A Qantas B747-400, not on a passenger-carrying flight, did London to Sydney in 20 hours 9 minutes. That was in 1989. The return route has never been attempted since it would fly against the prevailing winds but would naturally take much longer.
Was it not the delivery flight of the first Qantas B744 trying to set a record. I say this as I travelled (quite by chance) on the delivery flight of the second Qantas B744 from LHR in late Oct 89. This flight was not non-stop and only had two dozen or so passengers.
I believe a number of the Qantas A330s were delivered nonstop from Toulouse to Sydney. Also during the 1993 Paris Air Show an A340 departed the show, flew nonstop eastbound to Auckland, New Zealand, refuelled and carried on eastbound back to Paris, arriving just over 48 hours later, including the stop, so just under 24 hours each leg. Obviously going with the prevailing winds throughout.
I don't know whether your 21hr 10min for Sydney is eastbound or westbound, but I would expect it to take almost 2 hours more westbound than eastbound. Unlike Auckland, Sydney is sufficiently short of being halfway round the world that it wouldn't be worth carrying on eastwards.
I've said this many times before but pilot flight time rules would make this utterly, utterly impractical.
Such a route could only be flown by EU or Australian airlines. As far as the Europeans are concerned, there is quite enough blood on the carpet already over current and imminent FTL rules, which from memory go up to 17 hours absolute maximum. There is no way that European airlines would reopen that can of worms just for one route. The EU would never countenance another country's airlines operating into their territory with rules so divergent from their own.
Europe-Australia has never been that big a market and now Emirates etc have grabbed the lions' share of it. No point in stirring up a huge amount of grief re-writing the rule book just to be able to offer a product that arguably most passengers don't want or need anyway.
There is also passenger resistance to ultra-long non-stop flights. There is a trade-off between a shorter overall journey time and having a stop to stretch legs, buy overpriced duty frees, and so on.
I would add: there is also a fuel penalty associated with the non-stop flight, in that you're having to burn fuel to carry 20+ hours of fuel (plus the structural weight for tanks that size). I don't know whether that's outweighed by the fuel a lighter aircraft would burn in descent/landing/takeoff/climb from an intermediate airport.
I'd agree with The SSK that crew duty rules would also add huge costs to this. Two full flight deck crews and a dedicated crew rest area, perhaps? I'm far from convinced that any attainable yield premium (if indeed there is any) would overcome the operating cost disadvantage, especially as the existing big players on the kangaroo route (EK/EY/SQ etc) could rapidly and easily launch a price war to drive any new high-yield entrant away.
Just because a route might theoretically become technically feasible doesn't mean it's commercially sound (as the runaway commercial success of the A340-500 and B777-200LR has shown).
Cyrano: There are already two full FD crews on SIN nonstops, as far as I’m aware. For the extra five or so hours the unions would demand a fifth and even a sixth pilot, with dedicated bunk rest. And what about the cabin crew? They would need significant augmentation and far better onboard rest facilities.
But that’s only half the point. As you may or may not have noticed from the R&N forums, the European airlines are currently locked in an extremely bitter battle with the unions over the harmonisation of European FTL rules. The airlines’ goal is to come up with a package which will provide stability and predictability on what they actually and realistically want, which is nonstop capability to destinations defined by a perimeter of about 15-16 hours flying time, that is to say China, Japan, Singapore, Buenos Aires, W Coast USA.
There is a strong possibility that the airlines will get the package they want, or something pretty close, but it has been (and continues to be, as long as the issue is ‘live’) extremely bruising. Bear in mind that at one point the unions’ demands, based on the infamous Moebus Report, would have meant an end to nonstops by European airlines to Tokyo, HK, SIN etc (actually, double crew with a week’s hotel at the other end to ‘acclimatise’ for the journey home).
So, assuming the new EASA rules meet the airlines’ requirements, there is NO WAY that they will reopen the debate in the foreseeable future for the sake of a once a day nonstop with half the aircraft configured for those business passengers who absolutely need to save two hours, and the other half full of active and supernumerary crew and their rest facilities.
Wouldn't the ability for European airlines to fly non-stop to SYD (or anywhere else for that matter) enable them to win back traffic from the likes of EK and EY? The idea of a 'one-stop' trip is very appealing (which you get with EY, EK etc. flying direct from many European airports via their ME hubs), whereas it takes two stops with BA, LH etc. (routing via their European hub and then SIN, or BKK etc.).
20 hours is a long trip, but with enough IFE I would do it
For business, I will always choose direct over stopovers. Doesn't matter how long or how many airmiles I might lose by going with someone else. The total time is all that matters to me and many others. Hubs, stopovers are always a PITA.