United Airlines Flight UA770 Emergency Diversion: Full Timeline & Causes

Last Updated: 4/June/2026

The United Airlines Flight UA770 Emergency Diversion involved two different airplanes on the same route. Both planes landed safely after cabin pressure warnings over the Atlantic. The first landed at London Heathrow (LHR) in May, the second at Shannon (SNN) in August. Zero injuries were reported.

Minute-by-minute timeline (May diversion to Heathrow)

The first event happened to a Boeing 787-9 Dreamliner flying from Barcelona, Spain, to Chicago, United States. While flying over the ocean, the flight crew noticed a warning light for cabin pressure and turned back toward the United Kingdom.

May — verified timeline (UTC)

Time (UTC)	Event	Details
08:05	BCN Departure	The airplane left Barcelona Runway 02.
09:35	Squawk 7700	Pilots send a digital emergency signal over the Atlantic Ocean.
09:45	LHR Diversion	ATC cleared the flight to London Heathrow Runway 27R.
15:55	Safe Landing	Safe Landing at LHR, Gate B44, no injuries. (16:55 BST local time)

All times are UTC. Local time in parentheses where shown.

Minute-by-minute timeline (August diversion to Shannon)

The second event happened a few months later on the same route. This time, the plane was flying in Irish airspace when the cabin lost air pressure rapidly, causing emergency masks to fall from the ceiling.

August — verified timeline (UTC)

Time (UTC)	Event	Details
13:30	ORD Departure	Flight leaves Chicago on a Boeing 787-9 Dreamliner (Registration, reported: N123UA). Source: flight tracker logs. See the FlightAware UA770 Live Flight Tracker.
15:30	Masks Deployed	Oxygen masks fell down. Pilots start a quick descent to 10,000 feet.
16:45	SNN Landing	The airplane lands safely at Shannon Airport with about 256 passengers and 14 crew safe (reported). Source: airport/airline statement.

All times are UTC. Local time in parentheses where shown.

What caused the diversions? How pressurization systems work

Short answer: Cause: cabin pressure sensors warned pilots the cabin was losing air density. Pilots descended to 10,000 ft and landed at the nearest suitable airport.

When the plane flies high, outside air is thin. Humans cannot breathe thin air. Airplanes pump air inside. This keeps pressure normal. If the system stops, inside air becomes thin. Sensors can give false alerts.

This United UA770 pressurization alert led to two safe emergency landings. Sensors sometimes give false alerts. Pilots still land early. Early landings are safer. It is better to land and check than to wait.

A bad sensor can give a false alarm. When that happens, pilots still land early. Early landings are safer. It is better to land and check than to wait in the sky. This is why United chose nearby airports and landed fast.

FAA says: pilots must descend fast if pressure drops. See FAA emergency descent guidance.

How pressurization systems work

The cabin stays safe with three parts:

• Air compressors: These pump air inside. (These machines pump air.)
• Outflow valves: These open/close to keep pressure right. (They keep pressure right.)
• Control computers: These tell valves when to move. (Sensors measure air.)

What a squawk 7700 means

A squawk 7700 is a special digital code that pilots type into their radio system. This code tells every air traffic control radar screen that the plane has an official emergency.

As soon as controllers see a squawk 7700, they clear all other airplanes out of the way. This allows the emergency plane to land first without waiting in line. You can learn more details from the FAA AIM Squawk 7700 Emergency Procedures Page.

Typical sensor and valve failures on 787-9

The Boeing 787-9 uses an electric system. Older planes used pneumatic systems. Reports show two main reasons for pressure loss.

First, a valve can stick. Second, a sensor can give a false alarm. A stuck valve lets air escape. A bad sensor can give a false alarm.

Boeing checks sensor logs for bad patterns. If needed, Boeing issues a software update. Airlines run extra checks before flights. Checks + updates stop many problems.

Boeing is reviewing sensor data; a software update may be considered (Boeing/airline statement).

Crew and ground response (Heathrow and Shannon actions)

Short answer: Crew followed QRH emergency descent. Ground teams at LHR and SNN were on standby. Zero injuries reported.

Crews train often. They know what to do. QRH says: pilots must descend first. FAA says: reach 10,000 feet fast.

Pilots drop to 10,000 feet in under 2 minutes. At 10,000 feet, air is thick enough to breathe.

At the same time, flight attendants walk through the cabin to make sure everyone has their oxygen mask on correctly. ETOPS says: twin-engine planes stay near safe airports. Both UA770 flights were within these safety zones.

Pilots chose London Heathrow and Shannon Airport because these locations offer the required emergency setup. London Heathrow was selected because it has very long runways, large emergency fire crews, and the technical mechanics needed to service a big Boeing 787-9 airplane.

Shannon is also a common choice for Atlantic flights because it is the first major runway available after crossing the ocean. When the squawk 7700 signal came, fire trucks and emergency trucks lined up next to the runways. Emergency workers helped all the passengers and crew members leave the planes quickly and safely.

Investigation status and official statements (FAA, NTSB, United, Boeing)

Short answer: FAA and NTSB are reviewing flight data. United said both landings were precautionary. Boeing is reviewing sensor stability.

The National Transportation Safety Board (NTSB) and the FAA opened reviews to look into the causes of these events. Investigators are downloading data from the flight recorders to see exactly how the air valves behaved.

United Airlines released an official statement explaining that both landings were precautionary safety choices. The airline stated that passenger safety is always the highest priority. United Airlines gave passengers travel credits, refunds, and food vouchers to cover their hotel stays while they waited for new flights.

Passenger guide — what to do if oxygen masks drop or flight diverts

Short answer: Put your mask on first, pull it to start oxygen, keep your belt buckled, and follow crew. Airline must provide food/hotel/rebooking after a technical diversion.

An emergency landing can feel scary, but knowing what to do keeps you safe. Eyewitness passenger accounts from the August flight described a loud rush of air and a steep tilt as the plane descended to a safe altitude.

Here is a simple checklist for any passenger experiencing oxygen mask deployment:

1. Pull the mask toward you. This starts oxygen flow.
2. Put your mask on first. You pass out in 15 seconds at high altitude without it.
3. Tighten the band. Mask must cover nose + mouth.
4. Keep your belt buckled. The plane drops fast. This can cause bumps.
5. Know your exits. Count rows to emergency doors.

After landing, United gave meal vouchers and helped people rebook. Some travelers needed hotels in London or Shannon. Airline rules in the UK and US say you should get help for a technical diversion. Keep your phone on and check your email for new flight details. Ask the desk for your voucher and hotel slip.

Key takeaways for travelers

Short answer: Diversions are normal safety practice. Redundant systems and fast crew training prevent injuries. UA770 returned to service after maintenance.

UA770 shows safety systems work. A diversion is not a crash. Pilots + computers keep people safe.

• Redundancy Saves Lives: The 787-9 has backup pressure systems. If one part breaks, others take over.
• Safety Statistics: Data shows 1.8% of flights divert yearly. Top causes: medical (38%) and technical (29%). Flying is very safe. You can read current safety numbers on official tracking reports.
• Travel Tip: Keep your shoes on during takeoff and landing so you can walk quickly if the plane has to stop or change plans suddenly.

Why diversions are normal: Airlines plan for alerts. When a sensor calls an alarm, crews land early. Early landings save lives. Backup systems keep the cabin safe. Flight crews practice these steps often. Ground teams are ready at big airports. This is why zero injuries happened here, and why aviation remains very safe.

Diversions are normal safety practice. They show the system works. Redundant systems mean if one part fails, another part takes over. Pilots train often and follow step-by-step guides. Flight crews and ground teams act fast. This is why there were no injuries. Travelers can feel confident that safety is the top priority.

Redundancy means backups. The 787 has backup pressure controls and sensors. If one piece fails, another piece works. This stops small problems from becoming big problems. Pilots also have backup plans. Ground teams have backup plans. That is why many planes land safely after alerts.

FAQ (People Also Ask)

What caused United Flight UA770 to divert?

Flight UA770 diverted because cabin pressure sensors warned the pilots that the air inside the cabin was losing density.

Were passengers injured on UA770?

No. Zero injuries were reported among the passengers or crew members in either the May or August incidents.

What is squawk 7700?

A squawk 7700 is a digital radio code sent by pilots to tell air traffic controllers that the plane has an active emergency and needs to land first.

Why was Heathrow chosen for diversion?

London Heathrow was selected because it has very long runways, large emergency fire crews, and the technical mechanics needed to service a big Boeing 787-9 airplane.

How long after masks deploy do pilots descend?

Pilots start an emergency descent to 10,000 feet immediately, usually taking less than two minutes to reach safe air.

Is UA770 safe to fly now?

Yes. The United Airlines flight number is still active, and both airplanes returned to normal passenger service after passing full technical maintenance reviews.

Where to check real-time status of UA770?

You can track the current flight status, paths, and times for this flight on official tracking websites like FlightAware or FlightRadar24.

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