82 SA Flyer Magazine

WORDS:

CHRIS

MARTINUS

Several years ago,

there was considerable

excitement when ATNS

told us about ADS-B

(Automatic Dependent

Surveillance-Broadcast) and

PBN (Performance Based

Navigation). Is it going to

meet expectations?

T

HESE ‘modern’ schemes

are facilitated by satellite

navigation systems like

GPS, GLONASS, Galileo

and Compass, which,

together with a ground-

based augmentation system, promised

low-cost Global Navigation Satellite System

(GNSS) IFR approaches at small airelds

and the freeing up of airspace due to tighter

and more direct navigation – which would

also have the benet of lower fuel burn and

shorter commercial ights.

It became attractive for private pilots to

consider putting in the effort and expense

to obtain and maintain IF ratings, since this

would dramatically enhance the utility of

their aircraft. The CAA also embarked on

developing a new and simplied IF rating.

Things looked rosy indeed. Furthermore,

with ‘ADS-B In’ equipment installed in light

aircraft, with the prospect of having trafc

information and weather displayed, general

aviation would see a new era of innovation

and development.

Before GPS, both commercial and

general aviation were largely dependent

on ground-based navigational aids such as

NDB, VOR and ILS. Collision avoidance

relied entirely upon the naked eye and, in

proximity to major centres, ATC (air trafc

controllers) who possibly had radar to

monitor trafc in their areas.

ATNS then embarked upon

decommissioning dozens of NDBs and

VORs, many of which were unserviceable

anyway. But the promised cheap GNSS

approaches did not materialise and

there are only declarations of intent from

CAA and ATNS to require ‘ADS-B Out’

equipment to be made mandatory for

aircraft operated under IFR or in controlled

airspace by 2020. This equipment would

simply be Mode S transponders which are

capable of broadcasting on 1090ES.

STANDARDS AND TECHNOLOGIES

ADS-B and PBN are not really

technologies themselves, but are standards

which have a ‘layered’ approach, much

like the Internet standards which were

developed in the early 1970s. Instead of

standards being based upon technologies,

ADS-B and PBN are objective based.

PBN is ‘performance based’, meaning that

the standard hinges on the accuracy and

performance required, rather than the older

bottom-up approach of the standards being

dened by technologies like ADF and VOR.

The technological layers upon which these

more modern standards rest may then be

developed, changed or otherwise altered

without changing the standards themselves.

The internet owes its success to the big

picture approach, where user applications

are dened as the top layer, regardless

of whether the data itself is delivered by

a physical layer of bre cables, Wi-Fi,

ADS-B ... OR NOT TO BE

AOPA BRIEFING AIRCRAFT OWNERS & PILOTS ASSOCIATION – SOUTH AFRICA

How ADS-B works compared to radar.

Airways