Indonesian accident investigators on Friday issued their final report on last year's deadly crash of a Lion Air jet, saying both design flaws and maintenance issues contributed to the accident.

The report by the National Transportation Safety Committee was particularly critical of Boeing Co.'s design of the 737 MAX 8's anti-stall system known as MCAS.

"The investigation considered that the design and certification of this feature was inadequate," a press release by the committee said.

The system's reliance on one sensor made it "vulnerable to erroneous input from that sensor," it said, adding that the investigation could not determine that the installation test of the sensor in the accident plane was performed properly.

In addition, an absence of guidance from Boeing on MCAS made it "more difficult" for crews to respond to problems with the system, it said.

On Oct. 29 last year, Lion Air Flight JT610 crashed into the sea 13 minutes after taking off from Jakarta's international airport, killing all 189 people on board. The plane, which was bound for Pangkalpinang, had been put into service only two months earlier.

It is believed that incorrect sensor readings saying the aircraft was angled too steeply repeatedly caused MCAS to angle the nose of the plane downwards. The pilots tried repeatedly, and unsuccessfully, to counter the mechanism manually.

Another 737 MAX 8 series aircraft operated by Ethiopian Airlines crashed in March this year, killing all 157 people on board.

Airlines around the world have since grounded their own Boeing 737 Max planes following the two deadly crashes, with Boeing suspending deliveries and reducing production of the plane, affecting its bottom line.