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Several American pilots submitted complaints about the Boeing 737 Max aircraft months before the same model crashed in Ethiopia on Sunday, killing 157 people.

The complaints, first reported by The Dallas Morning News, were revealed before the Federal Aviation Administration on Wednesday issued an emergency order grounding the Max 8 and Max 9 jets.

The FAA said it decided to keep the jets out of the air after it found that the Ethiopian Airlines aircraft that crashed Sunday had a flight pattern very similar to a Lion Air flight that went down in Indonesia in October, killing all 189 people aboard.

“It became clear that the track of the Ethiopian flight behaved very similarly to the Lion Air flight," said Steven Gottlieb, deputy director of accident investigations for the FAA.

But well before the accident in Ethiopia on Sunday, at least five complaints about the Max 8 were made in October and November, and most mention issues with the aircraft's autopilot and the plane going nose down shortly after takeoff. One pilot wrote that the Max 8's aircraft manual was "criminally insufficient."

"I think it is unconscionable that a manufacturer, the FAA, and the airlines would have pilots flying an airplane without adequately training, or even providing available resources and sufficient documentation to understand the highly complex systems that differentiate this aircraft from prior models," one pilot wrote about the lack of instructions regarding the aircraft's maneuvering characteristics augmentation system or MCAS.

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The MCAS is a safety system installed in the Max 8 that would allow the aircraft to automatically correct itself if it enters a stall pattern, according to the Morning News. If the plane's nose begins to point too far upward during takeoff, the system would take over and push the nose down, the Morning News reported.

"I am left to wonder: What else don't I know? The Flight Manual is inadequate and almost criminally insufficient," the pilot wrote.

In many of the complaints, the pilots noted the aircraft going nose down during takeoff.

One pilot wrote that "within two to three seconds the aircraft pitched nose down" after enabling the autopilot during takeoff. Once the autopilot was disengaged, the captain was able to continue climbing and the remainder of the flight was uneventful.

"We discussed the departure at length and I reviewed in my mind our automation setup and flight profile but can't think of any reason the aircraft would pitch nose down so aggressively," the pilot wrote.

Those complaints were logged after a Boeing 737 Max 8 crashed in Indonesia, killing 189 people.

The FAA declined comment to NBC News about the complaints.

Despite the crashes and complaints — in addition to calls from aviation experts and consumer advocates asking for the Max 8 to be grounded — the FAA continued to insist the 737 Max 8 jets were safe until Wednesday afternoon.

Boeing announced Monday night that urgent updates to the flight-control software for its 737 Max fleet would be implemented in the "coming weeks." The FAA plans to mandate that change by the end of April.

The Chicago-based corporation said Wednesday it supported the FAA order and had recommended that the FAA ground its entire global fleet of 371 jets that are Max 8 or Max 9 models.

"Boeing has determined -- out of an abundance of caution and in order to reassure the flying public of the aircraft's safety -- to recommend to the FAA the temporary suspension of operations of the entire global fleet" of these jets, the aircraft manufacturing giant said.

"We are doing everything we can to understand the cause of the accidents in partnership with the investigators, deploy safety enhancements and help ensure this does not happen again," Boeing said.

It is still not clear what caused the crash in Ethiopia. The jet's black boxes were to be sent to France on Wednesday night for analysis.

The plane crashed six minutes after takeoff from Addis Ababa en route to Nairobi.