[Flightgear-devel] EGPWS issues (mk-viii module)

[Thorsten <br...@go...>]

Hi,

I've been working on some smaller issues with the Ground Proximity
Warning System. Is someone currently maintaining or actively working
on the mk-viii module, or is any help wanted?

* The "Bank angle!" warning wasn't working. It's because the module
reads the planes angle from
    /instrumentation/attitude-indicator/indicated-roll-deg
However, with the planes I have tested (B737, B747, B777, A380) this
value is never updated (value is constant at 40 degrees). This
sometimes triggers an incorrect "Bank angle!" warning (at lower
heights, where 40 degrees is outside the allowed range). Changing the
input property to
    /orientation/roll-deg
made the feature work for me. I'm not familiar with this attitude
indicator. Is anything broken so the property above isn't updated? Or
could we just change the module's input property? Alternatively, a
configuration property could be added, so the location of the input
property isn't hard-wired in the sources and could be configured for
every plane...

* The "Too low - flaps!" and "Too low - gear!" warnings are issued too
late. The planes I have tested did not select appropriate mk-viii
configuration modes. The default mode only matches small/light
aircraft. Issuing warnings only when below 150ft agl and below 148
knots (with no flaps and no gear!) certainly seems a little late for
an A380/B747 ;-) . Unfortunately, the manuals (see
http://wiki.flightgear.org/index.php/Ground_proximity_warning_system
and http://www.mail-archive.com/fli...@li.../msg01902/mk-viii-manual.tgz
) do not document the available configuration modes, e.g. for the
different supported aircraft types. You can only see them in the
sources - but documentation is also missing there. Maybe this explains
why few (maybe none) of the planes properly configure it... ;-)

* It's (almost) impossible to avoid "Glide slope! Glide slope!" call
outs in the last few moments before touchdown. The instruments also
show the glide slope is lost just before touchdown. I guess it's
because there is no ILS once the plane is beyond the transmitter and
above the runway. So it's probably better if the EGPWS suppressed
glide slope warnings in the very final moments.

* With larger aircraft only the height call outs down to "20" feet are
triggered, the "10" feet call out is never issued. This seems to be a
problem with the radio altimeter in general. The plane's gear already
touches the ground before the radio altimeter is at 10ft agl. The
steeper the plane's angle of attack - the sooner its gear touches
ground... And it's not just a problem with the plane's angle. For some
planes the radio altimeter shows heights of 2-10ft even when taxiing.
According to http://www.pacificavionics.com/viewPage.php?pgID=84 :
"A properly calibrated radio altimeter indicates zero feet at the
moment the aircraft contacts ground. This requires taking into account
the height of the antennas above ground (at touchdown) [...] After
touchdown, the weight of the aircraft may cause the radio altimeter to
read slightly below ground level".
So I guess the radio altimeter isn't perfectly accurate right now - or
are there already configuration settings to tune/adapt the altimeter
to a specific plane? Maybe that's where the problem is...

If you want to test the mk-viii warnings yourself, you'll need the
latest GIT and probably also two additional patches from the bug
tracker (issues #98, #139).

Thorsten