[John C]

Yes, usually.

Strong headwinds are not usually the problem per se.

The strong headwinds mean extra fuel is required to make the trip, it isn't unusual to see 80-100 kts on the nose, particularly when you are heading southwest, but when weather at the destination requires an alternate or holding fuel, that's when you start having to get the abacus out and crunch some numbers.

It is pointless, in my opinion, to hold fuel for an alternate without giving yourself the fuel to fly a couple of approaches at the destination, the point of the exercise after all is to land at the destination.

If you carry destination fuel (one approach and missed approach) then off to the alternate, then you are in my opinion, setting yourself up for a divert.

The strong enroute wind case is less of an issue but if it is unexpected you can always drop into an enroute alternate on the way to gas and go. That usually never happens.

If you are tank capacity limited. I.e. The flight is so long that it requires full tanks to reach the destination then your options are much more limited. You can stop enroute for fuel, but you then have to ensure you are not landing weight limited at the enroute fuel stop port, or you can reduce weight (which reduces fuel burn).

If destination weather means an extra 30-60 minutes of fuel, and you were already MTOW constrained (I.e. You were taking off at the max takeoff weight for the runway and conditions) then you can't leave fuel behind, so the only option is offload pax and bags.

Fuel planning is a little different for international operations versus Australian domestic ops. Domestically we don't carry an alternate unless it is required by the TAF. Internationally most carriers (I say most because I don't know about all jurisdictions) carry an alternate. When the weather is good they may well carry a "technical" alternate. For example a Brisbane arrival might carry Cooly, a Sydney arrival might carry Canberra, but if the weather is crappy and the weather system impacts all the airports in the area, then you may need to carry an alternate much further away, which means more fuel.

Also the planning books usually stipulate landing with 30 minutes fixed reserve and that's pretty much it.

As long as my **** pointed towards the ground I wouldn't plan to land with 30 minutes, so I always carry more. Our company planning policy is to arrive with 60 minutes, and that is reflected on the flight plan, so it is usually not an issue, though in some cases I decide to take more, but do so having considered all the relevant factors - I don't carry more for "mum and the kids".

The planning books are really only a document to use as a datum when comparing things, not as a real world document.

The other thing that the planning books don't consider is PDA's which is the percentage that the particular airframe performs under/over book. Some new airframes can perform a couple of percent better than book and older more battered airframes can perform up to 10% worse than book. This is often (but not always) accounted for in the flight plan with a PDA which tweaks the burn to suit the particular airframe. It requires a significant effort on the part of performance engineering to properly determine the pda for each airframe and isn't super accurate.