Each sensor reading included over 80 values, consisting of continuous (numerical) and discrete data (Boolean) and sampled with a frequency of 1 Hz. Data came from bus systems in the air conditioning system and flight data system. Most were temperature data and valve state data. The sensor data are described in the following multi-page table (Table 8).
Description Bus Type
Total Air Temperature Air Data
Computer Numerical
Pressure Altitude (1013 hPa) Air Data
Computer Numerical
Present Position Lateral Inertial
Reference System Numerical
Present Position Longitude Inertial
Reference System Numerical Cabin Compartment Temperature Group 1 Zone Control Numerical Cabin Compartment Temperature Group 2 Zone Control Numerical Cabin Compartment Temperature Group 3 Zone Control Numerical Cabin Temperature Regulation Valve Position Group 1 Zone Control Numerical Cabin Temperature Regulation Valve Position Group 2 Zone Control Numerical Cabin Temperature Regulation Valve Position Group 3 Zone Control Numerical
Duct Overheat Warning Group 1 Zone Control Boolean
Duct Overheat Warning Group 2 Zone Control Boolean
Duct Overheat Warning Group 3 Zone Control Boolean
Duct Temperature 4 Times Limit Exceedance Group 1 Zone Control Boolean Duct Temperature 4 Times Limit Exceedance Group 2 Zone Control Boolean Duct Temperature 4 Times Limit Exceedance Group 3 Zone Control Boolean
Duct Temperature Group 1 Zone Control Numerical
Duct Temperature Group 2 Zone Control Numerical
Duct Temperature Group 3 Zone Control Numerical
G + T Fan OFF Zone Control Boolean
Hot Air Switch Position ON Zone Control Boolean
Minimum Bleed Air Pressure Demand Zone Control Numerical
Nacell Anti Ice - Engine 1 Zone Control Boolean
Nacell Anti Ice - Engine 2 Zone Control Boolean
Recirculation Fan Left Hand Fault Zone Control Boolean
Recirculation Fan Right Hand Fault Zone Control Boolean
Trim Air Pressure Regulation Valve Disagree Zone Control Boolean
Trim Air Pressure High Zone Control Boolean
Trim Air Pressure Regulation Valve Close Zone Control Boolean
Trim Air System Inoperational Zone Control Boolean
Zone Main Control Inoperational Zone Control Boolean
Zone Secondary Control Inoperational Zone Control Boolean
Abnormal Pressure - Engine 1 Bleed Monitoring
Computer Boolean
Abnormal Pressure - Engine 2 Bleed Monitoring
Computer Boolean
APU Bleed Push Button ON Bleed Monitoring
Computer Boolean
APU Bleed Valve Fully Closed Bleed Monitoring
Computer Boolean
APU Command Bleed Monitoring
Computer Boolean Bleed Push Button Position ON - Engine 1 Bleed Monitoring
Computer Boolean Bleed Push Button Position ON - Engine 2 Bleed Monitoring
Computer Boolean
Cross Feed Valve Auto Closure Bleed Monitoring
Computer Boolean
Cross Feed Valve Auto Opening Bleed Monitoring
Computer Boolean
Cross Feed Valve Manual Closure Bleed Monitoring
Computer Boolean
Cross Feed Valve Manual Opening Bleed Monitoring
Computer Boolean Cross Feed Valve Position Fully Closed Bleed Monitoring
Computer Boolean Cross Feed Valve Position Fully Open Bleed Monitoring
Computer Boolean Cross Feed Valve Selected Position Open Bleed Monitoring
Computer Boolean Cross Feed Valve Selected Position Shut Bleed Monitoring
Computer Boolean
Cross Pressure Regulation Valve Command Close Bleed Monitoring
Computer Boolean
Engine 1 Precooler Inlet Pressure Bleed Monitoring
Computer Numerical Engine 1 Precooler Outlet Temperature Bleed Monitoring
Computer 1 Bleed Monitoring
Computer Numerical Engine 1 Precooler Outlet Temperature Bleed Monitoring
Computer 2 Bleed Monitoring
Computer Numerical
Engine 2 Precooler Inlet Pressure Bleed Monitoring
Computer Numerical Engine 2 Precooler Outlet Temperature Bleed Monitoring
Computer 1 Bleed Monitoring
Computer Numerical Engine 2 Precooler Outlet Temperature Bleed Monitoring
Computer 2 Bleed Monitoring
Computer Numerical Flap Actuator Valve Position Fully Closed - Engine 1 Bleed Monitoring
Computer Boolean Flap Actuator Valve Position Fully Closed - Engine 2 Bleed Monitoring
Computer Boolean Flap Actuator Valve Position Fully Open - Engine 1 Bleed Monitoring
Computer Boolean Flap Actuator Valve Position Fully Open - Engine 2 Bleed Monitoring
Computer Boolean High Pressure Valve Fault - Engine 1 Bleed Monitoring
Computer Boolean High Pressure Valve Fault - Engine 2 Bleed Monitoring
Computer Boolean High Pressure Valve Position Full Open - Engine 1 Bleed Monitoring
Computer Boolean High Pressure Valve Position Full Open - Engine 2 Bleed Monitoring
Computer Boolean High Pressure Valve Position Fully Closed - Engine 1 Bleed Monitoring
Computer Boolean High Pressure Valve Position Fully Closed - Engine 2 Bleed Monitoring
Computer Boolean Over Pressure Valve Position Full Open - Engine 1 Bleed Monitoring
Computer Boolean Over Pressure Valve Position Full Open - Engine 2 Bleed Monitoring
Computer Boolean
Overheat - Engine 1 Bleed Monitoring
Computer Boolean
Overheat - Engine 2 Bleed Monitoring
Computer Boolean
Over Pressure - Engine 1 Bleed Monitoring
Computer Boolean
Over Pressure - Engine 2 Bleed Monitoring
Computer Boolean Precooler In Pressure 10/60 - Engine 1 Bleed Monitoring
Computer Boolean Precooler In Pressure 10/60 - Engine 2 Bleed Monitoring
Computer Boolean Pressure Relief Valve Auto Closure Control - Engine 1 Bleed Monitoring
Computer Boolean Pressure Relief Valve Auto Closure Control - Engine 2 Bleed Monitoring
Computer Boolean Pressure Relief Valve Low Regulation Bleed Monitoring
Computer Boolean Pressure Relief Valve Position Full Open - Engine 1 Bleed Monitoring
Computer Boolean Pressure Relief Valve Position Full Open - Engine 2 Bleed Monitoring
Computer Boolean Pressure Relief Valve Position Fully Closed - Engine 1 Bleed Monitoring
Computer Boolean Pressure Relief Valve Position Fully Closed - Engine 2 Bleed Monitoring
Computer Boolean
Start Valve Closed - Engine 1 Bleed Monitoring
Computer Boolean
Start Valve Closed - Engine 2 Bleed Monitoring
Computer Boolean
Transferred Pressure - Engine 1 Bleed Monitoring
Computer Numerical
Transferred Pressure - Engine 2 Bleed Monitoring
Computer Numerical
X Feed Command Bleed Monitoring
Computer Boolean
Pack 1 Out Temperature Pack Control Numerical
Pack 2 Out Temperature Pack Control Numerical
Pack Flow 1 Pack Control Numerical
Pack Flow 2 Pack Control Numerical
Pack Water Extractor Temperature 1 Pack Control Numerical
Pack Water Extractor Temperature 2 Pack Control Numerical
Pack Outlet Temperature 1 Pack Control Numerical
Pack Outlet Temperature 2 Pack Control Numerical
Table 8: A320 sensor data description
Figures 40 and 41 show where the sensors are located in the aircraft.
Figure 40: A320 AeroBytes data description 1
Figure 41: A320 AeroBytes data description 2
Data analysis showed a maintenance action after approximately 930 flight hours (FH) (Gerdes, et al., 2017). Samples for the decision tree generation were created by taking 1024 sensor data points after the aircraft reached a height of 30,000 ft. This equals 17 minutes of data in cruise flight and yields about 3400 data samples; 25% were used for training and 25% were used for testing.
Samples were randomly taken from the flight data to avoid having the training data overlap with the test data and to ensure that the number of samples per class was not equally distributed. The data samples were divided into ten categories. The first category equalled all data samples with a time stamp lower than 10% of the RUL of the system, i.e., 930 FH. The maintenance action during the duration of the recorded data was assumed to be the end of the lifetime and the first data point is the beginning. We did this because no data above the whole life of the system are available.
However, this should be sufficient to validate the concept. The last category contained samples with a timestamp between 90% and 100% of the RUL. All categories in between were split equally, each covering a 10% range of RUL.