Re: [SystemSafety] Boeing 787 position flaw

From: Peter Bernard Ladkin < >
Date: Wed, 16 Dec 2015 09:58:36 +0100

Hash: SHA256

On 2015-12-16 01:31 , paul_e.bennett_at_xxxxxx

> On 15/12/2015 at 11:51 PM, "Bernd Sieker" <sieker_at_xxxxxx

>> On 15.12.2015 18:08, Martyn Thomas wrote:
>>> Can anyone on this list explain how this works? ....

>> My understanding is that the transponder does reject the malformed packet and goes into
>> dead-reckoning mode, extrapolating the course from previously received well-formed
>> packets......
>> This behaviour seems reasonable to deal with an occasional single packet garbled in
>> transmission.
>> In effect, the airplane would send position reports as if it were continuing straight on
>> instead of making the planned turn at the waypoint.
> In which case there should be a limit to the number of estimated positions it made. Even
> including a marker that states the position is estimated would be a help.

One issue is how airplane systems handle undefined cases. Another issue is the air-ground communication protocols. A third is how the ground-based systems handle the data. There is plenty of scope there for system-local requirements that do not globally cohere.

I am guessing that no one involved with the specifications thought about end-to-end data validation in this specific case, and appropriate requirements got somehow missed out. Such has happened with other air-ground data transmission protocols.

End-to-end data validation issues are all over lots of critical systems. It's a routine undergraduate topic in most computer science curricula (in the simple form of parity bits and Hamming codes), but most of the people putting these protocols and systems together are not so trained.

However, there is a lot more detail in the specifications of data packets and their handling than I feel inclined to wade through. So I have a query out.

PBL Prof. Peter Bernard Ladkin, Faculty of Technology, University of Bielefeld, 33594 Bielefeld, Germany Je suis Charlie
Tel+msg +49 (0)521 880 7319

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