Air Traffic Control

The Need to Make Flying Safer

It was a difficult and complex task to establish reliable air schedules. An important new and essential development was Air Traffic Control (ATC). Croydon was the major innovator in this area. It employed Civil Aviation Traffic Officers and Radio Officers and invented a number of the first procedures and concepts still used for Air Traffic Control today.

On the 25th February 1920 the Air Ministry detailed the specification and construction of the world’s first technical building to control air traffic, the “Aerodrome Control Tower”, to be installed at Croydon Aerodrome. This was also the first time that the “Control Tower” terminology was used. The Air Ministry specification stated that the “platform of the tower to be 15 feet above ground level”,  “have large windows placed in all four walls”, “with a “wind-vane to be fitted to the roof of the hut with a geared- down indicator placed inside”,”enabling the control officer to read changes of wind”. The world’s first Air Traffic Control Tower was born.

Radio Position Fixing was a Croydon based procedure approved by the Air Ministry in 1922. This was a new system using aircraft radio transmissions to fix an aircraft’s position – an essential first step in establishing a radio based global air navigation network.

G.J.H “Jimmy” Jeffs, Croydon Civilian Air Traffic Officer, was one of the great innovators in developing the new discipline. Issued with Air Traffic Control Licence No.1 in 1922, Jeffs developed many of the systems and procedures that were approved by the Air Ministry. Having established over twenty-five ATC Units in the UK, it was the United States who asked that Jeffs lead the establishment of the North Atlantic Airspace. Jeffs had a distinguished career in civil and military Air Traffic Control, culminating in the award of the CVO, OBE and the US Legion of Merit.

The step from the use of radio telegraphy (Morse code) to radio telephony (speech transmissions) saw the need for a new way to use language to ensure clearly understood messages. F.S. “Stanley” Mockford, Croydon’s Senior Radio Officer, conceived the distress phrase “Mayday, Mayday, Mayday” in 1923. The British Government embodied the Mayday distress call as part of the required radio procedures to be used in an emegency, promulgating its use in The Air Pilot: Great Britain, published in 1924. Adopted by the International Radiotelegraph Convention of Washington in 1927, “Mayday” became the international standard distress phrase. It still saves lives today.

Air Traffic Control Tower

The Control Tower is an outstanding, bold and distinctive design. Instantly recognisable for its square shape, and unusual amongst ATC Towers that are generally circular, it is striking in its restrained classical design that ingeniously houses many technical and operational functions that are not obvious to the onlooker. In sheer scale it is impressive. As well as the world’s first designed ATC Tower, it was the also largest, constructed over four floors with three floors dedicated to supporting Air Traffic Control functions. Many Control Towers built after this did not surpass it in design complexity for many years.

The descriptive term “Control Tower” originated to describe the timber structure at the first London Croydon Airport and its use can be traced back to 1920. The 1928 building was a step change improvement on the timber structure it replaced on the site and was designed around the operational experience gained by the first Air Traffic Controllers (originally known as Civil Aviation Traffic Officers- C.A.T.O.). It is interesting to note, that Control Towers only became compulsory in 1944.

The innovation of the London Airport Control Tower was to utilise height and a vertical construction and to give each level a clear function. The vertical nature and height of the Control Tower provided three technical advantages for the ATC functions:-

  • Clear 360 degree visibility of airborne air traffic, improved visual range and commanding view of airfield movements
  • Increased operational range of radio installations mounted on the Control Tower’s roof
  • Reduced topographic air mass interference to the meteorological equipment installed atop the radio mast

The Air Traffic Control Tower was built around the need to incorporate technical equipment into the design of the building and to provide effective working areas for each function employed in the Tower. The Control Tower was a world first and, when built, was the world’s tallest and largest Control Tower. In addition to the operational advantages the Control Tower brought, each level and part of the structure served a specific function designed to facilitate improved Air Traffic Control. There was continuous innovation and experimentation regarding the equipment and procedures used in Air Traffic Control.

The tall central mast on the Tower ingeniously provided a dual purpose. It incorporated a wind anemometer feeding data down through the centre of the building to a Dines anemograph machine located on the first floor Meteorological Office of the Control Tower and also provided two way communications between the Radio Officers, Air Traffic Controllers and aircraft.

Three clocks located on the airfield sides of the balcony were visible to the pilots to ensure that the aircraft’s clock was synchronised to the correct time. The Tower’s three clocks were linked into the Administration Building’s electronic master clock system and accurate to two seconds per week. Time is a key element required for navigation and safe in-flight aircraft separation.

The top floor of the Control Tower was accessed by a spiral staircase which led into a room divided into two sections- the Control Room and the Radio Room. These were for the working positions of the Civil Aviation Traffic Officers (C.A.T.O.), Traffic Assistants and the Radio Officers- each had a specific task. The Radio Officers were licensed to operate and communicate with the airliners by radio-telephony (speech) and wireless telegraphy (Morse code) with custom-built equipment built by the Marconi Wireless Telegraph Company. Marconi’s equipment was itself important in the facilitating of Air Traffic Control. The C.A.T.O.’s, supported by the Traffic Assistants, managed the departing and arrival air traffic to and from the UK. The area of coverage extended across the English Channel to the French Coast to the South and the Dutch coast to the North.

Part of the advanced design of the Control Tower was the facility to remotely control airfield facilities and the remotely-located radio transmitting station. The radio transmitting station located three miles from the airport (for safety reasons) was equipped by Marconi with four 3 kilo watt custom built transmitters and featured four 103 ft tall steel radio masts. Marconi personnel had an office and a large presence at the airport.

 Additionally, airfield facilities such as inset runway lighting could be remotely controlled from the Control Tower. Inset runway lighting was an important step as it helped pilots land and take-off safely in poor visibility. Specialised runway markings (the chalk line) aided pilots during take-off and landing as it helped pilots maintain orientation and thus prevent loss of control of the aircraft, especially in conditions of poor visibility. These features have been further developed and are standard features in runway design today.

 Air Traffic Control Towers are an instantly recognisable architectural feature that are synonymous with air travel. Speech radio transmissions were the new cutting edge technology of the 1920’s that were essential for the development of Air Traffic Control. Air Traffic Control is a critical part of the global air transport network and was an essential development that wholly stemmed from the necessity to manage the safety of airliners.

As a European reference to a different approach to the above design, Germany developed a low rise “Radio Room” building at the first Tempelhof c.1925. This approach was later abandoned in later German airport buildings for the now standard Control Tower format. The format designed and constructed at London Croydon Airport is now the standard design of all Air Traffic Control Towers.