What began as a tragedy is starting to look like something worse.

In the span of just four months, two Boeing Co. 737 Max jets have crashed, killing a total of 346 people. Both planes — Lion Air Flight 610 on Oct. 29 and Ethiopian Airlines Flight 302 on March 10 — experienced serious trouble shortly after takeoff. In a third case, reported last week by Bloomberg News, a similar disaster was narrowly averted.

What these incidents appear to have in common is a safety feature known as the Maneuvering Characteristics Augmentation System, or MCAS, which was added to the 737 Max to reduce the threat of aerodynamic stalls due to a new engine design. In the Lion Air crash, investigators suspect that a faulty sensor caused MCAS to repeatedly push the nose of the plane downward; the pilots, bewildered, kept fighting the automated system until they lost control. After data from the Ethiopian crash suggested a similar pattern, the jets were grounded worldwide.

A lot remains unknown about these incidents. But they’re nonetheless cause for profound concern. As a start, three questions need answering.

First, why didn’t Boeing warn pilots about the risks of the new system? A big selling point of the 737 Max was that it wouldn’t require much retraining for aviators accustomed to other 737s, a benefit the company boasted would save “millions of dollars” per fleet. By one account, U.S. pilots received less than an hour’s instruction on the new plane. Most flight manuals didn’t mention MCAS — let alone what to do if it malfunctioned — and pilots say they weren’t told of it. What was the rationale for these omissions?

Second, what did regulators know? For years, the U.S. has been criticized for delegating too much air-safety oversight to manufacturers like Boeing. Doing so isn’t inherently foolish; the FAA lacks the staff to inspect every feature of new aircraft, and companies have every incentive to get things right. But by all indications, this process broke down. Most worryingly, a safety analysis that Boeing submitted to the FAA understated the risks of the new MCAS system in crucial respects. Was this deliberate? And did regulators knowingly give the company excessive leeway for commercial reasons?

Finally, why weren’t these planes grounded much sooner? As Bloomberg News reports, federal investigators from the Justice Department and the Department of Transportation began probing Boeing’s certification process shortly after the first crash. And yet for months, the FAA — part of the Department of Transportation — insisted the 737 Max was safe. Even after the second crash, the U.S. refused to ground the planes until nearly every other country had done so. If the problem was so glaring as to warrant a grand jury probe, surely some added precaution was in order?

An awful lot hangs on the answers to these questions. If Boeing minimized the risks of its new design to sell more planes, that would be an extraordinary corporate scandal. If the FAA has become so deferential to companies that it overlooked a potentially fatal flaw in hundreds of jets, its mission is fundamentally compromised. And if the U.S. knew of a serious problem with these planes even while vouching for their safety, it may have put lives at risk.

There may yet be innocent explanations. And it’s important to remember that — awful as these crashes are — getting on a plane is a stunningly safe way to travel. But that’s no coincidence; it’s due to years of meticulous regulation. The same rules that make flying so burdensome also make it secure. This tragedy suggests the full horror that can result when that balance is tipped.