Does more accurate navigation increase probability of accidents?

George Clark writes: … A recent posting in the Risks Digest suggests that there is a risk from the more accurate navigation delivered by modern avionics. The original source, along with comments is found at Blog posting by Harvard's Philip Greenspun that discusses this in the context of the Brazilian airliner crash.

You can read the original or click the "read more" link where I've reproduced the posting in it's entirety. I've also included a poll to get your opinions on the matter. This is a new variation on the questions - Should you fly +/- 50' off-altitude? and Should you really dead-center the needle crossing a VOR?

(Not mentioned on this blog, Philip Greenspun is a pilot and flight instructor at BED and owns a SR-20. He has another blog entry about the NYC Cirus crash and points out this table of airspeed and bank angle vs. turn radius

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The original article is reproduced here under the Creative Commons

The recent mid-air collision in Brazil of a new regional airliner (fitted out for use as a business jet) and a Boeing 737 has people baffled. How could two brand-new airplanes with advanced avionics, flown by two professional pilots in each plane, collide at 37,000′? The precision of modern avionics may well have contributed to this collision.

Airplanes under instrument flight rules fly from one navigation beacon to another along published standard routes. In the old days, with radio navigation receivers and pilots flying by hand, a plane wouldn’t fly its clearance exactly. The airways include a tolerance for error of +/- 4 miles. If you’re 4 miles to the right of course, in other words, you’re still legal and safe from hitting mountains or other obstacles. Altitude was similarly sloppy. If you reached for a drink of coffee or to look at a chart, you might drift up or down 200′. Air traffic control wouldn’t get upset.

How does it work now that the computer age has finally reached aviation? The GPS receiver computes an exact great circle route from navaid to navaid. All GPS receivers run from the same database of latitude/longitude coordinates, so they all have the same idea of where the Manchester, New Hampshire VOR is, for example. The autopilot in the plane will hold the airplane to within about 30′ of the centerline of the airway and to perhaps 20′ in altitude. If two planes in opposite directions are mistakenly cleared to fly on the same airway at the same altitude, a collision now becomes inevitable.

Almost any other system would be safer. If you sent airplanes up to fly in random point-to-point paths, e.g., from Boston to Denver, they’d be less likely to encounter one another. If you kept the airway system, but introduced some extra logic into the avionics so that planes always flew 1 mile to the right of an airway and + or - 200′ in altitude, they’d be less likely to encounter one another. If you replaced the precise autopilots with imprecise humans, planes would be less likely to encounter one another. If you replaced the high-precision GPS receivers with low-precision VOR receivers, planes would be less likely to encounter one another.

What's your opinion?

%VOTE{id="NavigationAccuracy" select1="Does greater accuracy increase the risk of accidents?" options1="Yes,Maybe,Sometimes,Never" select2="Shoud enroute navigation systems introduce slight artificial errors" options2="Good Idea,Maybe,Never,Are you crazy?"}%

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-- GeorgeClark - 21 Oct 2006