The CAA's revised guidance says airlines should conduct their own risk assessments, look for ash damage before and after flights and report any incidents to the regulator.
The government says it will soon publish revised guidance, encouraging local authorities to use risk-free land first, and obliging developers to pay for flood defences when they build on risky land.
This agreement, called the Basle Accord, is being revised, largely because the original makes only crude distinctions between loans' different levels of risk.