On 7 April 2004, a Boeing 737-7BX (737) aircraft registered VH-VBT, operating under the instrument flight rules (IFR), was en route from Townsville and descending for a landing at Brisbane. A Neico Lancair IV-P aircraft registered VH-LDJ, operating under the visual flight rules (VFR), was en route from Maroochydore to St George, on climb to flight level (FL) 1651. Both aircraft were operating in radar Class E airspace at the time of the occurrence.
The Lancair pilot reported to the Air Traffic Services (ATS) controller that he had departed Maroochydore at 0718 Eastern Standard Time2, although in accordance with the National Airspace System (NAS) procedures, there was no requirement for him to do so3. The controller issued the Lancair pilot with a discrete transponder code to assist with his situational awareness. Published NAS procedures stated that:
In Class E airspace, IFR and VFR flights are permitted. IFR flights are provided with an air traffic control service, are separated from other IFR flights, and receive traffic information on VFR flights as far as is practicable. VFR flights receive a Radar Information Service (RIS)4 on request.5
Those procedures also stated that, for VFR aircraft operating in Class E airspace, '…no flight notification was required…' and pilots of aircraft conducting operations under the VFR were required to monitor the appropriate radio frequency. The Lancair pilot submitted flight notification details to ATS prior to departure from Maroochydore, and reported that departure to ATS.
In accordance with those procedures, the controller was not providing traffic separation6 to either aircraft, and advised the 737 crew accordingly. Recorded ATS audio information showed that the controller provided traffic information about the Lancair to the 737 crew on three occasions between 0721:58 and 0725:08. At 0722:17, and again at 0725:38, the controller provided the Lancair pilot with traffic information about the 737, although there was no requirement for him to do so in Class E airspace. During the first transmission at 0722:17, the controller advised the Lancair pilot that the 737 was crossing traffic which would pass in about 15 NM and was on descent into Brisbane. During the second transmission at 0725:38, the controller advised the Lancair pilot that the 737 was 'in your 2 o'clock at 8 miles now'. ATS radar data showed that, at 0725:38, the 737 was 8.8 NM from the Lancair. At 0725:47, in response to that broadcast, the Lancair pilot advised the controller that he had the 737 in sight.
As the 737 was passing through about FL157 at 0726:01, the crew reported that they observed a traffic alert and collision avoidance system (TCAS)7 traffic symbol on the aircraft's navigation display, about the Lancair. They attempted to visually acquire the Lancair, but were unable to see that aircraft. Recorded data from the 737's flight data recorder (FDR) showed that, at that point, the crew commenced manoeuvring the aircraft by reducing the rate of descent. At about 0726:18, the crew received a TCAS traffic advisory (TA)8. The crew reported that they were still unable to visually acquire the Lancair and were uncertain of its relative position. Recorded FDR data indicated that at 0726:34, the crew disengaged the autopilot and commenced a right turn away from the Lancair. They subsequently levelled the 737 at FL153 and then climbed to FL154. At 0726:40 and at 15,420 ft the 737 received a TCAS resolution advisory (RA)9 aural warning instructing them to climb, in response to the proximity of the Lancair. They subsequently climbed the 737 to FL166 and continued the turn to about 15 degrees right of track. The duration of the RA was 10 seconds and commenced when the Lancair was about 650 ft vertically lower and about 0.7 NM to the left of the 737.10 Recorded ATS radar data showed that, at about 0726:45, the Lancair altered track 8 degrees to the right away from the 737, just before passing behind and below the 737. The Lancair pilot reported that he did not experience the effect of wake turbulence from the 737. The minimum distance between the two aircraft was about 600 ft vertically at about 0.3 NM laterally.11
The Class E airspace in which the 737 and the Lancair were operating at the time of the occurrence was introduced as part of NAS phase 2b on 27 November 2003. Prior to NAS phase 2b, that volume of airspace was classified as Class C airspace. In Class C airspace, both aircraft would have been subject to an ATS airways clearance and would have been separated in accordance with prescribed standards.
In Class E airspace, the pilots of aircraft operating under the IFR and VFR were required to:
…maintain vigilance so as to see, and avoid other aircraft.12
The NAS Implementation Group reference guide, distributed as part of the NAS phase 2b implementation, stated that:
The other important change is that the pilot of a VFR flight should not make broadcasts on ATC frequencies.13
It also stated that:
Pilots of VFR flights may monitor the ATC frequency to enhance situational awareness.
Please do not make broadcast transmissions or engage in chatter on an ATC frequency. The safety of others depends on you not doing this.
Pilots are not precluded from responding to any ATC or pilot transmission when they believe their safety is at risk from another aircraft.
Part 2, Section 2, paragraph 2.2.4.1 of the Manual of Air Traffic Services (MATS) stated that:
Before providing a radar service to an aircraft, radar identification shall be established.
Although the controller did not advise the Lancair pilot that the Lancair was radar identified, the controller issued a discrete transponder code to the Lancair pilot and radar-identified the aircraft before providing a Radar Information Service to the pilot.
Part 4, Section 1, paragraph 4.1.1.1 of MATS contained information regarding ATS controller responsibilities for providing aircraft separation. The manual stated that:
Separation shall be provided by ATC using approved separation standards and procedures.
In the circumstances of this occurrence, the ATS controller was not required to provide separation to either aircraft in respect of the other and there were no separation standards applicable in these circumstances in Class E airspace.
Part 4, Section 1, paragraph 4.1.1.3 of MATS stated that:
Nothing in this chapter precludes a controller from using discretion and initiative in any particular circumstance where these procedures appear to be in conflict with the requirement to promote the safe conduct of flight.
In the circumstances of this occurrence, the ATS controller provided traffic information to the crews of both aircraft in respect of the other, although under NAS procedures there was no requirement for him to provide traffic information to the pilot of the Lancair on the location of the 737.
Part 5, Section 1, paragraph 5.1.13 of MATS provided information regarding provision of safety alerts. Paragraph 5.1.13.1 stated that:
A safety alert shall be issued to an aircraft when a controller is aware the aircraft is in a situation which is considered to place it in unsafe proximity to terrain, obstructions, or other aircraft.
The controller reported that, once the Lancair pilot broadcast that he had the 737 in sight, there was no necessity to broadcast a safety alert to either the Lancair pilot or the 737 crew. The controller also reported that if that pilot had not broadcast that he had the 737 in sight, his next option was to issue a safety alert. MATS did not provide any guidance to controllers on what might be considered '…unsafe proximity…', or when to issue a safety alert.
The NAS Implementation Group reference guide contained information for VFR pilots regarding separation from other aircraft when operating in Class E airspace. Page 16 of that guide stated that:
When you are flying in Class E airspace you are responsible for separation from other aircraft. The onus is on you to look out and see and avoid other aircraft.
Part 12, The Rules of the Air, Division 1, of the Civil Aviation Regulations (CAR) 1988, contained information regarding right of way, prevention of collision, operating near other aircraft and responsibilities of flight crew to see and avoid aircraft. More specifically, CAR 161 contained information regarding right of way and stated that:
(1) An aircraft that is required by the rules in this Division to keep out of the way of another aircraft shall avoid passing over or under the other, or crossing ahead of it, unless passing well clear.14
(2) The pilot in command of an aircraft that has the right of way must maintain its heading and speed, but nothing in the rules in this Division shall relieve the pilot in command of an aircraft from the responsibility of taking such action as will best avert collision.
CAR 162 (1) contained information regarding prevention of collision and stated that:
When 2 aircraft are on converging headings at approximately the same height, the aircraft that has the other on its right shall give way…
Although not specifically referring to converging aircraft, CAR 162 also stated that '…each shall alter its heading to the right…', and when referring to the aircraft other than the aircraft having right of way, '…shall keep out of the way of the other aircraft by altering its heading to the right…'.
CAR 163 (1) contained information regarding operating near other aircraft and stated that:
The pilot in command of an aircraft must not fly the aircraft so close to another aircraft as to create a collision hazard.
The 737 was on the Lancair's right and, in accordance with CAR 161 and CAR 162 (1), had right of way. The Lancair pilot reported that he had the 737 in sight. While the crew of the 737 had observed a traffic symbol on the TCAS display, they reported that they did not see the Lancair, despite attempts to do so.
Information obtained from the crews of both aircraft, the ATS controller, recorded flight data from the 737, ATS audio recordings and radar data, was consistent and indicated that the crews of both aircraft and the ATS controller complied with the published procedures for Class E airspace under NAS.
Based on the factual data, and the definition contained in Regulation 2.2 of the Transport Safety Investigation Regulations 2003, the incident was classified as an airprox event.15
1 16,500 ft with an altimeter pressure sub-scale setting (QNH) of 1013.2 hPa.
2 The 24-hour clock is used in this report to describe the local time of day, Eastern Standard Time (EST), as particular events occurred. Eastern Standard Time was Coordinated Universal Time (UTC) + 10 hours.
3 Aeronautical Information Publication (AIP), ENR 1.1, Sections 3.4 and 18.3.2.
4 Radar Information Service (RIS) is defined in Part 10, Section 1 of the Manual of Air Traffic Services as:
An add-on ATC service within radar coverage, which provides information to flights, not otherwise receiving a separation service, in order to improve situational awareness, and assist pilots in avoiding collisions with other aircraft.
5 AIP, ENR 1.4, Section 2.1.4 and pages 12-13 and 40 of the NAS Implementation Group Reference Guide - How to Operate in the National Airspace System, effective from 27 Nov 2003.
6 Separation is defined in Part 10, Section 1 of the Manual of Air Traffic Services as:
A controlled condition using defined standards to prevent collisions between aircraft.
7 The Boeing 737-NG Operations Manual, Volume 2, states that:
TCAS alerts the crew to possible conflicting traffic. TCAS interrogates operating transponders in other airplanes, tracks the other airplanes by analysing the transponder replies, and predicts the flight paths and positions. TCAS provides advisory, flight path guidance, and traffic displays of the other airplanes to the flight crew. Neither advisory, guidance, nor traffic display is provided for other airplanes which do not have operating transponders. TCAS operation is independent of ground-based air traffic control.
8 A traffic advisory (TA) is generated when the other aircraft is approximately 40 seconds from the point of closest approach, dependent upon aircraft altitude.
9 If the other aircraft continues to close, a resolution advisory (RA) is generated when the other aircraft is approximately 25 seconds from the point of closest approach, dependent upon aircraft altitude. The RA provides aural warning and guidance as well as manoeuvre guidance to maintain or increase separation from the traffic.
10 The recorded ATS radar data and the 737 flight recorder data was consistent. However, the accuracy of that information is dependent upon the tolerances associated with both aircraft altimeters and the ATS radar equipment.
11 The horizontal distance was determined using the radar positions that were recorded every 5 seconds. By interpolating between those points to derive a position every second, the minimum horizontal separation was 0.3 NM, dependent upon the tolerances previously mentioned.
12 Civil Aviation Regulations 1988, 163A - Responsibility of flight crew to see and avoid aircraft.
13 Page 8 of the NAS Implementation Group Reference Guide - How to Operate in the National Airspace System, effective from 27 Nov 2003.
14 The investigation was unable to locate a CAR definition of '…well clear…'.
15 An airprox event is defined in Regulation 2.2 of the Transport Safety Investigation Regulations 2003, as:
…an occurrence in which 2 or more aircraft come into such close proximity that a threat to the safety of the aircraft exists or may exist, in airspace where the aircraft are not subject to an air traffic separation standard or where separation is a pilot responsibility.