United Boeing 787-9 Diverts to Chicago O’Hare due to Display Failures

Introduction

On October 4th, 2024, a United Airlines Boeing 787-9, registered as N27958, was en route from Los Angeles, California (USA), to London Heathrow, England (UK), when the crew encountered a critical system malfunction at 35,000 feet over Hudson Bay, Canada. The incident involved the primary flight display (PFD) and navigation display (ND) of the captain going blank, alongside the flight management computers (FMCs) entering a degraded mode. This article provides an in-depth analysis of the incident, examining its technical aspects, crew response, and implications for flight safety.

Incident Overview

The flight, designated UA-231, was proceeding smoothly until the crew noticed significant malfunctions affecting the captain’s displays. The flight’s position at FL350 placed the aircraft over a remote region, complicating any potential diversion or emergency landing.

Upon recognising the display failures, the crew took immediate and decisive action. They declared a Mayday—a distress signal indicating an urgent situation requiring immediate assistance. After evaluating the situation, the crew diverted to Chicago O’Hare International Airport (ORD), approximately 1,100 miles from the flight’s original destination. The aircraft landed safely on runway 10C about 140 minutes later.

Technical Overview of the Boeing 787-9

The Boeing 787-9, a derivative of the 787 Dreamliner, is a long-range, wide-body, twin-engine aircraft designed for improved fuel efficiency and passenger comfort. Equipped with state-of-the-art avionics, the 787 features advanced fly-by-wire technology, integrated electronic flight instrument systems (EFIS), and dual flight management computers that work in tandem to ensure navigational accuracy and operational safety.

Primary Flight Display (PFD) and Navigation Display (ND)

The PFD and ND are critical components of the aircraft’s cockpit display system. The PFD presents essential flight data, including airspeed, altitude, vertical speed, and attitude information. Meanwhile, the ND displays navigational data, such as waypoints, routes, and air traffic. Both displays rely heavily on the aircraft’s flight management computers, which process data from various sensors and systems.

In the event of a failure in these displays, the pilot’s situational awareness can be severely compromised. Pilots are trained to respond to such scenarios, relying on backup instruments and alternative navigational methods.

Nature of the Incident

As the United Airlines flight operated over Hudson Bay, the crew reported that both the PFD and ND for the captain went blank. This failure indicates a significant issue within the cockpit displays, likely linked to either an electrical fault, a software malfunction, or a failure within the FMCs.

According to the Canadian Transportation Safety Board (TSB), upon failure of the primary displays, the FMCs entered a degraded mode, limiting the aircraft’s capabilities. While lateral navigation was unavailable, the aircraft retained heading and track modes, allowing the crew to maintain some control over the flight path.

The specific reasons for the display failure and subsequent FMC degradation would be the focus of the investigation, but potential causes include:

1. Electrical Malfunctions: Disruptions in the aircraft’s electrical systems can lead to display failures. The 787’s extensive use of electrical systems makes it particularly susceptible to electrical issues, including power fluctuations or component failures.

2. Software Glitches: Modern aircraft systems are heavily reliant on software algorithms. A software error within the avionics could result in both displays going blank, as well as causing the FMCs to enter a degraded mode.

3. Sensor Failures: The PFD and ND depend on various sensors for accurate data. Failures in these sensors or the data transmission systems could lead to erroneous or missing data, resulting in blank displays.

4. Environmental Factors: While less likely, extreme environmental conditions such as severe turbulence or icing could potentially affect the aircraft’s systems.

Crew Response and Emergency Procedures

The flight crew’s response was exemplary in the face of a challenging situation. Recognising the critical nature of the display failures, they promptly declared a Mayday, alerting air traffic control (ATC) to their urgent situation. This declaration not only informed ATC of the need for priority handling but also initiated emergency procedures.

Upon declaring the Mayday, the crew took the following actions:

1. Navigation via Alternate Means: With lateral navigation unavailable, the crew relied on heading and track modes, utilising their situational awareness and available navigation aids to guide the aircraft towards Chicago O’Hare. The use of ATC vectors would facilitate this navigation.

2. Communication with ATC: The crew maintained communication with air traffic control, receiving vectors and altitude adjustments as necessary. This cooperation ensured that they could navigate safely to the diversion airport while maintaining awareness of any potential traffic in the vicinity.

3. Preparation for Landing: As the aircraft approached Chicago, the crew executed standard landing procedures, ensuring that they were prepared for any additional contingencies that might arise due to the prior system failures.

Post-Incident Investigation

In the aftermath of the incident, the Transportation Safety Board of Canada (TSB) initiated an investigation to identify the root causes of the display failures and FMC degradation. Investigations of this nature typically encompass several areas:

• Avionics Analysis: Investigators will conduct a thorough examination of the aircraft’s avionics systems, focusing on the PFD, ND, and FMCs. This analysis includes reviewing data from the flight data recorder (FDR) and cockpit voice recorder (CVR) to understand the sequence of events leading up to the failures.

• Maintenance Records Review: The aircraft’s maintenance logs will be scrutinised to identify any prior issues with the displays or flight management systems. This review will also consider any software updates or repairs made to the avionics systems.

• Pilot Reports and Training: The actions and decisions of the flight crew will be assessed, along with their training regarding display malfunctions and emergency procedures.

• Operational Environment: Investigators will consider the operational environment at the time of the incident, including weather conditions and air traffic density.

Implications for Aviation Safety

This incident underscores several critical considerations for aviation safety:

1. Importance of Redundancy in Systems: The Boeing 787 is designed with numerous redundancies; however, this incident highlights the need for rigorous testing and validation of these systems. Any failure in primary displays can create significant challenges, emphasizing the importance of backup systems and protocols.

2. Regular Maintenance and Software Updates: Continuous monitoring and maintenance of avionics systems are crucial to ensuring reliability. Regular software updates and checks of electronic components can help mitigate potential issues before they escalate.

3. Enhanced Pilot Training: Crew training programmes should include comprehensive scenarios involving display failures and FMC degradations. Simulators can provide an effective platform for pilots to practise their responses to such emergencies, ensuring that they remain composed and effective during real-life situations.

4. Communication Protocols: Establishing clear communication protocols between pilots and air traffic control is essential during emergency situations. This cooperation enables efficient routing and prioritisation of emergency landings, enhancing overall safety.

Conclusion

The diversion of United Airlines flight UA-231 due to the failure of the captain’s primary flight and navigation displays serves as a reminder of the challenges faced in modern aviation. The swift and professional response from the flight crew, coupled with the subsequent investigation, will provide valuable insights into enhancing aviation safety protocols.

As the investigation continues, the findings will contribute to improved training, maintenance practices, and technological advancements aimed at preventing similar incidents in the future. The collaboration of aviation professionals—engineers, pilots, maintenance crews, and regulatory authorities—will play a vital role in ensuring the safety and reliability of air travel in an increasingly complex operational environment.