American Airlines’ pilots’ union has hit back at Boeing for insinuating that some responsibility for the two crashes of its 737 Max jets lies with the pilots, and claimed AA pilots made several suggestions to Boeing to fix the plane’s anti-stall systems before the second crash.

Describing Boeing’s position as “inexcusable”, Dennis Tajer, a spokesman for the Allied Pilots Association, accused Boeing of unfairly blaming foreign pilots involved in the Lion Air and Ethiopian Airlines crashes.

Tajer told CNN: “Shame on you. We’re going to call you out on it. That’s a poisoned, diseased philosophy.” Asked if the Ethiopian crash might have been prevented if Boeing had acted on the US pilots’ concerns, Tajer said: “I think that’s a fair conclusion.”

Tajer said the Ethiopian Airlines pilots did what they were instructed to do, but that Boeing’s controversial anti-stall software (MCAS) forced the plane into such an aggressive nosedive that the pilots could not recover. “They had wired that thing so that it was irrecoverable. It just blew us away,” Tajer said.

In the original exchange with Boeing, the audio of which was released earlier this month, pilots angrily confronted a Boeing official about the MCAS system implicated in both crashes.

“These guys didn’t even know the damn system was on the airplane,” a pilot said.

In recent weeks, Boeing has tried to shift blame for both crashes from its software systems. In April, Dennis Muilenburg, the company’s chief executive, claimed the 737 Max was correctly designed and suggested the pilots did not “completely” follow the procedures that Boeing had outlined.

Ethiopian officials have insisted the Ethiopian Airlines pilots repeatedly performed all of Boeing’s procedures, but were unable to recover the plane. Ethiopian Airlines also complained that Boeing did not do enough to warn them about the system or provide functioning cockpit alerts about problems with sensors.

Earlier this week, US aviation officials said a bird strike may have triggered the faulty data that led to the MCAS system engaging. However, an Ethiopian Airlines spokesman said that the preliminary crash investigation report showed “no evidence of any foreign object damage”.

At a meeting on Thursday, 33 international aviation authorities will meet the Federal Aviation Administration (FAA) to discuss the process of review for the software fixes Boeing is to make to fix the MCAS system and give pilots greater control.

FAA’s acting administrator, Dan Elwell, rejected the idea that the twin crashes involving the aircraft have shaken trust between foreign regulators and the FAA. He said the FAA and the other regulators remain in “constant, close communication”.

But he would not predict a timeline for certifying Boeing’s software fix. When asked whether plans to return the 737 Max to service in August were realistic, Elwell admitted recertification could be pushed to October or beyond.