A fresh “potential risk” to Boeing’s grounded Boeing 737 Max could mean further delays to the aircraft returning to service.

The US Federal Aviation Administration yesterday revealed the new glitch without giving details.

The US manufacturer is s upgrading anti-stall software, which is the focus of investigators following two crashes killing a combined 346 people leading to the grounding off all 737 Max aircraft in March.

The FAA said in a tweet: “On the most recent issue, the FAA’s process is designed to discover and highlight potential risks. The FAA recently found a potential risk that Boeing must mitigate.”

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The regulator last month indicated that approval of Boeing’s changes to the 737 Max could come in late June. That would have allowed test flights in early July.

There were initial hopes among airlines that the 737 Max would be back in the air during the summer, but that timetable was pushed back to late this year even before the latest issue emerged.

Boeing said: “During the FAA’s review of the 737 Max software update and recent simulator sessions, the FAA identified an additional requirement that it has asked the company to address through the software changes that the company has been developing for the past eight months.

“The FAA review and process for returning the 737 Max to passenger service are designed to result in a thorough and comprehensive assessment.

“Boeing agrees with the FAA’s decision and request, and is working on the required software. Addressing this condition will reduce pilot workload by accounting for a potential source of uncommanded stabiliser motion.

“Boeing will not offer the 737 Max for certification by the FAA until we have satisfied all requirements for certification of the Max and its safe return to service.”

The FAA said it was following a “thorough process, not a prescribed timeline” for returning the 737 Max to passenger service.

“We will lift the aircraft’s prohibition order when we deem it is safe to do so,” the administration added.

The loss of Ethiopian flight ET302 in March was the second fatal accident involving a 737 Max in the space of five months.

A near identical aircraft, owned by the Indonesian carrier Lion Air, crashed in the sea off Jakarta in October 2018.

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