Peter wrote:
The thing is… when you are flying to your alternate, and you don’t have fuel to mess around, you are in a mayday situation, and the only Q is whether you formally declare it or not.
If you get yourself into a “Mayday-situation” in the event of a diversion, then there’s something wrong with your fuel planning. It would be normal (and also acceptable in commercial flying) to arrive at the alternate in “minimum fuel” condition. But this is not yet a Mayday, it only tells the controllers that no further diversion will be possible and any delay or holding might actually force you to call Mayday.
If it were different, in fall and winter where diversions occur more frequently, we would hear Mayday calls all the time.
What I was getting at is just the logic… you need one alternate legally, and in practice that is what most people (including commercial ops) plan for.
And that alternate has no alternate 
So you have to land there. So anything that prevents that is a mayday situation.
That is, of course, unless you happen to have loads of fuel, which happens in GA where the penalty for flying with full tanks is negligible (less than 1-2kt on a TB20).
But how many alternates could say Easyjet deal with, on a worst-case route – not say Gatwick to Skiathos, where half a dozen islands will be within reach, even if they have to do one after the other.
There was a famous accident in Germany – a twin turboprop AOC op I believe – where one airport after another became inaccessible due to widespread convective wx, and after trying several, flying all over Germany in the process, they landed on some ex military piece of tarmac which had a blockage in the middle (to stop people using it) which took off their landing gear, but they did all walk away.
Peter wrote:
And that alternate has no alternate
Again, in a commercial operation it might. In poor weather conditions our company always plans with two alternates. And we are only allowed to depart when certain weather minima are met at time of arrival at destination and alternate(s). The planning procedure is quite complicated and occupies some space in our operating manual… It states, for example, that the destination can be planned with precision approach minima, but the the alternate needs to have non-precision minima. Otherwise we wait or cancel the flight.
But if you plan two alternates, what happens when you are on your way to the second one?
Peter wrote:
But if you plan two alternates, what happens when you are on your way to the second one?
If we plan with two alternates then we most certainly will meet “minimum fuel” state when arriving there. But a mayday condition? Hopefully not…
In real life the procedure will not usually be: go-around due to weather at destination → divert to alternate 1 → go-around due to weather → divert to alternate 2
But instead: Monitor ATIS/VOLMET/ask controller about weather when in range. Decide whether or not to try an approach at destination (if not violating the approach-ban; usually one diverts not at the minimum but long before commencing the approach!) → divert to alternate 1 or 2 depending on which has the more favorable conditions.
This is a sample fuel calculation on one of our operational flight plans. We use PPS where the layout can be adjusted individually for each company. It only shows one alternate as it automatically calculates with the more distant one. We are under no pressure not to take extra fuel so usually, at least in doubtful weather, we take as much as we can with respect to max. takeoff and max. landing mass.
what_next wrote:
It states, for example, that the destination can be planned with precision approach minima, but the the alternate needs to have non-precision minima. Otherwise we wait or cancel the flight.
That was the standard rule in denmark not many years ago even for PPL/IR pilots.
But instead: Monitor ATIS/VOLMET/ask controller about weather when in range. Decide whether or not to try an approach at destination (if not violating the approach-ban; usually one diverts not at the minimum but long before commencing the approach!) → divert to alternate 1 or 2 depending on which has the more favorable conditions.
Of course, what really happens is that faced with this situation you start working fast to see where the wx is ok – planned alternate or not.
But my point was that the time must come when you do have to land.
Peter wrote:
But my point was that the time must come when you do have to land.
Well, if all goes according to plan, you will find yourself at a place with good enough weather and more than Mayday-fuel. But I know what you mean, sometimes one takes a poor decision and gets oneself into a difficult corner. This usually happens when one arrives overhead the destination with weather below approach minima but a favorable trend. So instead taking the safe option of diverting right away there is a temptation to join the holding with everybody else and hope for the best… That’s usually one of those lose-lose situations. If you divert, then probably five minutes after you left, the RVR will be more than 550ft and everybody else lands happily. If you hold and eat into your reserve the weather will not improve and you fuel state will either force you to divert or land. If it forces you to land, your decision making style will cost you the job instantly with (almost) every commercial operator.
what_next wrote:
550ft
Meters, I imagine
We’re talking semantics.
If you get to the point that you need to fly directly to your alternate and land immediately upon arriving, and that anything other than a direct to and immediate landing clearance, means that you a will land with too little fuel, then you are already in a difficult position.
Calling it a “Pan” a “Mayday” or “Fuel Emergency” doesn’t matter too much, we all know what it means.
I think the point Peter is trying to make (forgive me if I’ve gotten it wrong) is this:
1. If you declare a mayday because you have too little fuel, it means that you are going straight for the runway, and everyone else better get out of your way because you aren’t going to accept any deviation, because you can’t.
2. If you declare a fuel emergency, it effectively means the same thing. You are going straight for the runway, and everyone else better get out of your way because you aren’t going to accept any deviation, because you can’t. The only difference is that you haven’t used the “M” word, but you will do so, if you aren’t treated as if you’d said the “M” word.
So effectively the two things amount to the same thing.
My understanding is that the words “Fuel Emergency” came about firstly in the US, because of a number of airline accidents where the pilots ran out of fuel and were reluctant to declare a Mayday. It was felt that people might be more willing to say “Fuel Emergency” than “Mayday”.
dp
