[SystemSafety] Boeing 787 position flaw

[Bernd Sieker]

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On 15.12.2015 18:08, Martyn Thomas wrote:

> 
> Can anyone on this list explain how this works? Presumably the
> Lat/Long are provided by GPS, so why would one of them be missing
> in a data packet that contains the other? And why would the
> transponder software have been designed to handle such an
> occurrence and to extrapolate the missing value, rather than
> rejecting the packet and requesting another?

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. So it does not use the
single lat or long value from the malformed 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.


> 
> Martyn


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