June 19, 2025, 14:08:00 GMT
permalink Post: 11906053
I have read most of the thread (old and new). As a lawyer working in forensic investigations, I am constantly involved in problem-solving. My field of work also includes complex investigations related to insolvencies, which almost always require an analysis of the causes behind a specific, established outcome. In doing so, I naturally also have to deal with probabilities. However, it often turns out that the most likely or plausible explanation does not reflect what actually happened.
Many of the considerations I’ve read fail because the simultaneous failure of both engines is extremely unlikely, leading to a constant search for higher-order causes. It was suggested that an incorrect altitude setting led to an early thrust reduction. However, this would not explain the deployment of the RAT (Ram Air Turbine), especially since the thrust could have been readjusted. FADEC and TCAM are highly redundant systems, and TCAM failure is unlikely due to WOW (Weight on Wheels) logic, making a simultaneous engine failure after VR equally improbable.
With that said, and with regard to my question concerning the AD that relates to the fuel control switches (FCS), my thought—and it was nothing more than that—was that their activation becomes more probable if it can occur accidentally. That’s how I came across SAIB: NM-18-33.
Another user then brought up an iPhone. That notion would, of course, be dramatic—but how unlikely is it really that after approximately 10,000 actuations between December 2013 and June 2025, the two FCS no longer lock perfectly? Considering all of this, I find it quite conceivable that the A/T slightly reduced thrust in the first seconds after VR (e.g., if an incorrect target altitude had been entered) and that an object lying between the thrust levers and the FCS could have pushed the FCS into the “Off” position. Due to the buttons on top of the switches, which provide some resistance, it’s even possible that the object both pulled and pushed them.
But all of this is speculation. The investigation report will bring clarity.
Even if my theory is not confirmed, I still believe that the positioning and mechanism of the FCS are suboptimal. Switches of such critical importance should be better protected, and movements in the area in front of the switches (like reducing thrust) should not follow the same direction as shutting off the fuel supply. A different switching direction alone would provide more safety—especially considering that the FCS are protected laterally by metal plates.
Many of the considerations I’ve read fail because the simultaneous failure of both engines is extremely unlikely, leading to a constant search for higher-order causes. It was suggested that an incorrect altitude setting led to an early thrust reduction. However, this would not explain the deployment of the RAT (Ram Air Turbine), especially since the thrust could have been readjusted. FADEC and TCAM are highly redundant systems, and TCAM failure is unlikely due to WOW (Weight on Wheels) logic, making a simultaneous engine failure after VR equally improbable.
With that said, and with regard to my question concerning the AD that relates to the fuel control switches (FCS), my thought—and it was nothing more than that—was that their activation becomes more probable if it can occur accidentally. That’s how I came across SAIB: NM-18-33.
Another user then brought up an iPhone. That notion would, of course, be dramatic—but how unlikely is it really that after approximately 10,000 actuations between December 2013 and June 2025, the two FCS no longer lock perfectly? Considering all of this, I find it quite conceivable that the A/T slightly reduced thrust in the first seconds after VR (e.g., if an incorrect target altitude had been entered) and that an object lying between the thrust levers and the FCS could have pushed the FCS into the “Off” position. Due to the buttons on top of the switches, which provide some resistance, it’s even possible that the object both pulled and pushed them.
But all of this is speculation. The investigation report will bring clarity.
Even if my theory is not confirmed, I still believe that the positioning and mechanism of the FCS are suboptimal. Switches of such critical importance should be better protected, and movements in the area in front of the switches (like reducing thrust) should not follow the same direction as shutting off the fuel supply. A different switching direction alone would provide more safety—especially considering that the FCS are protected laterally by metal plates.
June 19, 2025, 14:36:00 GMT
permalink Post: 11906073
I have read most of the thread (old and new). As a lawyer working in forensic investigations, I am constantly involved in problem-solving. My field of work also includes complex investigations related to insolvencies, which almost always require an analysis of the causes behind a specific, established outcome. In doing so, I naturally also have to deal with probabilities. However, it often turns out that the most likely or plausible explanation does not reflect what actually happened.
Many of the considerations I\x92ve read fail because the simultaneous failure of both engines is extremely unlikely, leading to a constant search for higher-order causes. It was suggested that an incorrect altitude setting led to an early thrust reduction. However, this would not explain the deployment of the RAT (Ram Air Turbine), especially since the thrust could have been readjusted. FADEC and TCAM are highly redundant systems, and TCAM failure is unlikely due to WOW (Weight on Wheels) logic, making a simultaneous engine failure after VR equally improbable.
With that said, and with regard to my question concerning the AD that relates to the fuel control switches (FCS), my thought\x97and it was nothing more than that\x97was that their activation becomes more probable if it can occur accidentally. That\x92s how I came across SAIB: NM-18-33.
Another user then brought up an iPhone. That notion would, of course, be dramatic\x97but how unlikely is it really that after approximately 10,000 actuations between December 2013 and June 2025, the two FCS no longer lock perfectly? Considering all of this, I find it quite conceivable that the A/T slightly reduced thrust in the first seconds after VR (e.g., if an incorrect target altitude had been entered) and that an object lying between the thrust levers and the FCS could have pushed the FCS into the \x93Off\x94 position. Due to the buttons on top of the switches, which provide some resistance, it\x92s even possible that the object both pulled and pushed them.
But all of this is speculation. The investigation report will bring clarity.
Even if my theory is not confirmed, I still believe that the positioning and mechanism of the FCS are suboptimal. Switches of such critical importance should be better protected, and movements in the area in front of the switches (like reducing thrust) should not follow the same direction as shutting off the fuel supply. A different switching direction alone would provide more safety\x97especially considering that the FCS are protected laterally by metal plates.
Many of the considerations I\x92ve read fail because the simultaneous failure of both engines is extremely unlikely, leading to a constant search for higher-order causes. It was suggested that an incorrect altitude setting led to an early thrust reduction. However, this would not explain the deployment of the RAT (Ram Air Turbine), especially since the thrust could have been readjusted. FADEC and TCAM are highly redundant systems, and TCAM failure is unlikely due to WOW (Weight on Wheels) logic, making a simultaneous engine failure after VR equally improbable.
With that said, and with regard to my question concerning the AD that relates to the fuel control switches (FCS), my thought\x97and it was nothing more than that\x97was that their activation becomes more probable if it can occur accidentally. That\x92s how I came across SAIB: NM-18-33.
Another user then brought up an iPhone. That notion would, of course, be dramatic\x97but how unlikely is it really that after approximately 10,000 actuations between December 2013 and June 2025, the two FCS no longer lock perfectly? Considering all of this, I find it quite conceivable that the A/T slightly reduced thrust in the first seconds after VR (e.g., if an incorrect target altitude had been entered) and that an object lying between the thrust levers and the FCS could have pushed the FCS into the \x93Off\x94 position. Due to the buttons on top of the switches, which provide some resistance, it\x92s even possible that the object both pulled and pushed them.
But all of this is speculation. The investigation report will bring clarity.
Even if my theory is not confirmed, I still believe that the positioning and mechanism of the FCS are suboptimal. Switches of such critical importance should be better protected, and movements in the area in front of the switches (like reducing thrust) should not follow the same direction as shutting off the fuel supply. A different switching direction alone would provide more safety\x97especially considering that the FCS are protected laterally by metal plates.
July 11, 2025, 22:04:00 GMT
permalink Post: 11919871
Does anyone have a link to Special Airworthiness Information Bulletin (SAIB) No. NM-18-33. I did not find it in a quick search.
Last edited by Saab Dastard; 11th July 2025 at 22:26 . Reason: Removed errors
July 11, 2025, 22:12:00 GMT
permalink Post: 11919889
Spoiler
I wouldn't put too much significance in the "01 second" since this still is close enough for an unintentional cause.
No matter what: The design and position of the fuel cut off switches is potentially prone for mishaps.
July 11, 2025, 22:17:00 GMT
permalink Post: 11919895
Background
The Boeing Company (Boeing) received reports from operators of Model 737 airplanes that the fuel control switches were installed with the locking feature disengaged. The fuel control switches (or engine start switches) are installed on the control stand in the flight deck and used by the pilot to supply or cutoff fuel to the engines. The fuel control switch has a locking feature to prevent inadvertent operation that could result in unintended switch movement between the fuel supply and fuel cutoff positions. In order to move the switch from one position to the other under the condition where the locking feature is engaged, it is necessary for the pilot to lift the switch up while transitioning the switch position. If the locking feature is disengaged, the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation. Inadvertent operation of the switch could result in an unintended consequence, such as an in-flight engine shutdown.
...The table below identifies the affected airplane models and related part numbers (P/Ns) of the fuel control switch, which is manufactured by Honeywell.
...787-8, -9, and -10
The Boeing Company (Boeing) received reports from operators of Model 737 airplanes that the fuel control switches were installed with the locking feature disengaged. The fuel control switches (or engine start switches) are installed on the control stand in the flight deck and used by the pilot to supply or cutoff fuel to the engines. The fuel control switch has a locking feature to prevent inadvertent operation that could result in unintended switch movement between the fuel supply and fuel cutoff positions. In order to move the switch from one position to the other under the condition where the locking feature is engaged, it is necessary for the pilot to lift the switch up while transitioning the switch position. If the locking feature is disengaged, the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation. Inadvertent operation of the switch could result in an unintended consequence, such as an in-flight engine shutdown.
...The table below identifies the affected airplane models and related part numbers (P/Ns) of the fuel control switch, which is manufactured by Honeywell.
...787-8, -9, and -10
Last edited by 13 others; 12th July 2025 at 01:40 . Reason: Bold emphasis mine, fixed link
July 11, 2025, 22:18:00 GMT
permalink Post: 11919901
Agreed, it's most unfortunate that that the preliminary report hasn\x92t closed off speculation, it's simply created opportunity for more.
It confirms that both fuel cutoff switches were moved to OFF at Vr, within a one second interval which is as extreme and inexplicable as it gets. Then it gives us a CVR quote that\x92s so neutered, "Why did you cut off?\x94 / \x93I didn\x92t\x94, that it raises more questions than it answers. If the goal was to reassure or clarify, it\x92s had the opposite effect.
It confirms that both fuel cutoff switches were moved to OFF at Vr, within a one second interval which is as extreme and inexplicable as it gets. Then it gives us a CVR quote that\x92s so neutered, "Why did you cut off?\x94 / \x93I didn\x92t\x94, that it raises more questions than it answers. If the goal was to reassure or clarify, it\x92s had the opposite effect.
Action slip
SAIB NM-18-33
Intentional.
July 11, 2025, 22:28:00 GMT
permalink Post: 11919916
July 11, 2025, 22:43:00 GMT
permalink Post: 11919938
The SIAB relates to defective throttle units at the point of installation (on a different but related aircraft). I might be onboard with that theory if maintenance happened to have replaced the unit a day or 2 before the incident. But it's a tough sell that a defective switch that's used literally on every flight had flown for 2 years without someone noticing and snagging that the locking mechanism wasn't working
July 12, 2025, 00:08:00 GMT
permalink Post: 11920029
Timeline of known events with source attribution from the preliminary report:
08:07:33 ATC: Takeoff clearance
08:07:37 A-SMGCS: Aircraft starts rolling
08:08:33 EAFR: V1 153kts
08:08:35 EAFR: Vr 155kts
08:08:39 EAFR: Gnd-Air mode transition
08:08:42 EAFR: Max IAS 180kts, Eng 1/2 Cutoff switches activate within 1 second of each other
08:08:42 CVR: "Why did you cut off", "I did not" (exact time not specified)
08:08:42 A-SMGCS: RAT deployed (exact time not specified)
08:08:47 EAFR: Both engine N2 below min idle. RAT hyd pwr commences
08:08:52 EAFR: Eng 1 cutoff to RUN
08:08:54 EAFR: APU inlet door opens (auto start logic)
08:08:56 EAFR: Eng 2 cutoff to RUN
08:09:05 ATC: Mayday call
08:09:11 EAFR recording stops
Fuel cutoff switches operated within 1 second of each other suggests to me that the locking mechanism wasn't working as per (SAIB) No. NM-18-33. Any loose item could have accidentally (or not) operated the switches (including hands).
08:07:33 ATC: Takeoff clearance
08:07:37 A-SMGCS: Aircraft starts rolling
08:08:33 EAFR: V1 153kts
08:08:35 EAFR: Vr 155kts
08:08:39 EAFR: Gnd-Air mode transition
08:08:42 EAFR: Max IAS 180kts, Eng 1/2 Cutoff switches activate within 1 second of each other
08:08:42 CVR: "Why did you cut off", "I did not" (exact time not specified)
08:08:42 A-SMGCS: RAT deployed (exact time not specified)
08:08:47 EAFR: Both engine N2 below min idle. RAT hyd pwr commences
08:08:52 EAFR: Eng 1 cutoff to RUN
08:08:54 EAFR: APU inlet door opens (auto start logic)
08:08:56 EAFR: Eng 2 cutoff to RUN
08:09:05 ATC: Mayday call
08:09:11 EAFR recording stops
Fuel cutoff switches operated within 1 second of each other suggests to me that the locking mechanism wasn't working as per (SAIB) No. NM-18-33. Any loose item could have accidentally (or not) operated the switches (including hands).
Last edited by physicus; 12th July 2025 at 00:24 .
July 12, 2025, 01:51:00 GMT
permalink Post: 11920086
Nothing in the report suggests that the engines began to run down before the fuel was selected to cutoff. The report states a sequence of events for power loss which
begins
with the switches MOVING or BEING MOVED to cutoff. The maximum airspeed was immediately before the switches were moved, so there had not been a power rundown prior to that:
July 12, 2025, 07:42:00 GMT
permalink Post: 11920296
Timeline of known events with source attribution from the preliminary report:
08:07:33 ATC: Takeoff clearance
08:07:37 A-SMGCS: Aircraft starts rolling
08:08:33 EAFR: V1 153kts
08:08:35 EAFR: Vr 155kts
08:08:39 EAFR: Gnd-Air mode transition
08:08:42 EAFR: Max IAS 180kts, Eng 1/2 Cutoff switches activate within 1 second of each other
08:08:42 CVR: "Why did you cut off", "I did not" (exact time not specified)
08:08:42 A-SMGCS: RAT deployed (exact time not specified)
08:08:47 EAFR: Both engine N2 below min idle. RAT hyd pwr commences
08:08:52 EAFR: Eng 1 cutoff to RUN
08:08:54 EAFR: APU inlet door opens (auto start logic)
08:08:56 EAFR: Eng 2 cutoff to RUN
08:09:05 ATC: Mayday call
08:09:11 EAFR recording stops
Fuel cutoff switches operated within 1 second of each other suggests to me that the locking mechanism wasn't working as per (SAIB) No. NM-18-33. Any loose item could have accidentally (or not) operated the switches (including hands).
08:07:33 ATC: Takeoff clearance
08:07:37 A-SMGCS: Aircraft starts rolling
08:08:33 EAFR: V1 153kts
08:08:35 EAFR: Vr 155kts
08:08:39 EAFR: Gnd-Air mode transition
08:08:42 EAFR: Max IAS 180kts, Eng 1/2 Cutoff switches activate within 1 second of each other
08:08:42 CVR: "Why did you cut off", "I did not" (exact time not specified)
08:08:42 A-SMGCS: RAT deployed (exact time not specified)
08:08:47 EAFR: Both engine N2 below min idle. RAT hyd pwr commences
08:08:52 EAFR: Eng 1 cutoff to RUN
08:08:54 EAFR: APU inlet door opens (auto start logic)
08:08:56 EAFR: Eng 2 cutoff to RUN
08:09:05 ATC: Mayday call
08:09:11 EAFR recording stops
Fuel cutoff switches operated within 1 second of each other suggests to me that the locking mechanism wasn't working as per (SAIB) No. NM-18-33. Any loose item could have accidentally (or not) operated the switches (including hands).
Last edited by sorvad; 12th July 2025 at 08:03 . Reason: Clarification
July 12, 2025, 09:14:00 GMT
permalink Post: 11920399
When I was a young F/O, some of the captains I flew with had the (annoying) habit of resting their hands just behind the thrust levers on their PM (PNF) sectors to 'be ready' to reject the takeoff. This would put the hands in the vicinity of the Fuel Cutoffs, which would, in turn, increase the chances of an unintended action on these switches. Is this a possibility, or am I way off?
Last edited by Senior Pilot; 12th July 2025 at 09:25 . Reason: Quote
July 12, 2025, 09:33:00 GMT
permalink Post: 11920418
Well, speaking of fuel-cut switches, I read
NM-18-33 SAIB
with attention, and as a not-that-fluent english speaker, I stumbled on this sentence (my bold):
I could hardly figure what the "disengaged" word meant in this context, so I did a Google search for the switch part numbers (especially "766AT614-3D") to figure the difference between them, and
a page from this chinese web site
was part of the results.
And while I was painfully crawling the thread, I noticed the following picture about an "undesirable condition":
Incorrect lock tab position on fuel cut-off switch
If this incorrect mounting is actually possible, it would possibly remain unnoticed from the pilots (normal "pull-up then move" action is unaffected), but it would cancel the protective function of the so-called "locking tab", and even limit the travel of the switch handle in both directions, making it more vulnerable to an undesired change of state.
The photos above seem convincing enough, but I'd be very grateful for an informed opinion on this assembly mistake. Even if this is possible, the probability of both switches being unexpectedly snapped seems very remote to say the least, but not as remote as previously estimated.
If the locking feature is
disengaged
, the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation.
And while I was painfully crawling the thread, I noticed the following picture about an "undesirable condition":
Incorrect lock tab position on fuel cut-off switch
If this incorrect mounting is actually possible, it would possibly remain unnoticed from the pilots (normal "pull-up then move" action is unaffected), but it would cancel the protective function of the so-called "locking tab", and even limit the travel of the switch handle in both directions, making it more vulnerable to an undesired change of state.
The photos above seem convincing enough, but I'd be very grateful for an informed opinion on this assembly mistake. Even if this is possible, the probability of both switches being unexpectedly snapped seems very remote to say the least, but not as remote as previously estimated.
July 12, 2025, 10:26:00 GMT
permalink Post: 11920464
Well, speaking of fuel-cut switches, I read
NM-18-33 SAIB
with attention, and as a not-that-fluent english speaker, I stumbled on this sentence (my bold):
I could hardly figure what the "disengaged" word meant in this context, so I did a Google search for the switch part numbers (especially "766AT614-3D") to figure the difference between them, and a page from this chinese web site was part of the results.
And while I was painfully crawling the thread, I noticed the following picture about an "undesirable condition":
Incorrect lock tab position on fuel cut-off switch
If this incorrect mounting is actually possible, it would possibly remain unnoticed from the pilots (normal "pull-up then move" action is unaffected), but it would cancel the protective function of the so-called "locking tab", and even limit the travel of the switch handle in both directions, making it more vulnerable to an undesired change of state.
The photos above seem convincing enough, but I'd be very grateful for an informed opinion on this assembly mistake. Even if this is possible, the probability of both switches being unexpectedly snapped seems very remote to say the least, but not as remote as previously estimated.
I could hardly figure what the "disengaged" word meant in this context, so I did a Google search for the switch part numbers (especially "766AT614-3D") to figure the difference between them, and a page from this chinese web site was part of the results.
And while I was painfully crawling the thread, I noticed the following picture about an "undesirable condition":
Incorrect lock tab position on fuel cut-off switch
If this incorrect mounting is actually possible, it would possibly remain unnoticed from the pilots (normal "pull-up then move" action is unaffected), but it would cancel the protective function of the so-called "locking tab", and even limit the travel of the switch handle in both directions, making it more vulnerable to an undesired change of state.
The photos above seem convincing enough, but I'd be very grateful for an informed opinion on this assembly mistake. Even if this is possible, the probability of both switches being unexpectedly snapped seems very remote to say the least, but not as remote as previously estimated.
One other useful thing from that web site is a partial schematic which shows the connection of the 4 poles in the switch. I believe this is from a 737NG but it should be the same idea.
July 12, 2025, 10:43:00 GMT
permalink Post: 11920472
NM-18-33 SAIB
left me wondering the same thing. It give a procedure for detecting the defect but omits to explain the cause. I was thinking that the wrong switches had been supplied/fitted. Assuming the image from the Chinese web site is correct, it is disappointing that the actuator can get into that state. I did not see anything that said whether that was how the switch arrived from Honeywell or if there was a defect that allowed the actuator to turn.
One other useful thing from that web site is a partial schematic which shows the connection of the 4 poles in the switch. I believe this is from a 737NG but it should be the same idea.
One other useful thing from that web site is a partial schematic which shows the connection of the 4 poles in the switch. I believe this is from a 737NG but it should be the same idea.
If any of that were true why would it happen after Vr and why would one pilot ask: \x93why did you go to cutoff\x94. That is an observed deliberate action. Cmon folks enough with the nonsense!
Why are people shying around the truth!?
July 12, 2025, 12:25:00 GMT
permalink Post: 11920578
AI171 Threads by Subject
I have rebuilt the site that organises these three threads by subject here:
https://paulross.github.io/pprune-th...171/index.html
Changes:
Raise issues here https://github.com/paulross/pprune-threads/issues or PM me.
Changes:
- Build threads up to July 12, 2025, 11:59:00 (built at July 12, 2025, 13:03:09).
- Add thread about the published report: Preliminary Air India crash report published
- Add subjects: "Guards", "Timeline (Preliminary Report)", "EICAS", "RUN/CUTOFF", "Special Airworthiness Information Bulletin", "SAIB NM-18-33", "Gear Lever", "Startle Effect" and "Cockpit Area Audio".
- Minor improvements to the index.html page.
Raise issues here https://github.com/paulross/pprune-threads/issues or PM me.
July 12, 2025, 18:17:00 GMT
permalink Post: 11920727
"In order to move the switch from one position to the other under the condition where the locking feature is engaged, it is necessary for the pilot to lift the switch up while transitioning the switch position. If the locking feature is disengaged, the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation. Inadvertent operation of the switch could result in an unintended consequence, such as an in-flight engine shutdown.'
Since the preliminary report does not specify that this SAIB was actioned on this aircraft we do not know if it was fitted with defective switches.
In my personal opinion a defective locking feature does not explain the reported event sequence. That does not mean the switches were not defective.
July 12, 2025, 18:33:00 GMT
permalink Post: 11920736
That account, which is posted as being authoritative, appears to disregard SAIB NM-18-33 which states, in part:
"In order to move the switch from one position to the other under the condition where the locking feature is engaged, it is necessary for the pilot to lift the switch up while transitioning the switch position. If the locking feature is disengaged, the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation. Inadvertent operation of the switch could result in an unintended consequence, such as an in-flight engine shutdown.'
Since the preliminary report does not specify that this SAIB was actioned on this aircraft we do not know if it was fitted with defective switches.
In my personal opinion a defective locking feature does not explain the reported event sequence. That does not mean the switches were not defective.
"In order to move the switch from one position to the other under the condition where the locking feature is engaged, it is necessary for the pilot to lift the switch up while transitioning the switch position. If the locking feature is disengaged, the switch can be moved between the two positions without lifting the switch during transition, and the switch would be exposed to the potential of inadvertent operation. Inadvertent operation of the switch could result in an unintended consequence, such as an in-flight engine shutdown.'
Since the preliminary report does not specify that this SAIB was actioned on this aircraft we do not know if it was fitted with defective switches.
In my personal opinion a defective locking feature does not explain the reported event sequence. That does not mean the switches were not defective.
July 12, 2025, 20:04:00 GMT
permalink Post: 11920795
See here
NM-18-33 SAIB
left me wondering the same thing. It give a procedure for detecting the defect but omits to explain the cause. I was thinking that the wrong switches had been supplied/fitted. Assuming the image from the Chinese web site is correct, it is disappointing that the actuator can get into that state. I did not see anything that said whether that was how the switch arrived from Honeywell or if there was a defect that allowed the actuator to turn.
One other useful thing from that web site is a partial schematic which shows the connection of the 4 poles in the switch. I believe this is from a 737NG but it should be the same idea.
b79edb16af_5b3bb7a57d07fbf3c85529ab3f52308b609d82a3.png.webp
One other useful thing from that web site is a partial schematic which shows the connection of the 4 poles in the switch. I believe this is from a 737NG but it should be the same idea.
b79edb16af_5b3bb7a57d07fbf3c85529ab3f52308b609d82a3.png.webp
Last edited by RomeoTangoFoxtrotMike; 12th July 2025 at 20:28 .
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
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