The cause of the Ethiopian Airlines crash that killed 157 people is still being investigated but similarities to the Boeing 737 Max 8’s flight path to that of Lion Air flight 610, which plunged into the sea off Indonesia last year, have been noted by air-safety experts, airline regulators, and worried passengers.

While the US’s airline regulator says the plane is still safe to fly, Boeing said yesterday (March 11) it has been working on a new software update for the planes with US officials for “the past several months” and planned to release it “no later than April.“

One thing that is known: Both planes—new versions of the Boeing aircraft—took erratic up-and-down journeys marked by “unstable vertical speed” before taking fatal dives minutes after takeoff, according to FlightRadar24.

Several countries have grounded their Boeing MAX fleets, including China, Ethiopia, and Indonesia, and Australia. Yesterday, the Association of Flight Attendants formally requested the US Federal Aviation Administration (FAA) conduct an investigation into the 737 Max.

In the Lion Air crash on October 29, 2018, investigators determined that a faulty instrument reading forced an automated “safety feature” to send the plane into the sea even as the pilots struggled to keep it aloft. All 189 on board were killed. (Boeing put out a bulletin afterward advising airlines on how to deal with erroneous sensor information that would lead to “uncommanded nose down” maneuvers.)

After the Lion Air crash, the FAA—which, with EU airline regulators, generally sets the tone for aviation safety worldwide—issued a new “airworthiness directive” to US operators of the Boeing 737 8 and 9 planes, warning that an “unsafe condition” exists on the models and providing flight crews “with runaway horizontal stabilizer trim procedures to follow under certain conditions.”

Straightforward safety upgrades to the jets’ software to fix the automated safety feature, were originally expected in January according to multiple reports. But they were delayed until April, the Wall Street Journal reported Feb. 10, because of “engineering challenges,” “differences of opinion” between federal and Boeing officials, and the 35-day government shutdown, during which “consideration of the fixes was suspended.”

It remains to be seen whether any software fix would have prevented the Ethiopian Airlines crash this week. In a statement yesterday, the 61,000-member Air Line Pilots Association cautioned “against speculation about what may have caused this tragic accident.”

Warnings on how shutdown affected safety

During the shutdown, the longest in US government history, FAA activities deemed crucial, including air-traffic control and safety oversight, continued, although the workers involved were unpaid. Many other activities were stopped.

Donald Trump forced the shutdown after refusing to sign a government spending bill that didn’t have billions he wanted to build a wall on the US southern border. After 35 days, he signed a spending package that didn’t have the budget, then declared a “national emergency” to get the funds from the Pentagon instead. Warnings about the Transportation Security Administration and the FAA being stretched too thin during the shutdown brought the political situation to a head.

The 61,000-member pilots association warned Trump of the dangers in a letter on Jan. 2, noting specifically that complicated oversight of manufacturing activities had stopped or were “significantly reduced”:

For example, at the Federal Aviation Administration (FAA) there are fewer safety inspectors than are needed in order to ensure the air traffic control infrastructure is performing at its peak levels of performance. There are also airline and aircraft manufacturing oversight activities that either stop or are significantly reduced. These safety and oversight inspections will potentially allow for the introduction of safety issues that put passengers and airline crews at risk.

The pilots, sounded the alarm again Jan. 10, in a letter to Trump, House speaker Nancy Pelosi, and Senate majority leader Mitch McConnell: