Hi guys, sometimes I got confused about, if I was told due to weather I plan an alternate airport which is 30 mins away from my destination. For the minimum requirement of fuel, this 30mins fuel should be added like extra fuel like INTER/TEMPO or need to include in flight fuel and give it a 15% variable reserve?

Fuel is one of

(a) flight (and diversion) fuel - ie what you expect you might use. Time to the alternate is irrelevant to the considerations
(b) variable reserve - some or all of which you expect to use on a contingency basis
(c) fixed reserve - typically for short term emergency holding at the destination should things go awry
(d) holding fuel for any weather or traffic requirements and, also, any likely clearance delay time
(e) margin fuel - spare fuel which you could use should the need arise. Typically, this is either just plain old comfort factor spare fuel or, for larger aircraft, often tankered fuel to play the different fuel price here and there game or sufficient fuel for PNR in flight replanning
(f) ballast fuel - fuel which you need to carry but isn't available for use

For an alternate, and you actually fly to the alternate (which is what you expected to do), that is no different to the desired A to B flight, so alternate fuel attracts the relevant variable reserve. Should you get to B and find you can land and don't have to go to the alternate, then chalk one up for you .. you just had a good day.

Good reply John. Sometimes I present this to a class 'surprise and no surprise'. For example-

The variable reserve accounts for things that would be no surprise if they happened en route. Such as unexpected headwinds, inability to maintain the planned VFR level or in-flight diversions. It is logical to assume that these things could also happen on the way to the alternate, so the variable reserve applies for the flight to the alternate as well. You plan your flight as though the alternate was your intended destination.

The fixed reserve accounts for things that would be a surprise (maybe a nasty surprise) if they happened . For example on downwind at the destination you find that the undercarriage does not extend, or you find that the only runway is occupied by a previous aircraft that landed with the wheels up! For a multi-stage flight, it is normal to carry only one fixed reserve since you do not expect to use it. If you do need to use it, you would have to re-plan the flight and take on extra fuel if necessary.

It is interesting to note that the fuel reserves are actually specified in a Civil Aviation Advisory Publication (CAAP), so they are advice, not law. Back in the 'olden days' it was law. Now CAR 234 simply says that you must have sufficient fuel-

(2) An operator of an aircraft must take reasonable steps to ensure that an aircraft does not commence a flight as part of the operator’s operations if the aircraft is not carrying sufficient fuel and oil to enable the proposed flight to be undertaken in safety.

However, every charter operator must operate under a company operations manual, approved by CASA, and the operations manual must contain a fuel policy that specifies how that company intends to comply with the CAR. Most companies simply say that they will adopt the recommendations of the CAAP.

CASA is currently considering reintroducing the legislation to specify what reserves must be carried by law.