One of the reasons why 16/17 December 1943 was so disastrous was the extreme limitations of landing aids. In the very heavy fog, there was little chance of crews seeing the lights of the airfield circuit which ended in a funnel on the selected runway. Nor would the angle of glide indicators be visible to ensure the correct approach: an amber if too high, a red if too low, a green if on the correct glide path.
This image at the IWM (IWM ART LD 5593) conveys a rather pretty, and also pretty optimistic, view of FIDO.
Gee, a radio navigational aid which was very accurate over England, would help the returning aircraft to locate their home airfield, but it was too imprecise to direct them down onto a runway. The only facilities available for landing guidance in such severe bad weather conditions were FIDO and a system known as SBA.
FIDO, the Fog Investigation and Dispersal Operation, was at that time only operational at three airfields: Graveley six miles north-west of Bourn; Downham Market 35 miles to the north-east (the installation barely completed); and Fiskerton, close to Lincoln, 95 miles to the north.
FIDO was a very new system, which had only come into operational use at Graveley, the prime test site, that November after a long series of trials and modifications.The official statement on FIDO, put out by Bomber Command shortly after the war ended and the need for secrecy had passed, summarises what had become a desperate situation:
The electrical beam [SBA] could help the pilots to approach to within 100 or 200 feet of the runway but they were then still flying absolutely blind at over 100 miles an hour with the imminent danger of crashing the aircraft, and killing themselves and all their crew, because they could not actually see to land. Fog over British airfields [had become] more of a menace than flak over Germany…
FIDO was designed to disperse the lethal cloud and fog, but the mechanism by which it accomplished this was somewhat alarming. Vast pipes, carrying thousands of gallons of petrol, had been installed down all sides of the runway at Graveley. The pipes were pierced with holes, from which a fine jet of petrol spurted forth when the pumps were in operation. To fire up each section of the system, a man manually set alight to the first burner and then ran like hell when it ignited with a whoosh. The heat dispersed the fog and cloud, and the glow of the flames provided a flarepath.
Bennett, the AOC of the Pathfinders, was a dedicated proponent of FIDO:
As was always his way with new equipment, Bennett personally tested it:
I took a Lancaster myself from Oakington over to Graveley one night, and did the first landing with FIDO burning. I had vague thoughts of seeing lions just through a hoop of flame at the circus. The glare was certainly considerable, and there was some turbulence, but it was nothing to worry about.*
Considerably less daunting than FIDO but more difficult to use was SBA, Standard Beam Approach, which was installed at all the Pathfinder airfields. However, as is made clear by the quotation above from the official post-war statement, SBA was limited in effectiveness: “[SBA] could help the pilots to approach to within 100 or 200 feet of the runway but they were then still flying absolutely blind at over 100 miles an hour”.
Referred to as ‘landing on the beam’, SBA employed signals emitted by beacons in line with the main runway. These beacons sent out a code to the pilot which showed if he was straying off course, dots to one side, dashes to the other, and just a steady note if he was right on track. The pilot first picked up the sound from the outer marker of the airfield and, once on top of it in ‘the cone of silence’, checked his altimeter to determine his angle of approach to the runway. He then passed on to the inner marker for a similar procedure. If his height and speed were correct, it was okay to land – blind, for he still could not see the runway in front of him.
The theory was fine but the practice infinitely more difficult – the planes which would try to land on 16/17 December 1943, in such appallingly low visibility, would be travelling at around 100 miles per hour, a speed which took them right across the airfield in little more than 30 seconds.
SBA approaches had been practised by some aircrew during training, but such exercises could not possibly repeat the conditions of coming home from a very long raid, exhausted, having burnt up most of your petrol, and with the considerable additional pressure of knowing that many other aircraft needed to land at the same time.
Squadron Leader Mackenzie
At RAF Station Bourn, it is thought that Squadron Leader Mackenzie, who crashed just to the north of the airfield around midnight, actually knocked out the outer marker when he tried to land. Unfortunately, Mackenzie and three of his crew died in the subsequent crash.
Quotation from D C T Bennett, Pathfinder: Wartime Memoirs (Frederick Muller Ltd, London. 1958), p.221.
Still the best guide to FIDO …