DO-160 Section 5 is one of the environmental qualification tests in RTCA DO-160, and section 4 asks whether your equipment survives at temperature extremes. Section 5 asks a different question: how fast can the temperature around it change before that rate itself becomes the problem.

What DO-160 Section 5 Covers, and Why It Exists

Section 5 sets a minimum rate of temperature change your equipment has to tolerate, and the rate depends on where it sits. Equipment external to the aircraft or in Category A locations must handle at least 10°C per minute. Equipment in a non-temperature-controlled or partially controlled internal location (Category B) must handle at least 5°C per minute, and equipment in a temperature-controlled internal location (Category C) at least 2°C per minute. Usefully, equipment qualified to Category B is automatically considered to have met Category C. Above 10°C per minute the standard treats it as thermal shock, Categories S1 and S2, with S2 the conservative default when the actual rate isn’t known.

It exists as a separate section from Section 4 because rate of change stresses different things than steady-state extremes. Dissimilar materials expand and contract at different speeds, and a fast swing puts real stress on seals, potted joints, and bonded interfaces before the assembly can move together as one piece. The standard is also explicit that this test isn’t meant to evaluate wet or icing behavior, chamber humidity is controlled to avoid condensation, which keeps Section 5 deliberately separate from Section 6.

The Typical Failure Pattern

A unit can carry plenty of margin at both temperature extremes from Section 4 and still fail here, because nobody specifically checked the transition. The common real-world failure isn’t dramatic, it’s cumulative: a seal that takes a small permanent set each cycle, a potted joint that develops a hairline crack after enough thermal swings, a bonded interface that slowly delaminates. We don’t have a single headline incident to point to for this section, and that’s worth saying plainly, this is a degradation mechanism that surfaces as nuisance failures and warranty returns over years, not as a single event that makes the news.

Why This Hits Galley Equipment

Galley equipment lives this pattern daily. An oven or water boiler cold-soaked overnight, then powered up at the gate, sees a genuine rate-of-change event every single cycle, on top of the ground-to-cruise transition. The question that matters for a galley program isn’t whether the unit survives one chamber run, it’s whether its seals, fasteners, and bonded joints survive that cycling repeated over years of service. That makes Section 5 more of a material selection and cyclic-durability question for galley equipment than a one-time qualification box to tick.

How to Mitigate This

• Confirm the installation location and pick the matching rate category, don’t default to the lowest rate without checking
• If you lack measured data on the actual rate of change, qualify to S2 rather than assuming S1 applies
• Treat seals, potted joints, and bonded interfaces as the parts most likely to show stress, not the electronics
• For equipment that sees frequent ground-to-cruise cycling, consider cyclic life testing beyond the minimum qualification cycles, since the real failure mode is fatigue, not a single excursion

Further reading: NTSB accident report archive.

How Eminent Helps: If you’re choosing a temperature-variation category, or worried that a galley unit will pass qualification but accumulate seal and joint fatigue over years of daily cold-soak-to-operating cycling, that’s the durability question we help teams get ahead of. See how we support galley insert programs.