What aircraft was involved and where did it happen?

The accident on 2010-06-21 involved a 1. Cirrus Design Corp. SR22, at nahe Eisenach, DE.

What was the probable cause of the accident?

The close proximity was caused by a reduction in vertical separation to 100 feet between an IFR flight and a VFR flight, exacerbated by the SR22 crew's inability to maintain visual contact with the Mitsubishi aircraft due to cloud cover.

Mid-air proximity between VFR and IFR aircraft near Eisenach

A Mitsubishi Mu 2B-26A and a Cirrus SR22 experienced a close-range encounter in controlled airspace due to vertical separation loss.

What happened

On June 21, 2010, at approximately 08:05 local time, a mid-air proximity occurred in controlled airspace roughly 13 nautical miles southwest of Eisenach, Germany. The incident involved a Mitsubishi Mu 2B-26A operating under Visual Flight Rules (VFR) and a Cirrus SR22 operating under Instrument Flight Rules (IFR).

The Mitsubishi aircraft was climbing from Eisenach-Kindel toward Egelsbach. Simultaneously, the Cirrus SR22 was en route from Bremen to Nuremberg at flight level 70.

At 08:04:22, air traffic services provided the crew of the SR22 with traffic information regarding a VFR aircraft at the 10 o'clock position, 4 miles away, at an indicated altitude of 5,900 feet. The SR22 crew noted they had the aircraft on their traffic system but could not establish visual contact due to cloud cover. The pilot reported that the other aircraft subsequently climbed through the SR22's position and disappeared into the clouds.

Shortly after, at 08:04:43, the pilot of the Mitsubishi aircraft was notified of traffic at the 2 o'clock position, 4 miles away, at flight level 68. The pilot reported seeing the traffic and increased the climb rate to 3,000 feet per minute. While the Mitsubishi pilot believed they maintained visual separation at a vertical distance of approximately 1,200 feet, radar records indicated a much closer encounter. Radar data showed the Mitsubishi aircraft was at flight level 69 while the SR22 was at flight level 68, resulting in a horizontal separation of only 0.28 nautical miles and a vertical separation of just 100 feet.

The investigation

The BFU examined radar recordings and air traffic service communications. The investigation also reviewed meteorological data, which confirmed a thick cloud layer with bases around 500 feet AGL and high moisture content in the area.

Findings

The primary cause of the close proximity was the loss of vertical separation between the two aircraft.
The SR22 was flying through a layer of clouds, which prevented the crew from establishing visual contact with the VFR traffic despite having the aircraft on their traffic system.
The Mitsubishi aircraft was not equipped with an ACAS (Airborne Collision Avoidance System), whereas the SR22 was equipped with an ACAS, though no TCAS Traffic Advisory (TA) or Resolution Advisory (RA) was triggered during the event.
Meteorological conditions included heavy cloud cover and moisture, which limited visibility for the IFR flight.