Pilots are allowed up to 14 days to report a crash, CAA Corporate communications manager Mike Richards said.
He believed the microlight was performing a routine "go-around operation" manoeuvre and potentially pilot error was responsible.
"At this stage there doesn't appear to be any critical safety learning from it," Mr Richards said.
"Every accident is a concern we do still want to find out what caused it."
Auckland Regional Microlight Aircraft Club president Richard Seymour-Wright was aware of the incident and was liaising with the families of the injured pilots.
Police said the injured men were initially given first aid by friends and fellow flying enthusiasts who were part of a small gathering at the field.
Aged 61 and 63, the men were thought to be experienced pilots and the microlight was a professionally constructed machine.
Weather conditions were fine and were not thought to have contributed to the crash.
The owner of the microlight was not one of the vehicle's occupants.
