The ash from an Eyjafjallajokull glacier volcanic eruption in Iceland that forced the cancellation of more than 4,000 flights in Northern Europe this morning has raised some questions about the rights of air travelers, and particularly how EU laws handle displaced passengers.

Here are a some of them. You can also read this afternoon’s Washington Post chat on the topic.

Why can’t my plane fly in a cloud of volcanic ash?

Volcanic ash can damage aircraft engines, and in one notable case almost led to a crash. A British Airways Boeing 747 caught in the aftermath of the Galunggung volcano in Indonesia in 1982 lost thrust from all four engines and descended from 36,000 feet to 12,500 feet before all four engines were restarted, according to the aircraft manufacturer. The airplane, on a flight from Kuala Lumpur, Malaysia, to Perth, Australia, diverted to Jakarta and landed safely despite major engine damage. The aircraft subsequently had all four engines replaced before returning to service. Here’s an interview with the captain of that flight.

If my plane happens to fly into a cloud of volcanic ash, and if, by chance, I’m the pilot, what kind of announcement should I make?

Perhaps Captain Eric Moody of BA 9, the flight that nearly crashed in 1982, said it best:

Ladies and gentlemen, this is your captain speaking. We have a small problem. All four engines have stopped. We are doing our damnedest to get it under control. I trust you are not in too much distress.

(Thanks to commenter Clifw for the reminder of the legendary announcement heard by Speedbird 9′s passengers.)

How bad is it this time?

Brent Bowen, the head of Purdue University’s aviation technology department, says hundreds of thousand of transatlantic passengers are going to see their flights cancelled, delayed or diverted. “The short-term impact will be the greatest we have seen since Sept. 11, 2001. Unfortunately, post- 9/11, the airlines have significantly scaled back their excess capacity, and these travelers will find themselves extremely inconvenienced or even stranded,” he says.

How long before it’s safe to fly?

According to the Handbook on the International Airways Volcano Watch a “Green Alert” must be issued for the area, which means the skies are free of volcanic contaminant. Since the volcano is reportedly still erupting, no one really knows how long flights could be grounded.

What are my rights as an airline passenger?

Your rights are outlined in EU Regulation 261/2004. I would advise reading the rule carefully, as opposed to letting an airline employee interpret it for you. The rule applies to any flight within the EU and to the EU, so if, for example, you’re flying from Washington to London today, read up on this.

Your airline will probably try to invoke a clause that says during “extraordinary circumstances which could not have been avoided even if all reasonable measures had been taken,” the airline is off the hook. So it really depends on your definition of “extraordinary circumstances.”

American carriers flying domestically routinely cancel flights without compensation when there’s an “Act of God” (this is written into their legal contracts) but even when the airline says you’re out of luck and isn’t operating as scheduled, you’re still entitled to a full refund for your ticket.

Under a more customer-friendly interpretation of EU 261, you would be entitled to food and overnight accommodation. I wouldn’t bet on that, though.

How can I find out my airline’s interpretation of EU passenger rights laws?

Check out its contract of carriage on its Web site. They’re sometimes also referred to as conditions of carriage. Here’s British Airways’ for example. Interpretation of the contract and of EU 261 can vary between airlines and even between employees. Which is why you’re better off having the actual contract and law in front of you when your flight is canceled.

What about my travel agent?

If you booked your flight through an agent — and remember, even Expedia, Orbitz and Travelocity are agents — then phone the company now. Agents can re-route you around the volcano, possibly even at no extra cost. If you booked directly through an airline, and you’re dealing with a company that cares about its passengers, then rescheduling your flight won’t be a problem — assuming, of course, the plume of ash doesn’t spread, crippling air travel to all of Europe. Then your best option is to take the train (if it’s within Europe) or to cancel your trip.

Would travel insurance do any good?

Maybe. Some policies cover natural disasters, some don’t. Read your policy carefully before making a claim, and get everything in writing. In other words, if a representative tells you to “go ahead and cancel your trip” — which I’ve heard of them doing — be certain you have an email or letter to back up their suggestion that you’ll be covered. Or that your policy explicitly says you’re covered. Sadly, it’s too late to insure your Europe trip against a volcano now that one has erupted.

How do you pronounce “Eyjafjallajokull”?

I have no idea, and I’m not about to try.

(Photo: slworking2/Flickr Creative Commons)