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WindTech DFMS — Technical Writing

8 min read • Published on: Feb 4, 2024 • Tags: #featured,#projects

Non-functional requirements for a drone fleet management system (DFMS)

This exerpt is from a project vision and scope document for a drone fleet management system, written for the INFO 380: Product and Information System Management.

Non-Functional Requirements

Scalability

We aim to develop a system with future growth in mind. Therefore, the system must have a modular architecture and optimized performance and meet the following requirements:

  • SCA-1: The system shall be able to accommodate annual growth of 10% new drone fleets a year across different wind farm locations without user-perceptible performance degradation.
  • SCA-2: The system shall scale to handle simultaneous maintenance on at least 50% of the wind turbines at any given location for at least 60 minutes.

Availability

During working hours, maintenance technicians and other stakeholders must access the system to schedule maintenance, deploy drones, and view real-time data to make relevant decisions. Thus, the system must be highly available during working hours, and at least available most of the time beyond working hours in case of emergencies. The system does not have to be as strictly available outside of working hours, as technicians are not actively scheduling and analyzing maintenance. Since 100% availability would be unrealistic and put unnecessary strain on WindTech’s budget, we instead strive for at least 99% availability during critical hours to balance the request for “high availability” and resource constraints. The system must be able to meet the following availability requirements:

  • AVL-1: The system must be at least 99% available on weekdays between 8 a.m. and 5 p.m. GMT+1 on weekdays, and at least 95% available on weekdays between 5 p.m. and midnight GMT+1.
  • AVL-2: Scheduled maintenance scheduled for Sundays between 8 p.m. and 3 a.m. GMT+1 does not count toward the calculation of availability.
  • AVL-3: WindTech shall inform employees one week before scheduled maintenance.
  • AVL-4: A user shall not be able to access the system during maintenance and downtime, and shall instead be shown a message indicating when the system is expected to resume operation.

Interoperability

The DFMS will be integrated with existing WindTech systems, thus we must ensure compatibility and functionality across different platforms. Since employees must sign into different systems depending on their tasks, single sign-on (SSO) support is necessary for consistency and security (see "Security Needs"). The DFMS must integrate with maintenance scheduling, weather forecasting, inventory management, reporting, training, and more. Therefore, data exchange capabilities and API compatibility are crucial.

  • IOP-1: Requests made to APIs outside of the DFMS to other WindTech systems shall return results within 5 seconds 99% of the time.
  • IOP-2: The DFMS API shall respond to external requests within 5 seconds 99% of the time.
  • IOP-3: The DFMS API shall throw specific error codes, messages, and appropriate responses.
  • IOP-4: A user shall log into the DFMS using the same single sign-on login information to access WindTech system information.
  • IOP-5: The system shall be able to export data in CSV and JSON formats.
  • IOP-6: The DFMS API shall keep an audit trail of API transactions for up to one week.
  • IOP-7: The DFMS API and related systems shall adhere to RESTful API standards (see "RESTful APIs").
  • IOP-8: In the case of concurrent data updates, the DFMS shall check for inconsistencies and, if found, throw an error requesting the user to conduct manual verification.

Sustainability

See "Environment and Noise Regulations" for more environmental sustainability requirements; this section will focus on sustainable IT (SIT) practices.

Green IT practices are increasingly crucial, as cloud computing produces up to 3.7% of global greenhouse gas emissions, exceeding that of commercial flights (Lavi, 2022). To ensure sustainability, the DFMS must meet the following requirements:

  • SIT-1: The system shall use a data center that can achieve a power usage efficiency (PUE) of 1.2 or less and is located in a region with abundant access to renewable energy (National Renewable Energy Laboratory, n.d.).
  • SIT-2: The system shall prohibit consecutive transmissions of redundant data within 10 seconds to minimize network usage.
  • SIT-3: Drones shall not be operated in inclement weather or harsh conditions, and shall be regularly maintained (see also SEC-8), to maximize their lifespan.

Security

Data security is crucial for the DFMS to ensure the integrity and confidentiality of operational data, prevent unauthorized access, protect against cyber threats, comply with local and federal regulations, and enable future capability expansions.

To secure data, the DFMS should adhere to the following requirements:

  • SEC-1: Data transmission between drones, ground control stations, and services within the DFMS, such as scheduling and maintenance logs, shall be encrypted end-to-end.
  • SEC-2: The system shall back up data daily at midnight.
  • SEC-3: A user shall only be able to log into the DFMS if they have two-factor authentication.
  • SEC-4: A user shall be able to log into the DFMS using WindTech SSO.
  • SEC-5: Only users who have Maintenance Technician or Operation Manager permissions shall be able to operate the DFMS.
  • SEC-6: Only users who have Maintenance Technician or Operation Manager permissions shall be able to unlock doors to drone storage areas using a security badge.
  • SEC-7: The VP of Operations shall conduct compliance checks and audits once every three months.
  • SEC-8: Operation Managers shall update drone firmware and software and conduct physical maintenance monthly to mitigate risks of malfunction.
  • SEC-9: Drones shall be authenticated before being integrated into the DFMS.
  • SEC-10: Drones shall not be able to fly further than the geographical boundaries of WindTech wind farms.
  • SEC-11: Maintenance technicians shall conduct spectrum monitoring every 30 minutes when drones are deployed.
  • SEC-12: If external interference is detected, drone operations shall be paused until the source of interference is verified and removed.

Doing so will protect data and prevent unauthorized drone operations. In addition to the above requirements, WindTech should:

  • Use secure, cloud-based solutions, such as Amazon Web Services (AWS) or Microsoft Azure, for storing and analyzing sensitive data such as inspection reports, maintenance logs, and data collected during drone operations.
  • Establish contingency plans in the case of drone malfunctions or external threats with the collaboration of the Chief Security Officer and VP of Operations.

Standards and Compliance

RESTful APIs

REST stands for Representational State Transfer, and following RESTful API standards can help ensure system scalability, flexibility, and independence. Compliant APIs adhere to the following principles:

  • Uniform interface, where the server returns information in a standardized format
  • Statelessness, where client requests are completed independently
  • Layered system, where the API can work with several servers with multiple components
  • Cacheability, where the client can store some server responses to improve response time
  • Code on demand, where the software code can be temporarily transferred to the client (Amazon, n.d.).

Accessibility Guidelines

To ensure the accessibility of materials relating to the DFMS project, developers must address the following requirements:

  • USE-1: All drone pilot training materials in audiovisual formats must have transcripts and closed captions.
  • USE-2: The information hierarchy in human-machine or human-system interfaces must be programmatically determinable through proper formatting, tagging, and labeling such that they are navigable by screen-reader or other access technologies.
  • USE-3: Crucial information, such as warnings and confirmation dialogues, shall be delivered with textual identification in addition to sensory characteristics, like size, color, and sound.
  • USE-4: Text and images shall have a contrast ratio of at least 4.5:1.
  • USE-5: Text shall be able to be resized up to 200% without additional assistive technologies.

Since system warnings are crucial to upholding the safety of wind turbine operations, warning messages and confirmation dialogues must be completely accessible to individuals of all abilities. Additionally, computer interfaces shall adhere to basic accessibility guidelines as dictated by the Web Content Accessibility Guidelines (WCAG) 2 (Web Accessibility Initiative, 2023).

Drone Regulations & Safety Requirements

Drones are considered unmanned aircraft systems. Because drones used for wind turbine maintenance fly close to large structures and may require complex flight patterns, they are classified under the “Specific” category. Operations in this category are regulated by Unmanned Aircraft System (UAS) Regulation (EU) 2019/947 Annex A Part B. To comply with the requirements, we must ensure the following:

  • SAF-1: WindTech shall apply for operational authorization with the registration number of the drone operator, the name of the accountable manager or operator, an operational risk assessment, a list of measurable risk mitigation measures proposed by the operator, an operations manual, and a confirmation of appropriate insurance coverage.
  • SAF-2: Drone pilots shall complete training before operating drones in areas such as situational awareness and error management; organizational safety culture, operational procedures, and organizational structure; stress management, fatigue, and vigilance; decision-making; automation and philosophy of the use of automation; specific UAS type-related differences; case-based studies; and drone piloting basic skills.
  • SAF-3: WindTech shall keep records of drone pilots’ training courses and qualifications for at least three years after they cease employment.
  • SAF-4: Interfaces for drone operations shall minimize the risk of pilot error by providing clear, intuitive, and distinguishable labeling and cause minimal fatigue.

The regulation outlines more guidelines that WindTech shall adhere to in its operations, but the above constraints are most relevant to the scope of our DFMS project (European Union Aviation Safety Agency, 2022, pp. 309–320).

Environment and Noise Regulations

The EU defines 55 dB as the threshold for noise exposure, measured as an annual average between day, evening, and night. However, noise levels above 40 dB are known to harm wildlife. Regulations do not impose limit values but rather dictate reporting thresholds. Governments must map noise levels, create action plans, and designate quiet areas. Most established guidelines and regulations focus on transport and industry sources, though some countries also have specific regulations for wind turbines (European Environment Agency, 2020).

Though there are no formal regulations for drone noise levels, these guidelines serve to help WindTech anticipate future policy developments and operate in good faith to protect the environment.

To best adhere to these guidelines, the DFMS shall adhere to the following constraints:

  • ENV-1: Drones deployed for wind turbine inspections shall not fly through government-designated quiet areas.
  • ENV-2: Drones operated by WindTech should not generate noise that exceeds 55 dB at ground level, measured following the European Union Aviation Safety Agency’s (EASA) noise measurement guidelines.

EASA Noise Measurement Guidelines

Typically, drone manufacturers can measure drone noise levels according to EASA guidelines and voluntarily provide the data. However, if the manufacturer does not provide compliant noise ratings for its product, WindTech can refer to the EASA’s Guidelines on Noise Measurement of Unmanned Aircraft Systems Lighter than 600 kg Operating in the Specific Category (Low and Medium Risk) for testing conditions, including terrain, obstacles, temperature, humidity, precipitation, windspeeds, and procedures (European Union Aviation Safety Agency, 2023).

General Data Protection Regulation (GDPR)

Besides employee data, the drone project may also inadvertently collect civilian personal data, such as faces, house fronts, and vehicle registration plates (DroneRules.eu, 2018). To comply with the EU’s GDPR, the DFMS project must adhere to the following requirements:

  • SEC-13: DFMS administrators shall maintain detailed documentation of collected data to present to regulatory authorities if necessary.
  • SEC-14: Only users with Operation Manager and Safety Officer permissions shall have access to employee training histories.
  • SEC-15: In addition to safety training, drone operators shall also complete data privacy training (Wolford, n.d.).
  • SEC-16: Drone operators shall delete any footage that collects personal data irrelevant to wind turbine inspection, including, but not limited to, faces, house fronts, and vehicle registration plates.

Photo by Karsten Würth on Unsplash