Boeing Co. has run its new software update in some 500 test flights of 737 Max planes, which remain grounded globally since March after two fatal crashes during a five-month period, CNBC reported, citing CEO Dennis Muilenburg.

Muilenburg said in an interview at the Global Business Travel Association conference that he was on two of those test flights and other employees also wanted to be part of the tests, CNBC reported. The CEO expects the troubled model to make a comeback early in the fourth quarter.

Boeing swung to a loss in the second quarter year over year as the continued global grounding of its troubled 737 MAX aircraft dragged earnings lower by $8.74 per share and revenue by $5.6 billion.