Description

On 31 December 2011 a Beech 200 C12 being operated by the USAF on a ferry flight to the US was flying from Prestwick to Stornoway as part of that mission. During a non precision approach to Stornoway in day IMC, it descended into conflict with a Saab 340 being operated by Loganair on a scheduled passenger flight from Edinburgh to Stornoway which, after seeing the conflict on Airborne Collision Avoidance System (ACAS), descended early to increase separation.

Investigation

An Investigation was carried out by the UK Airprox Board. It was noted that although a report on the incident had been requested from the US Third Air Force, no such report had been forthcoming. It was also noted that the incident had occurred in uncontrolled airspace and with only procedural ATS available and with APP and TWR duties being performed by one controller and an assistant.

It was established that both aircraft had been cleared by ATC to make an approach using the Runway 18 LOC/DME/NDB (L) procedure involving a DME at the threshold. The diagram below reproduced from the official report shows this procedure.

The C12 had been No 2 and had consequently been instructed to remain at 3000 feet on QNH 990 hPa outbound until advised and had correctly read this back but without mention of hPa (or mb).