SOME new types of K.L.G. spark plugs for piston aero engines have recently gained Air Registration Board approval and have been undergoing intensive field trials with several operators and engine manufacturers over the past year. These plugs are believed to be the first in the world to have iridium electrodes, instead of the conventional platinum alloy electrodes. The aim is to increase the life of spark plugs, which at present arc prone to premature failure under certain kinds of operating conditions.