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Fly On Track Radar Replay #2
Stansted CTA

You can view a real radar replay of an infringement here if you have Windows Media player.... but before you do, read the following to understand what you are seeing.... a classic example of what can happen when G.A. pilots could use Mode C on their transponders but then don't bother in practice. Mode C gives a controller an indication of your altitude (through conversion from the flight level transmitted). If they see your aircraft without Mode C in a position where you could be BELOW controlled airspace, the controller has to assume you know what you are doing (well, you have been trained properly haven't you?), and that you do know where you are (because you have not told anyone that you do not!), and therefore, the instructions given to aircraft within controlled airspace have to assume that you ARE below that airspace and out of the way.

This month we look at an incident in 'overhanging' controlled airspace, where a 'CTA' extends out at altitude beyond a CTR. This situation happens with most of our provincial airports, and allows G.A. traffic quite legally to pass UNDER the CTA 'shelf'. In this case, the airspace in question is North East of Stansted, and comes down to 1500' above sea level. This particular block above 1500' is used to manoeuvre instrument traffic onto the ILS for runway 23 at Stansted. The Stansted traffic doesn't need to be below 1500' this far out, but has to be down to something like 2000' to give a normal descent on the ILS once it gets closer and enters the CTR. Hence the airspace below the CTA is Class G, to allow G.A. traffic unrestricted access below the level that any Stansted instrument traffic will operate. The fact that this is Stansted is not important, this situation of controlled airspace above, free airspace below, exists in many parts of the country.

You will see an aircraft being manoeuvred round to the ILS into Stansted. Very soon after the playback starts, it will be briefly highlighted for you with a blue label, and it's squawking 1035. Below the Squawk is the 'SS' to show the aircraft is inbound to Stansted (EGSS) and there are two further figures. The green figure (initially '41') shows the current altitude in 100s of feet, so the '41' means 4100'. The orange/brown number (initially '40', then '30' then quickly '20') shows the altitude that the aircraft is cleared down to level off (if no further descent is given). So the '40' means cleared down to 4000' and eventually the '20' means cleared down to 2000'. At the very start you will see a radar track very close by heading North West, but ignore it, this is very high level traffic way above and the 'squawk detail' has been removed so not to obscure the Stansted traffic here.

A few seconds into the replay, you will see a '7000' squawk heading towards Stansted, briefly highlighted for you in RED, but as the Mode C is not switched on, as you will see from the three dashes --- where the level should be. The orange/brown NMS shows 'No Mode S' information available, but in fact, it is the lack of 'Mode C' which is important here. In fact, the pilot of this aircraft is 'unsure of position' but hasn't told anyone (yet). The controller therefore takes the '7000' squawker (which has not at this stage declared he is lost) as being UNDER 1500'. So in other words, you have the benefit of hindsight, there is nothing to tell the controller there may be a problem here at the moment. The altitude of the infringer is given at the bottom of this script, but why not try it first without knowing?

The Stansted runway is where the ILS approach line ends. The markers on the ILS approach line are 2 nm apart. Play the replay a couple of times trying to ignore the hindsight, and also, whilst you are at it, work out what altitude you do NOT want the 7000 'squawker' to be at. You may need to replay the sequence more than once and of course, pause it. When you've decided you want to know the altitude of the 7000 squawker, there's a link at the bottom of the page to reveal the answer. Then replay everything again with that knowledge. On the other hand, you can probably guess what altitude the 7000 is at. We know, because the pilot finally declared to another unit he was unsure of position, and reported his altitude.

Click on the image on the left to launch the radar clip. It is currently only available in 'wmv' format, therefore Windows Media Player should be used. Many thanks to all at NATS who have gone out of their way to make the public viewing of this clip possible. A different infringement and analysis will appear every few weeks - until they stop! When you have played it a couple of times and want to know the altitude of the infringer and 'lessons learned', click here.

The latest radar replay (#7) shows an aircraft starting in the Manchester Low Level Corridor then infringing the CTR with the controllers breaking off approaches ahead of it.

The latest radar replay (#6) shows a small aircraft slowly transiting Stansted CTR.

Radar replay (#5) shows an aircraft not noticing the lowered airspace ahead near Compton VOR and breaking in at altitude.

Radar replay (#4) shows a student lost and crossing the Luton CTR and extended runway centre line.

This radar replay (#3) shows disruption caused by a short infringement into a layer of the LTMA over Sussex, eventually descending to the correct altitude but not early enough.

This radar replay (#2) shows a problem caused by a pilot NOT squawking Mode C and then getting lost eventually turning up close to the extended centreline of Stansted in the CTA. Due to the lack of Mode C the controller didn't know he was in the CTA.

The original radar replay (#1) shows the disruption caused when a pilot makes a navigation mistake and enters the Heathrow CTR and heads down towards final approach without realising it (at first!)