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Thousands of airline passengers are finally heading home tonight. Flight operations have resumed in most of Europe, after a five-day shutdown caused by Icelandic volcanic ash. But many airports remain closed as a new ash cloud moves in. Hundreds of tourists are still trapped at OR Tambo Airport in Johannesburg.

The early signs were encouraging but, like the cloud itself, the flight schedule was patchy. For many it was another day of dashed hopes. One British tourist was consoled by the President Jacob Zuma when he came to open a new terminal there.

South African Airways (SAA) got as far as issuing boarding passes for a flight to Heathrow - only to have to cancel it.
SAA has 10 000 stranded customers - half of them are at airports overseas. So far, the delays have cost airlines world wide over a $1-billion.
Meanwhile, policymakers and markets trying to react to the volcanic gas cloud paralysing air travel in Europe face a host of variables, unknowns and hard-to-measure risks that make modeling almost impossible.

No one can accurately predict what the volcano - or its larger neighbour, which might also erupt soon, will do.
Short-term weather forecasts might be good but long-term weather forecasting is a notoriously inexact science. Worst of all, no one can categorically say how much ash is dangerous to aircraft.

Predicting accurately the economic and market impact is not much easier. Businesses and consumers are in unknown territory and no one knows quite how they will react or what methods they may find to get around the flight restrictions and reach their destinations safely . – additional reporting by Reuters