Summary
On an unspecified date, a Boeing 737-8Q8 (registration C-FTAH, serial number 29351) operated as Sunwing Airlines flight 531 from Toronto–Lester B. Pearson International Airport, Ontario, to Cozumel International Airport, Mexico. The aircraft carried 189 passengers and 7 crew members. During the take-off run, at about 90 knots indicated airspeed, the autothrottle disengaged after take-off thrust was set. As the aircraft approached the critical engine failure recognition speed, the first officer (pilot flying) noticed an AIRSPEED DISAGREE alert and transferred control to the captain, who continued the take-off. During initial climb, a stall warning (stick shaker) activated, followed by a flight director command to pitch 5° nose-down. The captain, operating in visual conditions, recognized the commands as erroneous, ignored them, and maintained a climbing attitude. The crew returned to Toronto, landing without further incident. An emergency was not declared, but aircraft rescue and firefighting services were requested as a precaution for an overweight landing.
History of the Flight
The flight was planned with the first officer as pilot flying and the captain as pilot monitoring. A reduced-thrust take-off was permitted based on runway length and gross weight. V1 was determined as 149 knots indicated airspeed (KIAS). The first officer's flight director was selected as master, providing information for both displays except during take-off and initial climb.
The tower controller cleared the flight for take-off on Runway 23. The aircraft began the take-off run at 0656:49 Eastern Daylight Time. At 60 knots, the captain's flight director commanded a 15° nose-up pitch. At 80 knots, the captain called "80 knots," though the first officer observed a lower speed. At 90 knots, the autothrottle disengaged and the master caution light illuminated; the captain cancelled it and verified thrust. At approximately 139–149 knots, the automated V1 call sounded, and the first officer noticed low airspeed and the AIRSPEED DISAGREE alert, transferring control.
The captain rotated at 150 knots, liftoff occurred at 166 knots. At 179 knots and 219 feet above ground level, a 6° disparity existed between the two flight control computers: the captain's commanded a 1° nose-up change, the first officer's a 5° nose-down change. The radio altimeter output a bias-out-of-view signal. Both pilots felt the stick shaker for 6–8 seconds; an overspeed clacker sound was heard on the captain's headset. The captain maintained a 12° to 15° pitch attitude by reference to instruments and the horizon. The flight director continued to give erroneous pitch commands until the TOGA mode disengaged at 1 minute 8 seconds. At 1 minute 25 seconds, the right-hand stick shaker activated for 3 seconds (the only recorded activation on the digital flight data recorder).
The crew executed the "Airspeed Unreliable" checklist, determining the left airspeed and altitude were reliable. They climbed to 3000 feet, where brief intermittent cloud was encountered. At 3000 feet, altitude mode was engaged on the flight director, and commands became normal. Brief altitude disagree indications occurred due to an incorrect position-error correction from the right air data inertial reference unit. Communication difficulty arose from an open microphone, resolved by the captain approximately 5 minutes after take-off. The aircraft landed at 0723, during civil twilight, without brake overheating.
Weather
Weather at the time was reported as overcast clouds at 1800 feet above ground level, visibility 15 statute miles, wind from 290° true at 11 knots, temperature 1°C, dew point −2°C, altimeter 29.98 inches of mercury. Weather did not contribute to the occurrence; visual conditions aided the crew in identifying erroneous instruments.
Crew and Aircraft
The captain held an airline transport pilot licence with 7500 total flying hours, 3000 on type. The first officer also held an airline transport pilot licence with 5000 total hours, 3700 on type. Both were certified and qualified, returning from 72 hours off duty and well rested. The aircraft was certified, equipped, and maintained in accordance with regulations.
Post-Flight Reports
The captain debriefed maintenance personnel; only airspeed unreliability and overweight landing were entered in the aircraft journey log. The captain also submitted a company Flight Safety Report mentioning airspeed unreliability and stick shaker, and a report to the chief pilot including stick shaker, overspeed clacker, erroneous flight director commands, altitude unreliability, autothrottle disengagement, engine electronic control reversion, and radio problems.