History of the Flight
The aircraft, an ATR 72-212A (registration EI-FCY), was operating a scheduled passenger flight from Cork Airport to Manchester Airport. The approach to Runway 23R was uneventful. The co-pilot, who was pilot flying, performed a normal landing. Immediately after touchdown, the aircraft began to deviate left of the runway centerline. The commander took control according to standard procedure, initially applying rudder and then attempting to use nosewheel steering (NWS) to correct the deviation. The aircraft continued turning left. The commander applied brakes and brought the aircraft to a stop on the left side of the runway.
The co-pilot observed that the Multifunction Computer (MFC) modules 1B and 2B switch lights on the overhead panel were both indicating a fault. The pilots reset the MFC modules, restoring all systems. They then taxied the aircraft to its stand without further incident. The commander later reported that NWS was ineffective during the landing roll and that no master cautions or warnings were displayed, but several engine indications were missing from the engine and warning display (EWD).
Multifunction Computers (MFC)
The MFC system comprises two independent computers, each with two modules (A and B). The system monitors, controls, and authorizes various aircraft systems, manages failures, and commands warnings in the Flight Warning System (FWS). The MFCs are switched on and off by four pushbuttons on the overhead panel, which also contain fault lights.
A failure of both MFC 1B and 2B modules renders several systems unavailable, including FWS Master Warning, Master Caution, aural alerts, amber alerts on EWD, nosewheel steering, and the touchdown protection element of anti-skid. The manufacturer stated that, on this aircraft variant, the MFC 1B and 2B switch light alerts illuminate and the master caution lights flash if both modules fail.
Flight Crew Documentation
The Flight Crew Operating Manual (FCOM) states that during takeoff, nosewheel steering guidance is recommended only for the very first portion of the run, as rudder becomes efficient above approximately 40 kt. For landing, it instructs: "as speed reduces, and not later than about 40 kt (estimated) Capt takes NWS control, co-pilot hold control column fully forward." The Minimum Equipment List (MEL) permits dispatch with NWS inoperative, with no additional operational limitations.
Analysis
Failure of both MFC 1B and 2B causes the weight-on-wheels system to become unavailable, leading to inoperative NWS. When the commander realized NWS was ineffective, she focused on stopping the aircraft and noted unusual EWD indications. The pilots diagnosed the dual MFC failure only after observing the fault lights on the overhead panel post-stop. The commander had applied rudder before attempting NWS; the FCOM indicates rudder effectiveness above 40 kt, but at the likely speed when she took control, rudder authority alone was insufficient to correct the deviation.
Safety Actions
The manufacturer issued a Service Bulletin recommending installation of MFC computers modified to S5 standard to address the cause of the dual MFC failure. Implementation was delayed due to technical issues. The manufacturer also identified inaccuracies in the FCOM, which it will amend. The operator introduced dual MFC failure scenarios into flight crew recurrent training.