Essex plane crash narrowly avoided near Rivenhall
Two planes had a "serious risk" of colliding in mid-air over farmland, a report has found.
The pilot of a X-Air Falcon said there had been a "high" risk of crashing with a PA-28 near Witham in Essex.
At the time of the incident, on 18 July, there were two pilots in the PA-28 but neither saw the other plane flying at about 2,000ft (600m).
The UK Airprox Board investigation said a collision had only been avoided "by providence".
According to the report, the Falcon pilot had been flying towards Earls Colne when "a blue, single-engine, low-wing aircraft passed from behind in close proximity on the right".
The report estimated it was 600ft (185m) away laterally and 20ft (6m) vertically when they were at their closest between Kelveden and Silver End.
At the time, the PA-28 was conducting a simulated IMC flight, in which a pilot flies fly by referring only to instruments, rather than outside visual references.
The Civil Aviation Authority (CAA) advice states that this kind of flight needs a "suitably qualified extra crew person to increase lookout".
But the report found the PA-28's other pilot would have been "under the hood" and "did not have the ability to lookout effectively" while the other would have been busy "monitoring the instruments".
The investigation said both pilots "shared an equal responsibility for collision avoidance" and gave the incident a rating of A, which means a "serious risk of collision exists".
It recommended that in future, pilots consider cancelling instrument-based practice flights if traffic is high or surveillance-based air traffic updates cannot be obtained.