Fun_People Archive
21 Apr
The software that worked too well

Date: Thu, 21 Apr 94 12:07:54 PDT
To: Fun_People
Subject: The software that worked too well

Forwarded-by: cate3@netcom.com (Henry Cate)
From: ???

SeaTac is the main Seattle-area airport.  Ordinarily aircraft landings
are from the north, and this end of the runway is equipped with all the
sensing equipment necessary to do ALS (Automatic Landing System)
approaches.

The early 747 ALS worked beautifully, and the first of these
multi-hundred ton aircraft set down exactly at the spot in the center
of the runway that the ALS was heading for.  The second 747 set down
there.  The third 747 landed on this part of the runway. ... As did
all the others.

After a while, SeaTac personnel noticed that the concrete at this point
at the north end of the ALS runway was breaking up under the repeated
impact of 747 landings.  So the sofware was modified so that 3 miles
out on the approach, a random number generator is consulted to choose
a landing spot -- a little long, a little short, a little to the left,
or a little to the right.

   THE MORAL:
   Don't assume you understand the universe without actually experimenting.

© 1994 Peter Langston