Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Confusion
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Clearance
Aircraft
On [our] flight the aircraft had a MEL for the FMS (Flight Management System). The First Officer and I discussed the MEL and talked about flying using VOR navigation. During our climb out we had to deviate around a weather cell. As we flew around it our winds readout on the MFD (Multi-function Flight Display) showed winds shifting in direction and velocity substantially. We queried ATC to find out what the winds were for other aircraft since we were close to a convective weather cell. We determined quickly that it was our systems malfunctioning as our winds showed a 200 knot quartering headwind and a loss of ground speed equaling 200 or more knots. The autopilot tracked the nearest NAVAID but tried to correct for the wind causing the aircraft to bank unnecessarily. The pilot flying selected heading mode to stay on course. ATC queried about our course as we were off slightly. We explained that we were having unusual indications and that we required assistance. ATC complied and helped us determine which cockpit indications we could trust. We elected to continue knowing that we could calculate fuel and have enough to finish the flight. We had to calculate fuel burn because our ground speed readout was showing us at half the ground speed we were actually traveling; as confirmed by ATC; so the fuel burn for fuel over destination could not be trusted. The flight ended with vectors to capture the localizer. It was determined that the autopilot and flight director should be deselected so that it would not try to course correct for the 200 knot crosswind that did not exist on approach. We landed visually. When the aircraft began banking unusually to correct for winds aloft the flight crew began discussions of how odd the aircraft reacted to the weather. Once the flight crew realized the autopilot was reacting to faulty inputs we selected the most appropriate mode to maintain our course. We then requested further assistance from ATC and notified company via ACARS. The CRM during this event was very necessary and the First Officer did a great job working with me throughout the process. ATC facilities were very helpful and understanding as well. After discussing the event after landing causation thoughts between the crew and mechanics lead to something malfunctioning within the system that calculates air data. Personally I am very curious as to why the winds aloft readout stayed stuck at such a velocity.
CRJ-700 Captain reported requesting ATC assistance after noticing an FMC wind error that affected navigation and fuel planning.