Chart of the week #15: How far south does a A380 go on Sydney-Johannesburg?
On 30 September 2024, Qantas “upgraded” its Sydney-Johannesburg flight from the B787-9 to A380. This attracted a lot of interest from AvGeeks for a number of reasons, most intriguingly due to the potential for the aircraft to fly a more southerly routing than the twin engined B789.
As we’ve analysed before, prior to the COVID-19 pandemic Qantas operated the route utilising the B747-400. The B744 was retired during the pandemic and was replaced on the route by the smaller B789 resulting in a significant loss of capacity. Shifting to the A380 has allowed this capacity to be backfilled, albeit operating the larger A380 at lower frequency operation.
The simplistic view was that the four engined A380 wouldn’t be limited in how far south it could fly while the twin engined B789 would be. This view missed the evolution in regulatory environment over the last decade. Historically, airline operations were subject to ETOPS (Extended-range Twin-engine Operations Performance Standards) limiting the time from a suitable diversion airfield that a twin engined aircraft could operate.
For example, utilising the 180 minute maximum that CASA applied, SYD-JNB required a substantial diversion from the great circle route. This didn’t apply to quads, allowing the B744 to fly as far south as needed, often tracking significantly further south of the GC route on the westbound sector to take advantage of strong easterly winds (eastbound sectors typically track north of GC route).
Australia has since replaced ETOPS with EDTO (Extended Diversion Time Operations), with two consequential differences for the SYD-JNB route:
The maximum time limit was increased from 180 to 330 minutes subject to the aircraft and airline achieving the appropriate certification.
Unlike ETOPS, EDTO isn’t limited to twins but applies to all aircraft, including quads. Thus, the B789 and A380 are now both subject to EDTO.
The B789 has been designed with EDTO 330 in mind, meaning that it includes much of the redundancy in systems that are required to operate up to 330 minutes from a suitable diversion field. On the other hand, as a slightly older design the A380 doesn’t necessarily have the same in-built redundancy. For example, it may lack sufficient fire suppression to allow it to operate under EDTO 330, instead requiring a shorter limit (e.g. 240 or 180).
Four engines be dammed! Being subject to EDTO means that the A380 has no EDTO advantage over the B789. In fact, it may be subject to greater limits as its older design may not include sufficient redundancy.
Routings are optimised on a daily basis, taking into account the most recent weather data and forecasts. Furthermore, two different aircraft may have two different optimal routings, even if departing on the same route and at the same time due to varying climb performance, cruise speed and other operational differences. But let’s take an empirical look at QF63 SYD-JNB!
What does the data say?
We took the ADS-B position data from all QF63 flights since the change to the A380 on 30 Sep 2024. We only looked at the westbound sector since this typically takes a more southerly route compared to the eastbound return sector (QF64).
A challenge with ADS-B data is that significant chunks of the typical route lies outside of ADS-B coverage. As a result, the most southerly latitude on any given day represents the most southerly tracked rather than the most southerly latitude achieved. Luckily, the largest coverage gaps lie significantly to the west of the typically most southern latitude, limiting the impact on the analysis. Thus, the most southerly tracked latitude is strongly indicative of the most southern achieved latitude.
We tracked 37 A380 flights between 30 Sep and 17 Nov, and compared them to the last 37 B789 flights (18 Aug to 29 Sep). We plotted the most southerly tracked latitudes on a map and the result is awesome! There is no clear visual indication that the A380 goes further south. In fact, visually it looks like the B789 goes further south on average!
This is confirmed by observing the measures of central tendency. As is apparent from the map, there is also significant day-to-day variation in routings, affected by weather, the potential performance and operational constraints on the day, and even aircraft specific or temporary equipment limitations. The standard deviation shows that the variation is similar across the A380 and B789. This indicates that most of the day-to-day variation in routing appears to be exogenous and not a function of the aircraft.
There are some limitations to the analysis. Firstly, the measurement challenges between tracked and actual latitudes should be acknowledged, but don’t meaningfully affect the conclusion. Secondly, while we have used an equal number of flights on both aircraft, the time period during which they occurred varies. As the A380 operates on the route at a lower frequency than the B789 did, the A380 flights are spread over a wider period.
This exposes a challenge with seasonal weather variation that affect optimal routing. Just because the B789 has gone - on average - further south than the A380 we can’t conclude that this is due to the aircraft and not due to seasonal variations in weather. This will require analysis over a longer period to compare the aircraft with like-for-like seasonal variations.
So it’s a non-conclusion conclusion! The A380 has actually flown a few degrees further north than the B789, but we’re unable to establish if this is due to weather, aircraft performance, or EDTO. It’s not because of ETOPS since that doesn’t exist anymore.
Could it be small differences in EDTO limits? It could, but just to complicate matters remember that just because the B789 can operate with EDTO 300 it doesn’t mean it does on any given day. As the data shows, it was just as likely to fly well north of the EDTO 330 limits as it was to hug the EDTO 330 boundary, rather flying an optimal route. What EDTO does is increase the scope of potential routes!
In case you missed it, here is our last “chart of the week” from a few weeks back! Thanks for reading and remember to subscribe and share!
