It turns out pilots did file a stream of written complaints with the U.S. federal government about the dangers they faced flying the new Boeing 737 MAX 8.

Two of these planes crashed shortly after take-off within five months of each other, a puzzling event some experts now believe is due to a fatal design flaw in the aircraft.

Months before the second crash of a MAX 8 in Ethiopia on March 11, concerned pilots repeatedly wrote to the U.S. Federal Aviation Administration (FAA) through NASA about safety concerns relating to the Max 8, said a report by The Dallas Morning News.

The report said one captain described the MAX 8 flight manual "inadequate and almost criminally insufficient" several months before the Ethiopian Air crash that killed 157 people.

"The fact that this airplane requires such jury rigging to fly is a red flag," wrote this captain. "Now we know the systems employed are error-prone — even if the pilots aren't sure what those systems are, what redundancies are in place and failure modes. I am left to wonder: what else don't I know?"

His complaint confirms a story published by Aviation Week in November 2018 saying the 737 MAX flight crew operations manual does not mention MCAS. Boeing said it "decided against disclosing more details to cockpit crews due to concerns about inundating average pilots with too much information."

The News found five complaints about the MAX 8 in a federal database where pilots can voluntarily report aviation incidents without fear of punishment. It said the complaints are about the MCAS or the Maneuvering Characteristics Augmentation System.

MCAS is basically a stall protection system unique to the MAX 8 and not installed on the Boeing 737 Next Generation, the model that preceded the MAX 8. It was installed on MAX 8s after the crash of a MAX 8 owned by Indonesia's Lion Air in October 2018.

MCAS is safety mechanism that automatically corrects a plane entering a stall. If a MAX 8 loses lift under its wings during take-off and the nose begins to point too far upward, MCAS kicks-in and automatically pushes the nose down. The problem is the nose can stay down in the event of problems with the plane's angle of attach indicators.

After the Lion Air crash, the FAA issued an airworthiness directive saying "This condition, if not addressed, could cause the flight crew to have difficulty controlling the airplane, and lead to excessive nose-down attitude, significant altitude loss, and possible impact with terrain."

MCAS was cited as the probable reason for the Lion Air crash that killed 189 persons.

Aviation experts probing the Ethiopian Airlines crash have gone public with their observations about the uncanny similarities between both catastrophes. The events leading to both crashes occurred less than 15 minutes after take-off when both planes were climbing to their cruising altitudes.

Boeing 737 MAX 8An American Airlines Boeing 737 Max 8, on a flight from Miami to New York City, prepares to land. American Airlines still flies the Max 8 despite the crash of a similar aircraft in Ethiopika on March 10 that killed all onboard. Photo: Drew Angerer/Getty Images

Records unearthed by The News show a captain who flies the Max 8 complaining in November 2018 that it was "unconscionable" Boeing and federal authorities allowed pilots to fly the planes without adequate training, or fully disclosing information about how its systems were different from those on previous 737 models.

"The United States should be leading the world in aviation safety," said John Samuelsen, president of a union representing transport workers, which called for the MAX 8 to be grounded. "And yet, because of the lust for profit in the American aviation, we're still flying planes that dozens of other countries and airlines have now said need to be grounded."

This article originally appeared in IBTimes US.