 15, 2019 5:28 pm
by fadecfault
WIederling wrote:
akoma wrote:
fadecfault wrote:
Fun Fact: Per my companies internal doc it shows Lion air averaged a 99.7% MAX mechanical dispatch reliability from sep 17 to nov 18. No other max carrier came close with each having normal drops in MDR that you would see with a new type a/c. Draw your own conclusion.


Interesting figure!

Interesting look at things!
Any numbers around for other MAX users ?


Here you go. Had to truncate the image due to obvious reasons.
Image

Re: Lion Air crash from maintenance perpective

Posted: Sat Feb 16, 2019 12:06 pm
by WIederling
fadecfault wrote:
Here you go. Had to truncate the image due to obvious reasons.
https://i.ibb.co/BjmNvQX/mdr.jpg


Thank you. the Fat Black LIne is overall average?

Re: Lion Air crash from maintenance perpective

Posted: Sun Feb 17, 2019 9:39 am
by fadecfault
WIederling wrote:
fadecfault wrote:
Here you go. Had to truncate the image due to obvious reasons.
https://i.ibb.co/BjmNvQX/mdr.jpg


Thank you. the Fat Black LIne is overall average?

No it's the subject carrier from the report.