This document discusses software development for safety critical systems. It covers: - Special considerations for safety critical systems where malfunctions can cause injury, including design, verification, validation, certification to standards. - The increasing complexity of avionics software over time with aircraft like the A380 and B787 having hundreds of millions of lines of code. - Key aeronautical certification bodies and standards like the FAA, EASA, ICAO, DO-178B/C, and ARP-4754. - Methodologies used in aeronautical system certification like fault tree analysis, common cause analysis, and design assurance levels (DAL). - How certification aspects apply to both software and hardware and

1. Budapest University of Technology and Economics
Department of Measurement and Information Systems
Software Development for
Safety Critical Systems
Ákos Horváth
Dept. of Measurement and Information Systems
Fault Tolerant Systems Research Group
FRENCH-HUNGARIAN WORKSHOP ON OUTER-SPACE

2. How to
avoid?
Safety Critical Software Development
2

3. Specialities of safety critical systems
 Safety-critical systems
o Informal definition: Malfunction may cause injury of people
 Special solutions to achieve safe operation
o Design: Requirements, architecture, tools, …
o Verification, validation, and independent assessment
o Certification (by safety authorities)
 Basis of certification: Standards
o IEC 61508: Generic standard (for electrical, electronic or
programmable electronic systems)
o DO178B/C: Software in airborne systems and equipment
o EN50129: Railway (control systems)
o EN50128: Railway (software)
o ISO26262: Automotive
o Other sector-specific standards: Medical, process control, etc.
3

4. History of avionics SW complexity
4
0
50
100
150
200
250
300
350
400
MIPS LOC Mbyte/10 Digital links
A-310 (1983)
A-320 (1988)
A-340 (1993)
Exponential
Growth
Both A380 and B 787 have
100’s of millions LOC
Ref: Subra de
Salafa and
Paquier

5. ARP-4754
Aeronautical Certification Bodies and Standards
5
ICAO
EASA
EASA
EASANational
Aviation
Authority
EASA CS-25
ARP-4754
define
supervise
supervise
EASA
EASAStandardization
Body
harmonize with
regulations
adopt
accepted
mean
define

6. ARP-4754
Aeronautical Certification Bodies and Standards
6
ICAO
EASA
EASA
EASANational
Aviation
Authority
EASA CS-25
ARP-4754
define
supervise
supervise
EASA
EASAStandardization
Body
harmonize with
regulations
adopt
accepted
mean
define
International Civil Aviation
Organization (1944)
European
Aviation Safety
Agency (2006)

7. ARP-4754
Aeronautical Certification Bodies and Standards
7
ICAO
EASA
EASA
EASANational
Aviation
Authorities
EASA CS-25
ARP-4754
define
supervise
supervise
EASA
EASAStandardization
Body
sarmonize with
regulations
adopt
accepted
mean
define
EASA CS 25.1309:
The airplane systems and associated
components, considered separately and
in relation to other systems, must be
designed so that-
1. Any catastrophic failure condition
a) is extremely improbable; and
b) does not result from a single failure;
and
2. Any hazardous failure condition is
extremely remote; and
3. Any major failure condition is remote.

8. Aeronautical System Certification
8

9. Aeronautical System Certification
9
Methodologies for safety assessment
processes are guidelines
E.g., fault tree analysis, common cause
analysis
Certififcation aspects of complex aircraft
system  cannot be shown by test only.
Design Assurance Level (DAL)

10. Aeronautical System Certification
10
Methodologies for safety assessment
processes are guidelines
E.g., fault tree analysis, common cause
analysis
Certififcation aspects of complex aircraft
system  cannot be shown by test only.
Design Assurance Level (DAL)

11. Aeronautical System Certification
11
Provide guidelines for production of
software for airborne systems.
Objectives, activities and evidences
Certififcation aspects of hardware elements
from concept to airworthy equipment
development

12. Aeronautical System Certification
12

13. Future and Related Fields
 Automotive industry
o Drive-by-wire
o Automated parking/driving
o No strict authorities for SW
certification
• EU pushing for standards
• Safety related issues
 UAV
o In the same civil airspace
o Needs to take into consideration
the environment
o Equipment can fail
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 Space and Satellite
o Uses avionics concepts
o Similar certification processes
by ESA
o How advanced concepts will
appear?
 Avionics
o Modern development methods
(DO-178C annexes, 2013)
o MDE, OO languages, formal
methods, tool certification
o Flightpath 2050
o Passengers/year
from 2.5bn to 16bn
o 31000 new aircrafts