[Flightgear-devel] randomized ceiling

[John D. <sf...@av...>]

Hi --

I just added a feature to the _Sport Model_.

This has been on my wish list for a long, long time.  I
implemented it this morning, and I've been having quite
a lot of fun trying it out.

Here's the scenario:  Suppose you are on an instrument
approach.  You know the weather is marginal, but you
can't be sure whether it is slightly above minimums
or slightly below.

This motivates you to
  a) Fly the approach very precisely, because if you're
   even a little bit off, you won't be able to land, and
  b) Be prepared for the miss.  Remember, if you're not
   prepared for the miss, you're not prepared for the
   approach.

It's hard to simulate that scenario in a self-instruction
simulator situation ... unless there is some randomization.
So that's what I did.

     In the clouds popup, there is a new "Plus/Minus" field that the
     pilot can use to create a ceiling with some uncertainty.  If the
     Plus/Minus field is set to x, the cloud base is perturbed by a
     random amount uniformly distributed on the interval [-x, x].
     The randomness is applied when you hit the Apply button or the
     OK button;  there is no time-dependence.

     Screen shot:
       http://www.av8n.com/fly/fgfs/random-ceiling.jpg

     IFR checkride standards call for maintaining the MDA plus 50,
     minus 0 feet.  So, we say there is a band from MDA-0 to MDA+50 for
     maneuvering in.  Therefore, in preparation for a non-precision
     approach, it makes sense to set the nominal cloud base field (on
     the Clouds popup) to MDA+50 and set the Plus/Minus field to 100 or
     thereabouts.  That way there will be a 50% chance of having clouds
     intruding below the top of the allowed maneuvering band, and a 25%
     chance that clouds extend even below the MDA.  You'll never know
     whether the approach will terminate in a landing or in a miss.
     This is very good practice for real-world IFR operations.

     Similar ideas apply to precision approaches.  Set the nominal
     cloud base to DH+50 and set the Plus/Minus field to 100 or
     therabouts.

     After landing, it pays to check the Clouds popup again.  If there
     is an overcast cloud base below the MDA, you shouldn't have
     landed.

There are more than a few folks who think this sort of feature (and
the similar features in gremlins.nas) are the greatest part of the
raison d'etre of simulators.
  -- You can practice more cheaply than in a real aircraft;
  -- You can practice almost as well; and
  -- In some ways you can practice better, because there are some
   emergency situations that you would like to practice, but can't
   be safely practiced in the real aircraft.




For details on how to get yourself a copy of the sport model, see
    http://www.mail-archive.com/fli...@li.../msg11530.html