Longitudinal separation in MNPS airspace

[Gin Slinger]

Can anyone confirm to me the speed differential required between the lead and following aircraft to reduce longitudinal separation in MNPS airspace down from 10 minutes to 5 minutes?

[Broken Wings]

From the Bristol GS notes:
"If the aircraft in front is going faster by at least M0.02 and it is possible to ensure that the time interval exists using radar or another approved means the separation can progressively reduced down to 5 minutes if the one in front is M0.06 faster"
Hope this helps.

[Gin Slinger]

Don't understand that. Is it saying that the a/c in front is travelling M.02 faster, but in fact is capable a further M.04 increase?

Also, if the a/c in front is travelling faster, how is it possible to reduce the separation anyway?

[eyeinthesky]

I think what he is asking refers to the need for aircraft to be 10 minutes apart when EXITING MNPS airspace at the same level. The mach numbers which are allocated by Oceanic Control are calculated to achieve that based upon entry time into MNPS airspace. If you think about it, it is the EXIT time which is important, otherwise it would be like being stuck behind a caravan on a country road, with everything reduced to the speed of the slowest in front. With this system you can have a 747 (M 0.86)entering behind a 767 (M 0.80) provided enough time exists at the start to ensure 10 minutes at the end.

Were the situation above to be reversed (747 in front of 767) then the time separation could be reduced to 5 minutes (one assumes on ENTRY in this case otherwise the 767 would have to be in front of the 747 at the start to end up 5 mins behind at the end and this is not considered good practice without radar to help you overtake!) as the 767 will never catch the 747.

So there is in fact no catch-up involved.

The Bristol GS notes say it can be 'progressively reduced to 5 minutes'. What I don't know is whether that means that it could, for example be 7 minutes for a differential of M0.04 or whatever.

It is a long time since I was up to date on Oceanic practices, so this may all be completely wrong, in which case: Sorry!

[4PON4PIN]

You are referring to Mach Number Technique.
QTE: "To assist in ensuring longitudinal separation between successive a/c the mach number technique may be used.
Aircraft will be instructed to fly at a specific mach number FROM the oceanic boundary.
For each M.0.01 difference in speed the separation between 2 a/c is increased by 3 minutes when the following a/c is faster. (This increase is to ensure a minimum of 10 minutes at the point the flights LEAVE oceanic airspace and may need to be increased, or could be decreased, dependent on specific wind patterns on the day).
e.g. M0.81 behind M0.80 = normal separation of 10 mins + an extra 3 mins = 13 mins (at the oceanic entry point)
An aircraft cleared at M0.86 behind one at M0.74 would require at least 46 mins separation. (Not the best use of airspace!).
If the faster a/c is in front then the separation on entry may be decreased as the first a/c will pull away. A sliding scale is used down to a MINIMUM of 5 mins on entry.
e.g. M0.84 ahead of M0.80 = 7mins.

M.80 - M.80 = 10 mins M.86 - M.86 = 10 mins
M.80 - M.81 = 13 mins M.86 - M.85 = 10 mins
M.80 - M.82 = 16 mins M.86 - M.84 = 9 mins
M.80 - M.83 = 19 mins M.86 - M.83 = 8 mins
M.80 - M.84 = 22 mins M.86 - M.82 = 7 mins
M.80 - M.85 = 25 mins M.86 - M.81 = 6 mins
M.86 - M.80 = 5 mins
UNQTE:
Above taken from notes supplied by Shanwick Oceanic Control.
Note the need to ensure 10 mins separation on exiting oceanic airspace and dependent on length/routing of tracks.
M0.01 equates to approx 5kts.
Hope this clarifies.

[eyeinthesky]

Not a bad hazy recollection on my part then!!;)

[Gin Slinger]

Thanks 4PON4PIN - the veil of mystery is now fully lifted!

Thanks to everyone else too - ain't PPRuNe great for finding things out?