A third U.S. pilots’ union is raising concerns about what it says is a lack of information provided by Boeing Co. on a safety system installed on the new 737 Max aircraft that is under a spotlight after last month’s crash off the coast of Indonesia.

The Air Line Pilots Association, which represents United Continental Holdings Inc.’s flight crews, wrote to Federal Aviation Administration Acting Administrator Dan Elwell Thursday saying it was “concerned that a potential, significant aviation system safety deficiency exists” and asking for more details.

“There appears to be a significant information gap, and we want to ensure that pilots operating these aircraft have all of the information they need to do so safely,” wrote Captain Tim Canoll, ALPA’s president.

Two other pilot unions — the Southwest Airlines Pilots Association and the Allied Pilots Association at American Airlines Group Inc. — raised similar concerns on Monday.

A safety system on the Max apparently pushed down the nose of a Lion Air flight near Jakarta shortly before it dove into the Java Sea on Oct. 29 with 189 people aboard, according to investigators in that country. Boeing says pilots could have dealt with the issue using an existing emergency procedure, but issued bulletins to carriers that was followed by an order to update flight manuals by the U.S. FAA.

A Boeing representative didn’t immediately respond to a request for comment. The company said Monday that it was confident in the safety of the 737 Max family of jets.

“The bottom line here is the 737 Max is safe,” Chief Executive Officer Dennis Muilenburg said later on Fox Business Network. “This airplane went through thousands of hours of tests and evaluations, certification, working with the pilots, and we’ve been very transparent on providing information and being fully cooperative on the investigative activity.”


–With assistance from Julie Johnsson.

©2018 Bloomberg L.P.

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Photo Credit: Crewman tow in a Boeing Max 737 jet after landing at King County International Airport, in Seattle, finishing the company's first flight of this new aircraft on January 29, 2016. The safety system on Boeing’s new Max 737 is in the spotlight after a crash of a Lion Air flight, with a third pilots union expressing concern. Mike Kane / Bloomberg