In real world aviation a common structure that is used for failure management is called DODAR. There are many different forms that the acronym takes but this is very commonly used. It stands for Diagnosis, Options, Decision, Assign Tasks, Review.
It can really be used for anything but I thought I would demonstrate how it works with a low fuel state below.
It is easy to say the problem is that we have low fuel, but it really achieves nothing if you define the problem but not it’s implications. There are four parts to a diagnosis in aviation, these are:
Weather - Some failures will affect landing capability, you may need a particular cloud base for example to be able to fly an approach. In this particular case, low fuel will not limit the aircraft capability, however you may want to consider weather that is less likely to cause a go around (i.e. strong crosswinds, windshear etc)
Landing Performance - What distance do you need to land? Of course a hydraulic failure would potentially mean you need a long runway, but in the case of fuel, this shouldn’t be much of a factor.
Time - Fuel is time! You need to know how much time you have to deal with the issue. Let’s put some figures to this as an example. Firstly let’s look at your current fuel, let’s say you have 3000kg left, now look at what your fuel burn is, let’s say it is 6000kg per hour. From this you can work out that you have 30 minutes of fuel left. Now the most important bit is working out your range, what airports can you reach? Take your groundspeed and divide it by 60, so if you have a GS of 360kts, then that means you are travelling at 6 miles a minute. Therefore with 30 minutes of fuel, you have a range of 180 miles.
The ‘X’ Factor - Unfortunately not a singing contest. Some failures may have implications that will affect your decision making and may need to be taken into account. With fuel, I wouldn’t suggest there is much else to consider.
So what have we diagnosed?
We have said that we don’t need special weather but ideally good conditions to minimize the threat of a go-around. We don’t need a particularly long runway, just the normal length for our aircraft type. Time wise we have 30 minutes left of fuel and 180 miles of range. And there isn’t an ‘x’ factor to consider. Now what?
There are always three main options:
Continue - Well if the destination is within 180 miles and the weather seems okay, then this is a valid option.
Divert - Look at other airfields in the area, are there airports that have better weather or are closer than the destination that will give us more fuel and therefore more time to make an approach?
Return - If you have already past the Equi-Time-Point (ETP), i.e. past the halfway mark then unless you have extra fuel, this is unlikely to be an option.
So now to choose. So working with some of the details of your flight: we can’t return to Sydney, we could continue to LAX but it’s busy airspace, they are using the other runway, and range wise; we have 180 miles and there is 150 miles to go, maybe that’s too close for comfort? So you decide that there are quite a few airports you can divert to and you choose the best one out of the bunch.
In real world this would include talking to ATC, Cabin Crew, the passengers, as well as briefing eachother and setting the aircraft up for the approach. In IF, not much of the above is applicable, but if you tend to use approach charts then I suppose you can get these up for the new airport, and most importantly, if you are under ATC radar control already, let them know. Change your flight plan and ask for a radar service such as FF or RV. If you are with tower, turning away and asking for a frequency change should be enough.
Now that you have set your diversion in motion, is it still the right decision? Re-visit the diagnosis, has anything changed? Check your range, will you still make it to the new airport, should you come up with a plan B in case this plan doesn’t work out? The list goes on…
Hope the above model helps, it seems like a lot but if you can just remember the acronym DODAR, it should help you when it comes to decisions that seem unclear to start with.
And also just to confirm the above comments about real world ATC procedures, there are two that are recognized by ICAO (the world standard for aviation). These are ‘Minimum Fuel’: you are committed to land at a specific aerodrome and any change in the existing clearance may result in a landing with less that planned final reserve; and ‘Mayday Mayday Mayday Fuel’: which declares a fuel emergency when landing at the nearest suitable aerodrome, where a safe landing can be made, will be with less than planned final reserve fuel. The Mayday Fuel declaration is known as ‘Emergency Fuel’ state but we don’t say that on the radio!
Lastly: final reserve fuel is 30 minutes flying time at 1500ft AAL (above aerodrome level) at the destination aerodrome.