(LOS ANGELES) United Airlines ordered a nationwide pause on many departures after a sudden IT outage on August 6, 2025, hit its core flight operations system, forcing at least a dozen flights to remain on the ground at LAX. The failure struck just after 6:00 p.m. Eastern Time, affecting Unimatic, the internal tool that helps calculate an aircraft’s weight and balance—the numbers pilots need before every takeoff.
At United’s request, the Federal Aviation Administration issued ground stops for the carrier’s mainline flights at major hubs, including Los Angeles. United confirmed later that evening that the technology issue was resolved, but delays and missed connections carried into the night as crews tried to restart flights and reposition planes and staff. The airline said the event was not tied to a cyberattack. Instead, the problem came from a failure in the system that feeds vital flight data into other tools across operations—freezing a process airlines treat as non-negotiable for safety.
What happened at LAX
Passengers at LAX described sitting on planes at gates or on taxiways while crews waited for clearance. Several aircraft returned to gates so customers could deplane. United stressed that United Express regional flights were not affected; only the mainline fleet—planes such as Boeing 737s, 777s, and the Airbus A320 family—was held. Flights already airborne continued to their destinations.
Customers on social media shared photos and short clips of packed gate areas, aircraft waiting for open gates, and pilots relaying updates from cockpits as they received them. Some flights pushed back, then returned to gates to allow passengers to stretch, get water, or make new plans. United told customers to check their flight status and watch for rebooking offers.
United and FAA confirmations
United Airlines said it moved quickly to contain and fix the outage and warned customers to expect ongoing delays as the carrier rebuilt its schedule. The FAA, coordinating with United, issued ground stops that reached multiple United hubs—Los Angeles, Chicago O’Hare, Houston, Denver, Newark, and San Francisco—until United could validate that weight-and-balance and linked systems were stable. The agency lifted those holds after United restored its tools.
The airline emphasized again that the incident was not a cybersecurity breach. Industry technicians said Unimatic’s failure had a cascading effect, blocking the flow of numbers used by dispatchers and flight crews to set fuel loads, cargo placement, and takeoff performance. Because those tasks rely on precise data, any break in the chain stops departures.
Manuals exist for calculating some performance figures by hand, but for a carrier of United’s size, doing that at scale would have compounded delays and safety risk—so the pause was the safer course.
United’s pause lasted several hours. By late evening, the company reported its systems were back online, but crews still faced the knock-on problems that follow any large interruption: aircraft and pilots out of position, airport gates backed up, and passengers needing new itineraries. Nationwide, hundreds of United flights were affected, with at least a dozen departures held at LAX according to airline statements and traveler accounts.
Why weight-and-balance systems matter
Safety rules require airlines to verify an aircraft’s weight and balance before takeoff. That includes:
- Passengers, carry-on and checked bags
- Cargo
- Fuel
- Distribution of weight inside the aircraft
These figures affect how fast an aircraft can safely lift off, how much runway it needs, and how it handles in flight. If the data pipeline breaks, crews can’t confirm those numbers—and departures must stop.
Industry technicians explained:
- The failure froze the flow of critical numbers into systems used by dispatchers and pilots.
- Some performance calculations can be done manually, but not quickly enough for a large carrier without adding safety and operational risk.
- Therefore, grounding flights is mandatory for safety when dependable calculations are unavailable.
Recovery and passenger impacts
United said its teams focused first on restoring the weight-and-balance flow and then on clearing the backlog once systems were stable. Flights already in the sky were not recalled because their performance numbers had been set before departure and remained valid. The mainline pause focused on departures that still needed those final checks.
At LAX, impacts stretched into the late hours:
- Longer lines at agent counters as passengers rebooked missed connections
- Aircraft, pilots, and flight attendants repositioned to meet operational needs
- Delays to long-haul operations that depend on specific aircraft types and rested crews
United encouraged travelers to use its mobile app for live updates and electronic rebooking instead of standing in lines where possible.
Practical guidance for affected travelers:
- Check flight status often.
- Allow extra time at the airport for gate or schedule changes.
- Consider later departures if you have tight connections.
- Use United’s mobile app for rebooking and updates.
Contact information:
– United customer service: 1-800-864-8331
– United website: united.com
– FAA national dashboard: https://nasstatus.faa.gov
During the outage and recovery, United also posted updates on its verified social media channels.
Broader industry concerns
Aviation analysts compared this outage to earlier industry failures, including the 2024 CrowdStrike Windows crash and Alaska Airlines’ July 2025 interruption. The pattern points to:
- Aging systems
- Complex software networks linking crew timing, baggage routing, maintenance, and dispatch
- High vulnerability when a single critical node fails
According to analysis by VisaVerge.com, events like this highlight why large carriers must invest in stronger backup systems and clear recovery playbooks.
Industry voices say the outage will increase pressure on airlines to:
- Replace older systems
- Build greater redundancy
- Undertake multi-year technology projects that safely integrate with crew scheduling, maintenance, dispatch, and airport partners
Regulators may also consider new guidance to ensure carriers test backups more often and plan faster recoveries when a core tool fails.
Key takeaways
- The outage on August 6, 2025 was caused by a failure in Unimatic, United’s weight-and-balance data tool, not a cyberattack.
- Ground stops affected major hubs and produced nationwide disruption; at least a dozen flights were held at LAX.
- Safety protocols require verified weight-and-balance data before departure—when that data pipeline fails, grounding flights is the necessary, mandated response.
- Systems were restored the same evening, but operational ripple effects left many travelers delayed or rebooked.
While systems were restored the same night, the incident underscored a simple fact: airlines run on people and software working together. When the software falters, pilots, dispatchers, gate agents, and mechanics are the ones who bring the network back. For customers, that can mean waiting on a warm aircraft for an update or rushing to a new gate after midnight. For the industry, it means more investment in stable tools that keep planes—and people—moving.
This Article in a Nutshell
On August 6, 2025, an Unimatic IT outage halted United mainline departures after 6:00 p.m. ET. FAA ground stops hit major hubs. United confirmed no cyberattack; weight-and-balance data failure forced mandatory grounding. Systems returned that night, but delays, missed connections and repositioning caused widespread passenger disruptions and recovery work into the night.
