The curious case of the declining "golden triangle"

In Australian aviation circles, the “golden triangle” refers to the high-volume domestic routes between Brisbane, Melbourne and Sydney. In 2019, these three routes accounted for 28.7% of all Regular Public Transport (RPT) domestic traffic in Australia.

Melbourne-Sydney alone accounted for 15.0% and by any metric is one of the busiest and most lucrative routes in the world. While substantially smaller, Brisbane-Sydney and Brisbane-Melbourne are still the 2nd and 3rd largest routes in the country, accounting for 7.9% and 5.9%, respectively.

RPT refers to scheduled airline services in Australia that are available to the public for purchase. This excludes charter flights, including FIFO mining charters that are a significant portion of air travel in Australia. FIFO flights are not available for sale to the public and rarely serve major routes, rather serving remote mine sites.

The dominance of triangle isn’t surprising given the concentration of population around the physical triangle forms by the three cities. The broader metropolitan areas of these cities accounted for 51% of Australia’s population. In fact, their dominance in Australia’s population results in the “center of population” lying just to the west of the “triangle” near the town of Ivanhoe, NSW.

What is surprising though is how the dominance of the triangle has waned in the aftermath of the COVID-19 pandemic. This wasn’t a slow or consistent decline, but what appears to be a structural downward shift.

In the 12 months to October 2025, the triangle represented 26.7% of domestic passengers, with a relative peak of 26.9% in April and May of 2025. This is significantly lower than the the 28.7% in 2019, and the relatively peak of 29.0% observed for several months in late 2017 and early 2018. Not only is the current proportion lower than the pre-pandemic period, it’s the lowest recorded since the late 1980s, before the deregulation of the Australian domestic airline market.

The data shows a clear structural break which likely has significant implications, yet we’ve heard very little in the public and policy discourse. While the trends have been noted by the ACCC’s monthly reporting on domestic airline competition (for example, see February 2025), there’s been no substantive analysis or discussion of it. This is surprising (and concerning) given the acute attention on competition policy and market regulation in the domestic aviation market in recent years.

It suggests that policy makers are flying blind. This isn’t a critique of the ACCC’s work, but rather of the broader policy ecosystem including Parliament and multiple government departments and agencies that don’t conduct regular and ongoing market analysis. Simply put, most analysis conducted in the public sector has been superficial.

Unusually, our analysis didn’t open with a question that we were looking to answer, or hypothesis that we were looking to test. Instead, this analysis is descriptive, highlighting a surprising and unexplained observation. It raises the obvious questions: why has this occurred and what’s driving the change? In our analysis we propose some potential drivers, however no single cause appears to explain the change.

Analysis

Our first consideration is whether there’s been any change in the size of the market, i.e. has the size of the total market simply grown quicker than the triangle, or has the triangle shrunk relative to the total market?

To do this we need to look at absolute number rather than proportions. In the 12 months to October 2025, domestic flights carried 60.1 million revenue passengers, 2.1% fewer than the 61.4 million carried in 2019. Yet, 16.1 million traveled on the triangle in the 12 months to October 2025, 8.7% fewer than the 17.6 million in 2019. Meanwhile, 44.0 million passengers traveled on all other routes in the 12 months to October 2025, 0.6% more than the 43.7 million in 2019.

This is a clear indication that traffic on the triangle is below its historic benchmark, while traffic on all other routes is reaching its historic benchmark. It’s indicative that the structural break has been to the triangle rather than the market as a whole (i.e. the change in the proportion is due to a change in the numerator rather than a change in the denominator).

We can also examine if there are variations between individual routes. As previously noted, Melbourne-Sydney is significantly larger than the other two routes, and has also seen the largest declines in both absolute and relative terms. Having accounted for 15.0% of all traffic in 2019, it only accounted for 13.5% in the 12 months to October 2025. Meanwhile, Brisbane-Sydney declined from 7.9% to 7.3% of all traffic, while Brisbane-Melbourne saw a slight increase to 6.0% from 5.9%.

While Melbourne-Sydney has led the declines, the proportional data may mask underlying weakness in Brisbane-Sydney and Brisbane-Melbourne as well, as all three have experienced declines in absolute traffic. Melbourne-Sydney has experienced a dramatic decline of 11.6% since 2019, while Brisbane-Sydney also declined by a 9.4%. Meanwhile, Brisbane-Melbourne declined by just 0.3%. These data dispel the notion of the decline being led by just Melbourne-Sydney, with significant declines also observed on Brisbane-Sydney, and suggests that the cause is likely more systematic.

The analysis so far has simply compared trends in the three golden triangle routes to all other routes combined. These include other routes to and from Brisbane, Melbourne and Sydney (e.g. Melbourne-Gold Coast or Adelaide-Sydney), but also other routes that are not to or from Brisbane, Melbourne and Sydney (e.g. Adelaide-Gold Coast).

It would be useful to separate these to understand whether the underlying trends expose if the systematic challenges on the triangle are specific to the triangle or specific to Brisbane, Melbourne and Sydney. Conceptually, are passengers flying less Melbourne-Sydney and instead flying more Melbourne-Newcastle or Sydney-Adelaide? Or are they just flying fewer Melbourne and/or Sydney routes altogether? We are able to assess this by looking at the difference in aggregate passenger volumes by airport, adjusting these data to exclude passenger volumes on the triangle.

Methodological note: airport passenger volume data double counts route passenger volume data. For example, if one flies a one-way trip on Melbourne-Sydney you’ll count as a single passenger for the route, but you’ll count twice in the airport data, once as a departing passenger for Sydney and once as an arriving passenger at Melbourne. Since BITRE’s airport passenger volumes count both departing and arriving passengers, the aggregate of all airports will be a double count of route specific volumes.

Once the triangle routes were excluded, large declines in passengers volumes to/from Melbourne and Sydney were observed, with Sydney experiencing a significantly larger net decline than Melbourne. This result wasn’t consistent as Brisbane experienced a net increase in passenger volumes:

• Sydney handled 2.4 million fewer passengers in the 12 months to September 2024 than it did in 2019, however Melbourne-Sydney and Brisbane-Sydney accounted for 1.1 million and 465,575 passengers, respectively. Excluding these routes, Sydney handled 820,176 fewer passengers in the 12 months to September 2024 compared to 2019.

• Melbourne handled 1.6 million fewer passengers in the 12 months to September 2024 than it did in 2019, but when adjusted for the triangle routes, Melbourne handled 534,439 fewer passengers.

• Brisbane handled 160,240 fewer passengers, but when adjusted for the triangle routes it handled 329,511 more passengers.

A good picture of the market is now emerging: utilising credible and consistent data, we have observed the declining dominance of the triangle has been driven by systematic declines in travel to and from Melbourne and Sydney, and not just travel between Melbourne and Sydney. Travel to and from Brisbane hasn’t decline, however travel between Brisbane and Sydney has, likely a function of the weakness of the latter.

These changes aren’t explained by changes in methodology and thus represents a clear downward structural shift since the COVID-19 pandemic. Furthermore, the slope hasn’t changed, indicating has been more sudden rather than gradual, albeit with a large gap in time due to the pandemic. None of the analysis so far has explained why this has occurred and there doesn’t appear to be a smoking gun. We do have some hypothesis that should be tested:

1) Has population shifted?

There is a popular narrative that the COVID-19 pandemic results in significant shifts in population away from some major urban centers, internal migration has been offset by the growth in the aggregate population.

Between 2019 and 2024, Australia’s population has grown by 1.8 million people, an increase of 7.2%. Melbourne and Sydney’s populations grew 5.4% and 4.6%, respectively, and while this is slower than the national average, it still represents large absolute increases in population in these cities. Brisbane grew by 10.6%, possibly explaining why Brisbane fared a better and didn’t experience an absolute decline in passenger numbers.

While not part of our core analysis, the 14.3% increase in Perth’s population coincides with the increase in passenger numbers to and from Perth, reinforcing the relationship between population growth and passenger numbers, and highlighting how the trends Melbourne and Sydney’s passengers numbers simply don’t coincide with the increasing population in these cities. We can put this hypothesis to bed pretty quickly

2) Competition: Tigerair, Rex, Bonza

Rex launched jet services on the triangle in March 2021 and ceased flying these routes in July 2024. Rex’s jet services weren’t dedicated to the triangle with significant flying to/from Adelaide and Gold Coast. The impact of Rex’s entry and exit appears limited since there’s been no change in the trends since they exited these routes.

It could be argued that Bonza drove traffic away from the triangle as they focused on point-to-point routes and didn’t fly to Sydney at all. Nevertheless, Bonza only operated for a short period between January 2023 and April 2024 with very limited capacity (only 4 aircraft). In the 18 months since their demise there’s been negligible change in the trends. Again, it appears any impact of Bonza was negligible.

We’ve quickly forgotten about Tigerair who were absorbed into Virgin Australia during their administration process in 2020. Tigerair were far more concentrated on the triangle than other carriers with 41% of their sectors flown in 2019 being on the triangle. This was significantly higher than the industry average, with Qantas, Jetstar and Virgin flying 21%, 19% and 26% of their total sectors on the triangle (22% weighted average excluding Tigerair).

Methodological note: BITRE route data doesn’t disaggregate volume by airline, however their on-time performance data measures sectors flown by each airline on each route on a monthly basis, allowing sectors flown to act as a proxy of capacity. Furthermore, as is probably now evident, the various BITRE data sources have difference months for their most recent data. We’ve used the most recent data for each unless making a direct comparison between them where we’ve used the most recent available for both.

So could Tigerair’s demise have contributed through a significant decline in capacity on the triangle? This impact may be limited though since Tigerair accounted for less than 10% of the sectors flown on the triangle in 2019. Nevertheless, as Tigerair was a fully owned subsidiary of Virgin and was subsequently absorbed during their administration, we can compere their combined capacity before and after.

On a combined basis, the proportion of sectors flown on the triangle by Virgin and Tigerair declined from 28.0% in 2019 to 26.6% in the 12 months to November 2025. However, this mirrors a similar decline from 20.5% to 19.5% by the Qantas Group, limiting the weight that we might attach to Tigerair’s demise as a contributing factor.

As a point of interest, the decline within the Qantas Group wasn’t consistent with Qantas decline from 20.9% to 18.4%, while Jetstar increasing their proportion from 19.4% to 21.9%.

3) Impact of international connecting traffic

An well-described phenomenon in the post-COVID world was the rapid resurgence in international travel, albeit significantly slower than domestic travel. This was partly due to the fact that domestic travel declined significantly less than international travel due to longer International border closures and the lack of international coordination that made International travel challenging in the immediate aftermath.

Thus, by March 2021, international travel in the preceding 12 months was only 1.9% of its 2019 total, while domestic travel was 21.1% of it’s 2019 total. By April 2023, domestic travel has recovered to 89.5% of its 2019 level, while international travel lagged significantly at just 63.9%.

Following a rapid resurgence in international travel from the middle of 2023, a crossover in November 2024 where both domestic and international travel had recovered to 96.3% over the preceding 12 months. Since then international travel has continued to recover more quickly and by April 2025 international travel had exceeded its 2019 level. In the most recent month (September 2025), international travel stood at 103.2% of its 2019 baseline compared to domestic travel at 97.6%.

But what has this got to do with it? One argument is that more international travel has shifted away from Sydney, with more direct services to Brisbane and Melbourne, thus reducing connecting traffic carried on Melbourne-Sydney and Brisbane-Sydney flights. There is some evidence in support of this as the return of international traffic has been more rapid at Brisbane and Melbourne, reaching 104.4% and 102.6% of their 2019 baseline in the 12 months to September 2025, compared to Sydney at 100.7%.

The absolute difference is 284,278 and 309,193 at Brisbane and Melbourne, and 113,316 at Sydney, amounting to a net change of 480,155 (i.e. Brisbane plus Melbourne, less Sydney). While this is significantly less than the declines on the triangle (e.g. 1.1 million on Melbourne-Sydney and 466k on Brisbane-Sydney), it could be a contributing factor, accounting for as much as one-third of the change.

Discussion

It’s clear that the dominance of the triangle has waned since the COVID-19 pandemic, declining to its smallest share of the total market since the deregulation of the airline market in Australia. The change represents a structural shift rather than a gradual decline, and it also appears as though the change is systematic to Melbourne and Sydney, although not Brisbane, rather than simply a decline in patronage on the triangle routes alone.

However, the cause of these changes is less clear, as are the implications. There are no clear answers, but the lack of broader discourse and analysis likely contributes to a lack of plausible hypothesis to consider. Nevertheless, it’s not likely affected by population dynamics or changing competition dynamics. One contributing factors is a reduction in connecting traffic flowing onto the triangle as Brisbane and Melbourne have experienced more rapid increases in international traffic, and thus some passengers bypassing Sydney. Even so, this is a small factor, contributing to one-third of the decline at most.

There are several caveats to this analysis, the most significant is whether the triangle was overtraded before the pandemic and the recent trend is a reversion to the mean with the pandemic serving as the point for a reset. It’s unclear how to assess this, but it isn’t supported by a variation in load factors before and after the pandemic on the triangle and all other routes. For example, load factors on the triangle increased from 84% in 2019 to 86% in the 12 months to October 2025, however load factors on all other routes combined increased from 77% to 79%. This is indicative that capacity is matching demand in a similar manner on both the triangle and other routes.

Despite the lack of a clear explanation for why it’s happened, the data provides an intriguing and provoking result that we’re interested to hear your views on, what’s driving the relative decline in domestic travel to and from Melbourne and Sydney?

Thanks for reading and we hope you enjoyed the analysis. If you liked our analysis, then please share it widely!