Figure: NAT Region, from Eddie's notes.
Regional differences from the ICAO standard can be found in ICAO Document 7030 and your Jeppesen Airway Manual. Both of the sources, however, can be out of date. See International Operations Manual / Regional Introduction for ideas about getting up-to-date information.
As countries around the world update navigation systems and procedures, it becomes increasingly important to speak with somebody who has been to the airport recently or have a contact in country with local knowledge. As we say in the military, there is no substitute for boots on the ground.
You should also be aware that the North Atlantic Track System includes track with reduced lateral separation, as announced by Flight Service Bureau Ops Notice 11/15.
What follows comes from the references shown below. Where I think it helpful, I've added my own comments in blue.
ICAO Doc 7030, §NAT, ¶3.4.1] Within the NAT Region, aircraft equipped for SATCOM voice shall restrict the use of such equipment to emergencies and non-routine situations. An unforeseen inability to communicate by voice radio constitutes a non-routine situation. Since oceanic traffic typically communicates through aeradio facilities, a SATCOM call due to an unforeseen inability to communicate by other means should be made to such a facility rather than the ATC centre unless the urgency of the communication dictates otherwise. Dedicated SATCOM telephone numbers (short codes) for aeradio facilities and air traffic control facilities are published in national AIPs.
HF is required for U.S. Operators for just about every oceanic region in the world, though SATCOM can be used. The North Atlantic places this additional restriction on the use of SATCOM in place of HF for position reports. More about this: Procedures & Techniques / HF.
This region is moving from a mix of navigation requirements to the system of Performance Based Navigation outlined in ICAO Document 9613. Current navigation requirements are available on Jeppesen Airway Manual Air Traffic Control pages and Chapter 4 of each region covered by ICAO Document 7030.
[ICAO Doc 7030 Amendment 1, §NAT, ¶188.8.131.52.]
Keep in mind RNP 10 is an exception to the rule of Required Navigation Performance standards, "RNAV 10" retains the "RNP 10" designation for matters of convenience.
[ICAO Doc 7030 Amendment 1, §NAT, ¶184.108.40.206.1.]
The MNPS has been replaced by the North Atlantic High Level Airspace (NAT HLA) but ICAO Doc 7030 hasn't caught up yet. For now, you can just associate NAT HLA with MNPS. More about this: Airspace / North Atlantic Airspace (NAT HLA).
All three countries listed in the NAT region, the Azores, Greenland, and Iceland are listed as WGS-84 in the Jeppesen WGS-84 website, but Greenland is listed only as partially compliant in their Jeppesen Airway Manual ATC page, dated 16 Aug 2013.
More about this: International Operations / World Geodetic System 84 (WGS-84).
[ICAO Doc 7030 Amendment 1, §NAT, ¶4.2.1.] RVSM shall be applicable in that volume of airspace between FL 290 and FL 410 inclusive in all FIRs of the NAT Region.
More about this: Procedures & Techniques / Reduced Vertical Separation Minimum (RVSM).
Transition altitude and level procedures vary by country.
More about this: International Operations / Transition Altitude / Layer / Level.
[NAT Doc 007, ¶3.3.1] The North American Routes (NARs) consist of a numbered series of predetermined routes which provide an interface between NAT oceanic and North American domestic airspace. The NAR System is designed to accommodate major airports in North America.
The NARs used to be in an easy to find location in paper copies of Jeppesen Airway manuals but not so much with the electronic version. The link provided by NAT Doc 007 died years ago. JeppView contains a few paragraphs about the "North American Route Program (NRP)" but little else. I have been assigned NARs and I do see them on my PlaneView Charts. The best source other than the G450 cockpit: http://www.nyartcc.org/pilotcenter/narsw.
[NAT Doc 007, ¶3.3.8] The NERS exists to provide an interface between NAT oceanic and European domestic airspace. The scheme is similar in concept to the NARS which has been in use in North America by NAT traffic for many years. It consists of a numbered series of predetermined routes, designed to accommodate eastbound traffic exiting the NAT en route to a number of major European airports.
[NAT Doc 007, ¶2.1.1.] As a result of passenger demand, time zone differences and airport noise restrictions, much of the North Atlantic (NAT) air traffic contributes to two major alternating flows: a westbound flow departing Europe in the morning, and an eastbound flow departing North America in the evening. The effect of these flows is to concentrate most of the traffic unidirectionally, with peak westbound traffic crossing the 30W longitude between 1130 UTC and 1900 UTC and peak eastbound traffic crossing the 30W longitude between 0100 UTC and 0800 UTC.
[NAT Doc 007, ¶2.1.2.] Due to the constraints of large horizontal separation criteria and a limited economical height band (FL310–400) the airspace is congested at peak hours. In order to provide the best service to the bulk of the traffic, a system of organised tracks is constructed to accommodate as many flights as possible within the major flows on or close to their minimum time tracks and altitude profiles. Due to the energetic nature of the NAT weather patterns, including the presence of jet streams, consecutive eastbound and westbound minimum time tracks are seldom identical. The creation of a different organised track system is therefore necessary for each of the major flows. Separate organised track structures are published each day for eastbound and westbound flows. These track structures are referred to as the Organised Track System or OTS.
[NAT Doc 007, ¶2.1.4.] Over the high seas, the NAT Region is primarily Class A airspace (at and above FL55) (See ICAO Doc. 7030 - NAT Regional Supplementary Procedures), in which Instrument Flight Rules (IFR) apply at all times. Throughout the NAT Region, below FL410, 1000 feet vertical separation is applied. However, airspace utilisation is under continual review, and within the MNPS portion of NAT airspace, in addition to the strategic and tactical use of 'opposite direction' flight levels during peak flow periods the Mach Number Technique is applied.
[NAT Doc 007, ¶2.3.1.] The agreed OTS is promulgated by means of t h e NAT Track Message via the AFTN to all interested addressees. A typical time of publication of the day-time OTS is 2200 UTC and of the night-time OTS is 1400 UTC.
[NAT Doc 007, ¶2.3.5.] The hours of validity of the two Organised Track Systems (OTS) are normally as follows:
Each country departs in some ways with the ICAO standard and common US practices. Pilots should always refer to the Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures pages for each country on their itineraries for differences with ICAO Standards, Recommended Practices and Procedures. More about this: International Operations / US versus ICAO.
The following are a sampling of some of the differences, there are many more. You should check the Jeppesen Airway Manual State pages for every country you takeoff, overfly, or land.
[NAT Doc 007, ¶220.127.116.11.] Unable to obtain oceanic clearance using HF voice.
Note.— Failure of HF communications often stems from poor signal propagation, frequently because of sun spot activity, and is likely to simultaneously affect multiple aircraft operating in a particular region. ATM systems dependent on HF are designed around the assumption that communication may be temporarily interrupted and that aircraft affected will continue to operate in accordance with the last received and acknowledged clearance, until communication is restored.
[NAT Doc 007, ¶9.3]
Communications failure prior to entering NAT Region
Communications failure prior to exiting NAT Region – Cleared on filed flight plan route
Communications failure prior to exiting NAT Region – Cleared on other than filed flight plan route
Note.— The relevant State procedures/regulations to be followed by aircraft in order to rejoin its filed flight plan route are specified in detail in the appropriate national Aeronautical Information Publication.
These are exceptions to ICAO Lost Comm procedures. More about this: Abnormal Procedures / Lost Communications.
[NAT Doc 007, ¶8.5.2.] This [SLOP] procedure provides for offsets within the following guidelines:
[Jeppesen Airway Manual, Air Traffic Control, State Rules and Procedures, Europe, Iceland, 16 Aug 2013] SLOP is not allowed in airspace where the applied lateral separation is less than 30 NM. /since the lateral separation may be as low as 7 NM below FL285 in the Reykjavik CTA the following applies:
SLOP is encourage in the North Atlantic except for the Iceland restriction noted.
More about this: International Operations / Strategic Lateral Offset Procedure (SLOP).
ICAO Doc 7030 - Regional Supplementary Procedures, International Civil Aviation Organization, 2 2008
ICAO Doc 9613 - Performance Based Navigation (PBN) Manual, International Civil Aviation Organization, 2008
NAT Doc 007, North Atlantic Operations and Airspace Manual Doc 007, Edition 2013
Jeppesen Airway Manual