More MAX information

[Zimme83]

Upcoming preliminary report says that the Ethiopian pilots indeed followed the procedures to disable the electric trim but that the MCAS was activated at least 4 times afterwards.

It was not immediately clear whether the crew had chosen to re-deploy the system, which pushes the nose of the Boeing 737 MAX downwards, but one person with knowledge of the matter said investigators were studying the possibility that the software had kicked in again without human intervention.

It is possible that they choose to reengage the electric trim if  they could't regain a nose up attitude with manual trim but its also possible that disabling the trim didn't disable MCAS.


https://www.reuters.com/article/us-ethiopia-airplane-software/boeing-software-engaged-repeatedly-before-crash-sources-idUSKCN1RF0YU

[Toad]

It was not immediately clear whether the Ethiopian crew chose to re-deploy the system, which pushes the Boeing 737 MAX downwards to avoid stalling...

...The Wall Street Journal reported earlier that the pilots had initially followed Boeing’s emergency procedures but later deviated from them as they tried to regain control of the plane...

[Toad]

I love the Embraer.  We have temp sensors.   In the green at line up we are good to reject.

The G450/550 won't display V speeds if the brakes are too hot for the takeoff conditions. Also, it will give you a cooling time so you know when you will have the necessary brake energy for T/0.

[MiloMorai]

Toad, is that in case a take off has to be aborted?

[Shuffler]

If you are disconnecting the ability for the software to manipulate the hardware. That should end all control by the software.  They are now getting into movie mode of robots repairing themselves it looks like.

[Toad]

Toad, is that in case a take off has to be aborted?

Milo, yep.

When you do your takeoff initialization in the FMS the system looks at the parameters (weight, runway length, etc.) and ensures you have enough brake energy available for an RTO.

So for a simple example ,if you do a heavyweight landing on a short runway, quickly drop off a passenger without shutting down and go back out for T/O, the system will tell you if the brakes have enough energy left for an RTO on this short runway at this weight. If not, it will tell you how long it's going to be before you have sufficient brake energy. Obviously, you don't T/O if you don't have sufficient BE remaining.

[ACE]

The G450/550 won't display V speeds if the brakes are too hot for the takeoff conditions. Also, it will give you a cooling time so you know when you will have the necessary brake energy for T/0.

Toad, do you have any pictures of the rotors on these jets? I’m assuming after one landing you’d want the plan to relax and cool the brakes off right? 

[CptTrips]

I haven't followed this too closely, so you may have already seen this.

https://www.cnbc.com/2019/04/03/pilots-followed-boeings-emergency-steps-before-737-max-crash-report.html

[Toad]

Toad, do you have any pictures of the rotors on these jets? I’m assuming after one landing you’d want the plan to relax and cool the brakes off right?

Go here:  http://aerospaceandaviation.ohio.gov/documents/meetings/Meggitt%20OAATC%206.23.16.pdf

Scroll down to "Carbon Brake Applications - Business Jets" There are pics of the G650/550/450 brake assemblies.

Generally, Gulfstream biz jets have AMAZING stopping capabilities. It's pretty hard to actually get hot brakes. In normal ops, the T/Rs do much to help slow the jet so not a lot of brake energy is used. It would be a rare case where you had to delay subsequent T/O due to insufficient brake energy.

[Busher]

I haven't followed this too closely, so you may have already seen this.

https://www.cnbc.com/2019/04/03/pilots-followed-boeings-emergency-steps-before-737-max-crash-report.html

It's worthwhile to keep in mind that this is an Ethiopian investigation and that protocol dictates all investigation results are released through their aviation agency. Furthermore, Ethiopian Airlines has already suggested in the news, that Boeing's reputation with the 737 will not recover.
Re-engaging a runaway stab trim is tantamount to re-starting a burning engine because the fire was extinguished.
Nothing negative about the actions of the pilots serves the interests of Ethiopia or its national airline but creating a broad based belief that the airplane is faulty, does.
It saddens me that truth is too often colored with political interests. I hope the NTSB's final report is not.

[Zimme83]

https://leehamnews.com/2019/04/03/et302-used-the-cut-out-switches-to-stop-mcas/#more-29790


The problem is that given their speed it was probably close to impossible to manually use the trim so cutting the electrical switch left the pilots with 2 options: Either let go of the control column so that they could manually trim the plane or reengage the electrical trim. Option 1 was obviously not an option given their low altitude and the nose down trim so they went with number 2, but that also reactivated MCAS..

[ACE]

Seems everything points to faulty engaging of the MCAS. Maybe the pilots could have done more to disable it? But why does it have to faulty engage? 

[Zimme83]

Seems everything points to faulty engaging of the MCAS. Maybe the pilots could have done more to disable it? But why does it have to faulty engage?

Thats because of a very bad design. it has a single point of failure (using only one AOA sensor for information) and when that fails MCAS is activated. And to make it worse it is repeatedly activated as long as the sensor is faulty. Such system should rely on at least 3 sensors.

[Vraciu]

See rule #4

[FLS]

Seems everything points to faulty engaging of the MCAS. Maybe the pilots could have done more to disable it? But why does it have to faulty engage?

From what I've read there is a bypass  switch on the yoke that doesn't work the same way as turning MCAS off on the console. This may have been the critical pilot mistake.