Boeing 737 Max jet to face separate flight test by EU regulators

A Boeing 737 MAX 9 jetliner sits on the production floor at the company's manufacturing facility in Renton, Wash., on Feb. 13, 2017. Bloomberg photo by David Ryder.

The European Aviation Safety Agency plans to send its own pilots to the U.S. to conduct flight tests of Boeing's grounded 737 Max jet before it is returned to service, it said Tuesday.

The European regulator is conducting what it calls an "independent" review of the 737 Max before it's returned to service after being grounded for almost six months since the second fatal crash involving a malfunctioning flight-control system.

"EASA intends to conduct its own test flights separate from, but in full coordination with, the FAA," Janet Northcote, an agency spokeswoman, said in an email in response to questions. "The test flights are not scheduled yet, the date will depend on the development schedule of Boeing."

The crashes -- one off the coast of Indonesia in October and a second in Ethiopia in March -- were triggered by a malfunctioning sensor known as an angle-of-attack vane that measured whether the plane's nose was pointed up or down relative to the oncoming air. Boeing has two such sensors on all its aircraft, while other manufacturers, including the Blagnac, France-based Airbus, have used three or more to ensure more redundancy.

EASA is also examining whether Boeing's use of two vanes is sufficient, Northcote said. The regulations don't necessarily require an additional one must be added. Safety could be addressed "through improvement of the flight crew procedures and training, or through design enhancements, or a combination of the two," EASA said.

EASA said two vanes are considered "the bare minimum requirement to meet the safety objectives," and in the agency's experience "an architecture with three vanes can more easily be found compliant with the regulation."

The European regulator's concerns include the ability of pilots to handle an angle-of-attack failure during takeoff or other critical phases of flight. In the two 737 Max crashes, the erroneous data from failed angle-of-attack sensors prompted multiple cockpit alarms, including a false stall warning and altitude and airspeed gauges that didn't agree with each other.

"We are not being prescriptive in the way these concerns should be addressed," Northcote said.

Requiring the addition of new equipment to the 737 Max -- and possibly other Boeing models -- would add a significant complication to returning the plane to service. If EASA broke with the U.S. Federal Aviation Administration on the issue, it could also roil the aviation manufacturing world, which in recent decades has striven to become more consistent between different governments.

The U.S., Europe, Canada and Brazil, which all have major airline manufacturing companies, have entered into multiple agreements to improve cooperation and to standardize their certification rules.

While the major regulatory agencies normally defer large amounts of the certification work to the nation where the plane is being built, it's also not uncommon for them to conduct additional reviews and separate flight tests.

The FAA is likely to conduct its certification flight for the 737 Max in October, according to people briefed on the matter. Boeing has estimated that the plane will return to service early in the fourth quarter of this year. The company had earlier said it wanted to submit its final certification package by September.