Systems engineering and control system software are vital elements of an electronic fuel control system. The System engineering function determines the overall control system by partitioning the requirements among the subsystems (software, electronics, hydromechanical fuel control, etc.) and verifying/validating the resultant designs and system performance. The information used comes from OEM requirements, technology availability, and regulatory requirements.
PECS designs engine control software to support flight critical applications with the highest level of reliability. Our system/ software designs and processes have been developed from many years of experience with real-time FADEC systems used on both fixed and rotary wing airframes. This includes handling all aspects of the software process from development of requirements through coding and verification. PECS also has considerable experience interfacing with both civilian / commercial regulatory agencies and military certification authorities as part of an engine qualification effort. PECS’s software development process is fully compliant with RTCA/DO-178B, level A.
Application examples of PECS systems and software capabilities have included the system design, analysis and verification test responsibility on both the LHTEC T800 engine powering the Boeing-Sikorsky RAH66 Comanche and Honeywell T55 engine used on the Boeing Chinook helicopters. PECS has also supported system design, software design, and analysis and verification test and certification responsibility for the Rolls Royce Model 250 FADEC controlled engines. These engines have been used on the Bell models 430 & 407, MD Helicopters MD600, Kiowa Warrior and Little Bird. Similar work is occurring on the LHTEC CTS800 engine being certified on the Westland Lynx helicopter. PECS continues it systems and software leadership with new programs supporting the US Army’s Advanced Control and Universal control programs, as well as development work for new commercial helicopter and general aviation applications.
Control system software is embedded into the electronic control hardware and defines both the functionality and operational characteristics of the electronic control. Software defines the functionality/characteristics for the speed governors, temperature limiters and torque limiters. The software interprets input data from engine sensors and data buses, processes the information, and drives output devices. These include solenoids and motors that modulate engine performance by metering fuel flow or activating subsystems such as the ignition or starter, or provide process/operational indications (lights and data bus) to the operator/pilot or maintenance crew. Software can also provide health, diagnostic and fault monitoring information on engine, control system and airframe performance and operation.
The embedded ECU software is divided into two main areas. These are the Operating System Software (OSS) and the engine control system software (CSS). The OSS provides the execution environment and low-level interfaces to the hardware. The CSS provides the overall engine control functions and external signal fault logic. The combined OSS and CSS control the engine in real-time by reading input signals, performing fault detection, selecting validated signals, executing engine control algorithms, and commanding output devices.
Development of software requirements, software top-level design, software detailed module design, module code, and integration are conducted per established procedures that have been successfully employed on previous certification programs. Software verification is accomplished by using a combination of reviews, analyses, and testing. The reviews and analyses provide an assessment of the accuracy, completeness, consistency, and verifiability of the software requirements, software architecture, and the source code. The test procedures provide additional assessment of the internal consistency and completeness of requirements. The execution of the tests provides a demonstration of compliance with the software requirements. PECS also has extensive code development experience in real-time operating systems, signal processing, and cross-channel, cross-engine and diagnostic communications.
