The day before a Boeing 737 Max 8 crashed off of Indonesia last year, killing all 189 people aboard, pilots struggled for control of the same aircraft but were saved by an off-duty pilot on the plane, a report says.

Lion Air Flight 610 slammed into the Java Sea on Oct. 29, and a preliminary investigation has focused on a malfunctioning flight control system. Information from the cockpit voice recorder suggests the pilots of the doomed plane pored over a handbook trying to determine why the jet was lurching downward in the desperate moments before the crash, according to multiple media reports.

The day before, a different crew struggled with the same issue on the flight. The problem was correctly diagnosed by the "deadhead" pilot flying in a jump seat, Bloomberg reported, citing multiple sources familiar with Indonesia's investigation of the crash.

The presence of a third pilot in the cockpit wasn’t contained in Indonesia’s National Transportation Safety Committee’s report, according to Bloomberg.

“All the data and information that we have on the flight and the aircraft have been submitted to the Indonesian NTSC. We can’t provide additional comment at this stage due to the ongoing investigation on the accident,” Lion Air spokesman Danang Prihantoro told Bloomberg.

According to a preliminary report issued last year, the first officer on board the doomed Lion Air flight reported a “flight control problem” to air traffic control two minutes after takeoff. Reuters reported Tuesday that it obtained the additional details, from the flight's voice recorder, via three investigation sources.

Less than five months after the Lion Air crash, Ethiopian Airlines Flight 302 was minutes into a Nairobi-bound flight from Addis Ababa when it slammed into a field March 10. The pilot immediately noticed trouble as the plane accelerated wildly after takeoff. The planeoscillated up and down by hundreds of feet before the crash.

Investigators said they found similarities in the Boeing disasters. Both flights crashed after drastic speed fluctuations during ascent. Both pilots made ill-fated efforts to return to their airport of origin after takeoff.

The 371 Boeing 737 Max jets flown around the world have been grounded pending further investigation. Also hanging in the balance are orders for more than 4,500 of the hot-selling planes. Boeing said last week it "paused" deliveries of the 737 Max although production continues.

The flight control system, new to the 737 Max planes, was designed to keep planes from stalling. The FAA said it expects Boeing to complete Max 8 flight control system enhancements – prompted by the Lion Air crash – by month's end.

It is not clear when the the planes will get the international green light to fly again.

Records show that federal aviation authorities received at least 11 reports concerning perceived safety problems with the 737 Max aircraft before the crashes.

Two pilots reported their planes unexpectedly pitched nose down after they engaged autopilot following departure. Another pilot reported a “temporary level off” triggered by the aircraft automation. Another pilot called part of the aircraft’s flight manual “inadequate and almost criminally insufficient.”

In an open letter Monday addressed to airlines, passengers and the aviation community, Boeing CEO Dennis Muilenburg said his company will soon release a software update and offer related pilot training for the 737 Max to “address concerns.”

"The tragic losses of Ethiopian Airlines Flight 302 and Lion Air Flight 610 affect us all, uniting people and nations in shared grief for all those in mourning," the letter said. "Our hearts are heavy, and we continue to extend our deepest sympathies to the loved ones of the passengers and crew on board."