The major problems which faced the 1958 meeting were those created by
the expected massive appearance of civil jet aircraft in commercial air
transport and the continuous increase of air-tourism during the summer
period of each year (end of May to end of September) and the gradual
extension of this type of traffic to States located in the Eastern part
of the EUR Region.
However, in order to reap the full benefits of this improved upper ATS
route network, it was believed that this required also a more effective
organisation of the air traffic control services serving this upper
airspace. One of the main aspects in this respect was the sub-division
of the European airspace into areas of responsibility of specific ATC
units (flights information regions (FIR) and associated control areas
(CTA)) and, within these, specific controllers. The size of such sectors
was normally determined by the maximum number of aircraft which were
likely to be simultaneously present in the sector and which could still
be handled safely by one man. Passing through different sectors involved
for pilots also a change of frequency in the available VHF channels
because each controller required an interference-free direct means of
communication with the aircraft under his control.
With the increased speeds of jet-aircraft, it became apparent that, in
many cases, the time spent within one sector, or even within a whole
CTA, as established for the lower airspace, would not permit the
controller, or even an ACC, to do more but noting the entry and, a few
minutes later, the leaving of the area by the aircraft concerned. This
is turn resulted in an appreciable workload-for the pilot because of the
numerous calls and frequency changes which he had to make if this
situation persisted on an appreciable portion of his flight. In fact, it
was found that, if the lower airspace organisation was retained for jet
aircraft, pilots on a 250 nautical mile flight could, in certain cases,
be required to make up to 30 calls and change frequencies up to 15
times.
It was for this reason that the idea was born to create a special upper
airspace structure consisting of a number of large upper FIRs and
associated CTAs which would be served by a reduced number of upper area
control centres (UCA), whereby the boundaries of these upper FIRs (UIR)
should not be determined by political boundaries but rather by
operational and technical considerations. To overcome the inevitable
political and juridical problems, it was believed that this could best
be achieved by the creation of an international executive organisation
to which all those States wishing to participate in this venture would
be parties. A project along these lines, started in 1959, culminated in
1963 in the creation of Eurocontrol. Needless to say that throughout its
development, the Paris Office of ICAO was participating in this work
and rendering any assistance it could.
Already during World War II responsive radar aboard aircraft had been
developed which permitted personnel on the ground to differentiate
between own and hostile aircraft. Improvement work on this equipment had
continued in the civil and military fields and had resulted in
world-wide ICAO standards of such a system for civil use under the name
of "Secondary Surveillance Radar" (SSR). It envisaged that an aircraft
could be assigned a specific code that would appear on the radar screen
beside the target representing the aircraft in question, thus
facilitating its identification. In a more refined version it was also
possible to obtain information on the altitude of the aircraft concerned
and, when used in conjunction with automatic data processing equipment
on the ground, the aircraft code could even be replaced by its flight
number or call-sign, thus avoiding the tedious mental conversion process
by the controller from a code to the name of the flight.
However, since SSR was a co-operative system (i.e. one which not only
required facilities on the ground but also corresponding equipment
on-board each aircraft participating in the system) it was necessary to
co-ordinate its implementation not only between States but also with the
operators of airlines likely to be affected by its use, especially when
this was intended to be made mandatory in specific areas.
Again a limited RAN Meeting was held in Paris in 1962 on this specific
subject and it was possible to develop the required technical and
procedural measures for the use of SSR in the EUR Region, together with a
staged implementation plan.
As to the use of automatic data processing by ATC, work on this subject
had been going on in ICAO since 1958. Progress in sophistication and
miniaturisation of electronic data processing equipment and a related
reduction in cost had made it possible to the industry to produce
equipment which was also of interest to ATC where appreciable amounts of
data on flights had to be accepted (in the form of flight plans,
position reports etc), recorded and processed in order to exercise the
required control functions. The increase in traffic and the increase in
speed of jet aircraft, with consequent faster control action, appeared
to make "automation" a "must" to ATC. However, to use it on an
international scale, with the need for equipment of adjacent ATC units
to correspond with each other, raised immediately not only the problem
of which equipment to use but also that of compatibility between
equipment of different manufacturers. The latter aspect was particularly
relevant because the costs of such equipment were (and are) still such
that any manufacturer was greatly interested to obtain the order for
such a system from his home administration. Therefore, the decision to
procure such a system could not only be based on purely technical and
operational considerations but had an eminent political touch to it.
Therefore, while work on compatibility regarding formats and message
conventions proceeded on a world-wide scale in ICAO, the Paris Office
was more involved with the development of a realistic implementation
programme of ATC automation in Europe which could only be realised
step-by-step over an extended period of time and which also had to take
account of the side-by-side existence of "automated" and "non-automated"
ATC facilities for many years to come. In this respect, it was
particularly important that "non-automated" ATC units were not faced
with an inordinate high workload, or specific supplementary procedures,
simply because they were required to co-operate with an ATC unit which
used already automatic processes.
The increasing presence of civil aircraft at and above 6000m or 20000
feet had also raised some problems in the field of altimetry. One of
these was the inevitable mixture with military flights and the other the
question of vertical separation. It was realised that the continued use
of QNH as the altitude reference was unsatisfactory because of the
frequent changes of the altimeter setting onboard aircraft and
transition problems at the boundaries of designated QNH areas between
aircraft operating at adjacent levels but in opposite directions. The
other was related to the fact that the decrease in atmospheric pressure,
especially at higher levels, does not occur in linear form but along a
curve, i.e. the difference in pressure corresponding to given interval
in altitude is much smaller at high levels and the inaccuracies,
inherent in the systems used to measure altitude in aircraft are
therefore more significant and could reduce dangerously the vertical
distance between aircraft flying at adjacent levels.
ICAO had therefore developed a new system of altimetry for use during
the en-route portion of flights which was based on the use of a standard
setting of 1013.2 hectopascals which, when used by all aircraft, served
as a world-wide standard reference datum and required no re-setting of
the altimeter, except for take-off and landing. The altitude indication
thus obtained in the aircraft was called "flight-level" (FL) and it
ensured that, regardless of changes in atmospheric conditions, two
aircraft operating at adjacent flight levels always maintained the same
vertical distance between them. This system also had the advantage that,
where altitude information was automatically transmitted to the ground
via secondary surveillance radar (SSR, Mode C) no conversion of such
data on the ground was required.. To compensate for the atmospheric
"inadequacies" described above, it was also agreed that the standard
vertical separation between controlled aircraft operating at adjacent
flight levels should be increased from 300m (1000 feet) to 600m (2000
feet) for flights above 8850m (29000 feet). If confusion was to be
avoided, the introduction of these two measures could only be done on at
least a regional basis and this for both, civil and military operators
in the whole of the European-Mediterranean Region extending from the
USSR to the edge of the North Atlantic and from Norway to the North
African coast. Thus the Paris Office became the focal point of
co-ordination of this important change to the air navigation system.
NAT Region
Traffic in the North Atlantic Region not only increased
continuously but the introduction, by the early Sixties, of four engines
jet-aircraft into NAT operations created also new problems, both-in the
air and on the ground. In the air, the use of jet-aircraft not only
brought a linear increase in traffic but, because of the reduction of
the flying time by half and the existing time difference between Europe
and North America, a crowding of traffic in both directions into that
comparatively small band of hours which permitted the scheduling of
flights so that reasonable departure and arrival times could be
maintained for passengers.
The first consequence was that, in 1959, a meeting was
held in Paris to review the fixed service situation in the North
Atlantic and to agree on those improvements which were required to allow
for a rapid flow of information (including new meteorological data on
the higher levers of the atmosphere) between all parties concerned. In
1961 the Fourth Regional Air Navigation Meeting for the NAT Region was
held in Paris and the entire NAT Regional Plan was reviewed and updated
so that it was capable of meeting expected demands within the
foreseeable future.
By 1965, it was however found that traffic developments
in the North Atlantic had gained such a momentum that a further special
meeting would be required, dealing with communications and air traffic
services. In this meeting, States agreed that, with existing and
expected problems in this vital area, it would be necessary to adopt a
systems planning approach to the Region as a whole and that such
planning should be a continuing process. To this end, the major provider
States formed the permanent North Atlantic Systems Planning Group
(NAT/SPG) and the Paris Office was charged with providing all necessary
assistance to this Group to permit its proper functioning. This Group
has met at about yearly intervals ever since and has become the central
planning body for the NAT Region.
As to the operational situation, air traffic across the
North Atlantic continued to increase at a considerable growth rate and
the number of operators flying this route also increased as more
large-size jet aircraft were brought into operation. The result was
that, during the preferred times, congestion problems arose which meant
that a number of flights either were delayed on departure if they
insisted on a slot within the comparatively small favourable flight
track or they had to accept flight paths which, vertically or
horizontally or both, were situated far away from the calculated
"minimum time track", with the inherent economic consequences.
It was therefore felt that, to improve the situation, two measures were required, one organizational, the other technical:
3. to obtain reliable information on the expected
development of air traffic within this important air traffic area, so as
to be able to prepare operationally meaningful traffic forecast over at
least the next 5 years; and
4.
to develop measures, primarily in the fields of air traffic
services and communications which, when applied, would improve the
traffic handling capacity of the air navigation system so that it was
capable of coping with the demands imposed on it. As regards traffic
forecasting, it was agreed that Canada, the United Kingdom and the USA
were to form a group which should prepare a North Atlantic Traffic
Forecast at yearly intervals, based on economic as well as operational
data and related to the major traffic generating areas on both sides of
the Atlantic and resultant likely routes to be flown. Necessary
secretarial and administrative assistance to this group was to be
provided by the Paris Office, which was also charged with the
publication and distribution of the yearly forecast to all parties
concerned.
With respect to practical improvements it was expected that
any organizational or technical changes would require comparatively
long lead times because most of these required joint action by the six
States (Canada, Iceland, Ireland, Portugal, the United Kingdom and the
USA) sharing responsibility for the provision of air navigation services
in the North Atlantic. It was therefore believed that changes in the
procedural arrangements regarding air traffic control offered the most
effective immediate means in order to increase the traffic handling
capacity in the Region.
To understand this it should be realised that, because of the
meteorological conditions existing over the North Atlantic, there is
generally only a comparatively small "corridor"' of limited vertical and
lateral extent available in which favourable conditions exist to effect
an economic crossing of the Atlantic. In addition, due to prevailing
wind conditions, the corridor for a flight from Europe to North America
is generally situated much further North than that for flights in the
opposite direction. Furthermore, the peak periods of use of these two
corridors occurs at different times due to the time difference between
Europe and the East Coast of North America, which operators have to take
into account to avoid that passengers arrive at some ungodly hour at
their respective destinations. In short, there are two peaks of traffic
and all aircraft try to get the most favourable track in the available
corridors.
The capability to accept traffic in these corridors by
ATC is, however, limited by the "separation" standards which has to be
applied in order to ensure that, even under most unfavourable
conditions, no collision can possibly occur between any two aircraft
while flying across the Atlantic. This in turn is dictated by a number
of factors over which ATC has very little influence:
5.
the reliability and compatibility of weather forecasts upon which individual pilots place their flight planning;
6.
the navigational accuracy which can be achieved by aircraft
while operating in an area where ground-based navigational guidance by
stationary navigation aids on the ground is not possible;
7.
the resultant accuracy with which pilots are able to report
their position and make estimates on the further progress of their
flight; and
8.
the speed and ease with which pilot's reports can be
received by ATC and resultant control instructions can be passed to
pilots for execution.
Based on qualified experience, the separation, practised in the North Atlantic was roughly:
9.
vertically 300 m (1000 feet) up to flight level 290 and above that level 600 m (2000 feet);
10.
longitudinally (i.e. aircraft behind each other on the same
track and at the same level) 30 minutes and, in some special cases 20
minutes (if the preceding aircraft was appreciably faster than the
following one); and
11.
laterally 120 nautical miles (NM) (i.e. aircraft flying
"side-by-side" on parallel tracks and on the same level). For reasons
already previously explained, there was little hope that, in the
immediate future, anything could be changed in the field of vertical
separation. However developments in the navigation field, and more
especially the introduction of inertial navigation systems onboard
aircraft, made it appear likely that reductions in longitudinal and
lateral separation could be envisaged with appropriate safeguards and
that these would, obviously, have immediate beneficial effects on the
traffic handling capacity of the ATC system.
It was for this reason, and based on studies which had
been conducted in the USA, that the Special NAT Meeting agreed on a
reduction in lateral separation from 120NM to 90NM as a first step to
alleviate traffic congestion in the North Atlantic. This decision met
however with strong objections on the part of pilots. It was therefore
agreed to suspend the application of this new lateral standard until all
parties concerned were convinced that it could be applied safely. To
obtain such an agreement, it was expected that the NAT SPG would propose
appropriate measures. In the meantime, the status qu4) was maintained
in the NAT Region with all its consequent economic penalties for the
operators.
Because of the numerous new problems facing the EUR Region
as described above, the Fourth Regional Air Navigation (RAN) Meeting for
the European Mediterranean Region was held in early 1958 in the UN
premises of the former Ligue of Nations in Geneva. This location had
been chosen because, by 1958, EUR Regional meetings had assumed
proportions in attendance (some 450 delegates) which were only slightly
smaller than the General Assemblies of ICAO. This posed many
organizational and procedural problems and the services of the
secretariat serving these meetings were strained to their limits. The
production of working papers, draft reports and, at the end of the
meeting a 300 and some pages Final Report, all in two working languages,
required not only a perfect Organization but also the burning of a lot
of "midnight oil". The conditions have, alas, almost become standard
feature of meetings organised by the European Office.
