Page 2 of 13 FirstFirst 123412 ... LastLast
Results 21 to 40 of 244

Thread: Lion Air 737-Max missing, presumed down in the sea near CGK (Jakarta)

  1. #21
    Junior Member
    Join Date
    Oct 2017
    Posts
    21

    Default

    I'm in no way part of the aviation industry (other than a passenger) but I'm obsessed with crashes (probably because my dad was a small plane pilot who almost killed me and the rest of my family a couple of times and I'm not exaggerating) so I beg your indulgence with a question that I've always wondered about:

    When maintenance is performed on a plane, what is the threshold and/or necessity for some type of testing (as in an actual test flight) to take place prior to the aircraft being returned to service? Obviously my thought with this example is something along the lines of maintenance supposedly fixed a pretty major issue the day before - as a passenger should I feel safe that the fix was really done correctly? We've all had times we've taken the car in for service and the mechanic didn't get it quite right!

    My guess as to my answer is that I've no doubt the carriers loathe this type of testing ($$$$) and that there are plenty of safeguards that would make this almost always unnecessary. And yet I still have to believe there *are* maintenance events performed that would suggest a test flight be conducted.

  2. #22
    Senior Member BoeingBobby's Avatar
    Join Date
    Jun 2009
    Location
    MIA
    Posts
    1,408

    Default

    Quote Originally Posted by Chris K View Post
    I'm in no way part of the aviation industry (other than a passenger) but I'm obsessed with crashes (probably because my dad was a small plane pilot who almost killed me and the rest of my family a couple of times and I'm not exaggerating) so I beg your indulgence with a question that I've always wondered about:

    When maintenance is performed on a plane, what is the threshold and/or necessity for some type of testing (as in an actual test flight) to take place prior to the aircraft being returned to service? Obviously my thought with this example is something along the lines of maintenance supposedly fixed a pretty major issue the day before - as a passenger should I feel safe that the fix was really done correctly? We've all had times we've taken the car in for service and the mechanic didn't get it quite right!

    My guess as to my answer is that I've no doubt the carriers loathe this type of testing ($$$$) and that there are plenty of safeguards that would make this almost always unnecessary. And yet I still have to believe there *are* maintenance events performed that would suggest a test flight be conducted.
    I can't wait to read the replies! Experts, I await the diatribes.

  3. #23
    Senior Member Evan's Avatar
    Join Date
    Jan 2008
    Posts
    6,577

    Default

    Quote Originally Posted by Chris K View Post
    I'm in no way part of the aviation industry (other than a passenger) but I'm obsessed with crashes (probably because my dad was a small plane pilot who almost killed me and the rest of my family a couple of times and I'm not exaggerating) so I beg your indulgence with a question that I've always wondered about:

    When maintenance is performed on a plane, what is the threshold and/or necessity for some type of testing (as in an actual test flight) to take place prior to the aircraft being returned to service? Obviously my thought with this example is something along the lines of maintenance supposedly fixed a pretty major issue the day before - as a passenger should I feel safe that the fix was really done correctly? We've all had times we've taken the car in for service and the mechanic didn't get it quite right!

    My guess as to my answer is that I've no doubt the carriers loathe this type of testing ($$$$) and that there are plenty of safeguards that would make this almost always unnecessary. And yet I still have to believe there *are* maintenance events performed that would suggest a test flight be conducted.
    I imagine the threshold would be: is this a problem that cannot be detected on the ground? For example, replacing a pressure bulkhead would require a pressure differential to determine if the work was done correctly, so that would warrant a test flight. Most things don't. For example, a malfunctioning probe can be replaced with one that has been pre-tested in production to withstand its environment. It can be inspected and mechanically tested on the ground. The same goes for a malfunctioning avionics unit. These are called LRU's (line replaceable units). They are designed to be replaced without the need for the aircraft to be ferried to a major maintenance base and flight tested. I think, if the problem persists, if the problem defies standard line maintenance, the aircraft would be taken out of service and more extensive testing, including any flight testing, would be done.

    But this is the most important thing to understand: aircraft components are expected to fail in flight. The aircraft are expected to be fail-operational. Some of that is by designed redundancy; some of that is by pilot preparedness and abnormal operations procedure.

    For example, a complete loss of airspeed data and autoflight should not result in a fatal loss of control. If it does, the problem lies in the quality of the pilots and the quality of pilot training. If there is a failure in that regard, then yes, they definitely need to be flight tested before re-entering service.

  4. #24
    Senior Member BoeingBobby's Avatar
    Join Date
    Jun 2009
    Location
    MIA
    Posts
    1,408

    Default

    Quote Originally Posted by Evan View Post
    I imagine the threshold would be: is this a problem that cannot be detected on the ground? For example, replacing a pressure bulkhead would require a pressure differential to determine if the work was done correctly, so that would warrant a test flight. Most things don't. For example, a malfunctioning probe can be replaced with one that has been pre-tested in production to withstand its environment. It can be inspected and mechanically tested on the ground. The same goes for a malfunctioning avionics unit. These are called LRU's (line replaceable units). They are designed to be replaced without the need for the aircraft to be ferried to a major maintenance base and flight tested. I think, if the problem persists, if the problem defies standard line maintenance, the aircraft would be taken out of service and more extensive testing, including any flight testing, would be done.

    But this is the most important thing to understand: aircraft components are expected to fail in flight. The aircraft are expected to be fail-operational. Some of that is by designed redundancy; some of that is by pilot preparedness and abnormal operations procedure.

    For example, a complete loss of airspeed data and autoflight should not result in a fatal loss of control. If it does, the problem lies in the quality of the pilots and the quality of pilot training. If there is a failure in that regard, then yes, they definitely need to be flight tested before re-entering service.
    Now explain DMI to the gentleman!

  5. #25
    Senior Member 3WE's Avatar
    Join Date
    Jan 2008
    Posts
    4,986

    Default

    Quote Originally Posted by BoeingBobby View Post
    I can't wait to read the replies! Experts, I await the diatribes.
    I am pretty sure there are somewhat complex and robust procedures and “thresholds” as to exactly how you test a repair.

    Am I correct?
    Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

  6. #26
    Senior Member Gabriel's Avatar
    Join Date
    Jan 2008
    Location
    Buenos Aires - Argentina
    Posts
    6,881

    Default

    There are many failure modes so it is not a simple answer. What I can say is that whether a flight test is required or not is not based only on the severity of the issue but also on the ability to test the affected system on the ground and on the confidence that what was fixed was the real cause of the issue.

    For example, something big like a full hydraulic system failing in flight may not require a flight test if, for example, it was identified that the hydro pump was not working and it was replaced and the hydro system is tested on ground.

    Even an engine replacement doesn't necessarily require a flight test.

    Most of the times a test flight is not required for individual issues and fixes.

    Major scheduled maintenance events, like a level D (where the plane is pretty much disassembled a re-assembled), always require tests flight.

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
    --- Defend what you say with arguments, not by imposing your credentials ---

  7. #27
    Junior Member
    Join Date
    Oct 2017
    Posts
    21

    Default

    Thanks everyone for your answers! I guess it brings me to the rather obvious question which is whether an incident the day prior to this accident should have necessitated a test flight. Unless I've got Capt. Sulley or Boeing's test pilot version of Neil Armstrong flying, I'd sure much rather have been the 2nd flight out after the maintenance than the first for the simple reason that, say what you will, unless the plane is airborne I'm not sure you could convince me you're 100% sure this problem has been fixed.

    The general consensus that every professional pilot should be able to handle this dealt hand doesn't really cut it with me for the simple reason that A. Whether or not this turns out to be what actually caused the accident remains to be seen, but it is certainly true that this type of issue has been known to throw pilots a big curve ball they don't always handle, and B. Just as in every other profession there are great, good, average, and bad levels of skill and the flight after a maintenance event that corrected an issue with critical data inputs is the day I'd rather have seen someone take the bird up for a spin before loading up with pax and crew. I would bring the maintenance person and their supervisor along for the check ride - extra motivation that they get the repair right the first time.

  8. #28
    Senior Member Gabriel's Avatar
    Join Date
    Jan 2008
    Location
    Buenos Aires - Argentina
    Posts
    6,881

    Default

    Quote Originally Posted by Chris K View Post
    Thanks everyone for your answers! I guess it brings me to the rather obvious question which is whether an incident the day prior to this accident should have necessitated a test flight. Unless I've got Capt. Sulley or Boeing's test pilot version of Neil Armstrong flying, I'd sure much rather have been the 2nd flight out after the maintenance than the first for the simple reason that, say what you will, unless the plane is airborne I'm not sure you could convince me you're 100% sure this problem has been fixed.
    1- We still don't know if the accident was related with the incident in the previous flight.
    2- IF IT WAS, I bet you a beer that something was done very wrong in the maintenance / repair process. Normally there are ways to verify that a problem was correctly identified and fixed, especially critical items. And if it can't, then more work needs to be done even before an eventual test flight. Having crews crashing on test flights is also not acceptable and from the point of view of the safety breach this accident would have been equally unacceptable (even when less severe) if it had killed "only" 2 pilots and a bunch of engineers and mechanics on board. Killing crews instead of pax is clearly not the solution.

    (3- There is a reason why the aviation authority revoked the licence of the technical director of the airline and the airline fired him... I hope that said reason goes beyond simple scapegoating, even is scapegoating is surely part of it)

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
    --- Defend what you say with arguments, not by imposing your credentials ---

  9. #29
    Junior Member
    Join Date
    Oct 2017
    Posts
    21

    Default

    Quote Originally Posted by Gabriel View Post
    1- We still don't know if the accident was related with the incident in the previous flight.
    2- IF IT WAS, I bet you a beer that something was done very wrong in the maintenance / repair process. Normally there are ways to verify that a problem was correctly identified and fixed, especially critical items. And if it can't, then more work needs to be done even before an eventual test flight. Having crews crashing on test flights is also not acceptable and from the point of view of the safety breach this accident would have been equally unacceptable (even when less severe) if it had killed "only" 2 pilots and a bunch of engineers and mechanics on board. Killing crews instead of pax is clearly not the solution.

    (3- There is a reason why the aviation authority revoked the licence of the technical director of the airline and the airline fired him... I hope that said reason goes beyond simple scapegoating, even is scapegoating is surely part of it)
    Definitely agree on #2 in that we don't want any loss of life. What I was thinking in terms of mitigation was that the test crew would be of the sort where they are somewhat used to high risk situations and therefore able to cope with any abnormalities much better than a regular line pilot. Makes me wonder who get picked to make the test flights when planes do come out of major maintenance events - are they specially trained and come from the manufacturer (Boeing, AirBus, ...) or does the carrier just draw lots and pick the lucky pair?

  10. #30
    Senior Member BoeingBobby's Avatar
    Join Date
    Jun 2009
    Location
    MIA
    Posts
    1,408

    Default

    Quote Originally Posted by Chris K View Post
    Definitely agree on #2 in that we don't want any loss of life. What I was thinking in terms of mitigation was that the test crew would be of the sort where they are somewhat used to high risk situations and therefore able to cope with any abnormalities much better than a regular line pilot. Makes me wonder who get picked to make the test flights when planes do come out of major maintenance events - are they specially trained and come from the manufacturer (Boeing, AirBus, ...) or does the carrier just draw lots and pick the lucky pair?
    They call out Steve Canyon or Chuck Yeager. DMI, DDG!

  11. #31
    Senior Member Gabriel's Avatar
    Join Date
    Jan 2008
    Location
    Buenos Aires - Argentina
    Posts
    6,881

    Default

    Quote Originally Posted by Chris K View Post
    Definitely agree on #2 in that we don't want any loss of life. What I was thinking in terms of mitigation was that the test crew would be of the sort where they are somewhat used to high risk situations and therefore able to cope with any abnormalities much better than a regular line pilot. Makes me wonder who get picked to make the test flights when planes do come out of major maintenance events - are they specially trained and come from the manufacturer (Boeing, AirBus, ...) or does the carrier just draw lots and pick the lucky pair?
    Who told you that the job done or required on this plane involved "major maintenance events"?

    --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
    --- Defend what you say with arguments, not by imposing your credentials ---

  12. #32
    Junior Member
    Join Date
    Oct 2017
    Posts
    21

    Default

    Quote Originally Posted by Gabriel View Post
    Who told you that the job done or required on this plane involved "major maintenance events"?
    I was speaking generically - curious who does the test flight for events that all would agree are "major".

  13. #33
    Senior Member Evan's Avatar
    Join Date
    Jan 2008
    Posts
    6,577

    Default

    Quote Originally Posted by Chris K View Post
    Thanks everyone for your answers! I guess it brings me to the rather obvious question which is whether an incident the day prior to this accident should have necessitated a test flight. Unless I've got Capt. Sulley or Boeing's test pilot version of Neil Armstrong flying, I'd sure much rather have been the 2nd flight out after the maintenance than the first for the simple reason that, say what you will, unless the plane is airborne I'm not sure you could convince me you're 100% sure this problem has been fixed.

    The general consensus that every professional pilot should be able to handle this dealt hand doesn't really cut it with me for the simple reason that A. Whether or not this turns out to be what actually caused the accident remains to be seen, but it is certainly true that this type of issue has been known to throw pilots a big curve ball they don't always handle, and B. Just as in every other profession there are great, good, average, and bad levels of skill and the flight after a maintenance event that corrected an issue with critical data inputs is the day I'd rather have seen someone take the bird up for a spin before loading up with pax and crew. I would bring the maintenance person and their supervisor along for the check ride - extra motivation that they get the repair right the first time.
    As far as I can tell, the previous flight had experienced an unreliable airspeed event. These tend to be transient, caused by meteorological phenomena, and leave no evidence. Ground maintenance can test everything, and even replace things that test ok as an added measure of caution, but chances are they will find nothing wrong. If, on the other hand, the event was caused by flight control issues and the problem cannot be replicated or detected on the ground and identified as an LRU issue(s), that aircraft needs to be removed from service, ferried back to a maintenance base and sorted out (the ferry flight being the first 'test fight'). We still don't know what the previous flight issue was and if it had anything to do with this crash.

    The general consensus that every professional pilot should be able to handle this dealt hand doesn't really cut it with me...
    Then you should give up flying, because this is what it comes down to and every professional pilot should be able to handle most failures that occur either by memorized procedure or by CRM using the cockpit resources. The main thing is that every professional pilot should be able to first stabilize the aircraft, not exacerbate the situation by erroneous commands, and then remain stabilized while working the problem. Yes, not all pilots are equal, but this must be the training standard that all pilots must meet. And yes, there are human factors that can cause these erroneous commands, but CRM procedures are written to overcome these factors and they must be learned and faithfully executed. The single biggest reason we still see these inexplicable crashes is that pilots and operators are still resisting or neglecting to embrace these measures. There is too much hubris and corner-cutting going on within certain pilot/operator/CAA cultures.

    There are almost no in-flight system failures that a competent crew can't fly out of. That includes flight control computer issues, even FBW ones. Modern aircraft are designed to selectively degrade down to the most basic flight control if needed. But that doesn't help if the crew isn't trained in that respect.

  14. #34
    Member
    Join Date
    Jun 2009
    Posts
    375

    Default

    Info on the logs from the previous flight

    https://theaircurrent.com/aviation-s...-social-media/

  15. #35
    Senior Member BoeingBobby's Avatar
    Join Date
    Jun 2009
    Location
    MIA
    Posts
    1,408

    Default

    Quote Originally Posted by 3WE View Post
    I am pretty sure there are somewhat complex and robust procedures and “thresholds” as to exactly how you test a repair.

    Am I correct?
    Gabe is not going to like this reply but, this is one of the times that if you have never been a line pilot for a 121/135 carrier, is hard to understand. Again, look up MEL, DDG, DMI.

  16. #36
    Senior Member Evan's Avatar
    Join Date
    Jan 2008
    Posts
    6,577

    Default

    Quote Originally Posted by BoeingBobby View Post
    Gabe is not going to like this reply but, this is one of the times that if you have never been a line pilot for a 121/135 carrier, is hard to understand. Again, look up MEL, DDG, DMI.
    Look, the concern was about whether a ground repair alone can sufficiently assure that a repair has been successful (and that the problem has been allieviated by that repair). DDG et. al. is a different issue.

    Chris: In order to be dispatched for passenger service, every commercial airliner has to be in a condition that meets the airworthiness requirements under which the aircraft was type certified. The DDG (MEL and CDL) assure that this is the case and do not deviate from that requirement.

    The part of this that might be relevant here is the MEL (Minimum Equipment List). This is an operator-specific manual that lists all the equipment that can be inoperative while still allowing the airplane to remain in service. Often, it includes requirements stating that, if one component is inoperative, another must be functioning, and/or limits the number of flight cycles that can be performed in the indicated condition. It is derived from the manufacturer's MMEL (Master Minimum Equipment List) which was used to certify the aircraft. The MMEL determines instruments and equipment that are either specifically or otherwise required by the airworthiness requirements under which the aircraft is type certificated and which are essential for safe operations under all operating conditions. The MEL can not be less restrictive than the MMEL. In short, as long as the aircraft meets the requirements of the MEL, it can be flown safely by competent pilots.

    There are some important caveats: The inop components must be properly flagged, entered into the maintenance log, and the pilots must be fully aware of the conditions. The level of equipment redundancy may also be reduced or (in the case of less-essential components) eliminated.

    What is interesting here is that there was a technician on board this flight. The company has stated that this is a standard precaution on new aircraft. Perhaps it had nothing to do with the condition of the aircraft or the crash. But it makes you wonder if a repair was made (or a fault could not be replicated and indentified after the previous flight) that left some doubt about the dispatch safety of the aircraft, and that this might have constituted a 'test flight' in itself.

    The only reason I would raise that suspicion is the history of the Indonesian aviation safety culture. In April 2007, the FAA downgraded Indonesia to Category 2 in its International Aviation Safety Assessment program. Category 2 means the nation does not meet ICO standards for aviation safety enforcement and compliance. They restored that to Category 1 in 2016 after certain reforms were made, but culture runs deep. And, last I checked, the EU continues to have a ban on all but five Indonesian carriers.

    So the DDG, the CDL and the MEL, are all pretty useless if the operator or its personnel are not abiding by them. It comes down to this.

  17. #37
    Senior Member BoeingBobby's Avatar
    Join Date
    Jun 2009
    Location
    MIA
    Posts
    1,408

    Default

    Quote Originally Posted by Evan View Post
    Look, the concern was about whether a ground repair alone can sufficiently assure that a repair has been successful (and that the problem has been allieviated by that repair). DDG et. al. is a different issue.

    Chris: In order to be dispatched for passenger service, every commercial airliner has to be in a condition that meets the airworthiness requirements under which the aircraft was type certified. The DDG (MEL and CDL) assure that this is the case and do not deviate from that requirement.

    The part of this that might be relevant here is the MEL (Mininum Equipment List). This is an operator-specific manual that lists all the equipment that can be inoperative while still allowing the airplane to remain in service. Often, it includes requirements stating that, if one compenent is inoperative, another must be functioning, and/or limits the number of flight cycles that can be performed in the indicated condition. It is derived from the manufacturer's MMEL (Master Minimum Equipment List) which was used to certify the aircraft. The MMEL determines instruments and equipment that are either specifically or otherwise required by the airworthiness requirements under which the aircraft is type certificated and which are essential for safe operations under all operating conditions. The MEL can not be less restrictive than the MMEL. In short, as long as the aircraft meets the requirements of the MEL, it can be flown safely by competent pilots.

    There are some important caveats: The inop components must be properly flagged, entered into the MEL report, and the pilots must be fully aware of the conditions. The level of equipment redundancy may also be reduced or (in the case of less-essential components) eliminated.

    What is interesting here is that there was a technician on board this flight. The company has stated that this is a standard precaution on new aircraft. Perhaps it had nothing to do with the condition of the aircraft or the crash. But it makes you wonder if a repair was made (or a fault could not be replicated and indentified after the previous flight) that left some doubt about the dispatch safety of the aircraft, and that this might have constituted a 'test flight' in itself.

    The only reason I would raise that suspicion is the history of the Indonesian aviation safety culture. In April 2007, the FAA downgraded Indonesia to Category 2 in its International Aviation Safety Assessment program. Category 2 means the nation does not meet ICO standards for aviation safety enforcement and compliance. They restored that to Category 1 in 2016 after certain reforms were made, but culture runs deep. And, last I checked, the EU continues to have a ban on all but five Indonesian carriers.

    So the DDG, the CDL and the MEL are all pretty useless if the operator or its personnel are not abiding by them. It comes down to this.
    If you say so....

  18. #38
    Member
    Join Date
    Jan 2009
    Posts
    251

    Default

    Quote Originally Posted by Evan View Post
    What is interesting here is that there was a technician on board this flight. The company has stated that this is a standard precaution on new aircraft. Perhaps it had nothing to do with the condition of the aircraft or the crash. But it makes you wonder if a repair was made (or a fault could not be replicated and indentified after the previous flight) that left some doubt about the dispatch safety of the aircraft, and that this might have constituted a 'test flight' in itself.
    Yes, some might think that. However, if I were worried about the safety, I would order the aircraft out of service until I was happy it was safe to fly even with test pilots. If I were trying to track down an intermittent problem that did NOT affect safety, then I would send the technician on the flight.

  19. #39
    Senior Member Evan's Avatar
    Join Date
    Jan 2008
    Posts
    6,577

    Default

    Quote Originally Posted by BoeingBobby View Post
    If you say so....
    Go on...

  20. #40
    Senior Member Evan's Avatar
    Join Date
    Jan 2008
    Posts
    6,577

    Default

    Quote Originally Posted by Schwartz View Post
    Yes, some might think that. However, if I were worried about the safety, I would order the aircraft out of service until I was happy it was safe to fly even with test pilots. If I were trying to track down an intermittent problem that did NOT affect safety, then I would send the technician on the flight.
    But what of the extent of the problem is yet unknown, or if the casual chain of events that leads to an unsafe condition weren't fully considered, or if a technically "safe" condition becomes unsafe in the wrong hands (often the case in aviation disasters)...

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •