First is the fall of tourism from the United States and the new tough line on Cuba adopted by the Trump administration. Through March of this year, the number of visitors from the United States is down more than 40 percent compared with 2017. This is partly because of travel warnings over safety issued by Washington, partly because of new travel restrictions put in place by President Trump and because after the initial boom of nostalgic tourism, Cuba is now competing for normal travelers with the rest of the Caribbean. Its beauty and charm do not easily outweigh other destinations’ far superior services and infrastructure, and lower prices. Today myriad start-up businesses — always thought to be too small and numerous to survive — that sprang up for United States visitors are failing as a result of falling tourism.

Second, American sanctions and Cuban fear of economic reforms have rendered the push for greater foreign investment somewhat futile. After an initial rush of highly publicized announcements, some United States companies have proved reluctant to run risks, particularly given Mr. Trump’s hostility toward all things Obama, and his dependence on Florida for re-election.

The economy has stopped growing, scarcities have re-emerged and new opportunities for employment and hard-currency earnings are not appearing. If one adds to this the government’s decision to suspend new cuentapropista or private self-employment permits, it is no surprise to discover that economic prospects are dim. Hence the appropriateness of the metaphor regarding the crash outside Havana: like the Cuban economy, the plane was old, poorly maintained, leased by the national airline because it was the only one it could afford, and the rest of Cubana de Aviación’s domestic fleet had already been grounded.

Which brings us to the third source of concern. Venezuela is no longer able to subsidize Cuba’s transition to a Vietnam-style socialist economy the way it did before.