Aerospace cables have wide ranging applications on aircraft and are used in everything from in-flight entertainment systems, to data applications and for signal transmissions. Aerospace grade data cables are used in Ethernet, Serial ATA, USB, fiber channel and the Digital Video Interface, among others. Due to the critical nature of their use, their durability and reliability is paramount.
To understand this kind of cabling, it is important to take note of its most notable applications and features as well as the standards that govern these products.
Selection of aerospace wire/cables
The choice of aerospace cable or wire that one makes, will depend on a number of factors including, but not limited to:
- The primary application of the cable
- The environment in which it is to be used
- Special constraints or conditions it will need to operate in (extreme conditions)
- Industry specifications – this will determine which cables meet the guidelines that you are required to adhere to
- Safety of the cable
- Quality of the cable
- Performance capabilities of the cable
With aircraft systems relying on the proper functioning of these cables, it is important that they be able to withstand any extremes of temperatures and pressures they might have to operate in. The wires must be able to operate during take-off and landing when subjected to major vibration/movement.
Getting the choice of cable right the first time can avoid the need for overhauls and save time and money in the long run.
Why weight matters
Depending on its end use, the wire may need to be heavyweight to be able to perform its role successfully. In other cases, a lighter weight cable can mean the aircraft can hit higher speeds due to the reduced drag from lighter cabling on board. Making a selection of the wire should not be done in isolation and needs to take into account not just the application it is to be used for, but its impact on the overall construct of the plane as well.
Cabling for passenger aircraft
For passenger aircraft, it is important to choose cabling that will emit the least smoke and harmful gases. This will allow passengers to breathe and see where they are heading as they make their way to the nearest exit in emergencies.
A Low Smoke Zero Halogen (LSZH) cable is a good choice when dealing with closed spaces with limited ventilation. This variety keeps damage to the minimum during fires. With almost no smoke or ash output and almost no harmful gases emitted, these are the safest option for manned aircraft.
Regulatory standards for wire/cable in the aerospace industry
The Society of Automotive Engineers (SAE), the Institute of Electrical and Electronic Engineers (IEEE), and the National Electrical Manufacturers Association (NEMA), have a set of guidelines to be applied to the aerospace industry. These dictate the norms for cable/wire used in applications in the industry.
Other widely accepted standards are those first created by Boeing Material Specifications and the U.S. Department of Defense (military specifications also known as MIL-specs).
MIL-spec numbers versus SAE or NEMA specifications
Some products could feature both SAE or NEMA specifications and MIL-specs. This is because these standards organizations have translated MIL-specs to their own standards, but popular nomenclature may still use MIL-spec numbers. As such, these cable/wire products end up with the MIL-spec number and the new SAE or NEMA spec. However, what is more important is that you check your own set of guidelines and requirements to ensure that the product meets all the needs for your project.
BMS cable specs
BMS refers to Boeing Material Specification and relates to a variety of products including aerospace optical fiber cables and data-bus cables. These cables will have a different shield, jacket material, insulation, conductor, temperature rating and type. A number of different BMS specs are in existence in the market today.