Re: Terrain-following radar for airliners?

From: (James K. Kuchar)
Organization: Massachusetts Institute of Technology
Date:         02 Sep 93 04:12:59 PDT
References:   1
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In article <airliners.1993.569@ohare.Chicago.COM>, (Peter Lisner) writes:
|> There seem to have been many approach accidents due to the terrain
|> being higher than expected by the pilot. These incidents include
|> running into hills because the wrong VOR was tuned in, or the aircraft 
|> descending more quickly than planned due to distraction from other
|> things going on in the cockpit.

Controlled Flight Into Terrain is the single largest cause of fatalities
worldwide. Overreliance on ATC to provide terrain separation & a lack of
intuitive terrain information on the flight deck are 2 principle problems.

|> I was wondering if civil aircraft designers have ever considered
|> using terrain-following radar like some military aircraft do. 
|> I understand that these point forward as well as down, thus causing
|> the aircraft to pull-up in time if there is an obstruction. Apparently
|> very high-speed fighters can fly safely at very low altitudes using
|> this radar. 
|> Could this technique be applied for airliners as well? Obviously, such
|> a system would have to "cut out" at a certain altitude so that the
|> aircraft could actually land! I'm not a pilot, just an enthusiast, so
|> I'm sure I am ignorant of many important points here. But I would like
|> to hear what others think. 

We've been doing quite a bit of work in this area at MIT. Sundstrand makes the
current Ground Proximity Warning Systems (GPWS) for jets, and are also interested
in new technology as are Boeing and several airlines. Current GPWS looks straight
down using the radar altimeter & extrapolates terrain closure rate to determine
if there's a hazard. The latest GPWS versions are very effective. We think,
though, that there could be some benefit to a more advanced system that uses
knowledge of the 3D topography around the aircraft. Whether it's from an onboard
database or a look-ahead sensor is still an issue. Such a system, though, would
have to be different than military systems since the idea is to stay away from
terrain, not follow it. Impacting short of the runway & flight into precipitous
terrain are 2 areas that need improvement. Of course, things get very complicated
quickly & you don't want to be giving the pilot nuisance alerts, yet you still
want to provide enough time to maneuver & avoid the terrain. Just a brief
overview of what's going on out there. I'd be happy to elaborate if someone's

Jim Kuchar