Recommendation

Introduction



Between October 1995 and July 1997, the Bureau of Air Safety
Investigation undertook a study of the safety of Australian
regional airlines. The objectives of this BASI safety study were
to:



(a) identify safety deficiencies affecting regional airline
operations in Australia; and



(b) identify means of reducing the safety impact of these
deficiencies.



The Regional Airlines Safety Study involved analysing data obtained
from:



(a) responses to a survey of Australian regional airline
employees;



(b) discussions with Australian regional airline employees and
managers; and



(c) air safety occurrence reports in the BASI database involving
regional airlines over a 10-year period (1986 - 1995).



This interim recommendation addresses one of the safety
deficiencies identified as a result of this study.



Safety deficiency



The combining of air traffic service operator positions during busy
traffic periods can limit the ability of flight crew to exchange
essential position, emergency or traffic information.



Related Occurrences



BO9702957



A de Havilland Dash 8 and a Lockheed C130, travelling in opposite
directions on the same route, passed within 400 m of each other
while at the same level. Pilots of other aircraft operating on the
area frequency prevented the flight crews of the Dash 8 and the
C130 from communicating with each other in adequate time to arrange
separation. Two flight service positions were combined at one
console and there were reported to be 21 aircraft using the two
area frequencies, which were linked via a retransmission
facility.



BO9703696



The pilot in command (PIC) of a Beech B200 taxied at Smithton for
an IFR flight to Launceston. On departure he was unsuccessful in
establishing communications on 122.6 MHz to obtain traffic
information due to the volume of traffic on the frequency. The PIC
reported that the communications problem was due to the increased
traffic calls by aircraft taxiing at King and Flinders Islands,
visual flight rules (VFR) and instrument flight rules (IFR)
aircraft position reports and traffic requests for descent. The
problem was further exacerbated by the retransmit facility which
rebroadcast all transmissions on eight separate frequencies. The
pilot advised that he made six attempts before contacting Melbourne
to advise his departure, obtain traffic and to obtain a clearance
to enter controlled airspace.



Discussions with other pilots who operate in the same area and air
traffic service personnel in Melbourne, revealed that the frequency
congestion problems were most critical at weekends when frequencies
are combined.



BO9800106



At approximately 100 ft AGL after takeoff at Williamtown the left
engine on a Beech 1900D failed. The crew conducted emergency checks
and returned to the aerodrome and landed without further incident.
An emergency call to Sydney Flight Service was not possible due to
the large number of other pilots operating on the area
frequency.



Regional airline safety study



The results of the Regional Airlines Safety Study revealed that 72%
of respondents had experienced delays of more than two minutes due
to frequency congestion, while using flight service area
frequencies.



The study noted that frequency congestion appeared to be a problem
at a large number of locations across Australia, suggesting that
the problem was not isolated to one particular region.
Pilots'comments from the study indicated that congestion was worse
when frequencies were combined and particularly at weekends (when a
number a frequencies were usually combined and allocated to a
single operator position).



Reports since 1996



Reports since the study indicate that the problem of frequency
congestion is still occurring. However, it is now being experienced
on air traffic control frequencies since the transfer of some
flight service functions to air traffic control.



Equipment limitation



Aeronautical Information Circular H34/97 - Flight Information
Service Retransmission Facility, (December 1997) from Airservices
Australia, detailed an equipment limitation which can inhibit the
provision of services by air traffic services. The limitation was a
function of the retransmit facility used to network a number of
radio frequencies at an operator position. Airservices Australia
acknowledged the limitation and provided advice to assist pilots
operating on frequencies that may be retransmitted.



Analysis



Although Airservices Australia has endeavoured to address the
limitation inherent in the current equipment by issuing
Aeronautical Information Circular H34/97, more consideration of the
possible impact of the combining of air traffic service positions
is required.



Ready access to and use of the area frequency is essential for
crews of IFR flights to obtain traffic information from the air
traffic service operator. Ready access to the area frequency is
also essential for the exchange of position information between the
crews of IFR and VFR flights, in order for an assessment of
potential conflict to be made. The combining of two or more area
frequencies using retransmission may create a hazard for aircraft
operations.



Airservices Australia should develop procedures to assist operators
in evaluating the advantages of combining air traffic service
positions against the consequent potential for frequency congestion
and the possibility of a degradation of safety in the aviation
system.