Samsung’s disastrous Note 7 smartphone episode took a new turn today when one of its new replacement handsets started to smolder during a flight in the US on Wednesday.

The South Korean company recalled 2.5m smartphones during September after several reports of the devices catching fire during or after charging, offering replacement units to customers. Last week claimed it had replaced 60% of handsets in South Korea and in the US.

Samsung Note 7 owner Brian Green – whose phone had already been exchanged for a new one – claims that his handset started smoldering during a Southwest airlines flight from Louisville, Kentucky, to Baltimore.

Green confirmed to The Verge that he had collected the phone from an AT&T store on 21 September. A photograph of the packaging reveals a black square symbol, indicating that it as a replacement model.

The incident raises questions about the quality of the replacements handsets and the efficacy of Samsung’s recall program, which the company blamed on faulty batteries.

Customers who had bought the Galaxy Note 7 were entitled to trade it in for a new version of the smartphone that didn’t suffer from the same battery fault. If these phones are also vulnerable to the same problem, Samsung may have a much bigger problem on its hands.

In a statement a Samsung spokeswoman said: “Until we are able to retrieve the device, we cannot confirm that this incident involves the new Note 7. We are working with the authorities and Southwest now to recover the device and confirm the cause. Once we have examined the device we will have more information to share.”

Some analysts say the disaster could cost Samsung $5bn in revenues. The handset, which costs nearly $1,000, had initially been greeted by rave reviews when it launched in August 2016, but news of the recall wiped $11bn off the company value though the share price has since recovered.