Mistake fares: How can you tell if a cheap flight price is too good to be true?

Simon Calder, also known as The Man Who Pays His Way, has been writing about travel for The Independent since 1994. In his weekly opinion column, he explores a key travel issue – and what it means for you.

A trip to Ireland always delivers generously in anticipation. I can hardly wait to begin this week’s: travelling the northern half of the Wild Atlantic Way, from Malin Head in County Donegal to Westport in County Mayo.

Unlike my first visit to the republic, I will not be hitchhiking. Instead, I am taking advantage of airfares that are approaching “too good to be true” territory.

I fly out from London Heathrow to City of Derry airport at a civilised 8.45am on a comfortable Loganair jet. Last time I flew from London to the UK’s westernmost city, the departure airport was Stansted and the fare was £180. Given City of Derry is (regrettably) a niche destination served by a 49-seat commuter jet, that is not unreasonable. And with Heathrow’s handsome handling fees, I imagined the one-way fare this time would top £200. Instead, it is just £54 – including a checked bag and a cup of tea on board.

Coming back, the fare from Knock to Stansted with Ryanair certainly doesn’t include hot drinks or luggage. But the 400-mile flight at an agreeable 6pm on a Friday evening costs only £16. In travel, if something looks too good to be true, it may just reflect intense competition between airlines.

But there are limits. Last month there was a flurry of activity in frequent flyer circles when someone identified a pricing glitch through some Vietnamese online travel agents. It appears that the Amadeus Global Distribution System – the reservations system used by many airlines – was using an exchange rate for Vietnamese dong that was completely out of line with reality.

In particular, All Nippon Airways flights starting from Indonesia to the US were priced at unprecedented low levels.

As news of the “mistake fares” spread online, hundreds of travellers grabbed bargains. Typically fares were just one-10th of what they should have been, making business or first class travel extremely affordable. Marc R was among the travellers who nabbed a bargain, picking up two return business-class tickets from Bali to New York for around £400 each.

Once the unexpected surge of worldwide premium flight bookings made in Vietnam was noticed, what was…