United Airlines Boeing 777-200ER Diverts Back to London After In-Flight Vibrations
A United Airlines Boeing 777-200ER was forced to return to London Heathrow Airport on September 28, 2025, after the flight crew reported abnormal airframe vibrations while enroute to San Francisco. The incident, involving aircraft registration N788UA, prompted an emergency declaration and an immediate diversion back to the UK.
Flight UA939, carrying 271 passengers and 13 crew members, had departed Heathrow for San Francisco International Airport (SFO) and was cruising at FL310 (31,000 feet) over northern England near Blackpool when the crew detected unusual vibrations. According to reports from The Aviation Herald, the aircraft entered a holding pattern as the crew consulted with dispatch and maintenance teams to assess whether the vibrations originated from the engines or another structural source.
Passengers later reported that the crew shut down the left-hand Pratt & Whitney PW4090 engine as a precaution. With one engine secured, the aircraft maintained altitude before commencing a controlled descent back toward Heathrow. On the return journey, the crew performed a fuel dump procedure to reach a safe landing weight. The aircraft touched down safely on Runway 27L approximately 1 hour and 50 minutes after departure.
Aircraft Background
The aircraft involved, a Boeing 777-222ER, was delivered to United Airlines in July 1997 and is powered by Pratt & Whitney PW4090 engines. Though part of an older generation of United’s widebody fleet, the 777-200 remains a workhorse for transatlantic and long-haul operations. The airline has been gradually phasing out its oldest widebody aircraft in favor of more fuel-efficient Boeing 787 Dreamliners and incoming Airbus A321XLRs, but the 777-200 continues to operate heavily traveled routes such as London–San Francisco.
United Airlines’ Boeing 777-200 fleet averages 22 years of age, with the oldest 777-200s slated for retirement, while the younger 777-300ERs are expected to remain in service longer. Maintaining these older 777-200s is costly for the airline, which plans to replace them with new Airbus A350-900s or additional Boeing 787-10s.
Passenger Accounts and Airline Response
One passenger told reporters that the shutdown of the left engine was clearly announced during the flight, though the cabin remained calm. “The crew handled the situation very professionally. We knew something was wrong, but everything was controlled and safe,” the passenger said.
United Airlines confirmed that the flight returned to London due to a mechanical issue and that the aircraft landed safely. The airline did not provide further details about the cause of the vibrations but emphasized that passenger safety was never compromised.
As of the following day, the aircraft remained on the ground in London for inspections and maintenance, with the incident under review by engineers and aviation safety authorities.
Broader Context
The event highlights ongoing challenges with older widebody fleets, particularly aircraft powered by Pratt & Whitney engines, which have faced increased scrutiny in recent years. While the Boeing 777 family has an excellent overall safety record, incidents involving engine vibrations, compressor stalls, or other mechanical anomalies underscore the importance of rigorous maintenance on legacy fleets.
For passengers, the diversion caused delays and onward travel disruptions, though all travelers were re-accommodated on later flights.
The United Airlines Boeing 777-200ER diversion from London to San Francisco underscores both the resilience of modern long-haul aircraft and the caution exercised by flight crews when mechanical irregularities occur. Investigations into the exact cause of the vibrations are ongoing, but the safe return of UA939 illustrates the priority placed on safety in commercial aviation.
Related News: https://airguide.info/?s=unted+airlines, https://airguide.info/category/air-travel-business/travel-health-security/
Sources: AirGuide Business airguide.info, bing.com, avherald.com