The goal of this post is to show with simple use cases, how SyMAP technology performs real time predictive maintenance of airbus aircraft flight control system (FCS)

We start by presenting with Figure 1, flight control surfaces and 3 axes used by FCS, including roll axis, pitch axis and yaw axis. We show 3 use cases of SyMAP focusing on 3 primary surfaces: ailerons, spoilers and elevators.

Figure 1: Airbus Aircraft Flight Control Surfaces from Airbus Group

Each  surface  is  controlled  by one  or  two  actuators  and  each  actuator  is  connected  to  one  or two primary or secondary  computers .  For  example,  on  Figure 2 ,  the  left  inband  aileron  is  controlled  by  two  actuators:  one conventional actuator which is active during normal operation , and one EHA (Electro-Hydrostatic Actuator) which is damping during normal  operation. The conventional actuator is connected to primary computer P1 and secondary computer S2, and to the backup  control  module (B)  of computers. EHA  is  connected to primary computer P2 and secondary  computer S2. Flight  control  surfaces  are  controlled as follows. A computer receives order from human pilot  or  auto-pilot, it  computes a surface deflection  order and send  it to SV (Servo  Valve) of conventional actuator or MDE (Motor  Drive  Electronic)  of  EHA. The  feedback  LVDT (Linear  Variable  Differential  Transformer) gives the piston rod position of the actuator and computer fulfils the “inner” control loop.

Figure 2: SyMAP failure predictions related to left inband aileron

Figure 2 shows  how  SyMAP can  predict  two successive  faults  related  to one aileron (the left inband aileron) and propose two preventive actions to crew members in order to avoid that aircraft undergoes these failures even for a few moments. Conventional actuator of the left inband aileron is powered by green hydraulic system of the aircraft and EHA  is powered  by  the alternative  electrical  current  E2.  When  the  green  hydraulic  power  is  lost, there  is  a  protection mecanism  which  activates  the  EHA . But  this  protection  mecanism  takes   few  moments  to  make  the  reconfiguration. More  over it  is  not  always  availaible since  it  can be faulty also. During  these  few moments, the aircraft undergoes  the  failure, i.e., the left  inband  aileron is no longer available  and, the control of the aircraft along the roll axis during a turn becomes more complicated and therefore dangerous.

SyMAP is able to predict at time  t,  the green hydraulic lost at time  t+T1,  and propose to crew members to activate the EHA  at time  t+t1 such  that  t1 is between  t  and  T1, but  t1  is very close to  T1. Doing so,  SyMAP gives to pilot, the possibility to avoid  that  aircraft  undergoes  green  hydraulic  lost and left  inband  aileron lost during the small moment during  which  the protection  mechanism  inhibits the conventional  actuator and activates the EHA. In the case  where  the  protection  mecanism  is  also  faulty, SyMAP  acts  as a  fault  tolerance  system  of  this protection mecanism.

Figure 2 also shows that, SyMAP can combine two predictions and propose an appropriate prevention action. Based on prediction 1 (green  hydraulic  lost)  and  prediction 2 ( E2  electrical  source lost), i.e., the two actuators of the left inband aileron will be damping, so SyMAP propose right  inband  aileron  inhibition  to  maintain aircraft equilibrium according  to  roll  axis. Note  that,  in  this  use  case ,  prevention  actions  will  help  crew  members  to avoid  some consequences of green hydraulic lost or E2 electrical source lost, but SyMAP can also go beyond FCS to research and propose a preventive  action in the hydraulic system or in the electrical system in order to avoid green hydraulic lost or E2 electrical source lost. Figure 3 and Figure 4 respectively show other SyMAP similar failure predictions related to left spoiler 7 and left inband elevator.

Figure 3: SyMAP failure predictions related to left spoiler 7
Figure 4: SyMAP failure predictions related to left inband elevator
Simple use cases of SyMAP inside Airbus Aircraft Avionic Domain

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