RTCA DO-160H at publication stage: update to the aviation environmental test standard

RTCA DO-160 is the series of standards used to assess aviation equipment's resistance to environmental conditions. It defines topics such as temperature, altitude, vibration, humidity, shock, fluid resistance, lightning and electromagnetic compatibility as separate sections.

The way the standard is used is distinctive: there is no single "DO-160 conformity" for a piece of equipment. Which sections and which categories apply is selected according to the equipment's location in the aircraft and its conditions of use; that selection is recorded in an environmental qualification form.

A revision update does not automatically invalidate equipment qualified against the previous revision. What decides is which revision the project's and customer's specification refers to.

It makes sense to base new equipment development on the current revision; changing revision in the middle of an ongoing programme, however, can mean rebuilding the qualification file. The decision is one of programme management, not a technical one.

The most common mistake is leaving the selection of sections and categories to the test stage. Since category determines the test severity, a category upgraded later can force the whole series to be repeated.

The environmental qualification form is therefore filled in together with the customer at an early stage of design. Once the form is clear, sample count, timetable and cost become clear too.

The section-and-category mapping, test conditions and acceptance criteria are in the standard's text; we determine together at the proposal stage which series applies to your equipment.

For avionics equipment to be installed on an aircraft, two questions need answering: does the equipment withstand the environmental conditions of the flight environment, and were its software and hardware developed safely? This standard is the common language for the first question.

The environmental events it covers are organised into sections: temperature and altitude, temperature variation, humidity, operational shocks and safety, vibration, explosive atmosphere, waterproofness, fluid susceptibility, sand and dust, fungus, salt fog, magnetic effect, power input, voltage spike, audio frequency susceptibility, induced signal susceptibility, radio frequency susceptibility, radio frequency emission, lightning, icing, and similar.

Which sections and which categories a piece of equipment goes through is determined by its LOCATION in the aircraft and its function. A unit inside a pressurised cabin and a unit inside a wing see entirely different profiles; the phrase "complies with this standard" therefore carries no information on its own.

The output of testing under this standard is an environmental qualification form showing which sections the equipment passed and in which categories. The form lists the category letters section by section and clearly states which sections were not applied.

The party reading the form checks two things: whether the categories the aircraft requires are met, and whether the justification for unapplied sections is documented. A section not being applied is not a defect; leaving it unjustified is.

The report must also state which operating mode the equipment was in during the test and what the pass criterion was. The same test gives a different result when the equipment is powered and when it is not.

When a new revision is published, existing qualification reports do not automatically become invalid: whichever revision the aircraft programme's specification requires is applied, and ongoing programmes are usually completed with the revision they started with.

The effect is seen in new programmes and where existing equipment undergoes a change. When a unit's circuit board, enclosure or connection layout changes, the affected sections are retested; which sections need retesting is determined through a change-impact analysis.

When planning against a revision still in publication, the exact revision number and effective date are confirmed from the programme specification; this article describes the process and does not commit to a date.