When the track system is active, most random routes are either above or below the established levels
On an averge day the numbers of randoms routing above or below the OTS number two dozen max. However, as much as 25% of overall traffic can be on random routes, between 310/410 inclusive, outside (north or south) of the OTS. Particularly if the forecast WX changes significantly from the time the OTS is designed and published to when operators submit a FPL. LIDO/CIRRUS or equivalent systems will get a weather update post track publication and operators may well determine that a random route is more cost effective than any particular organised track. Given that a busy 24hr period can see 1400+ flights crossing the pond the numbers of random flights either side of the OTS can be significant; those above or below the OTS less so.
Does one still need to offset 15nm before descending in case of an emergency.
- no. See Mutt's post 4.
You
are required to offset 15 irrespective of flying on a published OTS or random route. Doc4444 15.2.2.3 states:
"Specifically, the pilot shall:
a) Leave the assigned route or track by initially turning at least 45 degrees to the right or left, in order to acquire a same or opposite direction track offset 15 NM (28 km) from the assigned track centerline. When possible, the direction of turn should be determined by by the position of the aircraft relative to any organized route or track system."
In addition, the SUPPS to Doc7030 state:
"9.1.1.1 Descent through the MNPS airspace
9.1.1.1.1 An aircraft that is not MNPS/RVSM-approved and is unable to maintain a flight level above MNPS/RVSM airspace should descend to a flight level below MNPS/RVSM airspace".
- going on, with regard only to those above F420 who do not have MNPS/RVSM approval, infringing the OTS during an emergency descent, to state:
9.1.1.1.2 An aircraft compelled to make a descent through MNPS airspace, whether continuing to destination or turning back, should, if its descent will conflict with an organized track:
a) plan to descend to a level below FL 280;
b) prior to passing FL 410, proceed to a point midway between a convenient pair of organized tracks prior to entering that track system from above;
c) while descending between FL 410 and FL 280, maintain a track that is midway between and parallel with the organized tracks; and
d) contact ATC as soon as practicable and request a revised ATC clearance.
The OP was referring to levels within MNPS:
If one is flying within the vertical airspace ie. FL285 to FL420 lets say FL360
To quote 9.1.1.1.2 whose procedures only apply to those operating above F420 without MNPS/RVSM approval, conducting an emergency descent through the OTS, when the OP seeks info for procedures applicable to F360, may be somewhat misleading.
We have had, (most recently from crew operating EINN - CYQX), telephone calls to our desk from biz jet crews who don't regularly jump the pond and who have apparently been provided with way out of date procedures or worse, none at all. However, asking for info re. procedures on sites like this has its risks - better just to provide the links, as per Bigears, and let the OP do the rest IMHO.