The reality is if the weather is suitable you carry minimum fuel, if the forecast is indicating marginal weather you carry extra fuel as a diversion could cost a lot of money and possibly run out of crew duty hours. As a Captain and professional pilot I would hope this is how the majority of people operate. In reality I know it is not as I see what other pilots load on as extra fuel and it is not required. Every time you land compare your remaining fuel with your MDF (Minimum Diversion Fuel) Normally you will see quite a margin, especially if you have loaded extra fuel.
If one was to divert when MDF was reached you would arrive at your alternate with only 30 minutes of fuel, at the most. "Fuel Emergency" I hear you all say this is my point for loading extra fuel! My point is to use your fuel correctly and professionally. If you had a slight delay on arrival at your destination which was going to put you below MDF, would you divert? This is a call to be made on the day! How is the weather? expected landing time? Number of runways? Is there a closer alternate? etc. As I said in my earlier post a Captain can use his or her fuel in any manner as long as a safe landing can be achieved with 30 minutes fuel remaining once dispatched.
Certainly in the case above you would land with more fuel at your destination by holding a little longer than diverting when MDF was reached. Yes I agree that you have now lost your alternate. From the other point of view what happens when you arrive at your alternate and that closes due to a runway closure etc?
This is why we have a minimum fuel policy like we do to mitigate against endangering passengers and ourselves from dangerous situations. The problem is that pilots come along and add their own factors and the fuel load get bigger than Ben Hur.
My closing statement is carry the appropriate amount of fuel for each flight don't just add fuel for the sake of adding fuel, can I justify the extra fuel I am carrying.
