With a dense fog obscuring much of the country on the night of 16/17 December, the RAF crews returning from operations were faced with enormous difficulties in landing.
At the PFF stations of Bourn and Gransden Lodge, conditions were probably the worst in the country. Visibility was dropping progressively with every minute that passed – by midnight, it would be down to 300 yards or less, and it took about 1,000 yards to stop a Lancaster. By the early hours of the morning, cloud base at Gransden Lodge would be at 100 feet and the fog would be meeting up with it. 405 Squadron, which was based at Gransden Lodge, would have as serious problems as 97 Squadron in trying to land their Lancasters; only 5 of the 13 aircraft operating that night would eventually touch down at their home station.
With 21 Lancasters due to land within the space of about 90 minutes, Flying Control at Bourn would be stretched to the limit. Those anxiously awaiting the returning crews knew that there would be serious problems when they arrived. The airfield was covered in thick fog and pilots descending blind through the clouds would not break into even partial visibility until 250 feet. There would be little hope of them seeing the lights of the airfield circuit which ended in a funnel on the NE.-SW. 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.
Technical aids for landing in such difficult conditions were in their infancy. 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 actually direct them down onto a runway. The only real facilities available to land in severe bad weather 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. Only 1 of 97 Squadron’s aircraft, that of the Coates crew, would land at Downham Market under very remarkable circumstances – it was to Graveley that at least 6 of the squadron’s aircraft would be diverted.
FIDO was a very new system, which had only come into operational use at Graveley, the prime test site, in the previous month 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 plain terrifying to the uninitiated. 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.
Considerably less daunting than FIDO but more difficult to use was SBA, Standard Beam Approach, which was installed at all the base airfields, including Bourn. 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 that night, 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. The margin for error was exceedingly small and each failed attempt brought an increase in danger. SBA approaches had been practised by some of 97 Squadron’s 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.
There was also the considerable additional pressure of having 12 or 15 other aircraft stacked up at different height slots on the circuit, all running short of fuel and all wanting to get down as quickly as possible. With Gransden Lodge with its own orbiting aircraft a mere three miles away, there was also an ever-present risk of collision though each squadron was flying a different circuit.
Flying Control at Bourn, which had been contacted by each plane as it returned, had followed established practice by transmitting the routine landing information together with instructions to join the stack already milling around overhead. Each new returning aircraft was also allocated a position, 500 feet higher than the previous one. Each would only be brought down 500 feet at a time as the lowest aircraft in the stack landed. Meanwhile, all the other crews could do was circle and wait. Many people on the ground that night recall how eerie and discomforting it was to hear the sound of the planes circling endlessly, or roaming blindly through the fog, searching in vain for another airfield on which to land.
Meanwhile, the petrol gauges just fell lower and lower. For the crews who came down out of the illusory safety of the sky, it was to be a terrifying experience as they tried to locate the runway with or without the help of SBA. As the inevitable crashes began to occur, crews still in the air sometimes saw, even despite the thickness of the murk, the burning glow of crashed aircraft as they descended below cloud cover. This added to the appalling stress that all the pilots and crews would experience that night.