Lahso

“At Melbourne there are certain traffic peaks during the day, [and] LAHSO helps us to manage a greater number of aircraft during these times,” Steven Clarke, Airservices’ southern operations manager, explains.

“The arrival rate at Melbourne Airport with LAHSO can be as high as 44 landings per hour. On the other hand, the arrival rate for single runway operations, when LAHSO is not operating, is around 24 movements per hour. In poor weather conditions this single runway arrival rate reduces further. Departing aircraft also need to be accommodated amongst these arriving aircraft.

“So in the peak hours at Melbourne, where traffic is in excess of 24 arrivals per hour, LAHSO helps us accommodate this demand. ” Unlike Sydney, Brisbane and Perth, Melbourne Airport has not implemented a runway demand management system (RDMS). A RDMS is a slot management scheme typically established at six-monthly intervals when airlines determine their seasonal flight schedules. All four airports operate Airservices’ Metron Harmony system to undertake pre-tactical demand planning for aircraft operations taking place the next day. In essence, the pre-tactical system adopts measures so that aircraft delay is effected on the ground rather than with in-air holding. In the case of Melbourne, the additional demand capacity at peak times enabled by LAHSO operations lessens the necessity for a RDMS or restrictions from a ground delay program.

In addition to Melbourne, LAHSO is used at Darwin Airport, but while services at Melbourne are provided by Airservices, Darwin air traffic control is undertaken by the RAAF.

LAHSO has also been used in Adelaide in the past, but the current arrival demand does not justify a high capacity mode for Adelaide and the use of LAHSO there has been suspended, and the future use of LAHSO operations at Adelaide will be reviewed over time.

LAHSO requires the airport to have a suitable crossing runway configuration along with taxiway and runway markings, and lighting. It is available to all Australian registered aircraft operating on a flight number callsign, while other Australian and international operators may be approved to operate LAHSO depending on the aircraft category and pilot competency, both subject to CASA approval. Air New Zealand is perhaps the most notable international airline that has been approved for LAHSO operations at Melbourne.

Weather conditions dictate whether LAHSO can be offered. Wind conditions cannot exceed 20kt crosswind, and 5kt downwind on a dry runway or no downwind when the runway is wet. The cloud ceiling cannot be less than the minimum vectoring altitude at the location, with visibility not less than 8km – although the visibility criteria may be reduced to 5,000m provided air traffic controllers can sight the aircraft and apply visual separation standards before the loss of surveillance separation standards. At Melbourne LAHSO operations take place on runways 34 and 27. Aircraft can land or takeoff on runway 27, with another aircraft landing on runway 34. Air traffic controllers issue instructions for the landing aircraft on runway 34 to hold short of runway 27. Both runway markings and lights denote the point on runway 34 that the aircraft must complete its landing run.

In July 2015 a double go-around by two aircraft at night occurred at Melbourne (a double go-around meaning that two aircraft on final approach to land on intersecting runways both elect to initiate a missed approach). Airservices, CASA and the Australian Transport Safety Bureau have all reviewed the circumstances.

“Although the double go-around occurrence was not triggered by an aircraft participating in LAHSO, it provided an insight into what we could do to continually refine the LAHSO procedures to manage operational risk,” explains Clarke.

“We suspended LAHSO operations at night while we reviewed procedures to evaluate whether they could be more resilient. We adopted three initiatives, namely development of procedures to be adopted by air traffic controllers and pilots in the event of a double go-around; introduction of a stagger to remove simultaneous operations; and a review of the risk profile of aircraft being within an unsafe proximity. Once the initiatives were in place we reintroduced nighttime LAHSO operations at Melbourne. ” New procedures, awareness and training have been provided to air traffic controllers and pilots in the event of a double go-around. For air traffic controllers, CASA has given approval to turn aircraft early within a splay area either side of the extended runway centerline. In many ways these new procedures are actions that were already available to air traffic controllers to recover an emergency situation.

Training has also been undertaken by pilots from Qantas, QantasLink, Jetstar, Virgin Australia and Air New Zealand about how to react to a compromised separation arising from a double go-around. Training personnel from the airlines and Airservices spent time in each other’s simulators. From Airservices’ perspective it was important to understand the actions that pilots would adopt to recover a potentially unsafe situation.

The most significant change, however, is the introduction of a stagger to LAHSO operations. It continues moves by Airservices to adopt more strategic and interrelated initiatives to manage the traffic flow.

In essence a stagger involves planning arrival times between two aircraft arriving on runway 34 and 27 at Melbourne so that they touch down around one minute apart. While continuing the capacity enhancement benefits that LAHSO offers, the stagger minimises the prospect of aircraft being in unsafe proximity in the event of a double go-around.

The introduction of the stagger to LAHSO is a continuation of high capacity mode initiatives adopted by Airservices. As mentioned, the non-availability of LAHSO at Melbourne can cause difficulty in meeting aircraft capacity demands at peak times. Airservices’ National Operations Centre (NOC) in Canberra reviews forecast meteorological conditions for the next day to determine if weather conditions will permit LAHSO operations at Melbourne. It then coordinates with the Melbourne traffic manager to set planned arrival rates for the following day to inform the ground delay program.

Should forecasts indicate that weather conditions would not be sufficient for LAHSO operations, adjustments to the departure and arrival schedules are made to smooth aircraft demand to meet the capacity of the ATM system. Typically this can mean that aircraft scheduled to depart Melbourne have their departure time put back. It can also mean that aircraft departing another airport, bound for Melbourne, may also be held on the ground to meet a predetermined arrival time.

New operational procedures have been implemented whereby LAHSO pairs are determined and managed at a distance more than 200nm from the airport. It involves en route controllers providing the pilots with feeder fix times or to arrange their flight to arrive over these points at a certain time. A feeder fix is a waypoint located around 40nm from an airport and is the starting point for an arrival procedure to the landing runway. Pilots need to follow standard terminal arrival speeds from the feeder fix so that the planned landing time under the stagger procedure is achieved.

Airservices’ flow management tool, termed MAESTRO, has been adapted to bring the LAHSO stagger into operation. A review of the MAESTRO aircraft performance data is underway as part of continuous improvement processes.

“The stagger is still a work in progress as we fine-tune air traffic controller and pilot procedures,” Clarke notes. “Compliance with procedures is managed between airlines and Airservices through the Airspace Capacity Enhancement (ACE) forum for Melbourne. At the moment we are achieving an 87 per cent level of reliability with the stagger. This means that 87 per cent of LAHSO pairs are staggered. Our target is to achieve a stagger reliability level in the high 90 per cent range. ” In another measure to assure the safety of the operation, the availability of LAHSO operations at Melbourne has been limited to times of high arrival demand. LAHSO operations are only availabe when the predicated traffic delay is five minutes or more. This means that at Melbourne LAHSO operations are generally only provided between 0700 and 0900 local time in the morning and 1700 to 1900 in the evening.

We suspended LAHSO operations at night while we reviewed procedures. STEVEN CLARKE