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19th Aug 2019, 20:19
Replies: 2,428
Views: 2,175,333
Posted By HighWind

Either Boeing ensures that the pilots can...

Either Boeing ensures that the pilots can mechanically overcome an trim runaway, or they ensure that it will newer happen.
The later requires that the Flight Control System for the trim is upgraded...
6th Aug 2019, 17:45
Replies: 2,428
Views: 2,175,333
Posted By HighWind

I you remove the code for MCAS then it can't...

I you remove the code for MCAS then it can't generate a runaway :)
But the Flight Control System have been connected to the trim for decades, and a bit-flip in other functions of the Flight Control...
5th Aug 2019, 22:17
Replies: 2,428
Views: 2,175,333
Posted By HighWind

No, this only protects against bit-flips in...

No, this only protects against bit-flips in memory, there is also a risk that the CPU registers get corrupted.
For this you need two ordinary CPU’s, or a lock-step CPU like TMS570.
A lock-step CPU...
5th Aug 2019, 19:57
Replies: 2,428
Views: 2,175,333
Posted By HighWind

There are many cases where a bit flip might not...

There are many cases where a bit flip might not be overwritten with the correct value the next control scan. E.g. if a filter or timer value is flipped to an out of range value, it can take hours to...
3rd Aug 2019, 20:39
Replies: 2,428
Views: 2,175,333
Posted By HighWind

The software that decide to activate the trim...

The software that decide to activate the trim motors based on AoA might be trivial when analyzed alone.
But a large part of the software is about being able to detect faults, in communication...
3rd Aug 2019, 18:52
Replies: 2,428
Views: 2,175,333
Posted By HighWind

Implementing a flight control system able to...

Implementing a flight control system able to catch all types of runaway will bring B737 in compliance with CS 25.671/25.672.
This will most likely require that the trim ‘relay logic' is implemented...
3rd Aug 2019, 13:18
Replies: 2,428
Views: 2,175,333
Posted By HighWind

I might completely have misunderstood the...

I might completely have misunderstood the description in the Seattle Times.
To me there is a big difference between having two independent systems, not sharing the same ‘state space’, where only one...
3rd Aug 2019, 12:47
Replies: 2,428
Views: 2,175,333
Posted By HighWind

Since the responsibility for preventing a runaway...

Since the responsibility for preventing a runaway is moved from the pilots to a more reliable flight control system (more reliable than the old system), the checklist might disappear?
The question...
3rd Aug 2019, 11:20
Replies: 2,428
Views: 2,175,333
Posted By HighWind

This is a huge task to design from scratch. ...

This is a huge task to design from scratch.
Even moving hardware from a more modern aircraft like B787 to B737, and then adapt the software to handle all the differences in hardware interfaces...
3rd Aug 2019, 10:54
Replies: 2,428
Views: 2,175,333
Posted By HighWind

This problem can be solved with continuous...

This problem can be solved with continuous integration, including automatic testing.
When an issue is detected, it is important to ad an test case for this.
The problem with this is if the...
27th Jul 2019, 20:33
Replies: 2,428
Views: 2,175,333
Posted By HighWind

B737 require that the runaway is handled way...

B737 require that the runaway is handled way before the trim stop is reached, or way before the maximum speed is exceeded.
My understanding of CS 25.671/25.672 is that, either:
- A trim runaway...
25th Jul 2019, 10:24
Replies: 2,428
Views: 2,175,333
Posted By HighWind

Agree. I did consider if I should mention this,...

Agree.
I did consider if I should mention this, but I decided not to mention anything about distribution, sigma, or quartile ..:-)
25th Jul 2019, 08:19
Replies: 2,428
Views: 2,175,333
Posted By HighWind

There is a difference.. VW knew they were...

There is a difference..
VW knew they were breaking the law..
Boeing knew that the B737 is not state of the art, but there is no evidence that Boeing knew that the design was dangerous.

However:...
23rd Jul 2019, 10:08
Replies: 2,428
Views: 2,175,333
Posted By HighWind

Agree.... The questions is what solution they...

Agree....
The questions is what solution they are aiming for.
1) DAL C'ish solution where the aircraft can be brought under control after a runaway. (e.g. via.a new alternate trim motor)
2) DAL A...
23rd Jul 2019, 08:37
Replies: 2,428
Views: 2,175,333
Posted By HighWind

Nowadays the high level flight control is...

Nowadays the high level flight control is designed with tools like SCADE or Matlab/Simulink.
Both tools generate a simple subset of C.
The projects I have been involved in used:
- SCADE / absint...
22nd Jul 2019, 18:14
Replies: 2,428
Views: 2,175,333
Posted By HighWind

https://www.rocelec.com/part/INTINTN80286-12 It...

https://www.rocelec.com/part/INTINTN80286-12
It is still possible to get some of the old CPU’s if they have been used in high numbers in embedded systems. (Some companies specializes in production...
19th Jul 2019, 10:16
Replies: 2,428
Views: 2,175,333
Posted By HighWind

Today it require 50 revolutions trimming end to...

Today it require 50 revolutions trimming end to end, with a gear this is will increase. I.e. it will take longer to restore trim manually.
The trim wheel speed when powered by the motor will also...
18th Jul 2019, 08:49
Replies: 2,428
Views: 2,175,333
Posted By HighWind

No doubt that the operational statistics on the...

No doubt that the operational statistics on the NG prove that this is very unlikely.
My concern is that the system have over achieved in the sense that the low runaway rate is not a result of the...
13th Jul 2019, 10:55
Replies: 2,428
Views: 2,175,333
Posted By HighWind

What is meant by ’Activate the control system’? ...

What is meant by ’Activate the control system’?
Are the system not allowed to perform control based on erroneous sensor data, i.e. have to perform fault insulation? (Logical)
Are the system not...
11th Jul 2019, 08:28
Replies: 2,428
Views: 2,175,333
Posted By HighWind

Certification requirements

Is the current CS 25 paragraph 671 valid for the B737, or are there grandfathering rights?
And how is paragraph 671 to be understood:

Is it required for the manual trim to be functional in the...
3rd Jul 2019, 05:50
Replies: 2,428
Views: 2,175,333
Posted By HighWind

I have had the same thoughts In the area of...

I have had the same thoughts
In the area of industrial automation there are plenty of variable speed ac drives with ‘Safe Torque Off’ conforming to SIL3 (Corresponding to DAL B)
Usually the control...
27th Jun 2019, 05:41
Replies: 2,428
Views: 2,175,333
Posted By HighWind

I had seen this coming.. ...

I had seen this coming..
https://www.pprune.org/10492558-post371.html

This needed computer hardware upgrade might be related to the risks of having a DAL C architecture instead of a DAL A...
25th Jun 2019, 21:49
Replies: 2,428
Views: 2,175,333
Posted By HighWind

CS 25.671Electronics with probability of failure...

CS 25.671Electronics with probability of failure less than 1 x 10-9 per flying hour, must be designed according to DAL Level A. In this forum DAL Level C have been mentioned, this is 10000 times less...
17th Jun 2019, 05:47
Replies: 2,428
Views: 2,175,333
Posted By HighWind

If EASA is interpreting the rules hard, then this...

If EASA is interpreting the rules hard, then this trim assist may need to fulfill DAL-A if the new system can result in a runaway.
Either you have a mechanical solution to handle put of trim...
13th Jun 2019, 05:21
Replies: 2,428
Views: 2,175,333
Posted By HighWind

From Falcon 7X accident report:...

From Falcon 7X accident report: https://www.bea.aero/uploads/tx_elydbrapports/hb-n110525.en_01.pdf

JAR 25.671: Control systems: General

From https://en.wikipedia.org/wiki/DO-178B
Level A,...
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