Eight months ago we learned what happens when aircraft engines fail, courtesy of an ash cloud from a volcano nobody could pronounce.
This week we learned what happens when European airports fail, courtesy of something less remarkable, snow.
If you pardon the pun, snow crystallised things. It separated the functional airports from the dysfunctional. Heathrow invested inadequately in infrastructure, Gatwick invested well.
Dublin fell somewhere between the two, de-icing runways in a manner as befits a country where snow comes fitfully and dumps come at 20 year intervals. In all three cases, passengers were badly hit.
Dublin stuttered back into action this morning, albeit with a few cancellations to Heathrow, Frankfurt, Gerona, Lisbon and some domestic flights.
The events showed once again the mismatch between the clear EU rules on customer care (phone calls, food, overnight accommodation) and what the airlines are actually willing or able to provide.
Information was in short supply as websites crashed or were not updated; call centres were overwhelmed and desks went unmanned or were staffed by youngsters with no idea of what was actually happening.
Many of the passengers already in the airport had no access to websites anyway. The angry customers include airlines as well as passengers.
On Wednesday, British Airways cancelled 150 flights on the basis of what it said turned out to be misleading guidance from Heathrow about when the second runway would reopen.
This morning, two days later, the backlog of stranded passengers at Heathrow still stood at 600,000, up to 25,000 Irish among them, despite the airport operating a full schedule of 1,200 flights yesterday.
This contrasts with Charles de Gaulle in Paris and Frankfurt, which cleared their backlogs within hours of re-opening.
Heathrow was the target of EU Transport Commissioner Siim Kallas's statement on Wednesday that he would be holding airports accountable for inadequate preparation against the weather.
Considering Kallas's lack of success in bringing airlines to book for failure in their duty of care to passengers, passengers should not get too much hope from this.
Irish airports will be taking heed of the Heathrow lesson when they plead they don't have the need to invest in the sort of snow-clearing infrastructure that kept Stockholm, Oslo and other northern airports open. Part of it is Michael O'Leary's fault.
Airports such as Dublin are running short of sources of income. Since they took to the skies in the mid-1990s, low-cost airlines are looking for more and more high-end investment in infrastructure, such as air bridges, for quick turnaround.
They also insist on paying less for them.
Dublin Airport Authority has been arguing for years that its fees are inadequate to pay for any investment in infrastructure, even discounting the enormous cost of Terminal 2.
Michael O'Leary's response has been to tell them that their retail outlets and food halls are the place to make the money.
Airports have now started to run out of money for infrastructure. But that is one side of the argument. O'Leary has long argued that private airports are run more efficiently than public or state-subsidiary airports.
Gatwick is no longer run by the British Airports Authority, and seemed to get its act together much better than Heathrow in recent days. If this week' snow teaches us how to run airports more efficiently, it will have done some good.
It is hardly consolation for those who will spend Christmas in an airport hotel, as now seems inevitable, or on a terminal floor.