Occurrence
On an unspecified date, an AirBC DHC-8 (ABL819) departed runway 26L at Vancouver under instrument flight rules (IFR) for Prince George, British Columbia. The tower controller cleared the aircraft to climb on runway heading and contact departure control. Upon contacting departure, the controller instructed ABL819 to maintain runway heading until 3,000 feet, then turn right to 335°. At that time, radar indicated ABL819 climbing at about 150 knots.
Shortly after, the tower cleared a Central Mountain Air Beechcraft 1900D (GLR738) to depart the same runway, also to climb on runway heading and contact departure. GLR738 acknowledged, took off, and accelerated rapidly to about 190 knots. The spacing between the two aircraft quickly reduced due to the airspeed differential, resulting in a loss of separation when they closed to within 2 nautical miles horizontally and 300 feet vertically, where 3 nm or 1,000 feet is required. The departure controller instructed GLR738 to reduce speed to 140 knots to stabilize spacing.
Contributing Factors
The tower controller was responsible for initial separation under MANOPS article 551.4, which relies on judgment based on aircraft performance. Controllers become familiar with types through on-the-job exposure. However, the Beechcraft 1900D had only recently begun operating in Vancouver, and controllers were not fully familiar with its characteristics. The aircraft has good acceleration and climb performance; although the manual recommends 160 knots for initial climbs, pilots may select other speeds. GLR738 climbed at about 190 knots with high vertical speed, motivated by a desire to keep moving quickly for faster jet traffic.
The tower released GLR738 when ABL819 was about 3¼ nm west of the airport, south of the extended centerline. No speed or climb restrictions were in GLR738's clearance. The Beechcraft first appeared on the departure controller's indicator module as an uncorrelated target without a speed data tag. The controller had not expected a high-overtake situation and recognized the rapid closure only after separation was lost.
Prior to this incident, other controllers had seen similar 'run-down' events involving the Beechcraft 1900D but had not formally reported them. In the following week, two more similar incidents occurred, but controllers anticipated the problem and maintained separation. After supervisory staff became aware, they issued operations letters coordinating with airlines operating the Beechcraft 1900D.
Aftermath
Twenty-six days later, a similar loss of separation occurred in Calgary involving a Beechcraft 1900D behind a DHC-8. Nav Canada conducted a preliminary investigation but did not disseminate results.
The tower controller noted on flight data that GLR738 filed a slightly slower cruise speed than ABL819. Based on that, he judged minimum spacing was acceptable and released GLR738 at about 3¼ nm. After takeoff, GLR738 accelerated to 190 knots, eroding the spacing. ABL819, three miles ahead, drifted south while tracking west; upon reaching 3,000 feet, it turned north to 335°, causing convergence that further reduced spacing.
The departure controller, not anticipating a problem, had little time to react. He applied speed control but did not level the Beechcraft at 2,000 feet, judging that continuing the climb would re-establish separation more quickly.
Safety Actions
Vancouver ACC and Tower supervisors issued operations letters to resolve the initial spacing issue, coordinated with airlines operating the Beechcraft 1900D. Central Mountain Air instructed its pilots to adhere to 160 knots when following DHC-8 aircraft. Nav Canada developed a new reporting system effective January 1, 1998, for better trend analysis.
The Transportation Safety Board authorized the release of this report on 10 September 1998.