A new software issue has been found in the embattled Boeing 737 Max planes that could mean further delays to getting the aircraft back in the air.
The planes were grounded earlier in the year after two deadly crashes involving the aircraft.
On Wednesday, Boeing said that the Federal Aviation Administration (FAA) had found an “additional requirement” for the 737 Max’s software changes that the manufacturer has been working on for eight months after the first crash.
In a statement Boeing said: “Boeing agrees with the FAA’s decision and request, and is working on the required software to address the FAA’s request.”
US government test pilots, who were testing the new software last week found a flaw that could mean the plane’s nose pitches down, according to two people close to the matter.
They added that the issue could be fixed through software changes or by replacing a microprocessor in the aircraft’s flight-control system.
One of the sources added that the new setback is likely to delay the plane’s return to service by up to three months.
In a statement, the FAA said that they would lift grounding of plane only when they deemed it safe.
The agency said: “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.”
The planes began flying passengers in 2017 and is Boeing’s best selling aircraft.
Despite this, less than 400 have been delivered to airlines
In October 2017, a Max aircraft operated by Indonesia’s Lion Air crashed, killing all 346 people on board.
A second crash happened in March in Ethipoia, killing 157 people, forcing regulators around the world to ground the plane.
Boeing is now scaling back the power of flight-control software, called MCAS. to push the nose down. It is also connecting the software’s nose-down command to two sensors on each plane, rather than relying on just one as per the original design.
It still is not known what kind of training pilots will get for the aircraft when it eventually returns to the skies.