Occurrence Overview
A Wildcountry Airways Chieftain operating under instrument flight rules (IFR) from Red Lake to Atikokan, Ontario, and a Fast Air Piper Navajo on a visual flight rules (VFR) flight from Winnipeg, Manitoba, to Sioux Lookout, Ontario, came into close proximity approximately 20 nautical miles northwest of Dryden. The Chieftain was at an assigned altitude of 7,000 feet asl, while the Navajo planned to cruise at 7,500 feet asl. The pilot of the Chieftain spotted the other aircraft at his two o'clock position on a collision course, transmitted a position report on 126.7 MHz without establishing contact, and took evasive action. Radar data later showed the aircraft were about one quarter of a mile apart laterally and 200 feet vertically when their tracks crossed.
Altimeter Settings and Aircraft Performance
Both aircraft were operating within the altimeter setting region and were required to set their altimeters to the Dryden altimeter setting. The Chieftain pilot had reset his altimeter to 30.08 inches of mercury as required. The Navajo pilot had not reset his altimeter after departing Winnipeg and still used a setting of 30.38 inches. Each difference of 0.10 inches of mercury corresponds to approximately 100 feet of altitude variation. Consequently, although the Navajo indicated 7,500 feet, its actual altitude was about 7,200 feet asl, reducing the vertical separation between the two aircraft by 300 feet below the required 500 feet.
Air Traffic Control Context
The incident occurred in Class E controlled airspace, where ATC provides separation only to IFR aircraft. The Kenora Sector was staffed by a single controller handling both radar and data duties. At the time, the controller was focused on data tasks and not monitoring uncorrelated target symbols. The Chieftain was radar identified with a discrete transponder code and full data block. The Navajo, on a VFR flight code 1200, appeared as an uncorrelated target with limited data but including altitude. The controller did not observe the targets merging until the Chieftain pilot reported his avoidance action. MANOPS Section 165.3 states controllers must provide traffic information to IFR aircraft if targets appear likely to merge, but this procedure may be deferred due to higher priority duties.
Pilot Actions and Communication
The Chieftain pilot maintained visual lookout and took evasive action. The Navajo pilot did not see the conflicting traffic until after the Chieftain maneuvered. The Navajo pilot did not request en route radar surveillance, which could have verified his altitude. He was monitoring 122.8 MHz, a frequency commonly used by VFR pilots in the region, rather than the recommended en route frequency of 126.7 MHz. Guidance on the use of 126.7 MHz in controlled airspace is found in the AIP's Airport Operations section and on IFR-oriented Enroute Low Altitude charts, which may not be readily accessible to VFR pilots.
Probable Cause and Contributing Factors
The Transportation Safety Board determined that the Navajo came within 200 vertical feet of another aircraft as a result of the pilot not resetting his altimeter to the pressure setting of the nearest station along his route of flight, as set out in the AIP. Contributing factors included ATS procedures that allowed controllers to prioritize data services over traffic information, the lack of clear publication of radio frequency guidance for VFR pilots, and the Navajo pilot not requesting en route radar surveillance.