Canadian investigators have disclosed that engineers replaced an air data computer on a Sunwing Airlines Boeing 737 Max 8 after the crew received spurious indications from the aircraft’s instruments.
The aircraft (C-GMXB) is less than six months old, having been delivered to Sunwing at the end of May.
It had been operating to Toronto from Punta Cana, in the Dominican Republic, when the incident occurred on 14 November.
Transportation Safety Board of Canada says the aircraft had been cruising at 35,000ft when the crew received “erroneous” indications on the captain’s side.
The first officer’s instruments, and the standby indicators, were functioning normally and the first officer took control of the aircraft.
It descended to 25,000ft as a precaution, in order to clear instrument meteorological conditions, but – as it passed 28,000ft – the weather radar and collision-avoidance system both failed. The aircraft was some 50nm north-west of Washington DC at the time.
The crew transmitted a ‘pan pan’ urgency call. The safety board says a left-side inertial reference system fault light also illuminated.
Investigators state that the flight proceeded to Toronto and landed without further incident, with no injuries among the 182 occupants.
Sunwing’s maintenance service replaced the left-side air data inertial reference unit (ADIRU) before returning the aircraft to operation.