ZZ procedure

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The ZZ procedure (QGX) was a ground-based, bad weather landing procedure carried out with the help of radio direction finding in the German Reich from the 1930s to the end of the Second World War . It was used when the simpler puncture process (QG) was not possible because it did not allow the weather, for. B. in the case of a cloud cover that was lower than 60 to 80 meters above the ground, or because the breakthrough was too dangerous due to landscape or structural obstacles at a great height near the airport. It required great concentration of the on-board and ground crew and a great deal of time. Soon after its introduction, it was expanded to include a landing beacon or beacon system.

history

Developed in the late 1920s, the process was tested by Deutsche Luft Hansa from 1931 and approved shortly afterwards. It was first used in 1933 on the night flight route between Berlin-Tempelhof and Königsberg ( Devau Airport ) and was also used in Switzerland that same year . Due to the lack of accuracy, the method was only suitable for relatively slow aircraft and airfields with a wide runway .

As early as 1933, VHF radio beacons with beacons were used as a further development of the process, such as the Lorenz beacon , named after the company C. Lorenz AG in Berlin , which played a decisive role in the development of the ZZ process and processes derived from it later. Ernst Ludwig Kramar , the engineer in charge of the company's radio navigation department , proposed automation very early on. The procedure using the “ultra-short wave landing radio” (LFF), as the Lorenz beacon was officially called, was then known as the “Lorenz ZZ procedure” or “Lorenz landing procedure” and installed at numerous airports around the world. After the end of the Second World War, the instrument landing system (ILS), which is based on the principles already developed in the Lorenz system, developed into the world standard .

Procedure

The procedure assumed that approach sectors were set up at all participating airports, within which there were no obstacles, such as high towers or chimneys. A bearing point was located on the approach baseline in an imaginary extension of the runway. In addition, minimum approach heights were fixed (MSA - Minimum Safe Altitude, or DH - Decision Height).

The aircraft first received information from the airport, such as the surface pressure report for correcting the altimeter, and initially flew over the airport, guided by bearings. As soon as the personnel of the ground station could tell from the noise of the aircraft engines that the overflight was taking place, they sent the aviation abbreviation QFG "You are above my station" in Morse code to the radio operator on the aircraft. After receiving this sign, the pilot had to move away from the airport with his aircraft in the direction indicated by the bearing point in order to get as close as possible to the planned approach base line of the airport after a curve of 180 degrees on the opposite course. Depending on the wind conditions, the pilot had to set up the process so that he could undertake a slow descent back to the airport in a flight time of seven minutes. On departure, the bearing station corrected the flight direction by sending QTE for true bearing or QDM for magnetic bearing . Since a 180 ° curve offset the aircraft by around 8 degrees, 8 degrees were added or subtracted from the direction specified when flying away, depending on whether a left or right curve was to be flown. After completing the curve, the aircraft reported its altitude with the code QAH and obtained another target bearing. It then sent its own bearing signals for about 20 seconds. The values ​​determined by the DF location were reported to the aircraft and the process was repeated every minute. In the last minute the aircraft no longer sent direction finding signals, but waited for a distant signal as in the push-through procedure. The direction finder on the ground determined the direction of the incoming engine noises and then sent the associated Morse code.

Approach signals
MN     - engine noise in the north MS     - engine noise in the south
MNE - engine noise in the northeast MSW - engine noise in the southwest
ME     - engine noise in the east MW     - engine noise in the west
MSE - engine noise in the southeast MNW - engine noise in the northwest

If the aircraft reached the airport border and the ground crew was of the opinion that all conditions for a safe landing had been met, the direction finding station sent the main signal ZZ . Between the two letters the last letter of the identification of the ground bearing station was inserted, for Berlin ZXZ resulted . Thereupon the aircraft sank until it reached ground visibility and was able to land. If there were any doubts, or if the aircraft had deviated from the approach baseline again, JJ ("gas-gas") was used to prompt it to take off and the procedure was restarted. The last letter of the license plate was also added in the middle of the signal to take off, i.e. JXJ for Berlin .

literature

  • Karl Otto Hoffmann: History of the air news force. The flight reporting and fighter control service 1939-1945, Verlag Vowinckel 1968
  • Anders / Eichelbaum: Delius Dictionary of Aviation, Quelleverlag 1941
  • Frank W. Fischer: The development of air traffic control in Germany , Part I: Air traffic control in Germany before 1945 , International Advisory Group Air Navigation Services (ANSA), 2014, p. 175

Individual evidence

  1. ^ Niels Klußmann, Arnim Malik: Lexikon der Luftfahrt , 3rd edition, Springer Verlag 2011, ISBN 978-3-642-22500-0 . P. 324
    ( limited preview in Google Book search)
  2. ^ Karl Herz: The technical development tendencies in electrical communications / navigation and air security , Volume 13 of the Working Group for Research of the State of North Rhine-Westphalia , Springer-Verlag 2013, ISBN 978-3-663-02952-6 . P. 40
    ( limited preview in Google Book search)
  3. ^ Frank W. Fischer: The development of air traffic control in Germany - Part I: Air traffic control in Germany before 1945 , International Advisory Group Air Navigation Services (ANSA), 2014, p. 175 f.
    ( limited preview in Google Book search)
  4. ↑ Former air traffic control procedures in Morse code. Landing aids . Extract from Hoffmann: History of the Luftnachrichten-Troop . On: Morse code page DK5KE , accessed on November 15, 2015