USA carrier Alaska Airlines says it has achieved 35 per cent emissions reductions by changing the way its planes descend for landing.

Its planes now use Required Navigation Performance, a technology that lands planes using a steady, continuous descent rather than a step-by-step landing procedure.

The 'Optimised Profile Descents' allow jets to idle their engines for more of the descent, saving nearly 60 gallons of fuel per flight and cutting greenhouse gas emissions.

By using the techniques fleet wide, Alaska expects to cut emissions by 22,000 metric tons per year, and save 2.1 million gallons of fuel.