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ATC FAQs

Why does so much need to be reconfirmed when contacting delivery after getting a datalink PDC?

The PDC system isn’t able to check stand number, aircraft type, Information received or the QNH (even if you type it into remarks). We need confirmation of stand number and aircraft type in case the system has it wrong and we start too many in one area or a push-back is given thinking it is on a different stand and creating a potential confliction/ safety hazard. QNH is a mandatory verbal confirmation, a CAA (SRG) requirement.

Two aircraft are on the same route, how is it decided who goes first?

Most of the time it’s first come first served at the holding point. Once the controller has taken into account any slot times or route restrictions then they try to choose the best order to achieve maximum runway capacity. It also depends on where the aircraft are at the holding point. Is it possible to get an aircraft to the front of the queue? Has one aircraft had a longer taxi than another? What cruising level have they requested en-route? Ideally the aircraft with the higher requested level on the same route will go first as this helps radar controllers in the subsequent sectors.

Why do we have to have a new slot because (ATC) can't get us airborne on the current one (20 mins away) due to airfield delays? I thought that was the whole point of a slot.

ATC slots aim to ensure that en-route radar sectors or destination airports do not become overload. When we operate start up delays we take all aircraft into account whether they have a slot time or not. It is not fair to further delay aircraft without slots just to get those with slots away. If after taking the full airfield situation into account it is deemed not possible to get you away in your slot then we will request a new one based on the time we expect to be able to give you start approval. If there is subsequently a delay greater than the current airfield delay we will contact CFMU and try to get a CTOT for your aircraft that is more appropriate.

UK ATC is fantastic in the air yet terrible at line up clearances. There is too much information in the clearance. Why?

This is a CAA (SRG) requirement which was introduced a few years ago. The idea is to improve situational awareness for both the aircraft in receipt of the clearance and for the benefit of other aircraft at the holding point, if you hear a line-up clearance for a holding point you are not positioned at, was that clearance actually for you?

Why do we get so many heading changes? I don't know the big picture but if all the SID and STAR routes are non conflicting then why not control separation via speed?

Most of the EGLL SIDs take aircraft under the holding stacks. Controllers vector aircraft off the SIDs away from the stacks in order to climb them earlier. Also agreements between different sectors dictate that aircraft are positioned in certain places. For example, EGLL CPT departures routing CPT-L9/N14 have to be positioned on the North side of L9 and not following the flight-planned route CPT-KENET etc.

The briefing says all a/c should advise ATC if unable to maintain 250kts etc i.e. most days on the 744. There was a time when large a/c such as the 744 /777 etc could ignore this request particularly with mode S transponders can we not (contrary to what it says on the NUBRIEF) assume that ATC know we will exceed 250kts?

All departures from EGLL must maintain 250Kts or less until passing FL100 (or instructed by ATC) with the exception of B744 aircraft who may accelerate to 280Kts. If aircraft other than B744 require a speed greater than 250Kts they must inform ATC.

Have a question not answered here? Send it to LHROps@nats.co.uk

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