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safetypee
July 12, 2025, 21:15:00 GMT permalink Post: 11920836 |
Check your switches
At this stage of the investigation, where the preliminary report is limited to
facts and evidence
, there may be insufficient knowledge to warrant urgent safety action.
However, some national regulators might choose to reiterate the FAA SAIB: NM-18-33, requiring that all switches must be checked i.e. not optional. Additionally, and independently, pilots might check the switches preflight (nice to know): - note the range of different types of aircraft and variants which could be affected - fleet size, number of switches exposed to the condition. Regulators might also enquire of the FAA how many 'non locking' switches were identified by the SAIB - what was reported; and 'non FAA' operators recheck their inspection results and action taken. … and how many operators did not check. If errant switches were identified, then was the original safety assessment reconsidered (FAA/Boeing), if so what arguments were made against inadvertent simultaneous operation. https://static-gi.asianetnews.com/co...nm-18-33-1.pdf Last edited by Pilot DAR; 12th July 2025 at 21:19 . Reason: typo |
AirScotia
July 12, 2025, 21:52:00 GMT permalink Post: 11920869 |
The fact that
SAIB: NM-18-33 was specifically mentioned, and that Air India's failure to inspect this airframe re the advisory was specifically mentioned, and that the exchange between the pilots specifically included wtte "I didn't", suggests to me that the report would like to hint at maintenance / build problems rather than deliberate pilot action.
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KSINGH
July 12, 2025, 22:04:00 GMT permalink Post: 11920875 |
The fact that
SAIB: NM-18-33 was specifically mentioned, and that Air India's failure to inspect this airframe re the advisory was specifically mentioned, and that the exchange between the pilots specifically included wtte "I didn't", suggests to me that the report would like to hint at maintenance / build problems rather than deliberate pilot action.
I had posted before (and it had been deleted for some reason) that is appears as if air india is taking a substantial hit on their widebody capacity at the moment and keeps cancelling routes right now (the latest being LGW), could they be doing specific extra maintenance/ checks having more insight than almost any other stakeholders at this point? |
rigoschris
July 13, 2025, 08:59:00 GMT permalink Post: 11921157 |
It\x92s not great that they mention the SAIB in the Preliminary Report but don\x92t give any details to the state of the particular switches of this airplane.
The metal parts of the switches seem intact in the picture, so it would be easy to check if the \x93lobes\x94 in the movable and stationary parts of the switches were there. A close-up picture would lay this topic to rest. This omission is causing a lot of speculation online. |
Someone Somewhere
July 13, 2025, 09:02:00 GMT permalink Post: 11921159 |
It\x92s not great that they mention the SAIB in the Preliminary Report but don\x92t give any details to the state of the particular switches of this airplane.
The metal parts of the switches seem intact in the picture, so it would be easy to check if the \x93lobes\x94 in the movable and stationary parts of the switches were there. A close-up picture would lay this topic to rest. This omission is causing a lot of speculation online. |
jimtx
July 13, 2025, 16:25:00 GMT permalink Post: 11921423 |
It\x92s not great that they mention the SAIB in the Preliminary Report but don\x92t give any details to the state of the particular switches of this airplane.
The metal parts of the switches seem intact in the picture, so it would be easy to check if the \x93lobes\x94 in the movable and stationary parts of the switches were there. A close-up picture would lay this topic to rest. This omission is causing a lot of speculation online. |
Andy_S
July 13, 2025, 16:30:00 GMT permalink Post: 11921428 |
There is a Special Airworthiness Information Bulletin (SAIB for short). It's not the same thing, and it's not mandatory to act on it's contents. You can draw your own conclusions as to why that is. |
fdr
July 13, 2025, 17:40:00 GMT permalink Post: 11921477 |
Hi,
I have a couple of questions. Forgive me for being late into this thread if any of them is already discussed: 1) I just read this in a Boeing manual:
The fuel control switches send signals to open or close fuel valves to operate or shutdown the engines.
There seems to be RDC's (remote data concentrators) and CDN (common data network) between those fuel switches and the fuel valves. Is there any possibility that there may have been an electronic control module or sensor fault to generate such a signal rather than mechanical switch movements?
- They send signals to the remote data concentrators (RDC) and the spar valve start switch relays. - The spar valve start switch relays use these signals to control the spar valve and the high pressure shut off valve (HPSOV) in the fuel metering unit (FMU). - The RDCs send the signals to the common data network (CDN) and then to the electronic engine control (EEC) to operate the FMU fuel valves (FMV and HPSOV). The fuel control switches have 2 positions: - RUN - CUTOFF. You must pull the switch out of a detent to select a position. 2) Looking at the incident timeline, one of the pilots takes corrective action to reswitch to RUN position 10 seconds after maximum air speed is reached and 5 seconds after RAT is deployed. Is this normal? It's not clear however that whether their conversation is after or before the RAT is deployed. (No visual or auditory cues in the cockpit for a critical fuel switch action? Not hearing the engines shutting down?) 3) The same pilot that turns on Engine 1's fuel switch, turns on Engine 2's switch 4 whole seconds later. Why not consecutively, right one after the other, just like they were turned off one second apart? If only he had done so the second engine might have recovered in time as well. 4) This aircraft's TCM has been replaced in 2019 and 2023, not related to a fuel switch issue. And there had been no fuel switch defect reports since 2023. One begs to ask if there had been a fuel switch defect report back in 2023 and what was the nature of it? Are TCM's replaced as a whole, including the switches, twice? If so, why wouldn't they install a TCM version at least in 2023 with redesigned switches (w/ enhanced locking mechanism) mentioned in the FAA SAIB? Have they installed old/used TCM's manufactured prior to 2018 SAIB? Please note that the RH and LH GE engines of the aircraft were only installed in March 2025 and May 2025 respectively, but they were used and dating from 2013 and 2012. Is this normal for a 12 year old Boeing aircraft to change so many mission critical components? Electronic parts somehow, but how durable are those GE engines? Thanks, C.A. When reading any of the data when it comes out, pay some attention to the sampling rate of the data being provided, it is quite possible to make erroneous assumptions where that is not taken into consideration. The data buses used to get data from the aircraft system to the recorder, and the recorders themselves use sequential sentences, and varyious rates. IMHO. |
GroundedSpanner
July 13, 2025, 21:34:00 GMT permalink Post: 11921685 |
SAIB NM-18-33 Interpretation
Reading
SAIB NM-18-33
My Interpretation/reading: Some 737 Operators reported incorrect/broken locking features on cutoff switches - PN 766AT613-3D If you have PN 766AT61 3 -3D installed - Replace it with 766AT61 4 -3D, which includes an improved locking feature. The other Aircraft listed - have switches with similar design. In the case of the B787, switch PN 4TL837-3D. Check those AC to ensure locking is OK, and if you do happen to find something odd, let us (the FAA) know. No-one, has ever found anything wrong with any of those other switches, or there would be AD's. Thus there is not a problem with 787 Fuel Switch locking features. |
Mrshed
July 14, 2025, 18:54:00 GMT permalink Post: 11922428 |
I think anyone still positioning a possibility other than physical movement of the switches at this point needs to bear in mind the following.
- The investigators and authors of the preliminary report clearly have more information than has been released in that report, a lot more. This includes, as per the report, the full recorded audio of the flight. - With that additional information comes a greater ability to rule in or out certain possibilities, if we presume competence (which we clearly should). - With all of that additional information and knowledge, *all* of the involved parties have explicitly stated there are no recommended actions regarding the airplane. This would be a pretty low threshold to issue even a precautionary advisory to check x,y,z if it was still deemed a possible cause. It is reasonable to say, I would say, that the investigators have largely ruled out the switches themselves or the electronics around them as a cause here. They are as aware as anyone on this forum of previous SAIB relating to these switches, and explicitly reference them in the report, and haven't even taken the incredibly easy step of "re-suggesting" this. This is telling and should be very carefully considered before further suggestions in this direction. I'd then suggest that everyone else also bears in mind the following. The investigators, with the information they have, have decided not to share some of that information. In my view, there are two likely reasons for this (combined): 1. They do not believe that releasing that information provides any additional safety benefit at this time *to other aircraft*. 2. The likely cause (or options of likely causes) demands exhaustive investigation to further check what the investigation is pointing to to date, and be positive of the cause to the highest possible threshold before even implying it. It may be frustrating that this leaves ambiguity, but this ambiguity is likely both intentional and necessary. In my mind, this alone (but especially when taken in conjunction with other evidence) likely rules out the option of an object causing the movement in the switches. It also probably rules out an incorrectly followed procedure as this again would likely be fed out. This really only leaves two options - completely erroneous action taken by a pilot (completely abnormal in its nature), or deliberate action taken by a pilot. Either of these demands full validation prior to concluding them publicly. The investigators, like us, probably have their views already on which is more likely (especially given the full CVR). The preliminary report, as has been said, is actually more detailed than normal, but there are, as others have said, some interesting omissions. When you think about what the purpose of the preliminary report is, and what the objectives are of those authoring it, looking at why certain information is there (and why some isnt), combined with what they are suggesting as next steps, it does in fact tell us almost all of the story here in my view, in terms of the overall picture (not the low level detail). Which doesn't mean the investigation may not ultimately take a different path - this is why they explore every possible avenue. Last edited by Mrshed; 15th July 2025 at 09:39 . |
Dani
July 14, 2025, 19:35:00 GMT permalink Post: 11922444 |
Breaking News: On Jul 14th 2025 India's DGCA instructed airlines to check the fuel switches on the Boeing 787 and Boeing 737 aircraft as used by Air India Group, Indigo and Spicejet for possible disengagement of the fuel control switch locking feature according to the SAIB released by the FAA on Dec 17th 2018. The checks have to be completed by Jul 21st 2025. Source: Avherald.com |
Mrshed
July 14, 2025, 19:41:00 GMT permalink Post: 11922448 |
If you think everything is said...
Breaking News: On Jul 14th 2025 India's DGCA instructed airlines to check the fuel switches on the Boeing 787 and Boeing 737 aircraft as used by Air India Group, Indigo and Spicejet for possible disengagement of the fuel control switch locking feature according to the SAIB released by the FAA on Dec 17th 2018. The checks have to be completed by Jul 21st 2025. Source: Avherald.com FWIW I don't think everything is said, and further elements may be uncovered - I just think the investigators have laid out pretty clearly areas they think are (and are not) likely causes when you read between the lines. Incidentally the above smacks of optics to me following it being shared that air India had not performed these checks, and the associated speculation of cause, but that's just a theory 😉 |
nrunning24
July 14, 2025, 19:59:00 GMT permalink Post: 11922466 |
If you think everything is said...
Breaking News: On Jul 14th 2025 India's DGCA instructed airlines to check the fuel switches on the Boeing 787 and Boeing 737 aircraft as used by Air India Group, Indigo and Spicejet for possible disengagement of the fuel control switch locking feature according to the SAIB released by the FAA on Dec 17th 2018. The checks have to be completed by Jul 21st 2025. Source: Avherald.com Realize this is a pilots forum, and its always easier to blame the engineers (me), but I'm surprised at the amount of people grasping at (at least what I think) straws to try and make this not a case of pilot error (either intentional or unintentional). I get lots of parts frequently break and pilots do frequently see things on MEL etc. I know our partner airline engineering teams would love to see increased reliability of certain components, but the certification scrutiny of flight critical items is very intense including isolation from each other. The likelihood of two flight critical components which are isolated from each other failing instantaneously is so small its basically impossible. Especially when you consider they also turn back on 10 secs later. Last edited by T28B; 14th July 2025 at 20:57 . Reason: pulled out the bottom line with formatting |
LTC8K6
July 14, 2025, 20:51:00 GMT permalink Post: 11922492 |
If you think everything is said...
Breaking News: On Jul 14th 2025 India's DGCA instructed airlines to check the fuel switches on the Boeing 787 and Boeing 737 aircraft as used by Air India Group, Indigo and Spicejet for possible disengagement of the fuel control switch locking feature according to the SAIB released by the FAA on Dec 17th 2018. The checks have to be completed by Jul 21st 2025. Source: Avherald.com |
AirScotia
July 15, 2025, 21:03:00 GMT permalink Post: 11923262 |
So why did they give so much space to a discussion of SAIB NM-18-33? It's obvious that the switches were not faulty, or they'd have said. If they couldn't tell if the switches were faulty, they'd have said. They do tell us that the throttle control module was swapped out and there's been no problem with the switches. So they don't need to mention it. It doesn't read to me as a logical part of the preliminary report, but as something they were under pressure to include to imply that there may have been a technical problem rather than pilot malfunction.
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Mrshed
July 15, 2025, 21:38:00 GMT permalink Post: 11923288 |
So why did they give so much space to a discussion of SAIB NM-18-33? It's obvious that the switches were not faulty, or they'd have said. If they couldn't tell if the switches were faulty, they'd have said. They do tell us that the throttle control module was swapped out and there's been no problem with the switches. So they don't need to mention it. It doesn't read to me as a logical part of the preliminary report, but as something they were under pressure to include to imply that there may have been a technical problem rather than pilot malfunction.
Simplest answer is often the best - they included it to show they had considered it? Imagine this forum if they hadn't included a nod to the SAIB - 90% of posts would be about the SAIB. can't really win on this one in the court of public opinion. Included or not, they made no recommendations for even proactive reminding of the SAIB to operators. This is more telling for me.
They are as aware as anyone on this forum of previous SAIB relating to these switches, and explicitly reference them in the report, and haven't even taken the incredibly easy step of "re-suggesting" this. This is telling and should be very carefully considered before further suggestions in this direction.
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WillowRun 6-3
July 15, 2025, 21:44:00 GMT permalink Post: 11923291 |
So why did they give so much space to a discussion of SAIB NM-18-33? It's obvious that the switches were not faulty, or they'd have said. If they couldn't tell if the switches were faulty, they'd have said. They do tell us that the throttle control module was swapped out and there's been no problem with the switches. So they don't need to mention it. It doesn't read to me as a logical part of the preliminary report, but as something they were under pressure to include to imply that there may have been a technical problem rather than pilot malfunction.
The prevalence of the 787 type. The quite recent travails of Boeing and the pace of its recovery (and some doubters that it can or will recover). The orders of magnitude increase in information, as well as misinformation or even disinformation, about this accident compared to .... well, compared to the UPS accident in Birmingham in 2013 (Flight 1354), cited as it was the first "current" accident occuring as of my stumbling across this forum and its threads. Sure, not a dramatic passenger aircraft accident but still valid for comparing the information environment then, and now. The persons responsible for this report, I think, did not act improperly if they included information not strictly necessary for the purpose of keeping aviation cognescenti updated about what is known with some (imprecisely defined) level of certainty and clarity. Such other information items could be intended to make some effort at mitigating ("minimizing" would be hoping for too much) the volumes of noise emanating from all over. Then there's the point about the report source knowing who did what, and when, but not providing specifics. Perhaps forensic analysis of the voice recording is ongoing, perhaps an analysis was completed but with reason to examine more closely. Regardless, I do not find it an affront either to solid, long-established principles of the Chicago Convention and Annex 13, or to the general ideas about advancing aviation safety, for the report sources to not treat the 30-day rule for preliminary reports as some "complete download demand function." Given what is reported about the fuel cutoff switches moving and the summarized cockpit statements, either way the final facts resolve will be tremendously impactful for the airline, the CAA of India, and the country (including but not only in its role as a major aviation Member State). I wouldn't hold this view if it was a question of deception. I see it instead as a matter of reasonable discretion, about both ..."what to leave in, what to leave out" (with apologies to Bob Seeger, "Against the Wind", 1980). |
Sailvi767
July 15, 2025, 22:04:00 GMT permalink Post: 11923302 |
So why did they give so much space to a discussion of SAIB NM-18-33? It's obvious that the switches were not faulty, or they'd have said. If they couldn't tell if the switches were faulty, they'd have said. They do tell us that the throttle control module was swapped out and there's been no problem with the switches. So they don't need to mention it. It doesn't read to me as a logical part of the preliminary report, but as something they were under pressure to include to imply that there may have been a technical problem rather than pilot malfunction.
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T28B
July 15, 2025, 23:29:00 GMT permalink Post: 11923347 |
For GroundedSpanner:
You seem to have left out the fatigue bit. ![]()
Originally Posted by
Garage Years
Originally Posted by
someone
Is it possible the switchers were improperly installed and it wasn't noticed/reported? I'd suggest yes since the SAIB was issued at all.
These same switches are used on about 7,000 aircraft. A new part (766AT614-3D) with a new locking mechanism that could not be installed incorrectly was made for the 737. The 787 uses an entirely different part number (4TL837‑3D). Read the entire Preliminary report, and pay particular attention to pages 5 through 9. Five different buildings were damaged, badly, because this aircraft hit five buildings as it came down with forward momentum. Parts of the aircraft hit some buildings and not others. There was a fire. The debris field was spread out over a large area. There were whole, and broken, and burned parts of this aircraft all over the place at the crash site that the investigators needed to identify and sift through, and then try to use, to come up with the who, what, where, why, when and how of this accident. The flight deck was found about 650 feet from the initial impact point. The overall extent of the debris field was roughly 1000 feet by 400 feet. That's about three football pitches/fields long (plus a bit) and one football pitch/field wide (plus a bit). Cut the investigating team a break, if you please, and exercise a bit of patience. |
EXDAC
July 16, 2025, 00:02:00 GMT permalink Post: 11923356 |
The SAIB describes a defect in the installation of the locking mechanism that, if present, could allow inadvertent activation. The SAIB does not state that the switch will snap back into cutoff. The SAIB inspection procedure would not be possible if the switch snapped back to cutoff - "1) Inspect the locking feature of the fuel control switch to ensure its engagement. While the airplane is on the ground, check whether the fuel control switch can be moved between the two positions without lifting up the switch. If the switch can be moved without lifting it up, the locking feature has been disengaged and the switch should be replaced at the earliest opportunity." The person you quoted has either seen a different switch defect or the authors of the SAIB didn't know what they were talking about. |