Last night’s 747 turnback to Sydney airport with one of four engines shut down was an inconvenient non-event for passengers, and unlikely to have any safety implications. But this is not true of another area of doubt at Qantas — safety oversight and record keeping.

These issues are in much sharper focus because of the industrial action by the Association of Professional Engineers, Scientists and Managers Australia, whose members sign off on the maintenance status of flights. They haven’t been working outside office hours since November 13, with their role at other times taken over by management proxies Qantas insists are fully qualified to do their work and, on occasions, their own members disobeying the work bans.

The claims that the management stand-ins and the union members are fully competent do not fit well with a dangerous situation involving a Boeing 737-800 that Qantas allowed to keep flying for three sectors after a blemish (not a crack) was found in a glass cockpit panel in February.

It turns out there is a current airworthiness directive for that model of 737-800 that requires immediate replacement if a defect is detected in that particular cockpit window. It must be replaced. It wasn’t replaced until the following day, when it was repaired at Canberra before making a flight to Melbourne. The jet flew for many hours and carried hundreds of passengers.

But this is the twist. It was signed off as legal to fly by a member of the professional engineer’s association, and Qantas is known to have instituted a peer review each morning by union members of all the relevant actions taken over line operations in the previous 24 hours. It wasn’t until the following morning that an error by a professional engineer was picked by one of his peers and immediate action taken.

How the airline, and the union member involved, could have been ignorant of the requirements of the airworthiness directive applying to the 737 is the really serious question here. However, Qantas insists  its interpretation of the AD allowed it to delay the repairs until the plane was in Canberra.

As the FAA says in its commentary on the supposedly well-known issues with 737 cockpit windows: “Loss of cabin pressure could cause crew communication difficulties or crew incapacitation”. Or in plain English, a crash. At cruising speed a shattered windscreen means, in medical terms, blunt force trauma and the ensuing terrible disaster.

Airworthiness directives are very serious documents. CASA was so concerned about Ansett’s inability to maintain proper paperwork and maintenance oversight, including the adherence to ADs, that it twice grounded its 767 fleet, once before Christmas 2000 and again before Easter 2001.

So what is going on at Qantas? CASA says it’s investigating a number of matters, including this one, raised by the professional engineer’s union. It may be that the new management at the safety regulator has found its purpose, and the courage to carry it out and tell the public what its concerns are in a timely manner.