On 17th July 2023, a United Airlines Boeing 767 lost an evacuation slide mid-air while it was on final approach to Chicago’s O’Hare International Airport. The crew did not even realize that the slide had fallen until maintenance workers noticed the missing slide upon landing.

The Boeing 767-300 with registration N666UA was performing flight UA12 from Zurich, Switzerland to Chicago O’Hare. However, while the aircraft was on final approach to Chicago’s runway 28C, an evacuation slide separated from the aircraft.

The evacuation slide landed in the backyard of a house underneath the approach path about 2.3nm short of the runway threshold. Flight UA12 continued for a safe landing.

a group of people standing next to a pile of garbage
Image via FL360aero

The residents of the house affected by the incident heard the impact while inside their homes and quickly went outside. They found the evacuation slide in their backyard and dragged the slide into the front of their house, where local police authorities took charge of the situation.

CCTV footage shared on the internet shows the slide falling from the aircraft. 

Thankfully, no injuries were reported, although the slide caused some damage to the roof of the house where it landed.

How Pilots Remained Unaware of the Situation?

Flight UA12’s crew remained unaware of the situation until the maintenance workers noticed it on landing, prompting them to alert the Federal Aviation Administration (FAA) about the situation.

The question arises: How could the pilots be unaware of the missing emergency slide during the final approach?

According to information obtained from the comments on the Aviation Herald, the Boeing 767-300 model has a unique configuration for overwing escape slides. Unlike other exits where the slides are typically stored in the doors, on this particular aircraft, they are located within the main section of the fuselage. 

Consequently, there is no Engine Indicating and Crew Alerting System (EICAS) associated with these slides, which would normally notify the pilots of any issues or malfunctions.

Evacuation slides are designed to deploy in the event of an emergency, but they can also be deployed accidentally. In this case, it is not yet clear what caused the slide to deploy. 

In the footage below, you can observe the deployment of this particular slide in a normal situation.

What Could Have Happened?

In a similar incident that took place earlier in Canada, investigators provided the following explanation for the occurrence:

The Boeing 767 incorporates an inflatable slide at the inboard rear of each wing to allow the evacuation of passengers who use the over-wing exits during an emergency. Slide deployment is initiated by opening the exit hatch from the inside. The hatch opening motion actuates electrical switches that simultaneously (1) operate a relay to ground out any position command going to the main hydraulic spoiler power controller actuator, and (2) fire the spoiler override actuator which rotates the inboard spoiler to the down position.

After a two-second time delay (from the spoiler actuator firing), the latch opening actuator is fired. The latch opening actuator opens the escape slide compartment door latches and fires the door opening actuators located in the escape slide compartment. The slide compartment door, with the escape slide packboard assembly attached, is rotated outboard by the actuators. When the door opens, a mechanical link to a high-pressure inflation cylinder triggers the release of gas that inflates the slide.

a police officer standing next to a tarp on the street
Image via Patrick Devitt | Laura Devitt

The FAA is currently investigating the incident, and United Airlines has said that it is working with the FAA to better understand the circumstances around this matter. 

“We immediately contacted the FAA and are working with our team to better understand the circumstances around this matter.”

United Airlines spokesperson

Feature Image via Patrick Devitt | Laura Devitt (FlightMode)