08 — Pressure, altitude and rapid decompression

DO-160 Display Qualification | A-P02 — Draft / Not Released

Learning objective: Define pressure requirements and distinguish decompression from explosion proofness.

Pressure is a separate axis of exposure

An altitude test represents reduced ambient pressure. It can affect cooling, dielectric behavior, trapped cavities, seals and bonded optical assemblies. Specify pressure as absolute pressure with the equivalent altitude and the adopted conversion basis. A gauge pressure number without its reference is ambiguous.

DO-160G §4.6.2 starts at the equivalent of 8,000 ft, reduces pressure to the aircraft maximum operational altitude within 15 seconds, and holds the condition for at least ten minutes or the equipment-specification duration, with the equipment operating as prescribed. The procedure is at ambient temperature. This is not a universal requirement to reach 65,000 ft. A customer may specify that final altitude or a much faster transition, but must identify it as an explicit requirement with a complete profile.

Section 9 explosion proofness concerns ignition in a flammable atmosphere. The term explosive decompression does not make Section 9 the applicable pressure method. Avoid informal terminology in a contract when it could send the laboratory to the wrong test.

Pressure history worksheet

Record initial absolute pressure, final absolute pressure, transition measurement points and timing definition, hold duration, temperature, operating mode, instrumentation and acceptance criteria. Include permissible pressure overshoot only as allowed by the adopted procedure or agreed deviation. Ask the laboratory to demonstrate that its chamber can meet the profile with the actual article volume and venting arrangement.

Display observations

Monitor image continuity and backlight behavior during the transient, then check touch and optical condition. Inspect trapped-air regions, bond edges, covers and enclosure seals. A cosmetic bubble can also distort symbols or grow into a structural concern; define permitted defects and functional limits before exposure.

Exercise

Two reports both state 55,000 ft. One is a stabilized altitude soak and the other includes a qualifying rapid pressure transition. Are they interchangeable? Worked response: no. The transient pressure differential and the steady low-pressure environment can challenge different mechanisms. Review each allocated subtest and its acceptance state. An endpoint alone is not a pressure test profile.

For context, DO-160G Table 4-2 gives approximately 75.26 kPa absolute at 8,000 ft and 9.12 kPa at 55,000 ft. Use the adopted table and specified tolerance for the actual procedure; do not use these rounded teaching values as chamber calibration instructions.

Three pressure tests answer different questions