Seattle - Two unions of U.S. pilots claim that the likely risks of a safety feature for the Boeing 737 MAX jets mentioned in a recent service bulletin after the Lion Air crash weren’t quoted enough in training manuals.

Boeing and the U.S Federal Aviation Administration (FAA) issued directives last week about the procedures in case of the false angle of attack data from a sensor that might be related to the fatal Lion Air crash in Indonesia.

According to the bulletin, the feature is designed to provide further protective measures if pilots lose control of aircraft due to false data from sensors. But two of the pilot unions for Southwest Airlines and American Airlines alleged that no any information was included in the training documentation for pilots concerning the system.

The criticisms from pilot unions of Southwest Airlines and American Airlines are notable because of the 737 fleet sizes of these operators and their 737 MAX orders.

Southwest is one of the largest 737 MAX operators with 26 737 MAX 8 in service and 257 on order. American Airlines has fifteen 737 MAX 8 in service and 85 on order.

This is not about silos and layers of bureaucracy; this is about knowing your airplane. We will always be eager and aggressive in gaining any knowledge of new aircraft,
said Dennis Tajer, a 737 captain and spokesman for the Allied Pilots Association at American Airlines.

We don’t like that we weren’t notified. The companies and the pilots should have been informed. It makes us question, ‘Is that everything, guys?’ I would hope there are no more surprises out there,”
said Jon Weaks, president of the Southwest Airlines Pilots Association.

In reply, Boeing stated that it is confident in the safety of its 737 MAX family aircraft.

We are taking every measure to fully understand all aspects of this incident, working closely with the investigating team and all regulatory authorities involved. Safety remains our top priority and is a core value for everyone at Boeing,
the manufacturer said in a statement by email.

So far, a few details have been shared with the public about the cause or causes of the Lion Air crash on October 29. According to the findings of investigators, an erroneous sensor caused the aircraft to enter into a sharp dive.

A new safety measure added on the Boeing's re-engineered single-aisles to help pilots keep control of the plane in case of the false angle of attack data, prompted the Lion Air's 737 MAX 8 to go nose down piercingly, according to the FAA and Boeing.

When the flight computer calculates the aircraft is close to a stall situation, it automatically gives a command to correct the angle of attack by lowering the nose. However, the sensor used to predict such circumstances was not functioning correctly on the Lion Air's 737 MAX 8. It fooled the flight computer to a sharp dive command.