80 SA Flyer Magazine
WORDS:
CHRIS
MARTINUS
In its presentations in New
Zealand to general aviation
delegates from around
the world, ICAO indicated
that it places great faith
in ADS-B and PBN. Last
month we took a look at
ADS-B, so an overview of
PBN should position us to
assess how these standards
may be of benet to non-
commercial aviation.
P
BN (Performance Based
Navigation) is not a
new technology. It is
simply a different way of
looking at standardising
and developing
aerial navigation systems. In the past,
navigational standards were technology-
driven. Old technologies like ADF were
developed during World War II, and
the VOR, DME and ILS systems that
superseded them similarly caused the
evolution of standards and procedures to be
followed by pilots and air trafc controllers
(ATC). Those procedures revolved around
how to use those specic technologies.
These ground-based beacons which
form the basis of ADF and VOR navigation
required considerable maintenance and
associated costs. In South Africa, most
NDBs and VORs have been, or are in the
process of being, decommissioned. The
few remaining are in the vicinity of major
airports.
PBN instead denes navigational
standards and procedures not by the
underlying technologies, but by the
requirements or ‘performance’ needed to
achieve those standards. Hence the name
‘performance-based’ navigation.
SATELLITE NAVIGATION
The use of satellite-based systems
such as GPS, GLONASS and Galileo have
revolutionised all forms of navigation. Not
only are satellite systems far more accurate
than ground-based systems, but they also
cover the entire globe and thus have far
greater coverage.
But, there are some even more
compelling reasons why satellite navigation
has been widely adopted. Although the
cost of launching a satellite into orbit is
substantial, there are other more massive
cost savings.
Barring the very low risk of the satellite
being stuck by high-velocity space debris,
implementers of space-based navigation
systems can expect a very long service life
from their equipment. Although it needs
some shielding from cosmic radiation, a
AOPA BRIEFING AIRCRAFT OWNERS & PILOTS ASSOCIATION – SOUTH AFRICA
PBN
GETTING NAVIGATION
OFF THE GROUND
Satellite-based navigation is more
accurate than ground-based systems,
and provides worldwide coverage.
81 SA Flyer Magazine
satellite is not subjected to the vagaries
of weather and corrosion. Furthermore,
satellites are not subject to tampering
or theft, a problem with ground-based
beacons in South Africa.
Perhaps the biggest appeal for satellite
designers is that the systems can be
powered entirely by solar energy, with little
or no need for batteries or other energy
storage. The sun shines all day in space,
with very short periods (if any) during which
the solar panels are eclipsed by the Earth’s
shadow, and solar photovoltaic panels
have a service life of over 25 years. Since
the sky is in line-of-sight with the ground,
global coverage is possible with a small
constellation of satellites utilising very low-
power radio transmitters.
RNAV AND RNP
The acronym ‘PBN’ gives rise to many
other complicated acronyms. The most
important of these are RNAV and RNP,
which deal with concepts which are largely
unfamiliar to the average private pilot
who mostly ies VFR, in other words with
reference to visible features on the ground
– no doubt assisted by a hand-held or
in-panel GPS.
RNAV is a rather stilted acronym for
‘area navigation’ or ‘random navigation’.
Also not something new, RNAV was
developed in the 1960s to allow IFR ights
to y direct to their destinations, rather than
zig-zagging from one ground-based beacon
to the next.
Of course, VFR pilots are not reliant
on ground-based beacons and can usually
identify visual waypoints along a direct
route – with a little help from the now
ubiquitous GPS. The IFR pilot does not
have this luxury of visual reference, so the
routes would be dened by NDBs or VORs
on the ground.
Although RNAV that was based on
ground stations was developed and
implemented long ago, the FAA revoked
all RNAV routes in the United States when
it realised that most airlines were using
inertial navigation systems instead of
the ground beacons to y direct to their
destinations. Inertial navigation requires
regular corrections from other navigational
sources and is therefore insufcient as a
sole navigational aid. Sufcient accuracy
and reliability of navigational data is
essential for safe reliance on instruments,
which brings us to RNP.
RNP
RNP stands for ‘required navigation
performance’. This is a cornerstone of
PBN and species the necessary accuracy
and reliability for the implementation of
many PBN procedures. The prescribed
repeatability of RNP may rely on multiple
navigational aids, including monitoring
by the pilot, and by ATC radar monitoring
and alerting, to achieve the requirements
to y a specic procedure or route within
a 3D airspace. This provides the basis for
precise procedures necessary for today’s
increasingly congested airspaces and for
curved three-dimensional routes through
inhospitable terrain and noise-sensitive
areas.
RNP accuracy is generally dened by a
simple number. For example, RNP 10 would
mean that the on-board system would
provide navigation within the connes of 10
square nautical miles with 95% accuracy.
An RNP 0.1 specication would require
navigational accuracy in a 1/10th nautical
mile (185 metres) square.
Satellite navigation is now the
technology that underpins PBN, and its
accuracy, reliability and redundancy have
made ground-based navaids obsolete.
THE QUEENSTOWN APPROACH
IAOPA delegates were treated to
a fascinating presentation by Air New
Zealand’s Captain Graham Cheal of how
the RNP 0.15 approach into Queenstown,
New Zealand was developed.
Due to the very rugged terrain, high
mountains and curved valleys on the
approaches to this airport, there were
some very special challenges. Not least
of these is that due to multipath and other
interference with satellite signals caused by
the surrounding mountains, and the lack of
ground-based GPS enhancement systems,
the accuracy of GPS signals can drift by
as much as 100 metres to each side of the
runway. This would necessitate that during
the RNP approach, the pilot would have
to switch from following the ight director
displayed on the head-up display (HUD) to
visually focusing on the runway threshold
for the last portion of the approach.
In practice, during the testing of the
approach, this didn’t work well. The pilots
would inexplicably be unable to visually
remain on the runway centreline, despite
them being adamant that they were not
looking at the HUD.
This resulted in a research effort of
tracking the pilots’ eye movements to
determine why they were having trouble
ying a simple visual approach. The
research discovered that the pilots would
subconsciously remain ‘locked on’ to
the ight director, which was displaying
inaccurate information.
Since Airbus’s procedures didn’t allow
for switching off the ight director, the only
solution was for intensive training, where
the captain would ‘over-learn’ the visual
runway intercept and the rst ofcer would
be trained separately to monitor the ight
director and be empowered to call a go-
around. Only after that exercise would the
AOPA BRIEFING AIRCRAFT OWNERS & PILOTS ASSOCIATION – SOUTH AFRICA COLUMNS
Performance Based Navigation (PBN), especially RNP routes, allows for curved
paths to be flown between waypoints.
82 SA Flyer Magazine
crew be trained together as a team.
The presentation highlighted some of
the technological and human factors which
still detract from PBN offering clear and
simple solutions.
BENEFITS FOR GENERAL AVIATION
The benets of standards like PBN and
ADS-B for general aviation are largely that
tighter procedures and more direct routing
for commercial ights operating under IFR
should open more VFR airspace for private
aviation. PBN, and the more sophisticated
equipment that comes with it, should also
relieve IF pilots from some of the more
onerous workload of instrument ying, thus
also enhancing safety of operations.
However, we are not holding our
collective breath. Commercial operators
are not keen to give up airspace and tend
to be determined to gobble up more and
more. The costs of certied equipment
for instrument operations are also likely to
remain prohibitive.
ICAO’S MOTIVATION
Although PBN was largely developed
for internationally harmonious procedures
for airline operations, the motivation for
placing emphasis on these standards
stems mostly from the alarming growth in
the numbers of unmanned aircraft crowding
into the skies.
PBN and ADS-B are seen to be ready-
made solutions to the wide incompatibilities
that still exist between drones, pilotless
passenger aircraft and conventional
manned aircraft operations.
However, this seems optimistic, and
there will undoubtedly need to be some
clearer objectives and technological
developments and standards to underpin
PBN in mixed manned/unmanned
operations.
These ICAO standards also don’t begin
to address the incompatibilities between
pilotless aircraft operating in harmony with
the traditional stick-n-rudder VFR pilots
who use visual separation for collision
avoidance in uncontrolled airspaces.
AOPA BRIEFING AIRCRAFT OWNERS & PILOTS ASSOCIATION – SOUTH AFRICA
Switch Board: +27 12 543 3196 • +27 12 543 0106 • Lande Milne 066 472 7848 • Facsimile: +27 12 543 2323
Email: L.milne@venture-sa.co.za • Hangar 49, Wonderboom Airport, Lintvelt Road, Doornpoort, Pretoria
2 X D1000 Dynon Sky View Touch 10” Display, EMS 220
Full Engine Monitoring System with Fuel Flow,
2 X Dual Back up Batteries with 1 hour endurance. Dual
ADHRS installed Dynon Auto Pilot, Dynon GPS 250
and Dynon Mode S Transponder, Garmin GTR 200 VHF
Radio, PMA8000BT Audio Panel. AVEO Eye Beam Touch
Cabin Lights and LED NAV/STROBE Lights
A fresh approach to Aircraft
refurbishing in South Africa
WE DO ALL INTERIOR REFURBISHMENTS
ON ALL AIRCRAFT & ROTORCRAFT
RV14A FOR SALE
NOW IMMEDIATELY AVAILABLE AT
R2.5 MILLION EX VAT
SA Flyer 2018|04
j
Queenstown IMC approach - the runway lies somewhere beneath those
clouds in the valley. Having accurate navigational equipment is essential.
Heads Up Display was complicating
the final approach into Queenstown
due to GPS signal interference.
Chris Martinus
