There has been much discussion on this Thread of the many weird and wonderful devices which have, over the years, been devised in various RAF ATC Local Control Towers with several objects in mind:
(a) to provide a visual display on the Local Control desk of the position of all aircraft taxying ,or in circuit at any one time; those which have cleared airfield and gone over to Approach frequency; and those which are returning to circuit under Approach Control (particularly on Controlled Descents and Instrument Approaches such as ILS or PAR "Talkdown").
This is primarily in order to provide Local Controller with a visual picture of the state of play at any one moment; to enable an instant "hand over" of the position at shift end, or for any other reason (when things may be very busy indeed); and to enable the Supervisor or SATCO to grasp the situation "at a glance" when said things may be going "pear-shaped"
, and another hand is needed - PDQ !
(b) by some ingenious arrangement of wiring, coloured "pea-bulbs", or squeaks/buzzers etc, to relay this information to the Approach Room (usually downstairs), to do with as they will.
The basic component on which all such systems are based is the Mapping Pin, and I can heartily endorse all that has been said (by
MPN11 - p.305 #6087 and others) about its capacity to inflict painful wounds with its diabolically sharp point. On the top you can Chinagraph three or four callsign letters or digits to indentify the "owner".
And as each such "owner" may need two or three Pins at once (for different purposes), and you may have 100 "resident" pilots (whose callsigns will be written on their "sets" - for Chinagraph quickly rubs off - it adds up to a lot of pins in the "pin-bank" on your desk (see
Warmtoast - p.305 #6091).
This begs the question of Who was going to keep all these pins moving ? When things are quiet, Local has only a few "live" callsigns on his plate at any one time, and can easily do it himself while keeping up the patter. But when an AFS really gets going full-throttle (and Strubby in my day was regularly clocking-up 500 movements a day (about the same then as LHR), it would keep your Assistant working like the proverbial "one-armed paper hangar". (I always use to reassure our new Controllers: "If you can hack it here, you can hack it anywhere - anything after this will be a rest-cure !")
And now there was an extra job for another Assistant, which leads me to:
(c) (but only on those AFS, when Bloggs is under training on jet aircraft), in order to save Bloggs, (who may be so wrapped-up in his new experiences that he forgets the passage of time and the voracious thirst of his jet engine or engines), from the inevitable result, by giving him a wake-up call (essentially: "Come in No.22 - your time is up !")
Most involved putting a second pin of his "set" in some form of time-frame, Assistant put this pin in at T/O time plus 30 mins (Meteor) or 40 ? mins (JP), and told Local when the clock reached that time. Local gave tongue accordingly.
But as Assistant was doing another dozen jobs at the same time, calls got missed: what was needed was a foolproof (automatic) system. Step forward F/Sgt Somebody-or-Other, who submitted his design, it was accepted, he collected a £250 Award,* and we (and other places ?) were stuck with it. (* Some disaffected persons maintained that he should have been put inside for wasting Service time and materials).
Now I shall describe what it looked like: You built a shallow open-topped wooden box about two feet square. Depth would be about nine inches at the bottom twelve at the top, so that it could more easily be read . The top consisted of a two-foot square of perspex, in the centre of which a "marine" type brass clock of about 8 inch diameter was buried with face flush with the perspex. This left a 8-inch "ring", marked radially in 60 one degree segments, with concentric rings about an inch apart, and a pin-hole in the centre of each "compartment" so formed. (I've never seen a photograph of the thing).
And that is enough for Part I, Part II will follow in a day or two when I have cudgelled my brains a bit more, and All will be Revealed. Stay with me !
Regards to all,
Danny42C.
Treats in Store !
PS:
Chugalug,
Too true ! ('Twas ever thus !)...D.