The US Department of Transportation (DOT) has requested its inspector general to carry out an audit of the certification process of the Boeing 737 Max 8.

A memorandum released by the transportation secretary read: "This is to confirm my request that the Office of Inspector General proceed with an audit to compile an objective and detailed factual history of the activities that resulted in the certification of the Boeing 737 Max 8 aircraft."

Questions have since been raised over Boeing's influence over the 737 Max certification process, as the US Federal Aviation Administration delegated the certification process task to Boeing.

Jet Airways has grounded another six aircraft, raising the number of grounded aircraft to at least 48 for defaults on lease payments.The airline's latest round of groundings forced India's aviation minister Suresh Prabhu to convene an emergency meeting.

The airline along with the ministry's secretary and the country's directorate general of civil aviation (DGCA), will hold meetings to discuss the grounding's impact on "advance bookings, cancellation, refunds and safety issues, if any.

Boeing chairman, president and chief executive Dennis Muilenburg has released an open letter reinforcing the company’s commitment to safety, as most of the global fleet of Boeing 737 Max aircraft enters its second week of groundings.

We’ve been working in full cooperation with the U.S. Federal Aviation Administration, the Department of Transportation and the National Transportation Safety Board on all issues relating to both the Lion Air and the Ethiopian Airlines accidents since the Lion Air accident occurred in October last year,” says Muilenburg.

In his letter, Muilenberg also reiterated that a software update and related pilot training for the Max will be released soon, which “will address concerns discovered in the aftermath of the Lion Air Flight 610 accident.