TRAFFICCONTROL BY MARK LACAGNINA Two’s Too Many

ngled taxiways limiting the collision, stopping their aircraft on the Auckland has a single runway — pilots’ view of the runway, runway within a few meters of each Runway 05R/23L, which is 3,635 m clearances issued and read other with no damage and no injuries. (11,926 ft) long and 45 m (148 ft) wide. back hastily and incorrectly, The first incident occurred on May “Six of the 10 taxiways [join] the runway andA crossed radio transmissions1 were 29, 2007, in daytime visual meteoro- at an angle of 30 degrees to the runway among the common factors involved logical conditions. Four employees of centerline to form rapid-exit taxiways in two “critical runway incursions” Airways New Zealand were on duty in for landing aircraft,” the report said. that occurred two months apart last the airport traffic control tower, includ- “For example, Taxiways A4 and A6 [are] year at Auckland International Air- ing an aerodrome controller who was rapid-exit taxiways for Runway 23L.” port, said the New Zealand Transport responsible for aircraft on the runway The parallel taxiway was used temporar- Accident Investigation Commission and airborne in the control zone, and a ily as a runway during the 1990s when (TAIC). ground controller who was responsible extensive repairs were being performed Both incidents involved twin- for aircraft movements on the ramps on Runway 05R/23L; although closed as turboprop regional aircraft, whose and taxiways. Both were qualified for a runway, the taxiway retains markings pilots took last-minute action to avoid all tower positions. as Runway 05L/23R.

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“The [control] tower was located about 500 ground controller to pass the flight progress The scene was set — m [1,641 ft] north of the intersection of Runway strip for [Link 383] to the aerodrome controller twice — for a collision 23L and Taxiway A5,” the report said. “Control- at the same time.” at Auckland. lers had an unobstructed view of all the taxiway Each flight progress strip contains essen- holding points for Runway 23L/05R.” tial information, such as aircraft type and call sign. After a controller issues a clearance to Wrong Call Sign the aircraft, he or she writes the clearance and The events leading to the first incursion began the time the clearance is issued on the strip when the ground controller cleared the flight before passing it to the next controller. “The crew of an Air Nelson Saab 340A, call sign strips for the Saab, Link 659, and the [Q300], Link 659, to taxi from the ramp via Taxiway Link 383, were correctly prepared, but the B5 to the runway holding point on Taxiway A5 distinction between the handwritten holding (Figure 1, p. 39). “The Saab pilots had complet- points, A5 and A3 respectively, was not clear,” ed their pre-takeoff checks and had changed the report said. to the aerodrome controller’s radio frequency After clearing Eagle 766 to land on (Tower) as they approached the holding point,” Runway 23L, the aerodrome controller and the report said. the ground controller discussed whether a The Saab captain told the aerodrome departure could be conducted between the controller, “Link 659 is ready in turn Alpha 1900’s landing and the next arrival. The Metro 5.” The aerodrome controller acknowledged holding on Taxiway A1 was the likely choice the transmission. The Saab was among seven because the crew had announced that it was aircraft that were being handled by the aero- ready for takeoff before the captain of the Saab drome controller. A Swearingen Metro was announced ready for takeoff from Taxiway A5. holding for takeoff on Taxiway A1; an aircraft “It was not determined why the aerodrome was departing; and four aircraft were arriv- controller had not already decided to depart ing. First in sequence for arrival was an Eagle that aircraft [the Metro] first,” the report Airways Raytheon Beechcraft 1900D, call sign said. Eagle 766. The ground controller suggested that Link Another Air Nelson aircraft, a Bombardier 659 could take off between the 1900 and the Q300 with the call sign Link 383, was taxiing next aircraft on approach, and she pointed at © Sam Chui/Airliners.net to the holding point on Taxiway A3. “The The pilots’ limited view This Air Nelson Saab 340A was among ground controller of the runway while seven aircraft that were being handled had instructed its holding on angled by the aerodrome controller when pilots to call Tower taxiways at Auckland the first incident occurred. when ready, but they International was a had not yet changed factor in two critical frequency,” the report incursion incidents. said. “The instruction to call Tower meant that control of the air- craft had passed from the ground control- ler to the aerodrome controller. Airways [New Zealand] pro- Follash/wikimedia.org cedures required the

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The ground controller noticed that the aerodrome controller was looking at Link 383 when she issued the takeoff clearance and reminded her that Link 659 was the Saab on Taxiway A5. The aerodrome controller attempted to amend the clearance by instructing the Saab crew to line up and wait on the runway after the landing 1900 passed by, but the radio transmis- sion was blocked by the Saab first officer’s read- back of the takeoff clearance. “The Saab captain said that he thought the aerodrome controller sounded busy and the tone of the line-up instruction meant ‘don’t muck around,’” the report said. “As the first of- ficer read back the clearance, the captain looked © Warren Williams/Airliners.net left and saw no aircraft on the runway.” He told investigators, however, that it was difficult to see The second incident the Saab on Taxiway A5. However, the ground the runway behind his aircraft because of the involved two Eagle controller was not at her normal position in the angle of the taxiway. Airways Raytheon tower; she had moved to accommodate an elec- “Pilots seated on the left side of aircraft Beechcraft 1900D trician who was working on a lighting control holding on Taxiway A3 or A5 have to look back flight crews who panel. As a result, the ground controller was over their shoulders through almost 150 degrees accepted a takeoff standing almost behind the aerodrome control- in order to see the runway threshold and can clearance meant ler, instead of next to her. see less of the runway and approach area when for only one of the The aerodrome controller, who was look- holding on Taxiway A5 than when holding on airplanes. ing in a different direction, decided to clear Taxiway A3,” the report said. Link 383, the Q300 holding on Taxiway A3, for Pilots entering an active runway from an takeoff. “The aerodrome controller said that her angled taxiway normally turn slightly off the normal practice was to read the [flight progress] taxiway centerline to improve their ability to strips for each aircraft that she controlled, rather visually check the runway and approach area. than relying on memorizing call signs and types, “However, if told to expect an immediate takeoff but whether she had read the strips before is- clearance, most pilots would stay on the center- suing the clearance to Link 659 was not deter- line to expedite the line-up, as the Aeronautical mined,” the report said. Information Publication encourages,” the report The aerodrome controller might have de- said. “That was what the Saab captain did, and, cided to clear the Q300 crew for takeoff because as a result, his look up the runway, already lim- the airplane was still taxiing and would have ited by the cockpit window design, was probably been able to line up on the runway without hav- less searching than normal.” ing to stop at the holding point, the report said. As the Saab moved toward the runway, the “An expeditious line-up by the [Q300] would aerodrome controller again tried to amend the have made good use of the available gap before takeoff clearance, saying, “Sorry, that’s behind the next landing aircraft.” the 1900,” but the transmission was blocked by However, the aerodrome controller used the one of the Q300 pilots, who radioed, “Tower, wrong call sign in the takeoff clearance. Instead 383 is ready A3.” of addressing Link 383, she radioed, “659, if you “The Saab captain, after hearing ‘1900,’ at can take an immediate, line up Runway 23L.” the end of the crossed transmission, looked left

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again and saw the landing [1900] bearing down The first officers of both Eagle 979 and Eagle as it turned off the runway towards Taxiway A6,” 171 read back the clearance at the same time. the report said. “Both aircraft were braked hard “The aerodrome controller contributed to the and came to a stop … about 10–15 m [33–49 ft] holding pilots mistaking the call sign by issuing apart.” the takeoff clearance immediately after the pilots of [Eagle 171] had called ready and by not using Similar Numbers phonetic pronunciation for the call sign num- None of the aircraft, pilots or controllers in- bers [of Eagle 979],” the report said. The report volved in the first incident was involved in the did not specify how the controller pronounced second incident the morning of Aug. 1, 2007. the call sign but said that is was not “niner seven Three aircraft were on the aerodrome control- niner” and noted that the numbers “71” and ler’s radio frequency: an aircraft on departure, “79” are similar. another on arrival but not yet on final approach, A recording of the crossed transmissions by and an Eagle Airways 1900D, call sign Eagle the first officers indicated that they ended with 979, that was holding for takeoff on Taxiway A2 “seven niner” and “seven one,” in that order. (Figure 2). The aerodrome controller told Eagle 979 to line up and wait on Runway 23L. About May 29, 2007 one minute later, the ground controller told Control the crew of another Eagle Airways 1900D, call Tower sign Eagle 171, which was nearing the hold- ing point on Taxiway A3, to switch to Tower frequency. The crew of Eagle 979 held on the runway B7 B6 B5 B4 B3 B2 B1 for two minutes while the aerodrome controller A6 A4 A1A and the crew of the departing aircraft discussed A5 A3 A2 A1 23L weather conditions west of the airport. “The Saab B1900D Q300 Metro controller was concerned that fog was approach- “Link 659” “Eagle 766” “Link 383” ing the airport, and he was considering whether Source: New Zealand Transport Accident Investigation Commission to implement newly introduced low-visibility procedures,” the report said. Current conditions Figure 1 at the airport included 30 km (19 mi) visibility and a broken ceiling at 500 ft. The weather de- teriorated to 3,000 m (about 1 3/4 mi) visibility Aug. 1, 2007 and a broken ceiling at 300 ft within the next 15 Control minutes. Tower When the discussion between the aero- drome controller and the departing aircraft ended, the first officer of the 1900 holding on Taxiway A3, radioed, “Eagle 171 ready.” The B7 B6 B5 B4 B3 B2 B1 report said that the call sign was “clipped … and A6 A4 A1A A5 A3 A2 A1 not unmistakably ‘one seven one.’” The aero- 23L drome controller heard the transmission but B1900D B1900D did not identify the call sign. “He intended to “Eagle 171” “Eagle 979” next clear the [1900] waiting on the runway, and Source: New Zealand Transport Accident Investigation Commission so … he transmitted, ‘Eagle 979, 23L, cleared takeoff,’” the report said. Figure 2 www.flightsafety.org | AeroSafetyWorld | August 2008 | 39 TRAFFICCONTROL

“The first officer of Eagle 979 said that off as being for them and entered the Among actions taken after the two in- he heard ‘seven one’ after he had fin- runway in front of the aircraft that was cidents was a revision by Airways New ished his read-back, which he thought taking off.” Zealand of its traffic management plan was strange, but he did not suspect The report said the following were for Auckland, requiring that departures crossed transmissions,” the report said. among problems that not only con- from Runway 23L be conducted only “The aerodrome controller said that he tributed to both incidents but increase from Taxiways A1A, A1 or A2. The heard the crossed transmissions, but he the risk of runway incursions at other runway-entry point for A1A and A1 did not associate them with either Eagle airports: is at the approach threshold, and A2 is flight. He had looked away from the angled toward the approach end of the runway to assess the weather and then • “The use of multiple runway- runway.2 instructed the [departing] aircraft to entry points increases the risk In addition, the layout of the flight change frequency. He did not see Eagle of runway incursions by creat- progress board in the Auckland control 979 start its takeoff or Eagle 171 move ing more points for potential tower and procedures for placing flight towards the runway.” traffic conflict and a potentially progress strips on the board were The captain of Eagle 171 said that higher workload for aerodrome revised. The board has separate bays he saw only the arriving aircraft on a ­controllers …; for the takeoff-holding points, and wide base leg when he looked back be- • “The use of angled taxiways for ground controllers are required to place fore taxiing onto the runway. Eagle 171 runway entry increases the risk to strips in the bays corresponding to the entered the runway about 10 seconds aerodrome operations by further assigned holding points. The revi- after Eagle 979 began its takeoff roll. limiting pilots’ view of the runway sion is a temporary measure, pending The first officer of Eagle 979 saw the threshold and of other aircraft …; implementation of an electronic flight registration number ZK‑EAH on Eagle progress strip system that “should give 171’s fuselage and radioed, “Eagle al- • “[Pilots] do not, or cannot, check all aerodrome controllers earlier advice pha hotel, hold. … Hold! Hold! Hold!” that the runway is clear before of impending departures,” the report “The captain of Eagle 979 had crossing the holding point …; said.  already initiated a rejected takeoff from • “Crossed radio transmissions This article is based on TAIC Aviation a speed of about 60 kt,” the report said. Occurrence Report 07‑005. “He swerved left almost to the runway remain a risk to aerodrome edge, while the captain of Eagle 171 ­operations …; Notes veered his aircraft to the right. Each • “Pressure to minimize runway- 1. The TAIC report said that a crossed aircraft was stopped on its respective occupancy times occasionally transmission — also called a blocked half of the runway.” The wing tips were leads to hastily delivered runway transmission — occurs “when two stations transmit at once [and] neither can hear the about 8 m (26 ft) apart. line-up and takeoff clearances and overlapped transmission but other stations too-quick compliance by pilots …; Common Problems on the frequency hear either a largely [and,] unintelligible ‘hash’ or the higher-powered Based on these findings, TAIC conclud- transmitter.” Controllers or pilots who ed that the first runway incursion “was • “The practice of not transferring detect a crossed transmission commonly initiated when the aerodrome control- control of aircraft from the ground radio “two at once” or “blocked” to alert ler mistook the call sign of the aircraft controller to the aerodrome others on the frequency. she intended to line up for takeoff and controller until they are near the 2. The report noted that the International thereby inadvertently instructed an- runway holding point reduces the Civil Aviation Organization’s Manual on other aircraft to line up in front of the situational awareness of control- the Prevention of Runway Incursions (Doc aircraft that was landing.” lers, as less time is available to 9870) recommends that “when using multiple or intersection departures, do The second incursion “was initi- review aircraft details, and of not use oblique or angled taxiways that ated when the pilots of the aircraft pilots, because they have less time limit the ability of the flight crew to see holding on a taxiway mistook the to listen on the Tower frequency the landing runway threshold or final ap- clearance for another aircraft to take before entering the runway.” proach area.”

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