Posts by user "EXDAC" [Posts: 27 Total up-votes: 55 Pages: 2]

How can an MCP ALT setting error explain the sequence seen in the videos? If the MCP ALT is set too low the aircraft levels off, reduces thrust to maintain set speed, - AND MAINTAINS MCP ALTITUDE. Sure it will get the crew's attention but it will not result in a uncontrolled descent.

I am familiar with that having worked on HUD development. However, what FD/GC mode would be be active that would command a descent after an altitude capture from below? I would expect FD and GC to be in ALT HOLD mode. I don't know the 787 but I would have expected GC to command ALT HOLD until low speed protection activated if thrust had been lost.

If thrust was lost the aircraft is coming down regardless of MCP ALT or GC command.

Exactly like the action of lifting the flap lever out of detent before moving it. What is significantly different is that you would have to do it twice. It is that which makes it improbable unless intentional.

787 MLG swing here -

The independent ADS-B Exchange receiver(s) didn't pick up the signal at all during the departure.

The caption seems to be in conflict with the video sequence. The caption, which may be all that is read/viewed, should be "bogies tilt, doors open, gear retracts.

But as previously posted a recorder is only as good as the systems that provide the data to it. If those systems, or some of those systems, are not powered the data is simply not available to be recorded. You need the DFDAU (or equivalent) to be powered and you need the systems that feed data to the DFDAU (or equivalent) to be powered and operational.

Edit to add - RIPS will likely maintain CVR function.

DO-178 unless propulsion systems are for some reason different from displays and flight controls.

I have been on the fringes of dissimilar hardware and dissimilar software designs (MD-11 flight controls). Sometimes it is necessary but there is a huge overhead in both development and test.

Edit to add - Even with dissimilar processor and software the requirements for both will trace up to some common high level system requirements specification. There is a non zero probability that those top level requirement were inadequate or included an error.

DO-178 unless propulsion systems are for some reason different from displays and flight controls.

I have been on the fringes of dissimilar hardware and dissimilar software designs (MD-11 flight controls). Sometimes it is necessary but there is a huge overhead in both development and test.

Edit to add - Even with dissimilar processor and software the requirements for both will trace up to some common high level system requirements specification. There is a non zero probability that those top level requirement were inadequate or included an error.

Well, I was looking at the drawings of the MD-11 thrust control module and there certainly are two sensors on each thrust lever. The sensors are implemented as a dual resolver on a common shaft. This level of redundancy is well understood by those who specify, design, test, and certify critical aircraft systems.

Edit - tdracer posted as I was typing. It seems 787 has even greater sensor separation.

That is certainly typical. The FADEC/EEC/ECU includes the resolver angles in its output data for consumption by other systems such as displays and flight controls.

How would the thrust lever idle condition have been satisfied?

In the CSV data set that can be downloaded from that link the first point with altitude data is 1630 ft short of the departure threshold. That point is 575. The highest alt recorded in the data set is 625. All the points with altitude data overlay the departure runway. I do not understand how anyone is using this data set to determine the maximum altitude which was way past the departure end.




Edit to add - I have made no attempt to correct the raw ADS-B altitude data. There is no need to make any correction to see altitude gain.

There seems to be an assumption that, if corrected for local altimeter, the lines all move down toward the runway as a set.

Wouldn't that only be true if the altimeter setting was the same on all the days those flights were made? Isn't that improbable?

I am not convinced that the FR24 graphic shows that.

The FR24 data shows that, for the accident flight, the first data point received on takeoff was one that included altitude. We know where the aircraft was and we know the uncorrected baro altitude at that point.

We do not know how the altitude of that first point compares to the altitude of the reference flights unless all flights have their altitude adjusted by the prevailing altimeter correction.

Each trace starts in about the same place over the runway but this may not be useful data. I don't think this is the ADS-B ground/air transition. I think it is the point at which reception of ADS-B data becomes possible because of transmission "line of sight". We don't know if data starts being received as a result of increased altitude or because of passing by whatever was blocking the signal.

I'm sure someone could research the altimeter setting for each of the reference flight and produce a corrected data set. That would be interesting and useful data.

That's just my interpretation of the data I have seen. It is not presented as fact.

Perhaps a necessary but not sufficient condition.

Some critical systems are designed with processing "lanes" having dissimilar processors as well as dissimilar code. Each lane is developed from separate requirements that trace up to one high level system requirements specification. If that high level specification has errors the errors flow into all the independent lanes of processing.

Testing may not find such errors since the system works as specified.

The issue with 5G was the potential for interference with some models of radio altimeter. I think we have been told that RA is used in 787 air/ground logic. We have also been told that air/ground state is used to enable TCMA.

I think it very unlikely that 5G interference was a contributing factor but I can see why someone would be interested in asking the question.

The last report received from ADS-B out is 625 ft but, at that point, the aircraft is still over the runway. The video shows the aircraft continued to climb after passing the departure end.

There is no conflict. Simply a lack of ADS-B data.

Edit - Add the ADS-B data points graphic that I had posted June 17.

Are you asserting that "the system would simply ignore a cutoff command with thrust levers above idle" is a nonsense statement?
or
Are you asserting that "the system would simply ignore a cutoff command with thrust levers above idle" is a description of how the system behaves?

Ok, thanks. I wanted to be sure what you intended before I told you it was nonsense.