The airplane’s nose can tilt down suddenly during takeoff, pilots aren’t being adequately trained on the autopilot system, and the operations manual is “criminally insufficient.” These are the complaints of US pilots in incident reports involving Boeing’s 737 Max 8 jetliner, the same model that was involved in two deadly crashes in recent months.

The reports, which were reported by multiple news outlets this week, cast a harsh light on the Max 8 jet that have been at the center of a global ban. More than 40 countries have grounded the airplane following two deadly crashes, one in Indonesia and the more recent one in Ethiopia. But the US Federal Aviation Administration continues to allow the plane to fly, and the Trump administration is being criticized for putting Boeing’s well-being over the safety of American passengers.

In one incident, an airline pilot reported that immediately after engaging the Max 8’s autopilot, the co-pilot shouted “DESCENDING,” followed by an audio cockpit warning, “DON’T SINK! DON’T SINK!”

“I immediately disconnected AP (Autopilot) (it WAS engaged as we got full horn etc.) and resumed climb,” the pilot writes in the report, which is available in a database compiled by NASA. “Now, I would generally assume it was my automation error, i.e., aircraft was trying to acquire a miss-commanded speed/no autothrottles, crossing restriction etc., but frankly neither of us could find an inappropriate setup error (not to say there wasn’t one).”

Another pilot said it was “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.”

That same pilot added, “I am left to wonder: what else don’t I know? The Flight Manual is inadequate and almost criminally insufficient. All airlines that operate the MAX must insist that Boeing incorporate ALL systems in their manuals.”

Boeing is under intense scrutiny following two crashes involving the Max 8, both resulting in the deaths of everyone on board. The Chicago-based company says it stands by the safety of the Max 8, but said it would also begin rolling out “flight control software enhancement” for its airplanes. The update was in the works before the crash of Ethiopian Airlines Flight 302 last Sunday, which killed all 157 people on board.

Boeing said it would update the Max 8’s flight control systems, pilot displays, operation manuals, and crew training. The FAA is expected to mandate the changes by the end of April. The software update was announced late Monday on Boeing’s website, and was prompted by the crash of a Lion Air aircraft in Indonesia last October, which killed 189 people.

The Lion Air investigation is ongoing, but has focused on the stall-prevention system, apparent maintenance lapses, and potential pilot error. The cause of the Ethiopian Airlines crash is unknown, but investigators have recovered the flight and data recorders.

Part of the planned update includes improving the Max 8’s “Maneuvering Characteristics Augmentation System,” Boeing said. According to The Air Current, the system was put in place to account for “some unique aircraft handling characteristics.”

This is because Boeing’s engineers had to relocate the engines and extend the nose landing gear several inches to achieve better fuel efficiency and make all the parts fit together. In doing so, they changed how the jet handled in certain situations, The Air Current explains. The Maneuvering Characteristics Augmentation System (MCAS) was installed to help pilots compensate for any movements caused by the realignment of the engines.

The MCAS pushes the jet’s nose down to prevent the risk of stalling during takeoff. It activates automatically (i.e. without the input of the pilot) when the angle of attack is high or when the flaps are up.

But rather than rely on multiple sensors, Boeing engineers determined that MCAS would need just a single sensor — measuring what is known as the angle of attack. This would be simpler to manufacture, and aligns with Boeing’s philosophy of keeping the pilot at the center of control in the cockpit, according to The Wall Street Journal.

This system is now under scrutiny in the wake of twin deadly crashes. According to Boeing:

A pitch augmentation control law (MCAS) was implemented on the 737 MAX to improve aircraft handling characteristics and decrease pitch-up tendency at elevated angles of attack. It was put through flight testing as part of the certification process prior to the airplane entering service. MCAS does not control the airplane in normal flight; it improves the behavior of the airplane in a non-normal part of the operating envelope. 

One pilot reported feeling confused by the anti-stall mechanism. “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 in an incident report.

Meanwhile, lawmakers have called on the Trump administration to follow the lead of other nations in grounding the Max 8 aircraft until the cause of Sunday’s crash in Ethiopia could be determined. The US is virtually alone in allowing the Max 8 to fly in its airspace, after aviation regulators in Europe, Canada, and China grounded the plane until investigators learn more about the crashes. But the FAA declined to act; President Trump was reported to have consulted with Boeing’s CEO this week.

On Wednesday, an ethics complaint was filed against Acting Defense Secretary Patrick Shanahan, an ex-Boeing executive, for “promoting Boeing in the scope of his official duties.” The complaint, filed by Citizens for Responsibility and Ethics in Washington, cites news reports in which Shanahan boosted Boeing in discussions at the Pentagon about government contracts, “saying that Boeing would have performed better than its competitor Lockheed Martin had it been awarded a DOD fighter jet contract.”