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Ok, I know what the others are but what is/was ZZ ?
I have heard of ZZ being used to refer to the Lorenz landing system.
Also here, This by Mr Carnaby
ZZ began in 1933 - Lufthansa seemed to be the instigator and as you say was used into WWII. It should have been replaced by Lorenz / SBA, but certainly c.1940 there was no way SBA or any other system would fit into a single seat fighter. RAF Northolt ORBs 1940-41 mention on many occasions, '... ZZ practice was carried out' .
The system relied on a ground controller, based in a hut at the upwind end of the runway, using direction finding to guide the aircraft to the airfield threshold on a dummy run. The pilot would then perform a 180 degree turn and fly away using a stopwatch for a period before repeating the exercise on a final approach.
The pilot had to be very experienced, as did the ground controller. They had to have total confidence in each other - this was rarely the case. The controller also had to physically 'see' the aircraft just before touchdown. Hence it was no good in very bad visibility.
It's called ZZ as, on final approach the ground controller would send a Morse 'ZZ' if it was OK to land, and 'JJ' if an abort was necessary (Why on earth these combinations - dah-dah-dit-dit, or dit-dah-dah-dah. What's wrong with dashes if its OK, immediately turning to dots if it isn't - I thought common-sense was in use until the late twentieth century).
Height finding didn't seem to be a problem (don't know why as it certainly was with later systems). The pilot did much of the work at 300 feet when in the Schneise (which I've just discovered is the approach path - a distant funnel eventually becoming a narrow line).
It was widely used at commercial airports in Europe and at eight aerodromes in the UK pre WWII (which eight!?). ZZ probably became obsolete when VHF-BA was developed c.1941 - it allowed the pilot of a single-seat fighter to interrogate a ground 'beam' beacon using his existing R/T set. I'll have a look through my notes over the next few days and see what I can add.
Here is the Aix thread LINK (http://www.airfieldinformationexchange.org/community/showthread.php?2180-ZZ-Blind-Landing-System)
Note - if our forum's search facility allowed a two character search (i.e. 'ZZ') you'd have found it.
Be wary. The ZZ suffix is often seen when referring to certain categories of explosives:
Category ZZ. Explosives having mass explosion risk with minor missile effect.
ZZ and JJ may have been used as they didnt sound like interference, thats my guess anyway!
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