Apr.18 (GMM) Starting in 2009, the introduction of the energy recovery system KERS in formula one will be gradual, the governing body has confirmed.

In a letter to teams that was seen by the German magazine Auto Motor und Sport, Max Mosley said the implementation of the ground breaking Kinetic Energy Recover Systems will be in three phases.

Following 2009, the next step will be in 2011, when more energy collected under braking will be permitted to be fed into the powertrain under acceleration by means of a driver-activated boost button.

The final step, involving the recovery of energy from multiple sources, will be in 2013, coinciding with the introduction of a new low cost engine formula; probably involving small turbo engines with about 600bhp, Auto Motor und Sport said.

Mosley's letter said teams and manufacturers are welcome to comment on the proposal before the next World Council meeting in June.