The Ethiopia Airlines and Lion Air flights both used 737 Max-8 aircraft.
The airline had to assign new planes to those flights after the grounding was ordered on those jets Wednesday. "They have to find the problem ... and they will find it", he said.
"We view the risk as less about near-term expenses, but the full year 737 delivery estimates for Boeing could be impacted", Herbert said in a research note.
On Wednesday, Ethiopian's CEO hinted in an interview that the black box was due to be taken to Europe for analysis given that Ethiopia lacked that expertise.
The low-priced carrier, a launch customer of the MAX 8 in 2017, said it was servicing those flights with available 737-700s and 737-800s.
Boeing's shares have sunk 10 percent since Sunday's crash, wiping more than $20 billion off the company's market value. "We are doing everything we can to understand the cause of the accidents in partnership with the investigators, deploy safety enhancements and help ensure this does not happen again", the company added. In total, there were at least 11 reports about the Boeing 737 MAX 8 logged on the Aviation Safety Reporting System between April 2018 and December 2018. The pilots of that flight reported that the plane's nose kept pitching down dozens of times before it crashed.
If the aircrafts' maneuvering characteristics augmentation system receives an erroneously high angle-of-attack sensor input, there is potential for repeated nose-down commands of the horizontal stabilizer, the FAA said, adding the condition would made it hard for pilots to control the plane.
Yesterday the FAA said 737 Max airliners would not be allowed to fly until new software had been "tested, approved and installed", a process likely to last until May, according to USA politicians briefed on the situation. The decision to send the recorders to France was seen as a rebuke to the United States, which held out longer than most other countries in grounding the jets.
The French agency, based in the Paris suburb of Le Bourget, has extensive experience in investigating crashes and other incidents involving commercial flights.
BEA said any information about the investigation would come from Ethiopian Airlines, which itself tweeted that it would only communicate through social media and its website.
"The fact the system was fighting the pilot was not an unintended outcome", because it should counteract a pilot error and correcting this is "challenging".
The delayed flight ET302 took off from Ethiopian capital Addis Ababa at 08:38 local time (05:38 GMT) and was bound for Kenyan capital Nairobi.