From World of Aviation.
FAA REVEALS PROPOSED CHANGES FOR 737 MAX
written by
Hannah Dowling August 4, 2020
In a new airworthiness direction (AD) dated 3 August, the US Federal Aviation Administration revealed its proposed design changes for the troubled Boeing 737 MAX.
The proposal aims to address the issues raised by the aircraft’s manoeuvring characteristics augmentation system (MCAS), which appeared to be at the heart of two fatal 737 MAX crashes in 2018 and 2019.
As such, the FAA has proposed four key changes to the aircraft, after previously determining that “final corrective action is necessary to address the unsafe condition” of the aircraft.
This first proposed design change is the installation of an entirely new flight control computer (FCC) software, with new control laws.
“These revised flight control laws would use inputs from both AOA sensors to activate MCAS,” the FAA noted.
This is in contrast to the original MCAS design, which relied on data from only one sensor at a time, and allowed repeated MCAS activation as a result of input from a single AOA sensor.
The new FCC and revised control laws are intended to prevent the “erroneous MCAS activation”, and ultimately give the pilots better control over the airplane pitch, an ability that was inhibited under the original MCAS design.
The second design change is the installation of new MAX display system (MDS) software, which essentially works to alert the flight crew should there be an error in one of the two AOA sensors.
The new display will have the capacity to create a visual alert on the airplane’s primary flight display (PFD), which informs the flight crew if there is a disagreement between the angles of attack measured by each of the plane’s two AOA sensors.
The third design change proposed by the FAA is to revise the existing Airplane Flight Manual (AFM), in order to appropriately incorporate new and revised flight crew operating procedures.
This change hopes to ensure that the flight crew have the means to recognise and respond to erroneous stabiliser movement and the effects of a potential AOA sensor failure.
A previous criticism of the 737 MAX was the flight crew were not appropriately trained or informed of the operating procedures under the new operating system.
The fourth proposed change is to change the routing of horizontal stabiliser trim wires, in order to restore compliance with the FAA’s latest wire separation safety standards.