Several million airline passengers took an unscheduled tour of travel purgatory last spring when the now-infamous drifting ash cloud from an erupting volcano in Iceland closed most European airspace. It was the biggest shutdown of civil aviation in Europe since World War II, grounding flights and stranding flyers, sometimes for days. Many travelers, anxiously running up bills for unplanned meals and hotel rooms, and shuffling, sleep-deprived, through airports, hadn’t the faintest idea what to do.

The volcano provided an extreme example of just how wrong travel can go. But as frequent travelers know, it doesn’t take a force majeure — act of God — to scramble travel plans. Dangerous weather, overbooked airplanes, mechanical failures, security breaches, strikes, crashing computers — all can result in extended flight delays, cancellations or involuntary bumping. When that happens, travelers need a smart Plan B.

Travel gurus advise crafting your Plan B before you leave home, making maximum use of consumer-friendly technology to arm yourself with information. They also advise travelers to know their rights. Aviation consumer protection laws are most finely developed in the United States and the European Union: Knowing government rules can make a world of difference in the event of a crisis.

Additionally, experts recommend printing out your airline’s contract of carriage and reading the fine print, loading your electronic devices with airline and hotel contact information for your departure and arrival airports and being prepared to speak up, nicely, to ask airlines for timely updates and other help. If you do get stuck, you’ll know how to rebook a flight, find a hotel or file a complaint. Oh, and ask for a refund, not an airline voucher, for your next flight. Vouchers come with numerous restrictions.

Kate Hanni is a California consumer activist who founded nonprofit flyersrights.org after being stranded on an American Airlines plane at Dallas-Fort Worth International Airport for nine hours in December 2006. Hanni said in an email interview that her group exists to help stressed-out flyers.

“Before you travel, you should download our iPhone application directly from our site; and our hotline number, 877 359 3776, should be in your speed dial,’’ Hanni said.”We are available 24/7 to help stranded travelers for free with their air-travel issues.’’

When you press the app, according to Hanni, “GPS is immediately activated, pinpointing the location of your plane on the tarmac. A timer begins, and at the end of three hours an alarm goes off, playing the theme song from Jeopardy, which politely and gently notifies the flight attendants of the three-hour rule needing to be implemented.”

Information on how to handle the stranding and your rights appears on the first page of the app and also on the website. The site lists toll-free numbers for dozens of airlines plus the U.S. Department of Transportation’s consumer complaints line (tel 202 366 2220).

Hanni frequently lobbies Congress and the DOT for tougher consumer protection, like a DOT rule implemented in April that requires major U.S. carriers with aircraft held on an airport runway for up to three hours to let passengers de-plane unless the captain decides that safety would be compromised. Failure to honor the rule can result in fines of $27,500 per passenger for the errant airline. Stranded flights on U.S. tarmacs were way down, at least initially, after the three-hour rule went into effect — to five in May 2010 from 34 in May 2009.

Beefed-up U.S. air-travel rules may be coming later this year. In June, Transportation Secretary Ray LaHood proposed, among other things, bringing foreign and U.S. regional feeder airlines under the three-hour tarmac delay rule, prompting airlines to provide more information about fees that add to the price of a ticket and raising to $650 and $1,300 (from $400 and $800) the compensation paid to travelers who are bumped involuntarily from overbooked flights. New rules or no new rules, Hanni said flyersrights.org will help consumers craft complaints to their airlines and to the DOT if they feel they have been mistreated or deserve compensation.

Several million airline passengers took an unscheduled tour of travel purgatory last spring when the now-infamous drifting ash cloud from an erupting volcano in Iceland closed most European airspace. It was the biggest shutdown of civil aviation in Europe since World War II, grounding flights and stranding flyers, sometimes for days. Many travelers, anxiously running up bills for unplanned meals and hotel rooms, and shuffling, sleep-deprived, through airports, hadn’t the faintest idea what to do.

The volcano provided an extreme example of just how wrong travel can go. But as frequent travelers know, it doesn’t take a force majeure — act of God — to scramble travel plans. Dangerous weather, overbooked airplanes, mechanical failures, security breaches, strikes, crashing computers — all can result in extended flight delays, cancellations or involuntary bumping. When that happens, travelers need a smart Plan B.

Travel gurus advise crafting your Plan B before you leave home, making maximum use of consumer-friendly technology to arm yourself with information. They also advise travelers to know their rights. Aviation consumer protection laws are most finely developed in the United States and the European Union: Knowing government rules can make a world of difference in the event of a crisis.

Additionally, experts recommend printing out your airline’s contract of carriage and reading the fine print, loading your electronic devices with airline and hotel contact information for your departure and arrival airports and being prepared to speak up, nicely, to ask airlines for timely updates and other help. If you do get stuck, you’ll know how to rebook a flight, find a hotel or file a complaint. Oh, and ask for a refund, not an airline voucher, for your next flight. Vouchers come with numerous restrictions.

Kate Hanni is a California consumer activist who founded nonprofit flyersrights.org after being stranded on an American Airlines plane at Dallas-Fort Worth International Airport for nine hours in December 2006. Hanni said in an email interview that her group exists to help stressed-out flyers.

“Before you travel, you should download our iPhone application directly from our site; and our hotline number, 877 359 3776, should be in your speed dial,’’ Hanni said.”We are available 24/7 to help stranded travelers for free with their air-travel issues.’’

When you press the app, according to Hanni, “GPS is immediately activated, pinpointing the location of your plane on the tarmac. A timer begins, and at the end of three hours an alarm goes off, playing the theme song from Jeopardy, which politely and gently notifies the flight attendants of the three-hour rule needing to be implemented.”

Information on how to handle the stranding and your rights appears on the first page of the app and also on the website. The site lists toll-free numbers for dozens of airlines plus the U.S. Department of Transportation’s consumer complaints line (tel 202 366 2220).

Hanni frequently lobbies Congress and the DOT for tougher consumer protection, like a DOT rule implemented in April that requires major U.S. carriers with aircraft held on an airport runway for up to three hours to let passengers de-plane unless the captain decides that safety would be compromised. Failure to honor the rule can result in fines of $27,500 per passenger for the errant airline. Stranded flights on U.S. tarmacs were way down, at least initially, after the three-hour rule went into effect — to five in May 2010 from 34 in May 2009.

Beefed-up U.S. air-travel rules may be coming later this year. In June, Transportation Secretary Ray LaHood proposed, among other things, bringing foreign and U.S. regional feeder airlines under the three-hour tarmac delay rule, prompting airlines to provide more information about fees that add to the price of a ticket and raising to $650 and $1,300 (from $400 and $800) the compensation paid to travelers who are bumped involuntarily from overbooked flights. New rules or no new rules, Hanni said flyersrights.org will help consumers craft complaints to their airlines and to the DOT if they feel they have been mistreated or deserve compensation.

Proactive travelers who empower themselves ahead of time can use the proverbial ounce of prevention to avoid struggling for a pound of cure.

“There’s a Boy Scout motto that says, ‘Be prepared,’ ’’ said David Castelveter, spokesman for the Air Transport Association, the trade group for 16 major U.S. airlines. “For people who fly with children, you bring food. I eat at home before I leave, or at the airport.’’ Worried about being stuck on a chilly, long-delayed plane? “Bring a sweater.’’

More broadly, Castelveter urged travelers to embrace technology: “I carry a BlackBerry. Most people do; they have some kind of PDA. You can identify hotels in your area, places to eat. Carry airline 800 numbers in your phone. A lot of aircraft have WiFi; I’ve watched people on board open their laptops and rebook themselves.’’ Airline contracts of carriage? “Every one of them has it on their website.’’

“Airlines do their absolute best,’’ Castelveter said. “When you fly a lot, things happen.’’