Hi, thanks for giving me the extra info.
The first point I have to make is that your travel begins outside of the United Kingdom, and our advice is generally aimed at those who are resident in the UK and not only begin their travel but also purchase their travel insurance on this basis.
Please check that the policy you have bought is appropriate for use by anyone commencing travel outside of the UK and resident outside of the UK.
The Aviation Authorities rarely if ever cancel flights. They closed air space in the two recent ash cloud events; however it is normally an airline that cancels a flight, not the authorities, so it is rare that you would be even trying to make a claim on that basis.
Flights can be cancelled for a variety of reasons, weather, technical, crew, operational etc., however in the first instance all flights departing from the EU are subject to EU regulations for delays and cancellations. All insurers will refer a customer to their rights under these before even considering any form of claim. You can read more here http://www.caa.co.uk/default.aspx?catid=125 Whilst this is a UK site the same rules apply in Eire due to EU wide ruling.
Once you are outside of the UK it depends on whether your flight is operated by an EU carrier or not. Only those who are EU based are affected by the rules, whilst those who are not or those who are merely flying to the EU who are not EU based do not have to apply the rules.
So if you had a flight cancelled by Air Canada or Continental and it was not departing Dublin, then you are reliant on the normal airline policy. Airlines flying long haul will tend to put you on the next available flight, re-route you or pop you in a hotel overnight to travel the next at their expense. So you will get there, just be delayed in your journey.
A travel insurance policy sold in the UK will normally offer the ability to claim for travel delay due to cancellations of flights as well as some additional costs, those that are not covered under EU261. These vary from policy to policy to be fair so if in doubt ring the AA for advice.
If you miss your flights it would depend on the reason. If you are connecting on one ticket from one flight to another then the airline has to sort you out. If you miss a flight due to the failure of say a bus or train or car getting you to an airport, you may be able to claim under missed departure if your policy has this and if your reason for missing the flight is covered by it. Again each policy varies, so do check the detail.
I hope that this helps advise you further.
Travel expert, www.travelsupermarket.com