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Another 737 MAX down.

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The theory is an interesting one but there are no tests and no engineering behind the idea. "Knowing all about blowback" from one's experience on a Draken, doesn't necessarily translate to the B737 type. There is nothing in the Boeing FCTM or FCOM that describes such a phenomenon. An aerodynamicist friend of mine indicates that this is likely not a plausible explanation for a continued dive.

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9 hours ago, Tango Niner said:

My point was the part about disabling it. As in, knowing, if needed, to hit the stab trim cutout switches- which have been present on the 737 since its mid-60’s inception.

I agree, moving the Stab Trim Cutout Switches to Cutout has been a part of the Stabilizer Trim Runaway NNC on B737s for decades BUT it has been step 5 of 8 in an NNC that has 2 memory items. Only after Lion Air 610 was the MAX only NNC changed to have the Stab Trim Cutout Switches to Cutout upgraded to a memory item and it still resides as #5 of 5 memory items and #5 of 8 in total.  There have been zero changes to the B737NG NNC.

 

I have a few issues with the way this has been handled, first, the MCAS system was designed and installed on production aircraft and no customers or pilots flying the aircraft knew anything about its existence other than a brief mention in the definitions section of the FCOM.

Second, MCAS has direct input to a primary flight control (Pitch) with no indications to the pilot and a single point of failure (Single AoA input) as seems to be the case in Lion Air at least. This is so contrary to established criteria and safeguards that without the significant loss of life it would be laughable in any safety orientated and risk managed environment. 

Third, the MCAS system when activated (erroneously or not) disables the normal Stab Brake function that has been available in B737 since the 1960s to mitigate Stab Trim Runaways but Boeing didn't think it was important to tell anyone that the system that was in 4500 B737s was NOT the same in the 250+/- MAXs.  Major Boo Boo.

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4 hours ago, Ex 9A Guy said:

I agree, moving the Stab Trim Cutout Switches to Cutout has been a part of the Stabilizer Trim Runaway NNC on B737s for decades BUT it has been step 5 of 8 in an NNC that has 2 memory items. Only after Lion Air 610 was the MAX only NNC changed to have the Stab Trim Cutout Switches to Cutout upgraded to a memory item and it still resides as #5 of 5 memory items and #5 of 8 in total.  There have been zero changes to the B737NG NNC.

 

I have a few issues with the way this has been handled, first, the MCAS system was designed and installed on production aircraft and no customers or pilots flying the aircraft knew anything about its existence other than a brief mention in the definitions section of the FCOM.

Second, MCAS has direct input to a primary flight control (Pitch) with no indications to the pilot and a single point of failure (Single AoA input) as seems to be the case in Lion Air at least. This is so contrary to established criteria and safeguards that without the significant loss of life it would be laughable in any safety orientated and risk managed environment. 

Third, the MCAS system when activated (erroneously or not) disables the normal Stab Brake function that has been available in B737 since the 1960s to mitigate Stab Trim Runaways but Boeing didn't think it was important to tell anyone that the system that was in 4500 B737s was NOT the same in the 250+/- MAXs.  Major Boo Boo.

There's  the post I was waiting for.  I don't fly the 737, never have, and I've been waiting for a succinct summation of the issue.  Thank you.

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10 hours ago, Ex 9A Guy said:

IThird, the MCAS system when activated (erroneously or not) disables the normal Stab Brake function that has been available in B737 since the 1960s to mitigate Stab Trim Runaways but Boeing didn't think it was important to tell anyone that the system that was in 4500 B737s was NOT the same in the 250+/- MAXs.  Major Boo Boo. 

Understatement for sure! Considering that Boeing also wants a common type rating (cost savings for airlines) then these types of differences were, at best, trained by an online course. A significant difference such as this should be required to have specific training in GS and in the SIM to emphasize the new operation of the system and break the habits, ingrained in training on the other 737 models.

I don't fly the MAX but every pilot I know who does said the 'transition course' (ground school only) say it was woefully inadequate considering the differences.

So, if the normal STAB BRAKE function in not available on the MAX what other 'adjustments' were made? Systems engineers will design a system but can't envision every single scenario or envision how a computer may interact with that system in all scenarios. They then rely on reverting to the pilot to intervene. How can a pilot intervene if they don't understand that system and have not been trained to deal with system failure scenarios?

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Welcome, vrefplus5.

FWIW, I'm not a believer in the notion that AoA would have saved either JT610 or for that matter, AF447. There is no proof that I have seen that crews flying airline transports knowing AoA when wrestling with control of their aircraft has saved the day.

AoA is for downstream computers, (ADRs/FCCs), in combination with ADIRUs including comparator systems that detect sensor faults and remove faulty sensor data from downstream users and displays for crews. Removal of bad data is an old philosophy that I think has a solid foundation in human factors.

The single MCAS input from the left AoA for the flight prior to the accident flight was ~20deg. The left sensor was replaced but the accident flight had the same ~20deg incorrect data as the previous flight. The sensor cannot be installed incorrectly, and it was tested prior to flight, (according to the snag). So I suspect that the problem with both JT610 & ET302 was downstream of the AoA sensor.

While the left AoA sensor can be, (and has been) damaged by incorrect placement or handling of the boarding bridge, in terms of movements, that would be statistically rare. A more common factor isn't the sensor, but either the ADR or the FCC, equally statistically-rare but plausible because all AoA damage reports, (in US ASRs) were discovered prior to pushback, but we have at least one event where FCCs, (the A330 PRIM) misbehaved, (QF72) which is not detectable prior to flight.

I don't believe the crew of JT610 were a primary factor in the accident, mainly because, in the moment, under stress from confusing warnings and aircraft behaviour, they did not have knowledge of the system that was the primary of their confusion and would not have assessed the stab as a "runaway". The absence of information in the logbook regarding aircraft behaviour during the previous flight, (and what they did) is a factor, I think.

There are questions regarding knowledge of one's aircraft systems, snag writing that is thorough, a culture of secrecy/punishment or simply scheduling pressures and limited or misappropriated resources perhaps, but those factors are for investigations and are not limited to the airlines involved.

Edited by Don Hudson

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Don, when you way the AOA sensor cannot be incorrectly installed, it gives me pause.  I've seen so many foolproof systems defeated, I have to think this would be just one more. 

That said, I know nothing about this particular part number or what connections have to be made (correctly) for it to work.  We have a rich history of trouble from bent pins, excessive solder, a pin hole puncture, kink, overtorque, and a couple of dozen I know you could easily add - and all that is assuming that the correct part went into the correct spot - is there a left and right to these things, does the NG take the same part number, etc etc.

Vs

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1 hour ago, Trader said:

Understatement for sure! Considering that Boeing also wants a common type rating (cost savings for airlines) then these types of differences were, at best, trained by an online course. A significant difference such as this should be required to have specific training in GS and in the SIM to emphasize the new operation of the system and break the habits, ingrained in training on the other 737 models.

I don't fly the MAX but every pilot I know who does said the 'transition course' (ground school only) say it was woefully inadequate considering the differences.

So, if the normal STAB BRAKE function in not available on the MAX what other 'adjustments' were made? Systems engineers will design a system but can't envision every single scenario or envision how a computer may interact with that system in all scenarios. They then rely on reverting to the pilot to intervene. How can a pilot intervene if they don't understand that system and have not been trained to deal with system failure scenarios?

An MCAS failure would never have formed part of a SIM script. However, a demonstration of the MCAS function might have been. Problem would be configuration load for the SIM (could you load the MAX database on to the NG SIM).

And Boeing has subsequently modified the memory items for STAB TRIM Runaway to include up to item 5 - CUTOUT SWITCHES. 

Because the MCAS system was designed to defeat some of the crew actions for the NG (stabilizer brake), MCAS activation in a non-stall scenario could become confusing (that may be the understatement of the century).

And AOA information was considered ‘optional’.

All in all, the commonality assumption for the 737 will come under a great deal of scrutiny. Hindsight always being 20/20. Engineers had the right idea, but the resulting system design had a fatal flaw (single source trigger). That should have been trapped early on in the MAX certification process (right after they realized that the aircraft lacked inherent stability).

Edited by rudder

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Just to clarify. The stabilizer brake is actually two independent brake systems to hold the stabilizer in place. Either one can hold the stabilizer in its trimmed position. If they both were to fail without pilot intervention (holding the trim wheel) air loads could drive the stabilizer to its mechanical stops. Main electric trim can resist this motion, but control column opposition (elevator) will make the condition worse. MCAS does not affect this brake system. The MCAS disables the control column actuated cutout switches which stop operation of the main electric and autopilot trim when control column movement opposes trim direction. 

Edited by Arctic Ace

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Hi Vs, all valid points & questions. The AMM shows that there are indexing pins for the -400 installation and I have to believe that the same applies to all Boeings, as would the testing processes after installation. Interestingly, the test involves moving the vane to the -20 & 20 degree position to measure electrical output, so the I believe the max readings are +/-20deg and that's where JT610's left sensor was reading ...

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Thanks Don.  Yes, that 20 deg value keeps coming up and while I've seen it associated with full scale deflection in a couple of other places, your AMM reference is definitive. The damage may ultimately hide the true state of that sensor and any installation-induced issues from us, but hopefully the investigators will be able to identify whether a bad ground, perhaps static discharge during installation or some other issue crept into the mix.

All the best

Vs

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I was looking at Flightaware, 28 B737 Max are indicated to be flying... Wasn't the entire fleet grounded when the FAA intervened?

Am i missing something?

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Southwest have/are moving several airframes to Victorville. 

Edited by blues deville

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41 minutes ago, blues deville said:

Southwest have/are moving several airframes to Victorville. 

American, according to reports, is looking to restart MAX flying in late April.

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They are cancelling their max operations up to April 24th , that was an update on CNN yesterday.

Southwest   appears to be planning for a longer delay.

Southwest Airlines Is Now Parking Boeing 737 MAX Aircraft In The Desert

 
By Bryan
March 24, 2019
 

Southwest Airlines is preparing for a long-term grounding of the Boeing 737 MAX. So much so, that the airline is beginning to send the aircraft to the Mojave Desert for storage. With the global grounding of the Boeing 737 MAX aircraft still in effect, a team from Southwest will be joining other US airlines in visiting the manufacturer soon to preview the aircraft updates.

Southwest sent a few of its Boeing 737 MAX 8 aircraft to the Mojave Desert for storage. Photo: Southwest.

737 MAX 8 fleet takes a trip to Victorville

On Saturday, Southwest Airlines began to migrate some Boeing 737 MAX 8 fleet to its long-term storage facility. Located at the Southern California Logistics Airport facility in Victorville, this is in the heart of the Mojave Desert. A total of six of the aircraft made the journey so far, which could be followed by others if the model continues to be banned.

Aircraft from around the US were ordered to be sent here by the airline. Two of the planes came from Nashville, and other individual aircraft came from St. Louis, Dallas-Love, Phoenix, and Indianapolis. The Southwest fleet includes a total of 34 Boeing 737 MAX 8. The remainder of the aircraft continue to be grounded in various locations around the US, awaiting further notice about the situation.

Mojave Desert is an airplane graveyard

Southwest frequently uses the desert to store planes being discontinued from its fleet. Most recently, it terminated the Boeing 737-300, all of which were sent to Victorville at the end of Q3, 2017. It’s known as an airplane graveyard thanks to the significant number of unused planes grounded here.

Although Southwest Airlines is expecting the Boeing 737 MAX 8 aircraft to return to its fleet eventually, the desert was still the best choice for storing the planes. The desert climate makes for perfect environmental conditions for long term storage of aircraft.

Southwest is preparing for long term storage of its Boeing 737 MAX 8 in lieu of the global grounding. Photo: Southwest.

Other airlines also have hubs for long term aircraft storage. American and United have also begun to sent parts of their Boeing 737 MAX 8 fleet storage locations. American has sent a few aircraft to Miami and Tulsa, while Houston has received some from United.

Sending its fleet to the desert signals that Southwest is expecting the grounding to last for a significant amount of time. With close inspection from the FAA and airlines alike, Boeing is hoping for good news in the upcoming weeks regarding the 737 updates.

All eyes on Boeing

The industry-wide grounding of the Boeing 737 MAX 8 aircraft occurred shortly after the second fatal crash of the model. The FAA has demanded Boeing perform updates before any airlines will use the aircraft again.

Reps from Southwest will visit Boeing’s factory to learn about the mandatory updates to the aircraft. Photo: Boeing.

In the upcoming week, Boeing will host representatives from the FAA and US airlines, including Southwest, to review the changes. Boeing are rolling out software updates of the MCAS system, as well as training updates to ensure the safety of the MAX.

Boeing is expecting to surpass all expectations of the inspections and reviews, but airline companies are a bit more hesitant to return the 737 MAX 8 to their active fleets so soon.

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"Pilots will be required to complete training on the new system, using thier I pads"

 

 Are you kidding me ? Leave the Pig grounded until Boeing gets it.

 I am still thinking it should be a different type endorsement for pilots.

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Quote

In Test of Boeing Jet, Pilots Had 40 Seconds to Fix Error

Excuse me......how many seconds do you have to fix an engine failure at V2????

Fwiw......my co. Issued us iPads with all the co. Manuals, JeppFD-Pro charts, and weather info....assuming we all knew how to use an iPad!! (For dinosaurs like me, I learn from my tech savvy first officers). Anecdotally, I have heard AA pilots had a 3 day course on the Jepp app.

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Watch On March 27 | 8pm ET | C-SPAN2

Senate Commerce Hearing on Airline Safety

Government officials testify on airline safety after a global recall of the Boeing 737 Max aircraft. A Senate Commerce subcommittee holds the hearing.

Alert me when this program is:
  • Available online
  • Airing on the C-SPAN Networks
More information about

Senate Commerce Hearing on Airline Safety

Program ID:
459047-1
Category:
Senate Committee
Format:
Senate Committee
Location:
Washington, District of Columbia, United States
Will Air:
Mar 27, 2019 | 3:00pm EDT | C-SPAN.org

Airing Details

  • Mar 27, 2019 | 3:00pm EDT | C-SPAN.org
  • Mar 27, 2019 | 8:00pm EDT | C-SPAN 2

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Can someone tell me if the the cut out switches are only on the Max or did previous generations of 737's have something similar.

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