The lamp was powered by a 12 volt battery carried in a Land-Rover and wired in parallel with the normal battery of the vehicle. ... Thus on the northward run the pilot had to use the compass to reach the northern marker which was on a track cut at ... northward runs the error on passing over the north marker was about half a swathe on the average or about 25 yards. ... The excess oil in the exhaust system was then sufficient to produce smoke to guide the aircraft through its turn beforeanbsp;...