En-Route Seperation
 

Just would like to ask what separation do ATC in Europe require at high levels if two aircraft are at the same Flight Level, Mach No. and are on the same route? I would also like to ask how you calculate what Mach No. to assign aircraft that are converging etc. Is is based on an ETA for a waypoint?

Many thanks!

Normally 5NM, the Mach number technique is usually used to keep the separation between aircraft on the same route or before sequencing for descend/arrival, when you early detect a conflict between converging airplanes you act adjusting their course by meants of radar headings or direct to a waypoint.

It's 5nm, and the easiest way to calculate the Mach number to use it to ask the one in front what they're doing and tell them to fly that or greater and the one behind does that Mach number or less. That should hold the gap at what we want.

Experience will tell me before I even ask if it's q question worth asking. For example, I won't try and run a 737-300 in front of a 737-800/A319 unless I absolutely have to in the cruise as most 300 series don't want to go above .75 and the 800 will want to be about .78. In the descent I'd happily do it.

In the case where the back one doesn't want to go that slow or the front one doesn't want to that fast then we negotiate or different levels are used or a direct routing for one if they're splitting up later on or as a last resort radar headings.

I've had 2 DC8s at M=0.82 about a mile apart at FL350.
They were handed over to me one on top of the other at 330 and 350, same route and destination, different airlines; the lower one asked for FL370 so with both pilot's consent, I cleared him for a VMC climbthrough.

Can't do it now in the UK, FL100 or below only.

Not in Class C airspace above FL195?

Technically yes, but there's something in the MATS somewhere that prohibits it

From the latest CAP493 (MATS 1) . Section 1, Chapter 3

It surprised me too !

5C. VMC Climb and Descent
5C.1 Controllers may authorise an aircraft to climb or descend in VMC provided:
(1) the manoeuvre is restricted to Class D, E, F and G airspace at or below FL100;
(2) it is during the hours of daylight;
(3) the aircraft is flying in visual meteorological conditions;
(4) the pilot of the aircraft climbing or descending agrees to maintain his own separation
from other aircraft and the manoeuvre is agreed by the pilot of the other aircraft; and
(5) essential traffic information is given.
5C.2 The application of VMC climb and descent could result in TCAS RA being triggered.
Therefore, in Class D airspace when surveillance services are being provided, VMC climb
and descent shall only be used where authorised and in accordance with any conditions
specified in MATS Part 2.

I posted this in ATC Humour about 10 years ago, but I think it shows the danger inherent in VMC climb/descent .....

Many, many years ago, an Aer Lingus inbound Manch told Preston Airways he had the BEA aircraft opposite direction in sight and asked for descent maintaining VMC which was given. The BEA skipper said "Aer Lingus , how do you know the BEA aircraft you can see is me?". Quick as a flash, the Aer Lingus skipper said " BEA, how do you know the Aer Lingus that just descended through your level was me ?"

TFC,

I wonder if the editor of MATS Pt.1 knows that Class F Airspace disappeared from U.K. FIRs about 2 years ago?
Interesting that it's still included.

Probably because these rules are straightforward copies of relevant ICAO 4444 paragraphs and it's easier just to keep them aligned.

The only way I know to do this today is to have a friendly tower controller visually identify both aircraft (with binos) and visually monitor separation until the new vertically separated levels are achieved. MATS is silent on this technique, but there is no altitude restriction on visual separation by a tower controller.