Adds comment from Boeing in paragraph 12

By Allison Lampert

June 18 (Reuters) - A California aerospace factory operated by GKN Aerospace plans to restart some production, sources and a county health agency said, after halting output in late May when an overheating tank raised fears of an explosion and prompted 50,000 nearby residents to evacuate.

Employees began returning to the facility this week to conduct safety checks "as the plant begins first steps needed to restart some operations in parts of the facility that were unaffected by the incident," according to a source and an online notice from the Orange County Health Care Agency.

The factory in the Los Angeles suburb of Garden Grove is a supplier of cockpit and passenger windows for multiple Boeing BA.N models including the 737 MAX, Airbus' AIR.PA A350 jet and F-35 manufacturer Lockheed Martin LMT.N.

The work would include machining and assembling transparent materials used for cockpit windows and canopies that would not involve the manufacturing of acrylic, the notice said. A spokesperson for GKN, owned by UK-based Melrose PLC MRON.L, was not immediately available for comment.

Multiple agencies, including the U.S. federal government and Orange County District Attorney Todd Spitzer, have launched investigations into the factory, while California's Occupational Safety and Health division is inspecting it.

An ‌overheating chemical tank at the California facility in late May triggered an emergency response and evacuation orders. A thermal issue was identified in a tank holding methyl methacrylate, a ​chemical used to manufacture plastics and resins.

Officials had warned that the tank could rupture, spilling up ‌to ⁠7,000 gallons (26,500 litres) of toxic material. Firefighters later said the tank was no longer at risk.

The plant, which has around 500 employees, had been expanding as both the commercial aerospace and defense sectors ramped up output of the windows.

One senior aerospace industry source said that only a limited number of suppliers such as PPG PPG.N and France's Saint-Gobain SGOB.PA make such products.

Saint-Gobain was not immediately reachable for comment. A PPG spokesperson said it was monitoring the situation.

Airbus said in a statement that there is no current impact on production of its A350 as the planemaker has "adequately managed stocks."

A Boeing spokesperson said the company continues "to work with our supplier to fully assess the situation and are taking steps to mitigate any potential impacts.”

Lockheed Martin said the company is currently “collaborating with stakeholders and other supply chain partners to evaluate a range of options to ensure we continue to deliver this important capability to the warfighter."

In 2024, GKN announced a new production line near the facility to double manufacturing capacity of F-35 canopies, with the expansion to be completed by January 2027.

GKN also cited demand from planemakers and the aftermarket at the time.