Separation issue involving a de Havilland Canada DHC-8-102, VH-WZI and Beech Aircraft Corp E95, VH-IJM, 17 nm north of Devonport, Tasmania, on 30 April 1993

On descent into Devonport regular public transport aircraft, VH-WZI, made radio calls on the Flight Service (FS) frequency and on Devonport Mandatory Traffic Advisory Frequency (MTAF) prior to leaving controlled airspace at 10000 ft. There was no response from any other aircraft. When VH-WZI was approximately 18 NM north of Devonport, FS asked Air Traffic Control (ATC)for the position of VH-WZI. A short time later FS advised VH-WZI that ATC had VH-IJM on frequency 17 NM north of Devonport tracking for Hobart at 7500 ft. At this, VH-WZI terminated the descent and initiated a climb to 8000 ft in visual meteorological conditions. VH-IJM was transferred to the FS frequency and separation was effected. The crew of VH-WZI sighted VH-IJM half a mile to the right and below but it was extremely difficult to see VH-IJM due to underlying cloud cover.

The pilot of VH-IJM was flying to visual flight rules. VH-IJM had transferred to the ATC frequency at least 20 NM north of Devonport in order to obtain a clearance into controlled airspace which starts north of Devonport. The pilot was monitoring one radio frequency at a time. He was unaware of VH-WZI until he saw it.

The captain of VH-WZI believes that on routes where there is traffic climbing or descending to locations under controlled airspace, then the design of the airspace should be such that frequency separation is not encouraged; otherwise, procedures should be established to cater for such occurrences.

The manager of FS advised that where an aircraft is single very high frequency (VHF) radio equipped (or a pilot is monitoring only one frequency), with similar circumstances a similar incident could reoccur.

The current procedures for pilots and air traffic personnel, combined with the existing airspace configuration, do not prevent this type of incident from occurring.

Significant Factors

The following factors were considered relevant to the development of the incident:

1. The pilots of both aircraft complied with existing rules and regulations.

2. Air Traffic Services provided more than the required service.

3. The combination of existing rules, procedures and airspace does not prevent this type of occurrence.