A Fairchild SA227-AC (Metro) aircraft was cleared to take off from runway 16R at Sydney. A Cessna 404 (Titan), holding at the Foxtrot intersection with runway 16R, was cleared to line up behind the departing Metro. The Titan pilot acknowledged the conditional clearance and reported lining up at Foxtrot. As the Metro was rolling under take off power, the pilot noticed the Titan moving onto the runway. The Metro pilot veered the aircraft sharply to the right to avoid a collision and passed the Titan at 77 kts. The wingtip clearance between the two aircraft was estimated to be 6m. The takeoff was aborted.
The investigation revealed that the Metro was cleared by air traffic control at 22:44 Eastern Standard Time to taxy to the Bravo One holding point on runway 16R. The aircraft was on a night freight operation to Brisbane and had two pilots on board. Bravo One was the most northerly of the taxiways on the eastern side of the north-south runways. The Bravo One taxiway entered runway 16R at the threshold allowing the full length of the runway for takeoff. The co-pilot reported ready for takeoff at 22:47:51, which was approximately 12 minutes before curfew. The Metro had taxied behind a Boeing 727 that was to depart first.
Aircraft movements between 23:00 and 06:00 local time at Sydney's Kingsford Smith Airport were regulated by the Sydney Airport Curfew Act 1995, the Sydney Airport Curfew Regulations and the Air Navigation (Aerodrome Curfew) Regulations. Aircraft that received a taxi clearance prior to 23:00 but subsequently departed after commencement of the curfew period were able to use the full length of the runway and were not required to reposition south of the intersection of runway 16R and taxiway Golf. However, aircraft that taxied after 23:00 were required to take-off from a position south of the intersection of taxiway Golf. That requirement was to minimise environmental noise in the residential areas to the north of the airport.
At 22:52:15, the controller had cleared the Boeing 727 to take off when the pilot of the Titan called for a taxi clearance. The Titan was scheduled for a single-pilot night freight operation to Canberra. The pilot of the Titan was instructed by the controller to stand by. Due to arriving traffic on runway 34L, the crew of the Metro was advised that a delay of around 10 minutes was probable. The Titan was then cleared to the taxiway Golf intersection, which was immediately changed to the taxiway Foxtrot intersection. The Foxtrot intersection was closer to the Titan's parking bay. Because the clearance was issued 7 minutes prior to curfew, taxiway Golf was not required for noise abatement purposes. The B727 departed and the controller then processed two other aircraft for landing on runway 34L before the Metro was cleared to line up at 23:04:12.
During the approximately 17-minute period that the Metro was waiting at the holding point, the controller made numerous transmissions to seven other aircraft, as well as the coordination with controllers in the Sydney terminal control unit. In addition, the controller had discussed the closures of taxiways with the safety officer in "Car 3" and had cleared an aircraft under tow on the north-east apron. All transmissions made by the controller sounded professional and confident.
When the second of the two landing aircraft had vacated runway 34L at taxiway Bravo 9, the Metro was cleared to take off from runway 16R. The clearance was issued at 23:05:00 and acknowledged by the pilot. Almost immediately, at 23:05:07, the pilot of the Titan was issued a conditional clearance to line up. The clearance was: "CSV, Metro departing, behind that aircraft line up". The pilot replied "Behind the Metro holding clear Foxtrot at the moment, lining up, CSV". Less than 30 seconds later, the Metro crew reported aborting takeoff.
Neither the Metro pilot nor the controller understood that the Titan pilot had said that he was lining up at the Foxtrot intersection during the read back of the conditional clearance. The replay of the audio recording confirmed that the Titan pilot's readback transmission was difficult to understand.
The controller in the tower was working the combined position of aerodrome control and surface movement control. Although five controllers were rostered for duty until 2300, three had stood down earlier; after the last international aircraft had departed. Such a reduction in staff coverage was common practice. The other controller was absent from the tower on a break. The occurrence happened at night in clear weather conditions. Works in progress on the north-east sector of the airport increased the normal lighting within the area with a number of flashing lights and lighting towers.
The Titan pilot said that he understood that the line up clearance was a conditional clearance but had thought the Metro was departing from taxiway Golf because they were in the curfew period. He looked right and left when entering the runway but did not see the Metro, which was using the full length of the runway. The Foxtrot intersection was 462 m from the runway threshold and the Golf intersection was 1039 m from the runway threshold.
During discussions with the Metro crew, the pilot in command reported that all of their aircraft's external lighting was selected on, including the landing lights. After veering to the right to miss the Titan that was lining up, the pilot considered the takeoff to be unstable and, therefore, aborted the departure. The aircraft returned to the apron.
The Manual of Air Traffic Services (MATS) stated at 220.127.116.11:
"An aircraft delayed by the traffic situation shall be issued traffic information if appropriate, and instructed to hold position off the runway, or shall be issued a conditional line-up clearance".
MATS did not provide a definition of a conditional clearance. However, there was a definition a conditional line-up clearance in the Aeronautical Information Publication (AIP).
The AIP 3.4 - 14 at paragraph 4.5 defined Conditional Clearances as follows:
"Phrases such as "behind landing aircraft" or "after departing aircraft", will only be used for movements affecting the active runway(s) when the aircraft or vehicles concerned are seen by the appropriate controller, pilot or vehicle driver. In all cases, a conditional clearance will be given in the following order and consist of:
- the condition (specify); and
- the clearance, eg:
ATS: "(aircraft callsign) A340 ON SHORT FINAL, BEHIND THAT AIRCRAFT LINE UP".
Pilot: "BEHIND THE A340 LINING UP (aircraft callsign)".
Note: This implies the need for the aircraft receiving the conditional clearance to identify the aircraft or vehicle causing the conditional clearance."
The aerodrome controller was relatively busy and involved with multiple tasks prior to the occurrence. Both of the incident aircraft had been holding for a lengthy period and the controller was attempting to expedite each of their departures. By issuing a conditional clearance to the pilot of the Titan, the controller achieved two outcomes. First the pilot was tasked to line up, which would expedite the aircraft's departure and notify the pilot that he was next. Secondly, the controller, in effect, transferred his responsibility for separation to the pilot by making the clearance conditional. The condition of the clearance was that the pilot would monitor the departing aircraft and line up behind it. That distanced the controller from the responsibility of watching and waiting for the Metro to roll for take off and then telling the Titan pilot to line up after the Metro had passed the intersection. The delegation of responsibility allowed the controller to concentrate on other tasks in the tower, such as the monitoring and control of taxiing aircraft around the tarmac area during the works in progress.
The Metro had been holding for departure for a significant period. The crew, when eventually cleared to line up and subsequently take off, responded quickly and accurately to fit in with what appeared on radio to be a busy and complex period. The controller sounded confident in the various instructions being issued and the crew would not have expected an aircraft to line up in front of them. The crew did not comprehend that the readback of the conditional clearance included advice that the Titan was at the Foxtrot intersection and was lining up. Their focus, once cleared for takeoff, would have been on takeoff checks and their departure profile.
The Titan had been holding for over 10 minutes and the pilot would have been keen to depart. He would not have been aware that the Metro was holding at the threshold of runway 16R. The Metro would have been difficult to see as its external lights would have blended in with the airfield lighting and the lights of Sydney to the north of the airport. When the Metro was cleared for takeoff, because its position at the threshold was not annunciated by the controller and it was during the curfew period, the Titan pilot assumed the aircraft was departing from taxiway Golf. While the lights of the Metro would not have been obvious to the Titan pilot when he looked briefly to the right as he began to enter the runway, the landing lights should have been seen. Nevertheless, they may not have been obvious if they were directed away from the runway centreline while the Metro was still in the process of lining up.
- The Titan pilot did not comply with the condition of the clearance that was issued.
- Aerodrome works and associated background lighting made sighting of the Titan, from the tower, more difficult.
- The controller did not intervene when the Titan began to enter the runway to line up.
Local safety action
As a result of the investigation, Airservices Australia advised that they were proposing a change to procedures in AIP and MATS. The changes proposed were to place the responsibility onto the pilot or vehicle driver receiving the conditional clearance to identify and avoid the aircraft or vehicle causing the conditional clearance, prior to proceeding, rather than relying on an implication that it was their responsibility. The other significant change proposed was to include "position" as a requirement of the conditional clearance. The proposed amendments were to be included in both MATS and AIP for consistency. As of 6 May 2002, the changes had been drafted for the final consultation process.
|Date:||15 May 2001||Investigation status:||Completed|
|Time:||2315 hours EST|
|State:||New South Wales||Occurrence type:||Loss of separation|
|Release date:||23 July 2002||Occurrence class:||Airspace|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
Aircraft 1 details
|Aircraft manufacturer||Fairchild Industries Inc|
|Type of operation||Air Transport Low Capacity|
|Damage to aircraft||Nil|
|Departure point||Sydney, NSW|
Aircraft 2 details
|Aircraft manufacturer||Cessna Aircraft Company|
|Type of operation||Air Transport Low Capacity|
|Damage to aircraft||Nil|
|Departure point||Sydney, NSW|