History of Flight
On June 21, 2022, at about 0945 eastern daylight time, United Airlines flight 2627, a Boeing 737-9 MAX (registration N37513), was cleared for a visual approach to land on runway 28C at Pittsburgh International Airport (PIT) in Pittsburgh, Pennsylvania. The flight crew subsequently landed on runway 28L instead. The airplane carried 174 occupants; none were injured, and the aircraft was not damaged. The regularly scheduled passenger flight operated under 14 CFR Part 121 from Chicago O'Hare International Airport (ORD) to PIT.
The captain was the pilot flying and the first officer the pilot monitoring. Before departure, the crew reviewed the flight plan, which indicated an arrival on runway 28L. The airplane departed ORD about 0845 EDT with autopilot engaged shortly after takeoff. During descent, the crew obtained ATIS information for PIT via ACARS and briefed the JESEY4 RNAV arrival, programming the FMCs for an RNAV approach to runway 28C.
Initial contact with PIT approach control occurred about 25 miles northwest of the airport. The controller advised expecting a visual approach to runway 32, but later offered radar vectors for a visual approach to runway 28C, which the crew accepted. The crew established communication with the tower controller about 6.5 miles east of the airport and were cleared to land on runway 28C.
During the approach, the captain requested the first officer extend the virtual centerline from the SUPPR waypoint. At that moment, both FMC control displays blanked, showing only the ACARS prompt. This occurred at 0940:13, according to FDR data, rendering lateral and vertical guidance unavailable on the MAX display system. The captain continued the visual approach using PAPI lights, which remained visible. The autopilot and autothrottle were disconnected at 0942:07 at about 2,300 ft AGL.
The FMCs recovered between 700 and 1,000 ft AGL, but no approach guidance was displayed. About 2 miles from the runway threshold, the first officer confirmed clearance to land on runway 28C with the tower controller, who affirmed. The airplane then aligned with and landed on runway 28L at 0944:42, subsequently exiting to the right. The tower controller observed the misalignment but decided not to issue a go-around due to the airplane's low altitude and the absence of traffic on runway 28L. Traffic volume was light with routine complexity.
Aircraft Information
The airplane was equipped with a General Electric Aviation (GE) FMC system comprising two computers and two control display units. After the incident, both computers were removed and evaluated by the manufacturer. Data showed that the dual blanking of the FMC displays was caused by a dual FMC reset during the descent into PIT, consistent with a known software exception related to a vector/discontinuity combination followed by a waypoint with required navigation performance. This problem was introduced in a version of the Boeing 737 flight management system software that included refinements to GE's earth model. The software exception produced a numeric error in the earth model. The FMC manufacturer developed a procedural workaround, and the error was corrected in a subsequent software version. Boeing issued a service bulletin about the update in May 2022.
Flight Recorders
The FDR was in good condition and contained about 27 hours of data. At 0940:17, parameters from the FMC showed an error pattern consistent with data loss from the FMC ARINC data bus. According to Boeing, the fault condition must be present for at least four successive data points to be annunciated. Based on sampling rates, data loss began at 0940:13. The error pattern continued for about 13 seconds, then transitioned to a no-computed-data error for about 6 seconds. Valid data resumed at 0940:36. The FMC valid parameter remained in the VALID state for the entire flight.
Additional Information
The Runway Awareness and Advisory System (RAAS) on the aircraft provided aural callouts and visual alerts to assist situational awareness. However, United Airlines had disabled airborne alerts announcing the runway being approached to maintain a quiet cockpit during final approach.
Federal Aviation Administration Order 7110.65Z prescribes procedures for air traffic controllers. It requires controllers to inform pilots if aligned with the wrong surface and issue control instructions. In this incident, the controller exercised best judgment, as permitted, by allowing the landing on runway 28L.