“I don’t think there’s been enough scrutiny to determine whether this product is airworthy,” said Chris Moore, whose daughter Danielle was killed in the Ethiopian crash. “Essentially, what happened is my daughter and 156 others were on the second phase of a flight test. They were guinea pigs.”
The Max featured larger engines than the previous 737, and they had to be mounted farther forward on the wings, changing the aerodynamics of the plane. In response, Boeing added an automated system, known as MCAS. The system malfunctioned in both crashes, sending the planes into unrecoverable nose dives.
While the plane was being developed, Boeing concluded that the system was not particularly dangerous, and key F.A.A. engineers never fully reviewed MCAS as part of the certification.
“At what point does it become a new plane?” Mr. Stumo said. “They never took a holistic look at the whole plane.”
Mr. Stumo and Mr. Moore also called for the resignation of the F.A.A.’s safety chief, Ali Bahrami.
Mr. Bahrami oversaw the creation of the F.A.A. office that certified the Max, and he was criticized by some in the regulator for being too deferential to Boeing. Mr. Bahrami then went to work for an aviation industry association that counts Boeing as a member, before returning to the F.A.A.
Last week, Mr. Bahrami defended the F.A.A.’s certification of the Max at a congressional hearing. The next day, Mr. Stumo’s wife, Nadia Milleron, and their son Tor met with Mr. Bahrami in Washington and were dissatisfied with his response.
“We think Bahrami is more concerned with getting the plane in the air than safety,” Mr. Stumo said.
The F.A.A. has said it will permit the Max to fly again only once it is convinced the plane is safe. But to the families of some victims, that is not sufficient.
“We do not want any more families to experience the pain, anguish, sadness and loss that we have experienced,” the families wrote in the letter. “We therefore respectfully request that you determine that a full recertification and mandatory simulator training is necessary before the Boeing 737 Max 8 is allowed to fly again.”