ATC IssuesA place where pilots may enter the 'lions den' that is Air Traffic Control in complete safety and find out the answers to all those obscure topics which you always wanted to know the answer to but were afraid to ask.
Just a quick question - why is it that the TWR controller will sometimes request your passing altitude before handing over to the Approach / Area controller on departure? I guess they are radar identifying the aircraft, but I don't quite understand why! (Although I am, admittedly, of little brain.)
I've noticed it at LHR (having just started flying there), but seem to remember it from LGW too.
At LHR if you're on a departure track which is going to cross the missed approach path for the other runway (if you're on a DVR off 27R or a BPK off 27L for example) and it's about time to transfer you over to radar then the controller will sometimes ask to verify your mode C read out before transferring you over.
This is so if the next a/c goes around we can vertically separate it from you knowing that your mode C read out is correct. If there's nothing about to touch down or if you're well clear horizontally at the time you're transferred then there's no need to check.
That's the most common reason anyway, I'm sure there may be others related to SVFR as well.
At my unit we often will call RP3A so we know that your through any VFR approach traffic that radar/approach are working. This prevents you having to call Approach just to be immediately instructed to contact Area.
If you're on a DVR or MID from 27L, we'll transfer you as soon as we see you turn (visually), or a few radar sweeps of you turning.
All ATCOs work under the premise that getting rid of you ASAP is A Very Good Thing. However, we need to ensure, if you're a BPK or WOB off 27L that we have a chance to get some separation from a 27R missed approach.
Occasionally, the timing works out that just as you turn towards BUR, the next a/c to land on 27R has just touched down, and the next one is therefore more than 2 miles out....so we can chuck you over straight away.
However, if the next to land on 27R is at 1 mile, or less, for example, we either keep you on frequency until you are well clear (suitable for slow climbing heavies), or we'll verify Mode C and get rid of you once you leave two thousand (i.e. through 2,400ft - more suitable for mediums).
Sometimes there might be low-level traffic on or off the lanes where a Mode C verification would be sought - usually either Police or Air Ambulance helicopters off-route.
Your scenario could happen....however, bear in mind that you're through 2.4 going to 6, and the GA is at 150ft(ish) just starting to go to 3. If it looks tight, we'll stop the GA at 2. It's just belt and braces...usually there's enough lateral separation to allow the GA to continue to 3....by which time you'll also be through 4, if not reaching 6!
The whole point of the exercise is to verify your Mode C. If the scenario you mention did happen, and we hadn't got a level check, then we wouldn't have the option of using vertical separation. Doing so just keeps our options open.
At Gatwick I'll ask you for a report passing 3A if the departure behind you may catch up longitudinally (usually happens when he/she is accelerating better than you) so that I can restrict that aircraft to 3A and hand you over clean to the TMA (after co-ordination). Probably commonest with slower types such as ATRs but sometimes even the same type will accelerate differently based on company,destination,weight etc. As a matter of interest, if you're in the following aircraft, it's also the reason you may get "report the altitude restriction to..." Because I have to co-ordinate through an intermediary (director) it's my way of ensuring TMA know I've taken positive action to ensure the separation on first contact.
DAL208 - not quite right, since we can't verify mode C as a tower controller, which is why we need a positive RP3A rather than just asking "report your passing altitude" to confirm any separation.
The ATM can be used to verify mode C at Gatwick also - by the same MATS1 rules.
The time it's most often used at Gatwick is for seperation between SAM and BOGNA departures from 26. These SIDs diverge at approx 6nm and therefore we cannot seperate them by means of a standard 60 second departure split, or indeed visually, since the divergence is too distant. Instead we can restrict the second aircraft to 3A and maintain visual seperation until the leading aircraft reports out of 3A or a verified mode C indicates as such.
As vespasia says, you may not be on these SIDs, since longitudinal separation can erode in many other instances - but this is the most common. Also the part about requiring coordination is correct, especially since the aircraft are usually transferring to discrete frequencies.
and why every time?
This is definitely not the case at Gatwick - although you may notice it more during the summer months for two reasons. The density of traffic is such that we're more likely to use this technique to maximise the capacity of the runway and the number of aircraft flying BOGNA/SAM routes often increases relative to the others due to increased numbers of flights to France, Spain and Portugal.
You will need to pass your passing (!) altitude everytime on first contact with a radar unit - so that the mode C can be verified.
At EMA, almost everybody is on a Daventry departure (bucket and spade!), nobody 10 minutes ahead or 10 minutes behind, the request is still made before handover to London. Is the controller just standardising the call so its never forgotten or is there a technical reason?
Apologies if I've missed the latest AIC but I thought only the cleared altitude was required not the passing?
Be gentle now... pilots are stupid...I've seen Pushing Tin!
We are required to verify the ModeC before we pass you on to the area controller, we have a radar display in the tower which we use to monitor only-cannot provide a Radar service whilst in tower-this display is approved though to allow us to check the Mode C readout and this is why you will be asked your level-please visit if you would like a demonstration!