AVRO LANCASTER SANGAMO BEAM APPROACH INDICATOR

When British Bomber Command began conducting nightly bombing raids over Europe, the returning fleets of Avro Lancaster, Wellington and Halifax heavy bombers often found themselves returning under darkness to airfields completely blacked out. Even worse, more often than not those same airfields would also be shrouded in a blanket of thick fog rendering any ground-based visual signalling next to useless.

In fact, RAF losses to fog and other adverse weather conditions would often outstrip any losses due to enemy action. This was never more disastrously demonstrated than on the night of 16th - 17th December 1943 - the RAF’s infamous, ’Black Thursday’.

Returning from a night time raid on Berlin, Bomber Command's original force of 483 Lancasters and 15 Mosquitoes had already suffered some significant losses from anti aircraft fire and Luftwaffe night fighters which had downed 25 of the Lancaster fleet over the target area. Unfortunately, these losses were nothing to what awaited the surviving aircraft upon their return.

What had been a light mist over much of southern England at takeoff, had turned into a thick blanket of fog by the time of their return. With visibility dropping by the minute, command centres were pushed to their limit as they tried to divert the returning fleet to alternative airfields.

Technical aids for landing assistance were still in their infancy with only three basic systems available to the pilots. One, GEE was a radio navigational aid which transmitted a homing signal to the aircraft’s Marconi R1155 Radio Receiver’s directional finding antenna which would then display a visual aid to the pilot via the Left/Right Beam Approach Indicator.  

The two floating cross-hair needles of the L/R Indicator provided the pilot with a visual indicator of the aircraft’s position in relation to the airfield's radio transmission - directing him to turn either left or right to stay on course.

Unfortunately, GEE could only guide the aircraft back to the airfield. It could do nothing to assist with landing safely in the dead of night, on a runway shrouded in fog.

Early experiments with another system designed to combat fog - FIDO, (the Fog Investigation and Dispersal Operation) consisted of huge lengths of piping being laid down either side of the runway spraying a volatile mist of vaporised fuel into the air which when ignited, went some ways to dispersing the ground hugging fog. Unfortunately this system was only available at one airfield.

This left only one other alternative, the SBA or Standard Beam Approach. Similar to today’s modern Beam Approach Beacon System – BABS, the original Standard Beam Approach System was a basic homing device where radio beacons on the airfield transmitted a continuous stream of signals to the approaching aircraft in a form of a narrow beam. 

Installed just in front of the pilot’s control column and slightly below the air speed indicator, the Sangamo Weston Blind Approach Indicator consisted of two main elements - one placed horizontally and one vertically and featured two neon lamps which would light up when passing directly over the appropriate marker beacon and a speaker output to receive the audio signal. The pilot would then check his altimeter and adjust his angle of approach to the runway.

When the pilot was lined up correctly, the signal received was steady and he knew he was aligned with the runway. If too far to the left or right, the signal became a stream of dots or dashes and he corrected his course until the signal changed to a steady pulse.

While SBA approaches had become part of the RAF’s training regime for its pilots and navigators, it was still a terrifying way to land an aircraft travelling at over 100mph - completely blind. Unfortunately the poor accuracy of existing altimeters at such low altitude rendered the system somewhat unreliable with often catastrophic results - as ‘Black Thursday’ was to prove.

RAF 97 Squadron’s ground command station of Bourn were expecting 21 Lancaster to land within a space of just twenty minutes that night, but with the airfield blanketed in a pea soup of fog, controllers could only instruct each returning aircraft to join the stack already circling overhead and wait for it to clear. 

With each returning aircraft allocated a position some 500 ft higher than the previous, crews were forced to circle in the darkness waiting for their turn to descend. As more and more aircraft joined the stacks, all with ever decreasing fuel levels and another airfield, Gransden Lodge juggling their aircraft only 3 miles away - the first of a number of midair collisions began to occur.

Station crew on the ground recount the eery and discomforting sound of the endlessly circling aircraft above desperately searching for the runways before their fuel gave out.

Many crews, with fuel tanks now empty were forced to bail out over the English countryside whilest others still in the air tried to bring their aircraft in by using the glow of crashed aircraft as a guide. 

It was a terrifying night for those in the air and on the ground and by first light, a total of 70 of the returning 483 Lancasters had been lost to the appalling weather. Nine of those Lancasters were from 97 Squadron and were their heaviest single loss of the entire war.

While missing one of its mounting lugs, this Sangamo Weston Beam Approach Beacon Indicator is in amazing condition for its age with a clear glass and dial, floating needle, lights and speakers and the Air Ministry AM & Crown stamp on the rear of its casing next to the Reference No: 10Q/4  S.47.

Combined with a fantastically detailed scale model of the iconic Avro Lancaster atop its 100yr Mango Wood Stand and its informative Fact Sheet, this Beam Approach Indicator Recovery Curios Collectable is guaranteed to capture the imagination of any aviation enthusiast as it celebrates the achievements and sacrifices of our aviation heroes.

This Avro Lancaster Instrument comes complete with detailed Scale Model, Mango Wood Stand & Plaque plus Printed Fact Sheet featuring photo of instrument in the aircraft cockpit.

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