de Havilland Canada DHC-8-102, VH-TQN

Investigation number

199703850

Occurrence date

24/11/1997

Location

25 km SSE Narrabri, Aero.

Report release date

01/11/1998

Report status

Final

Investigation type

Occurrence Investigation

Investigation status

Completed

Aviation occurrence type

Near collision

Occurrence category

Incident

Highest injury level

None

Safety Action Significant Factors Analysis Summary

The Bureau of Air Safety Investigation is investigating a number of safety deficiencies relating to aircraft operations in non-controlled airspace with a view to reducing the reliance on the unalerted "see-and-avoid" principle as the primary means of separation for fare-paying passenger flights.

For example, the Bureau issued Interim Recommendation (IR) 970155 to the Civil Aviation Safety Authority on 30 January 1998, which resulted from the analysis of a similar occurrence.

The interim recommendation stated in part:

"The greater use of larger and faster aircraft for RPT flights in non-controlled airspace increases the need for the adoption and use of "separation assurance" techniques in conjunction with "alerted see-and-avoid" procedures by all flight crews.

"Although the inclusion of "separation assurance" techniques in airline flight operations manuals would address the deficiency to some extent, procedures for other IFR and the majority of visual flight rules (VFR) flights are also essential. Many pilots may require guidance and training on "separation assurance" techniques.

"Alerted see-and-avoid" procedures used in conjunction with "separation assurance" techniques provide a fail-safe method of self-separation which enhances safety.

"The Bureau of Air Safety Investigation recommends that the Civil Aviation Safety Authority in conjunction with Airservices Australia:

"Review aviation regulations and instructions, with the aim of maximising the use of "separation assurance" procedures in conjunction with "alerted see-and-avoid" procedures by pilots of flights in Class G airspace.

'The Bureau of Air Safety Investigation further recommends that the Civil Aviation Safety Authority:

"Implement an education program for pilots to promote the use of "separation assurance" procedures in Class G airspace".

The first part of the recommendation was sent to Airservices Australia as IR970175.

Reports

The reason why the crew of the Dash 8 did not hear the Wee Waa departure report by the pilot of the Chieftain, or if they did, why they did not appreciate that there was the potential for conflict, was not determined.

The crew of the Dash 8 had previously reported their position and estimate for Narrabri on first contact with flight service. The reason the crew subsequently did not comply with AIP and company operating procedures, regarding a position report prior to descent, was also not determined.

The monitoring of the Tamworth ATIS transmission by the pilot of the Chieftain may have prevented him from hearing the Dash 8 crew report on descent. Consequently, he was unalerted to the Dash 8. If he had heard the transmission he may have initiated communication to ascertain if there was the potential for conflict. Under the current VFR procedures there was no third party, such as flight service, to alert the pilot to the position of conflicting traffic.

Environmental aspects

The Chieftain pilot reported that he was using the visor in the cabin but that he did not believe that his view from the aircraft was impaired. However, the fact that he was using the visor would indicate that the rising sun was of some concern and this aspect, in conjunction with the hazy conditions, probably limited his ability to sight potentially conflicting aircraft in his forward field of vision.

Unalerted "see-and-avoid" principle

Despite the Chieftain pilot's departure report, which was additional to that required for VFR flights, the crew of the Dash 8 remained unalerted to the pending conflict. This may have been due to the difficulty of assessing the potential conflict of other traffic from the limited details included in departure reports. In the dynamic aircraft operational environment, even with multiple flightcrew, it is not an easy task to develop a situational awareness of all potential conflicting aircraft.

The provision of a position report by the crew of the Dash 8 prior to commencing descent would have been the main opportunity for the pilot of the Chieftain to be alerted to the potential conflict. However, the report did not contain a reference to the position of the Dash 8 and the Chieftain pilot was unaware of the location of the Dash 8. Additionally, it was possible that the pilot of the Chieftain may not have heard or appreciated the significance of the Dash 8 pre-descent position report even if it had been provided, as he was probably monitoring the Tamworth ATIS at the time. Consequently, in either situation, separation was solely reliant on the pilots' ability to sight other aircraft and to manoeuvre their aircraft in sufficient time to avoid a conflict.

The limited radio reports required from pilots operating VFR flights place an over-reliance on the unalerted "see-and-avoid" principle to maintain separation from other aircraft. This aspect was one of the conclusions in the Bureau's research report titled "Limitations of the See-and-Avoid Principle" (1991) which stated, "Unalerted see-and-avoid has a limited place as a last resort means of traffic separation at low closing speeds but is not sufficiently reliable to warrant a greater role in the air traffic system. BASI considers that see-and-avoid is completely unsuitable as a primary traffic separation method for scheduled services". In that research report BASI recommended that "the CAA should take into account the limitations of see-and-aviod when planning and managing airspace and should ensure that unalerted see-and-avoid is never the sole means of separation for aircraft providing scheduled services".

A DeHavilland Dash 8 was conducting an instrument flight rules
(IFR) Air Transport flight from Sydney to Narrabri and tracked via
Richmond direct to Narrabri at flight level (FL) 180. The flight
was conducted in controlled airspace until approximately 130 NM
north-north-west of Sydney. The remainder of the flight was then
conducted in Class G non-controlled airspace. The crew of the Dash
8 contacted Sydney Flight Service (FS3) at 0721 Eastern Summer Time
(ESuT) and reported that the aircraft was maintaining FL180 with an
estimate for Narrabri of 0745. (All times are ESuT unless otherwise
stated.)

At 0732 the pilot of a Piper Chieftain conducting a visual
flight rules (VFR) flight from Wee Waa to Tamworth made an
all-stations broadcast on the FS3 frequency. The pilot reported
departing from Wee Waa at 0730, tracking 113 (degrees M) and
climbing to 7,500 ft. The pilot addressed the report to FS3 and to
any other traffic in the Wee Waa area. There was no acknowledgement
or response to this report by other aircraft or ground stations.
The pilot was rated and licensed for IFR flight but elected to
operate VFR for this flight and therefore FS3 was not required to
take any action in response to his broadcast.

Approximately 4 minutes after the Chieftain pilot's departure
report, the crew of the Dash 8 requested traffic information from
FS3 for their descent into Narrabri. FS3 advised that there was no
known IFR traffic. The crew acknowledged this advice and reported
that the Dash 8 had left FL180, but they did not include their
position relative to Narrabri in the transmission.

The track of the Chieftain crossed the track of the Dash 8
approximately 12 NM south-southeast of Narrabri.

As the Dash 8 was passing 8,000 ft, the crew saw a reflection to
the left of the nose of their aircraft. Subsequently, they saw a
twin-engine aircraft and manoeuvred their aircraft to avoid it. The
twin-engine aircraft passed from left to right approximately 300 m
in front of them and at about the same level.

The crew of the Dash 8 queried FS3 regarding the other aircraft
but were advised that there was no IFR traffic. The crew of the
Dash 8 then made an all-stations area broadcast in an attempt to
establish communications with the other pilot. The pilot of the
Chieftain acknowledged the call and advised the crew that he was
tracking from Wee Waa to Tamworth at 7,500 ft and that his aircraft
was a Chieftain.

Further discussion established that the pilot had neither seen
the Dash 8 nor heard the crew reporting on descent. The crew of the
Dash 8 did not remember hearing the departure report from the pilot
of the Chieftain.

Traffic information

In non-controlled airspace, flight service are required to
provide information to all IFR-category aircraft on other IFR
flights to assist crews in determining any conflict situations.
However, the flight service information system does not cover VFR
traffic. Therefore, in this instance FS3 was not required to
provide information on VFR flights to the crew of the Dash 8.

Aircrew are responsible for maintaining their own separation in
non-controlled airspace. IFR pilots use known position reports of
other aircraft to gain an appreciation of the disposition of
traffic and whether there is a need to arrange separation. Pilots
of VFR flights are only required to make a limited number of
position reports and generally rely on the unalerted "see and
avoid" principle to maintain separation from other aircraft; that
is, they maintain a continuous lookout for other aircraft.

Radio frequency monitoring

The Chieftain was fitted with two very high frequency (VHF)
radios. The pilot selected one to the common traffic advisory
frequency (CTAF) and one to the FS3 area frequency while in the Wee
Waa CTAF area. After leaving that CTAF area, he changed from the
CTAF to the Tamworth automatic terminal information service (ATIS)
frequency on one radio while continuing to monitor FS3 on the
second radio.

The investigation estimated from aircraft performance data that
the Chieftain would have reached the planned level of 7,500 ft just
prior to the Dash 8 crew requesting traffic information from flight
service. The Chieftain pilot reported that at about that time he
was probably listening to the Tamworth ATIS in preparation for
requesting a clearance to enter controlled airspace from air
traffic control.

The Dash 8 was also fitted with two VHF radios. While operating
in controlled airspace, the crew selected the air traffic control
frequency on one radio while the other was selected to the aviation
emergency frequency. Prior to leaving controlled airspace, the crew
selected the FS3 area frequency while continuing to monitor the
emergency frequency on the second radio.

Reports

The Wee Waa departure report from the pilot of the Chieftain was
recorded on the flight service automatic voice recording (AVR)
system and was clear and understandable. This departure report was
additional to the mandatory reports for VFR flights detailed in the
Aeronautical Information Publication (AIP) RAC 64.

AIP RAC 42 paragraph 32.2 required the crew of an IFR aircraft
to report their aircraft's position to flight service prior to
changing levels. Company operating procedures for the Dash 8
required the crew to make a position report prior to descent when
operating in non-controlled airspace. The AVR did not record a
position report from the crew of the Dash 8 prior to their
commencement of the descent.

Environmental aspects

The visibility was reported as hazy but in excess of 10 km. The
sun was low in the sky and the pilot of the Chieftain had lowered
the sun-visor in the aircraft cabin to shield his eyes.

Aircraft Details

Manufacturer

De Havilland Canada

Model

DHC-8

Registration

VH-TQN

Serial number

062

Operation type

Air Transport Low Capacity

Departure point

Sydney, NSW

Departure time

0642 hours ESuT

Destination

Narrabri, NSW

Damage

Nil

Aircraft Details

Manufacturer

Piper Aircraft Corp

Model

PA-31

Registration

VH-LTU

Serial number

31-7405462

Operation type

Private

Departure point

Wee Waa, NSW

Departure time

0730 hours ESuT

Destination

Tamworth, NSW

Damage

Nil