Air Canada Flight 003 Loss of Separation Incident

Incident Overview and Initial Clearance Air Canada Flight 003 (ACA003), a Boeing 747-238, departed London, England, at 1255 UTC for Montreal, Canada. Shortly after, Air Canada Flight 857 (ACA857), a Boeing 747-400, departed London for Toronto. For the oceanic crossing, ACA003 was cleared to flight level (FL) 360, while ACA857 was cleared to FL350. Both aircraft initially attained their assigned altitudes. ## Performance Degradation and Crew Response After leveling off at FL360, the aircraft experienced a gradual loss of airspeed. The flight crew, preoccupied with tasks such as a passenger address and preparing a position report, did not immediately monitor the aircraft's performance. The airspeed decayed from the target Mach 0.84 to Mach 0.75, and the pitch angle increased from about 3 degrees to 5.5 degrees. A slight ripple-type vibration, likely a pre-stall buffet, alerted the captain to the deteriorating performance. The crew increased engine power to maximum continuous thrust and began a descent to regain airspeed. ## Loss of Separation and Recovery As ACA003 descended through FL350, it encroached on the protected flight space of ACA857, which was on a near-identical ground track. A separation monitoring function alert was triggered at approximately 1332 UTC. Due to VHF radio range limitations, initial communication attempts between ACA003 and Scottish Oceanic En Route air traffic control were unsuccessful. ACA857, which had visual and traffic collision avoidance system (TCAS) contact with ACA003, relayed the descent request and moved left of track to maintain lateral separation. Communications were eventually established on 121.5 MHz and 125.675 MHz. ACA003 was re-cleared to maintain FL320, and the remainder of the flight to Montreal was uneventful. ## Contributing Factors and Safety Actions The investigation found that the crew did not adequately monitor the aircraft's performance after leveling off at an altitude near its performance limits. The better-than-anticipated climb performance may have reduced the crew's vigilance. Additionally, communication difficulties delayed the air traffic control agency from becoming aware of ACA003's intentions until after the loss of separation occurred. Air Canada subsequently published an internal Aircraft Technical Bulletin #405, dated 98-11-06, to address the incident.