Yo Parche - can you answer this question?

from an amateur aviation fan - why Gander?

http://www.avherald.com

I've been following that website every day for the last month or so, and see a lot of international flights divert to Gander.

/me wiki's Gander

Hawkeye-X

That is on the International route plan that the airlines use

These step by step instructions will show you how to correctly file an oceanic flight plan, using the example flight of ACA866 from Montreal Trudeau International (CYUL) to London Heathrow (EGLL)

Selecting the NAT

The NATs change twice a day,at 00z and 12z, which makes planning the day of the flight essential. Updated NATs are available two items up on the menu.
For this example let's say the following routings are current:

NAT East-Bound Routings

Track V - CYMON DENDU 51/50 52/40 53/30 54/20 DOGAL BABAN
Track W - YQX KOBEV 50/50 51/40 52/30 53/20 MALOT BURAK
Track X - VIXUN LOGSU 49/50 50/40 51/30 52/20 LIMRI DOLIP
Track Y - YYT NOVEP 48/50 49/40 50/30 51/20 DINIM GIPER
Track Z - COLOR RONPO 47/50 48/40 49/30 50/20 SOMAX KENUK

Which track to choose? Well it all depends on where you are flying from, and where you are going. Generally the most favourable winds are situated along the "middle" track, so unless this causes a gigantic detour it's a good idea to plan to use it. If however using this track would cause a rather large increase in distance you should consider a more southern or northern track.

The frequency is 128.45, or 135.45 - Callsign is Gander centre (CZQX_OC_CTR). If this station is not online the clearance can be requested from Gander Radio (CZQX_FSS) or ultimately Gander Domestic (i.e. the radar controller you are already talking to).
ATC will not initiate the communication. It is up to the PILOT to call ATC, not the other way around.

Below is the transcript of a typical Oceanic clearance:

Pilot: "Good evening Gander center, Air Canada 866"
ATC: "Air Canada 866, Gander center, Good evening go ahead"
Pilot: "Air Canada 866 request London Heathrow via track X-RAY Flight Level 360, Mach .80. Estimating VIXUN at 0243zulu"
ATC: "Air Canada 871 cleared to destination via VIXUN, track X-RAY, Expect FL360, Mach .80, cross VIXUN 02:43z"
Pilot: "Air Canada 871 cleared to destination via VIXUN, track X-RAY, Expect FL360, Mach .80, cross VIXUN 02:43z, TMI 230"
ATC: "Air Canada 871 readback correct, good night" - at this point the pilot will return to his previous controller.
Datalink clearance

:hi:

After Gander they follow established tracks over the North Atlantic, which change daily, and get handed off to Shanwick OCA, named for two ATC facilities, Shannon, Ireland, and Prestwick, Scotland. What you are seeing are not diversions; those are normal routes.