A near-miss between airplanes. There are slight differences between countries. The UK Civil Aviation Authority (www.caa.co.uk) defines an "Airprox" (Air Proximity) as follows:
"For every Airprox incident assessed the [Airprox] Board determines one or more causal factors. These tell us why events started in each instance and signposts the lessons to emerge. It is self evident that attention paid to 'cause' is worthwhile because it is likely to deliver and promote better prevention'. The UKAB database records record causal factors under 83 separate description.
"Risk level assessments are made on the basis of what actually took place and not on what may or may not have happened. There are four categories, agreed at international level, as follows:
? "A Risk of Collision An actual risk of collision existed
? "B Safety not assured The safety of the aircraft was compromised
? "C No risk of collision No risk of collision existed
? "D Risk not determined Insufficient information was available to determine the risk involved, or inconclusive or conflicting
evidence precluded such determination"
The US Federal Aviation Administration prescribes separation minima, but does not appear to have a similar level of classification for separation loss.