Keep safety sky high

IEC TC works to ensure electronic systems for aircraft operate reliably

By Morand Fachot

The safety of aircraft, even light aircraft, has become increasingly reliant on electronic systems – avionics – designed and manufactured for ADHP (aerospace, defence and high performance) applications. They must be especially robust and reliable. IEC TC 107 prepares standard processes (technical recommendations, specifications and the standards themselves) for the industry to ensure this is the case.

Aircraft operate in harsh conditions that avionics equipment must be capable of withstanding Aircraft operate in harsh conditions that avionics equipment must be capable of withstanding

Severe environment

Aircraft operate in a harsh environment; they are subjected to extremes of temperature, considerable turbulence and atmospheric radiation. Avionics equipment must be capable of withstanding these as well as of operating reliably for many years.

Supply chain issues

Initially avionics systems primarily integrated parts that had been designed specifically for them. Nowadays avionics manufacturers increasingly use COTS (commercial off-the-shelf) components, subassemblies or top level assemblies. One problem faced by the aerospace electronics industry is its dependence on materials and components that have been developed for other domains.

Another problem that is linked to this is the long lifecycle of avionics (15-40 years) which has to run in parallel with the much shorter lifecycle of the parts and board assemblies (3-5 years) developed by the components industry for other markets.

Specific remit

TC 107 does not prepare International Standards for the components (integrated circuits and assemblies) used in the avionics industry. This task is handled by other IEC TCs. What TC 107 does is to develop standard processes for using and managing these components in meeting the requirements of the avionics industry (cost, lifetime, quality, reliability, safety, performance, etc.). This must be achieved despite the preoccupation of the electronics industry with high-volume applications, rapid change, obsolescence and problems of wear.

TC 107 work focuses on tackling both technical and industrial issues. Technical issues include the impact of temperature, the effect of atmospheric radiation on avionics products and the use of lead-free solder in aerospace and defence electronic systems. Industrial challenges incorporate the availability of components and preventing the use of counterfeit parts.

To deal with these issues TC 107 has set up three WGs (Working Groups), a PT (Project Team) and 2 MTs (Maintenance Teams).

Temperature rising and… falling

Avionics products are used in a very wide range of temperatures. Some systems are subjected to very low outside temperatures at high altitude, whilst others are deployed in a higher temperature environment inside the aircraft.

Traditionally, industries that produce electronic equipment for ADHP applications have relied on the military specification system to supply their semiconductor device standards and upon manufacturers of military-specified devices to source the parts they require.

Typical ambient temperature ranges at which military specified devices are marketed are - 55 °C to + 125 °C. The respective ranges for industrial and commercial devices are - 40 °C to +85 °C and 0 °C to + 70 °C.

Over the years a number of device manufacturers have left the military market, resulting in the reduced availability of devices specified to operate over wide temperature ranges. In the absence of reasonable or practical alternatives, a potential response for equipment manufacturers is to use devices at temperature ranges that are wider than those specified by the device manufacturer.

To address this issue TC 107 has prepared IEC/TR 62240-1, Process management for avionics - Electronic components capability in operation - Part 1: Temperature uprating. IEC 62240-1 is a Technical Report that provides information regarding the methods and processes to be implemented when using semiconductor devices in wider temperature ranges than those specified by manufacturers. This is to ensure that the device and the system operate satisfactorily. However, this wider usage should be limited to temperature ranges that do not compromise the applications' performance and reliability.

TC 107 MT 2 work includes the use of semiconductor devices operating outside manufacturers' specified temperature range.

Closer to the sun

Another important factor that affects avionics products is the atmospheric radiation encountered at high altitude. Microelectronic devices may be affected by SEE (single event effect): the response of a component to the impact of a single particle induced by atmospheric neutrons from galactic cosmic rays or solar phenomena.

TC 107, through PT 62396, has developed the IEC 62396 series of documents to assess and accommodate atmospheric radiation effects within avionics electronic equipment via SEEs and to specify guidelines, system design and testing procedures to deal with these.

No more lead please!

Many countries and regions are introducing regulations limiting or banning the use of lead in industrial products. This is a substance that is widely used in electronic solder and electronic piece part terminations, and printed wiring boards. Lead-free tin finishes can be susceptible to the spontaneous growth of crystal structures known as "tin whiskers". These have been known to cause electrical failures.

To meet this challenge, TC 107 WG 1 has developed the IEC 62647 series of documents. They look at the preparation for producing a lead-free control plan and the mitigation of the deleterious effects of tin, as well as at testing and system guidelines.

Availability of avionics-specific components

As a number of manufacturers of ADHP components have abandoned the market, the avionics equipment industry has had to rely on COTS for components and assemblies. TC 107 has produced an ECMP (electronic components management plan) and is preparing an electronic assemblies management plan that will extend to the use of COTS.

Fighting fraud

Avionics systems are high-value products, and as such attract counterfeiters. The counterfeit "industry" is global and booming. It affects all domains, from fashion items to drugs, from toys to electronic goods and is expected to exceed USD 1 500 billion by 2015.

It has an obvious economic impact but may also present very serious risks if the counterfeit goods affect health (counterfeit drugs) or result in accidents (failure of counterfeit mechanical or electronic parts). This is particularly serious for aerospace products. Counterfeit electronics are the second most "valuable" sector of the counterfeiting industry after drugs. Counterfeit products may take the form of recycled parts fraudulently sold as "new" or "unused" components.

TC 107 WG 3 works on guidance for the development of a management plan to avoid the use of counterfeit electronic parts in avionic applications. The plan will maximize the use of authentic parts with correct traceability and conformance documentation.

It will help trusted manufacturers, suppliers and distributors identify and eliminate the use of counterfeit components in avionics products.

Constantly evolving and expanding work

The aerospace industry is a booming sector that employs a growing share of avionics products. TC 107 has 67 experts from 7 participating and 12 observer member countries that develop the wide and always expanding range of technical recommendations, specifications and standards to meet the industry’s needs. Its work programme is set to be extremely full for the foreseeable future.

Aircraft operate in harsh conditions that avionics equipment must be capable of withstanding Aircraft operate in harsh conditions that avionics equipment must be capable of withstanding
The cockpit of the next generation of Embraer E-Jets (Photo: Embraer) The cockpit of the next generation of Embraer E-Jets (Photo: Embraer)
Identifying counterfeit components can be impossible without sophisticated testing methods Identifying counterfeit components can be impossible without sophisticated testing methods