Flight simulations recreating the problems with the Lion Air plane that crashed last year have revealed pilots had less than 40 seconds to override an automated system to avert disaster, according to airline sources.

The pilots tested a crisis situation similar to what investigators suspect went wrong in Lion Air flight 610, which killed all 189 people on board after it crashed into the Java Sea.

In the tests, a single sensor failed, triggering software designed to help prevent a stall.

Once that happened, the pilots had just moments to disengage the system and avoid an unrecoverable nosedive of the Boeing 737 Max, according to two people involved in the testing in recent days.

Although the investigations are continuing, the automated system, known as MCAS, is a focus of authorities trying to determine what went wrong in the Lion Air disaster in October and the Ethiopian Airlines crash of the same Boeing model this month.

Lion Air plane crashes minutes after take-off from Jakarta Show all 13 1 /13 Lion Air plane crashes minutes after take-off from Jakarta Lion Air plane crashes minutes after take-off from Jakarta Indonesia President Joko Widodo inspects the items recovered from Lion Air flight JT 610 Getty Lion Air plane crashes minutes after take-off from Jakarta A member of Indonesian Search and Rescue Agency inspects debris AP Lion Air plane crashes minutes after take-off from Jakarta Rescue teams have been joined by fisherman and volunteers in the search for survivors Getty Lion Air plane crashes minutes after take-off from Jakarta Lion Air CEO, Edward Sirait (centre) speaks during a press conference at Lion Air Branch office at Soekarno Hatta Airport EPA Lion Air plane crashes minutes after take-off from Jakarta No bodies have yet been discovered among the wreckage of the Lion Air flight EPA Lion Air plane crashes minutes after take-off from Jakarta Indonesian search and rescue personnel prepare for a recovery mission Getty Lion Air plane crashes minutes after take-off from Jakarta Rescuers searching the site of the plane crash lift a body bag onto a nearby vessel EPA Lion Air plane crashes minutes after take-off from Jakarta A relative of passengers arrive at Lion Air's crisis center at Soekarno-Hatta International Airport in Tangerang, Indonesia AP Lion Air plane crashes minutes after take-off from Jakarta In this photo released by Indonesian Disaster Mitigation Agency rescuers inspect debris believed to be from a Lion Air passenger jet AP Lion Air plane crashes minutes after take-off from Jakarta A relative of passengers prays as she and others wait for news on a Lion Air plane that crashed off Java Island AP Lion Air plane crashes minutes after take-off from Jakarta A rescue team member points to the location where Indonesia's Lion Air flight JT 610 had crashed into the sea, at Tanjung Priok seaport in Jakarta Getty Lion Air plane crashes minutes after take-off from Jakarta Officials evacuate a body bag containing the remains of one of the victims of the crash EPA Lion Air plane crashes minutes after take-off from Jakarta Indonesian relatives of the plane crash victims cry as they wait for the news at the airport in Sukarno Hatta Airport EPA

The software, as originally designed and explained, left little room for error.

Those involved in the testing had not fully understood just how powerful the system was until they flew the plane on a 737 Max simulator, according to the two people.

In a tacit acknowledgement of the system’s problems, Boeing is expected to propose a software update that would give pilots more control over the system.

This would make it less likely to trigger erroneously, according to three people familiar with the private meetings and who spoke on the condition of anonymity.

There are common procedures in place to counteract MCAS, as currently designed.

If the system starts pushing the plane’s nose down, pilots can reverse the movement via a switch at their thumb, a typical reaction in that situation. To fully neutralise the system, pilots would need to flip two more switches.

That would shut off the electricity to a motor that allows the system to push the plane towards the ground. Then the pilots would need to crank a wheel to correct whatever problems had emerged.

In the Lion Air crash, pilots used the thumb switch more than two dozen times to try to override the system.

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The system kept engaging nonetheless, most likely because of bad readings from a sensor, until the plane crashed into the Java Sea, killing all 189 people on board.

The software changes require approval by the Federal Aviation Administration.