Aug 3 (Reuters) - Planemakers, airlines and repair shops are conserving aircraft windows after an incident at a key California factory worsened shortages of a part needed for both new aircraft and routine maintenance, companies and industry sources said.

GKN Aerospace, one of the world's biggest suppliers of cockpit and passenger windows, halted production in late May at its factory in suburban Los Angeles after an overheating tank raised fears of an explosion and prompted the evacuation of 50,000 nearby residents for several days.

While the incident has not derailed new plane production or airline operations, sources and executives said, it has led to parts delays and industry concerns over the supply of cockpit and passenger windows.

U.S. planemaker Boeing ( BA ) said it had communicated with operators on steps to manage window inventories after the incident.

Boeing ( BA ) advised airlines to replace windows only when necessary rather than for other reasons, such as aesthetics, according to a source at a North American carrier.

Boeing ( BA ) said in a statement it continues "to work with our supplier and are taking steps to mitigate any potential impacts."

GKN, owned by London-listed Melrose Industries, produces windows for several Boeing ( BA ) models including the 737 MAX, along with rival Airbus' A220 and A350 jets.

Melrose said on Friday it was working to restore the now partially opened window factory to full production by the end of 2026.

The shortages highlight some lingering post-pandemic weaknesses in the aerospace supply chain despite noticeable improvements in parts availability this year.

Companies and analysts say demand from planemakers increasing aircraft production is colliding with demand from maintenance shops needing replacement windows to keep aircraft flying, echoing engine shortages.

"There is a significant aftermarket for windows," said Matteo Peraldo, aerospace and defense partner at AlixPartners. "So the demand is not just production but is also compounded with the aftermarket."

Airbus has experienced A220 window shortages, but that had not delayed production, according to a source familiar with the program.

A spokesperson for the A220 program said with GKN Aerospace restarting production, they are "seeing positive progress so far toward a return to normal."

Maintenance provider Lufthansa Technik said the supply of aircraft windows for planes from both major aircraft manufacturers had long been strained.

"Lead times have increased substantially, while procurement costs have risen markedly," Lufthansa Technik said.

For most Boeing ( BA ) aircraft it services, window supply is often limited to instances when the part is absolutely needed to fix a grounded aircraft, Lufthansa Technik said.

PRIVATE JETS

Challenges in window supply have also impacted private jet makers including Canada's Bombardier and Brazil's Embraer ( EMBJ ), along with repair shops.

On Thursday, Bombardier CEO Eric Martel told reporters the incident's impact on window supply is among the supply chain challenges "we've had to manage." GKN Aerospace produces windows for the company's flagship Global 8000 jet.

Private and commercial jet maker Embraer ( EMBJ ) had already faced supply constraints for aircraft windows, and the GKN incident was causing fresh concern, a source said.

Kenn Ricci, chairman of private jet operator Flexjet, which flies Embraer Phenom and Praetor jets, told U.S. podcast Technology Business Programming Network in February that windows posed a problem for Embraer's ( EMBJ ) supply chain.

"If you ask Embraer ( EMBJ ), ask (Executive Jets President) Mike Amalfitano, ask them why are your deliveries slipping, they say it's the windows," Ricci said.

Flexjet declined to comment. Embraer ( EMBJ ) did not respond to repeated requests for comment.