Boeing Max 737 plane being inspected
Credit: Gary He/Getty Images

Boeing is still working to ready its 737 Max planes for service again after two deadly crashes in five months killed 346 people. But the process is taking longer than expected, and investigations have revealed new concerns.

The New York Times reports that Boeing's internal audit completed at the request of the Federal Aviation Administration found that two critical bundles of wires that help control the tail of the 737 Max could be too close together, opening the potential for a short circuit.

Boeing is still working to determine whether such a short circuit could actually occur. A senior Boeing engineer told The Times anonymously that finding these types of problems and fixing them wasn't unusual and that such a fix for the wiring would be relatively simple.

The internal audit is intended to determine whether Boeing accurately assessed the dangers of key systems on the planes, given new assumptions on how long it takes pilots and crews to respond to emergencies.

New software on the planes was partly to blame for the two deadly crashes, which triggered errors that sent the planes into nosedives. Boeing's software fix has yet to be approved, but regulators think the planes could fly by spring. American Airlines and Southwest Airlines have planned commercial Max flights in April.

Investigations into the two crashes found that pilots did not respond as quickly or as effectively to problems as Boeing and the FAA presumed they would. Under new assumptions, if the wiring caused a short circuit that affected the stabilizer, the plane could nosedive.

If the wiring needs to be fixed, Boeing says, it would take one to two hours a plane to separate the bundles using a clamp. But that work could itself damage the plane, so Boeing is hoping to avoid it if possible.

In addition, the engine manufacturers discovered a possible weakness that could cause a rotor to shatter, and Boeing found a manufacturing problem that caused workers to inadvertently remove panel coating that protects the fuel tank and fuel lines from a lightning strike.

After Boeing's CEO was fired last month, the interim chief executive and his replacement are contending with a share price that fell 21% and tens of billions in charges related to the 737 Max grounding.

Government officials, however, believe the plane could be cleared for a certification test flight as soon as the end of January. Such a flight, in which Boeing would have to demonstrate that the Max meets all safety requirements, would be the regulator's final exam and one of the last steps before the grounding could be lifted.