CNN  — 

Boeing CEO Dennis Muilenburg said Sunday he was “disappointed” the company was not more forthcoming with regulators about a problem with a safety feature on its troubled 737 Max airplanes, according to a published report.

Speaking at the Paris Air Show, Muilenberg said Boein will be more transparent going forward, the Wall Street Journal reported.

The 737 Max was grounded worldwide after a fatal crash of an Ethiopian Airlines jet in March, which followed a fatal crash of a Lion Air jet in Indonesia in October. Crash investigators have focused on an automatic safety feature on the jet as a contributor to the crashes. The airplane maker has been working on a fix.

Muilenberg again said he is unsure of when the Federal Aviation Administration will approve the fix and allow the restoration of service, the Journal reported. Earlier this week, both Boeing and the FAA told CNN Business they could not provide a time frame on when the grounded jets will be back in the air.

The Boeing CEO has previously apologized for the lives lost in the two crashes and promised “to earn and re-earn the trust of the flying public.”

He’s also said that Boeing will work with airlines on different forms of compensation for the grounding, including through supplying services or reduced costs of future purchases.

The 737 Max grounding has also halted deliveries of that plane, and it cut deeply into Boeing’s overall deliveries. Boeing gets most of its cash from the sale of planes at the time of delivery, so the grounding is hurting its bottom line.

Boeing has continued to build the 737 Max during the grounding, though at a reduced pace.

The company also reported no new commercial aircraft orders in May. It was the second straight month that Boeing’s orders were at a standstill in the face of the 737 Max crisis.

The drop in orders isn’t only because of the grounding of the 737 Max. Boeing also has a massive backorder of about 5,000 planes. Many of its customers do not need to place orders for additional jets right now.

–CNN Business’ Chris Isidore contributed to this report