Deliverable: D1.2a Requirements analysis document for aeronautic applications V1.1 /
DELIVERABLE NO / D1.2a
DELIVERABLE TITLE / Requirements analysis document for aeronautic applications
AUTHOR / Jirka Klaue (EADS)
DISCLOSURE LEVEL / Public
VERSION / V1.1
Copyright CHOSEN Consortium 2008-2011
Page 1
CHOSeNPublicDeliverable: D1.2a Requirements analysis document for aeronautic applications V1.1 /
Referenced Documents
[CHOSeN DoW]
-CHOSeN Annex I - “Description of Work”
[DO160F]
-Radio Technical Commission for Aeronautics (RTCA) DO-160F, Environmental Conditions and Test Procedures for Airborne Equipment
[DO178B]
-Radio Technical Commission for Aeronautics (RTCA) DO-178B,Software Considerations in Airborne Systems and Equipment Certification
[ABD0100]
-Airbus Directives (ABD) and Procedures, ABD0100, Equipment-Design, General Requirements For Suppliers
Abbreviation List
AFDX / Avionics Full Duplex EthernetCFRP / Carbon Fiber Reinforced Polymer
CIDS / Cabin Intercommunication Data System
CRP / Carbon Fiber Reinforced Plastic
CW / Crack-Wire
LRI / Line Replaceable Item
LRU / Line Replaceable Unit
MAC / Media Access Control
MRO / Maintenance, Repair and Overhaul
MTTF / Mean Time to Failure
NDT / Non Destructive Testing
OEM / Original Equipment Manufacturer
PAX / Passengers
PHY / Physical layer
SHM / Structural Health Monitoring
WSN / Wireless Sensor Network
Table of Contents
1EXECUTIVE SUMMARY......
2INTRODUCTION......
3AERONAUTIC APPLICATIONS......
3.1Crack-wire Monitoring for Supporting Structure
3.2Distributed Strain Monitoring of Hull Components
3.3Cargo and PAX Door Surrounding
4APPLICATION REQUIREMENTS......
4.1General
4.1.1Temperature......
4.1.2Pressure......
4.1.3Humidity......
4.1.4Water tightness......
4.1.5Shock......
4.1.6Vibrations......
4.1.7Chemical resistance......
4.1.8Others [ABD0100], [DO160F]......
4.1.9Safety and Security......
4.2Sensors
5USER REQUIREMENTS......
6ARCHITECTURE & FUNCTIONAL MODEL......
6.1Autonomous wireless sensor node (W)
6.2Gateway node (G)
6.3Central data collector (D)
6.4Functional analysis
6.4.1F1 - Data Acquisition......
6.4.2F2 - Communication......
6.4.3F3 - System monitoring......
6.4.4F4 - Human machine interface......
6.5System elements
7SYSTEM REQUIREMENTS DEFINITION......
List of figures
Figure 1: System & Structure Health Monitoring - Application Overview
Figure 2: Schematic overview of WSN architecture for SHM applications
Figure 3: Wireless Sensor Node [CHOSeN DoW]
Figure 4: Functional Tree......
Figure 5: Data acquisition functional tree......
Figure 6: Communication functional tree......
Figure 7: System monitoring functional tree......
Figure 8: HMI functional tree......
Table 1: Examples of physical parameters to monitor in different aircraft domains
Table 2: Design assurance level definition
Copyright CHOSEN Consortium 2008-2011
Page 1
CHOSeNPublicDeliverable: D1.2a Requirements analysis document for aeronautic applications V1.1 /
1EXECUTIVE SUMMARY
The present document aims on providing a general description of the aeronautic applications and to collect the corresponding system requirements that, together with the automotive requirements, shall serve as a guideline for the CHOSeN wireless sensor network design and development.
The INTRODUCTION section describes the general context of the aeronautic applications, the motivation and expected impact on the operation and maintenance optimization.
The AERONAUTIC APPLICATIONSsection provides a description of the aeronautic applications, where the general characteristics are outlined and the implications on the development of the CHOSeN platform are highlighted.
TheAPPLICATION REQUIREMENTS section enumerates and analyses the requirements regarding the sensors, communication, energy-consumption and functions.
The sections USER REQUIREMENTS and ARCHITECTURE & FUNCTIONAL MODEL enunciate the user requirements which have been identified in the phase of the application selection and describe the function of the systems components realizing the aeronautic demonstrator and briefly describes the main elements of the system.
TheSYSTEM REQUIREMENTS DEFINITION section collects all the aeronautic applications functional requirements emerged from the analysis done across the document. Starting from the CHOSeN general purposes described in the DoW, aeronautic applications capable of challenging the CHOSeN platform has been identified and analyzed.
In this document the Applications description has been shortened in contrast to the corresponding section in D1.2b.INTRODUCTION
In order to observe and assure the safety, functions and life-time of certain components of aircrafts, a lot of physical data has to be collected, processed and matched with system models. These measurements are related for instance with the temperature impact over time on different critical parts, the pressure, distension and torsion of parts of the landing gear and so on. Many of these measurements are done during the maintenance times of aircrafts; parts are disassembled, audited and possibly exchanged. The effort is huge and so are the costs of the maintenance times. So it is obvious that integrated system health monitoring could reduce both the time the airplane is maintained and disassembled as well as the maintenance costs.
It is also obvious that a lot of distributed measuring points with various functions are needed. These sensors will have different requirements in terms of power consumption, vibration and shock tolerance, etc. They will also have different capabilities in terms of data priority, data rate, latency and frequency. Some of these sensors could certainly be wired, while others can only be wireless due to their positioning. There are a lot of different aircrafts and aircraft configurations, and the future will certainly bring new maintenance models demanding more measurement points and/or other physical input. Therefore, it is desired to have a general communication infrastructure, including the sensor nodes, communication protocols and data collecting and presentation platform.
The sensor nodes should be able to organise themselves. That means that they “speak a common language”, are able to find among each other’s and to find ways to distribute their data in the sensor network. Some of these features are not needed for all types of sensors, and some sensors might not even have the power to perform all these tasks. Therefore the general sensor node platform must be programmable and configurable. A common platform for all types of sensors does also have additional advantages:
- Only one type of hardware to test and verify
- Easy design of new sensor components
- Low-cost because of high number of units
- Flexibility and scalability
The general sensor node design and communication platform would even allow using the same base system for structure health monitoring in other industrial fields.
Maintenance work on an aircraft is triggered by two usually disjoints events: unscheduled events raised by failures or malfunctions and scheduled events, which are regular maintenance. A typical relation between “unscheduled events” and “scheduled events” is respectively 60% to 40% on an events basis. The related maintenance efforts may differ, but grounding times split close to that ratio. Needless to say that unscheduled events lead to unplanned (even if somehow expected: 60%) grounding times during regular use costing aircraft carriers a lot of money and reputation.
Unscheduled events are split in turn in normal wear related maintenance (=lighter checks) and the heavier checks asked for by the certification authorities. Aircraft maintenance checks are periodic checks that have to be done on all aircraft after a certain amount of time or usage. Airlines refer to these checks as one of the following: A check, B check, C check, or D check. A and B checks are lighter checks, while C and D are considered heavier checks.
- A Check — this is performed approximately every month. This check is usually done overnight at an airport gate. The actual occurrence of this check varies by aircraft type, the cycle count (takeoff and landing is considered an aircraft "cycle"), or the number of hours flown since the last check. The occurrence can be delayed by the airline if certain predetermined conditions are met.
- B Check — this is performed approximately every 3 months. This check is also usually done overnight at an airport gate. An occurrence schedule similar to the one of the A check applies to the B Check.
- C Check — this is performed approximately every 12-18 months. This maintenance check puts the aircraft out of service and requires plenty of space - usually at a hangar at a maintenance base. The schedule of occurrence has many factors and components as has been described, and thus varies by aircraft category and type.
- D Check — this is the heaviest check for the airplane. This check occurs approximately every 4-5 years. This is the check that, more or less, takes the entire airplane apart for inspection. This requires even more space and time than all other checks, and must be performed at a maintenance base.
The use of WSN technology would enable the transfer of interventions from unscheduled maintenance to scheduled maintenance. At the same time the engineer would get feedback to replace unreliable spare parts by better ones. Therefore the closed loop to engineering is another major point.
The future is also to deal with certification authorities for maintenance on demand based on predictive models for unscheduled events plus A and B checks in order to break the rigid maintenance schedule scheme. To reach this goal, detailed and reliable data are needed “for all” LRIs, structures and system components.
The main benefits of this continuous monitoring with wireless, or rather "less wired", sensor networks and the targeted new maintenance and operation concept are:
-Simpler installation
-Less initial cost (bill of materials)
-Less weight
-Less volume
-Higher reliability
-Easier troubleshooting
-Easier re-configuration
-Low spares cost
For the end user that means:
-Lower costs
-Better comfort and service
-Higher safety and reliability
2AERONAUTIC APPLICATIONS
This chapter gives a short overview of the general scope of the applications for system and structure health monitoring in the aeronautic industry and the benefits that are expected for the whole aircraft operation processes – not only for the aircraft production – but also for the operators (e.g. the airlines), the OEM and MRO (Maintenance, Repair and Overhaul) services.
Figure 1 shows the general idea of distributed monitoring of various aircraft systems and parameters and the expected impact and benefits for the aircraft itself (left side) and the operator of the aircraft (right side). Single sensors are already integrated in current aircrafts and connected to existing communication infrastructure. Other sensors are only applied when the aircraft is on-ground or even partly disassembled for maintenance. Continuous monitoring of the health state of various systems and structure is not yet possible.
Figure 1: System & Structure Health Monitoring - Application Overview
The benefit that is expected from continuous monitoring of very different and distributed physical parameters is ultimately cost saving. These savings are expected mainly in the installation, maintenance and operation as explained Chapter 0.
In an aircraft there are a lot of different systems in various compartments where several different physical parameters are measured or are at least desired. A common measurement/monitoring infrastructure does not exist in the aircraft since most systems are designed independent.
Table 1gives an overview of a number of physical parameters that are measured in different compartments of an aircraft. The number of applications that depends on the monitoring of these parameters is very high and covers a broad spectrum of aircraft systems.
Physical Parameter / Aircraft DomainAerodynamics / Cabin / Engine / Structure
Temperature / / / /
Pressure / / /
Gas / /
Flow / / /
Humidity / /
Fire / /
Vibration / /
Proximity / /
Displacement / /
Strain /
Table 1: Examples of physical parameters to monitor in different aircraft domains
For maximum benefit - as explained in the previous chapter - all parameters shall be acquired, communicated, evaluated and stored by a common infrastructure and provided for maintenance and operation purposes in a central database/computer within the aircraft. The process of the identification of applications for WSN and their exact requirements is currently ongoing within the aeronautic industry and by no means finished yet. However, it is already apparent from the hitherto existing analysis that a certain set of requirements is common for all applications. In the following three specific applications are described which seem to be both promising and challenging in terms of requirements to the WSN to be developed within CHOSeN. The applications are selected so that the requirements cover a broad spectrum in order to meet the wide range of SHM applications. Afterwards, in Chapter 4, the requirements are derived and analysed.
2.1Crack-wireMonitoring for Supporting Structure
Crack-wires are simple sensors, which require not much effort from the actual sensor hardware side, and at the same time are very useful for the monitoring of cracks and crack growth in supporting structure elements. In case of cracks caused by overload the crack-wire breaks. This can be measured by electrical continuity. The energy consumption of the sensor itself is very low and thus suited for use with autonomous wireless sensor nodes.
[shortened description for public release]
2.2Distributed Strain Monitoring of Hull Components
Another possibility to assess the health of structure elements is to measure the strain (and temperature) continuously and apply certain aging models in order to predict the remaining lifetime of these structure elements. In principle there are three events that could induce extraordinary strain in the structure: (hard) landing, impact (e.g. bird strikes) and turbulences. If the exceeds certain thresholds, these events must be detected at the sensor locations in the structure and logged for later fusion and evaluation.
[shortened description for public release]
2.3Cargo and PAX Door Surrounding
The surrounding of the passenger and cargo doors is subject to additional stress induced by the docking of aerobridges and gangways.
[shortened description for public release]
3APPLICATION REQUIREMENTS
3.1General
Certain general requirements are to be met in order to justify the use of wireless sensors for maintenance optimisation. Especially the harsh environment conditions within an aircraft and the long projected lifetime (in the range of 30-50 years) are key requirements since it doesn't make sense to have maintenance helpers which need maintenance more often than the components they are monitoring.
Following requirement regarding the environment are general and basically based on the Airbus Directives and Procedures ABD0100.1.2 as well as the RTCA/DO-160F, Environmental Conditions and Test Procedures for Airborne Equipment. Only in exceptional cases for special scenarios other requirements can be valid.
However, since CHOSEN is a research project, these requirements are only established here as background information that should be kept in mind during development so that later production of airborne equipment is feasible at all.
3.1.1 Temperature
Operating temperature:-55°C … +70°C
Survival temperature range:-55°C … +85°C
Temperature changing rate:10°C/min
3.1.2 Pressure
Minimum environmental pressure:0.1bar (50.000ft)
Maximum environmental pressure:2.0bar
Decompression rate:< 15Sek
3.1.3 Humidity
Relative humidity:954 % at 55°C
3.1.4 Water tightness
Water tightness:splash watertight (DO-160F Sec. 10 Cat. S)
3.1.5Shock
Maximum shock load:20g, 11ms (all 6 directions)
3.1.6Vibrations
Frequency range:10 … 2000Hz
Level:7.9 g rms (1g = 9.81m/s²)
Spectral distribution: 10 – 28Hz:0.02g²/Hz
40 – 100Hz:0.04g²/Hz
200 – 500Hz:0.08g²/Hz
– 2000Hz:-6dB/oct
3.1.7Chemical resistance
Chemically resistant against:
Fuel:Aviation Jet Fuel Type A (Kerosene)
Hydraulic fluid:H537 / Skydrol
Lubricant:O-133 (petroleum base)
Solvents:Denatured alcohol
Defrosting fluid:Nato S-735 (DTD406B)
Insecticide:Dichlorvos (DDVP)
Wastewater:Dishwater/suds
Saline water:NaCl dilution (5%)
3.1.8Others [ABD0100], [DO160F]
Resistance against:
-Fire/flammability
-Sand/dust
-Fungal attack
-Icing
-Electrostatic discharge
-Radiation
3.1.9 Safety and Security
From the functional point of view the applications must be analyzed regarding the Design Assurance Level (DAL) of the system. These levels can then be used as guidelines for the communication safety, reliability and security analysis.
The required Design Assurance Level (DAL) is determined from the safety assessment process and hazard analysis by examining the effects of a failure condition in the system. The failure conditions are categorized by their effects on the aircraft, crew, and passengers.
Catastrophic:Failure may cause a crash.
Hazardous:Failure has a large negative impact on safety or
performance, or reduces the ability of the crew to operate
the plane due to physical distress or a higher workload, or
causesserious or fatal injuries among the passengers.
Major:Failure is significant, but has a lesser impact than a
hazardous failure (for example,leads to passenger
discomfort rather than injuries).
Minor:Failure is noticeable, but has a lesser impact than a major
failure (for example, causingpassenger inconvenience or a
routine flight plan change)
No Effect:Failure has no impact on safety, aircraft operation, or crew
workload.
DALFailure condition
ACatastrophic
BHazardous
CMajor
DMinor
ENo effect
Table 2: Design assurance level definition
According to the DAL the requirements on the communication regarding safety, reliability and security can be done.The applications considered in CHOSeN are only DAL E and maybe D. Therefore, the highest priority should be on: reliability, authenticity, integrity. Data loss or corrupted/wrong data have to be avoided and would be considered a security breach. On the other hand, the additional power consumption required for security measures should be as low as possible, since the energy availability at the sensor node side is one of the bottlenecks. But since the transmitted information only needs to be kept secret for several days, the performance (resistance to deciphering) shouldn’t be the highest priority. This is also supported by the fact that the processing power available at the sensor nodes is very limited due to the low power microcontroller needed there.
The environment in which the communication takes place is only inside the aircraft, external links are not involved. The equipment involved in the communications is static, no mobile devices and their special security challenges have to be considered.
The trade-off between storage and transmission of data regarding the energy-consumption is a key parameter of the considered SHM applications. For instance, a lot of measurements could be aggregated and stored for just one transmission later. However, the stored data should also be protected against alteration and unauthorized access.