Hi
On today’s QF74 landing in Sydney we were diverted to Brisbane because of ‘Fog’.
We refuelled then we’re back on our way for a 2.5hr flight to Sydney.
My question is on the Fog, Every other plane (bar 3 qantas flights) managed to land almost on time with no diversion to Sydney.
Why did Qantas have to divert?
Well, all of the flights that diverted were long haul. They would have departed the USA at their maximum take off weight, or very close to it. That means two things. Firstly the forecast that was used to plan the flight would have been issued somewhere around 18 to 24 hours prior to the planned arrival. Weather forecasts change, and, believe it or not, weather forecasters also get it wrong. So, if the forecast that was used did not mention fog, then there would have been no requirement to plan for it.
If the forecast mentions fog, then the fuel requirements increase dramatically. As the aircraft already depart the USA at maximum weight, the only way to get more fuel on is to remove cargo, and passengers. You won't be looking at slightly extra fuel, but more in the order of 10-15 tonnes, as a starting point. Some flights have little to no cargo anyway (Dallas) because they are already so heavy. So, up to 150 passenger have to be left behind. That won't be very popular, nor all that cost effective. Alternatives...well, if I can't get the fuel on...why not depart anyway, but use an in flight alternate. If there is no fog, great, I can go to destination, but if there is, I just have to drop in to the alternate. All pax get to fly, and in the worst case, the aircraft at least gets to Oz.
Yes but how come only Qantas / Virgin Diverted. How do the others avoid? Do they carry more fuel?
Well, at least some will totally ignore the rules. I recall once talking to a rather aggressive passenger, who was aggrieved because we had diverted to Amsterdam, whilst his mate on another airline had been able to get into London. As his friend was on an aircraft that was actually directly in front of us during the approach, we'd seen the weather they landed in. We were legal. There is no way they were, as the crosswind was well outside of the manual limitations. At the point where we went around, I would not have been able to guarantee hitting the runway, much less staying on it.
Fair question. Most aircraft can land in low visibility conditions, so on one level of analysis, this should not be a problem. However several issues arise when Fog interferes with the operations on an airport.
Not quite that simple. The aircraft has to be capable, the crew have to be trained and current, and the airport has to be capable. Australia is third world as far as its airports are concerned. Sydney now has Cat II capability to the north south runways, but as they took a cheap option and did not adequately space the runways (they are too close), there are limitations on timing of approaches. There is no guarantee that Australian crews would be low vis qualified. If they don't fly to places that need it often enough, airlines won't necessarily train or equip them. The QF long haul aircraft can all operate up to Cat III.
Fog causes delays on the ground and in the air. Aircraft have a greater separation on the ground and in the air in low visibility conditions. Ground activity is slowed down and aircraft take longer to depart the gate. In the air aircraft have a different set of landing rules in low visibility. This invariably causes delays. Delays mean that aircraft have to stay in the air longer before being able to land. No not to wait for fog to clear before landing but everything takes longer.
Correct. But it is MUCH slower. That means that even though you might well be able to land off an approach, you will have to hold for so long before you get a go, that other factors will force a diversion.
Aircraft can only carry so much fuel and the pilots must land and taxi to the gate and arrive with a certain minimum of fuel to remain legal.
The fuel requirement is actually at the end of the landing roll. You can get to the gate with much less than that. But, when it's foggy, you're going to need to carry that alternate fuel all the way to the end of the roll too. So, (380), the absolute minimum fuel might jump from 7 tonnes to 25 tonnes. That's a lot of fuel to pull out of your hat.
[Sometimes pilots make a decision early, to drop into an alternate airport early and not try to hold out as long as possible. A combination of weather prediction and predicted remaining fuel after factoring in delays in arrival will inform that decision.
Going early...is a good decision if flight time is an issue. If you waste a lot of time holding before you divert, that's time you no longer have available to fly back after the diversion. As a general rule, I would always go early, and not even enter a holding pattern if I though a diversion was likely. Going to the hold meant that I thought I'd get in.
Sometimes the term "Splash and Dash" is used. An aircraft diverts in order to refuel at an unplanned intermediate stop and almost immediately taking off for the original destination.
Generally not an option in the scenario being looked at here. You won't get away quickly, as ATC won't let you. It works when you are the sole aircraft diverting; which may happen simply because you were unlucky in 'flight level lotto', and were never able to get to the altitudes you needed.
