Hi ES,
On the A320 at fairly high weights, the fuel flow PER ENGINE is about 2500-3000 kgs/hr during take-off i.e. 5-6 tonnes per hour. Typical total burn to top of climb (usually FL350) is 2 tonnes. Cruise fuel flow per side is about 1200-1300 kgs/hr. Descent at idle is about 300kg/hr per side. Don't know about final approach - too busy - but it's high due to high drag configuaration.
The art of fuel management is complex. There are various ways of doing things but we are constrained by the requirements of ATC and arrival routings etc. But for example, descending at a slower speed is more economical than high speed. Why?
If you descend at a higher speed, you will start your descent later than if you were to descend at low speed. Therefore by descending earlier (slower) you spend less time in the cruise at cruise power and more time at idle and hence save fuel. Typical fuel burn approaching top of descent is about 40 kg/minute. So if you descend 1 minute earlier (say, 280 knots as opposed to 305 knots) you will save 40kgs in descent. (It works
).
Of course there are many other factors that can be taken into account to minimise overall costs - fuel just being one of them.
A4