Background
On a regularly scheduled commercial flight from Saint John, New Brunswick, to Fredericton, Air Atlantic Flight 427, a Jetstream 41 with three crew and 16 passengers, departed at 1122 Atlantic daylight time under an instrument flight rules (IFR) flight plan. The aircraft was cleared to Fredericton via the Frenn intersection at 5,000 feet above sea level. After departure, the crew requested a visual route around the camp, a common adhoc procedure in visual meteorological conditions that kept the Jetstream left of the airway centreline, up to 1.6 nautical miles off.
Meanwhile, Pirate 61, a military T-33 jet with one pilot, had departed Canadian Forces Base Greenwood, Nova Scotia, to participate in a training exercise named Nimrod Gale within the Gagetown restricted area CYR 724. The T-33 was operating under visual flight rules.
Flight Paths
The Jetstream followed the Saint John River to the north-west, staying clear of the restricted area. The T-33 pilot, arriving early at the southern boundary of CYR 724, was directed to hold at Initial Point Delta, located at the northern tip of Gagetown Island on the river, within the V310 airway. The pilot flew at 4,500 feet asl for noise abatement, fuel conservation, and navigation, and entered a left-hand racetrack holding pattern at approximately 11:28. Radar data showed altitude fluctuations of plus or minus 200 feet.
The Encounter
At 11:30:03, the Moncton Area Control Centre controller advised the Jetstream crew of westbound VFR traffic at their 11 o'clock, six miles, altitude unconfirmed at 4,300 feet. The crew saw a corresponding TCAS return but not visually. At 11:30:32, the controller reported the traffic at 12 o'clock, five miles, turning opposite direction at 4,100 feet. Again, the crew saw a TCAS return but could not see the aircraft visually. At 11:31:01, the controller placed the target at 12 o'clock for three miles at 4,500 feet and climbing. Radar data indicated the Jetstream was at 4,961 feet and began a shallow descent.
The captain then visually detected the T-33 on an apparent collision course. He steepened the descent and initiated a shallow right turn. Both crew members saw the belly of the T-33 crossing in front of them in a steep-banked climbing attitude, filling the pilot's windscreen. The crew estimated the separation at approximately 50 feet.
The T-33 pilot first saw the Jetstream descending and overtaking from his 7 o'clock while in a left-hand orbit. He estimated the distance at 300 to 500 feet. At approximately 11:31:28, the aircraft approached each other head-on at a closure rate of about 400 knots. The closest separation was less than 100 feet, based on pilot observations and radar data.
Communication and Detection
The T-33 was equipped with only a single-channel UHF radio, while civilian aircraft use VHF. The T-33 pilot was monitoring his operational UHF frequency and could not be informed by air traffic services of other traffic. The T-33 also lacked a TCAS. Both aircraft operated under the see-and-avoid principle, which relies on visual detection. The source noted that at closing speeds of 400 knots and above, escape from collision is primarily due to chance. The weather at the time was good with some haze; visibility 15 statute miles at nearby Gagetown.
Conclusion
The two aircraft came close to colliding after a series of advisories and visual searches. The Jetstream crew received traffic advisories but could not acquire the T-33 visually until the final moment. The T-33 pilot had no advisory of the Jetstream. The incident highlights limitations of the see-and-avoid concept, including the human visual system's difficulty detecting stationary targets on a collision course and the absence of detection-enhancing equipment.