04 — Public chapter: temperature limits, ramp rates and decompression

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

Learning objective: Interpret familiar numerical values without confusing operation, survival and pressure exposure.

Typical limits and how to specify them

Numbers such as −40 °C, −55 °C, +70 °C and +85 °C are useful reference points, but they do not define one universal display qualification envelope. Every value needs a purpose: normal operation, short-time operation, unpowered ground survival, or a customer-specific extension. Specify the temperature at the relevant test boundary, not an assumed internal panel temperature.

Operating temperature and survival temperature

Two examples from DO-160G Table 4-1 show why a temperature range needs a category and an operating state. These are selected examples, not recommended categories for every display.

The categories also carry installation and altitude assumptions; they are not merely temperature selections. A3 concerns a pressurized, controlled or partially controlled temperature location, while F2 concerns an unpressurized, uncontrolled temperature location up to 55,000 ft. Check the complete category definition before using either.

A procurement specification can require −40 °C to +70 °C operation or an extended −55 °C operating capability, but it must state how that requirement relates to the selected category. Likewise, +85 °C must be identified as an operating, short-time operating or survival condition. A display that survives an unpowered +85 °C soak has not thereby demonstrated a readable image at +85 °C.

For the Section 4 operating low/high tests, the specified operating period is at least two hours after equipment temperature stabilization. Ground-survival exposures include at least three hours at the specified temperature after stabilization. Applicable short-time operation is at least 30 minutes, with the prescribed preceding conditioning. These are different stages, not interchangeable dwell times. See DO-160G §§4.5.1–4.5.4 and Table 4-1.

For displays, tie these temperatures to startup time, allowable heater warm-up, image response, luminance, contrast, touch behavior and recovery. Chamber air, enclosure, panel and internal electronics can be at different temperatures; measure the points needed to substantiate the requirement.

Temperature cycling at 5 and 10 degrees per minute

The commonly specified 5 °C/min and 10 °C/min ramps are both in DO-160G Section 5. Its category letters are separate from Section 4 temperature/altitude categories.

Section 5 also provides S1/S2 temperature-shock categories for changes greater than 10 °C/min. Use their applicable procedures rather than treating any faster ramp as an interchangeable qualification.

For Categories A/B/C, the procedure requires at least two cycles, with additional cycles if needed to complete the required performance checks. It includes stabilization, operation during the prescribed transitions and specified power-off/restart stages. A cycle is more than one journey from cold to hot. See DO-160G §§5.2–5.3.1.

As an illustrative scheduling calculation, a −40 °C to +70 °C transition spans 110 °C: an ideal constant 5 °C/min ramp takes 22 minutes, and 10 °C/min takes 11 minutes. Neither includes dwell or stabilization. These are chamber-ramp calculations; they do not predict how quickly the glass, optical bond or electronics reach equilibrium. A combined Section 4/5 test must retain all applicable requirements of both sections.

Altitude and rapid decompression

65,000 ft equivalent is not the universal DO-160G decompression requirement. It may be a program-specific endpoint, but it should be traced to the aircraft or customer specification. DO-160G Table 4-2 includes 55,000 ft and 70,000 ft reference pressures; it does not contain a 65,000 ft row.

Section 4.6.2 starts with the operating equipment at 8,000 ft equivalent absolute pressure, then reduces pressure to the aircraft's maximum operating-altitude equivalent within 15 seconds. The reduced pressure is maintained for at least 10 minutes, or as specified in the equipment specification. The performance checks apply during that reduced-pressure period. For comparison, Table 4-2 gives approximately 75.26 kPa absolute at 8,000 ft, 9.12 kPa at 55,000 ft, and 4.44 kPa at 70,000 ft.

Use the term decompression for this standard test. If a contract calls for “explosive decompression,” define its initial pressure, final absolute pressure, pressure-change time or profile, temperature, power state and required display behavior. A much faster pressure collapse is a distinct requirement; an exposure completed within 15 seconds does not automatically demonstrate every faster profile. This is also separate from Section 9 explosion proofness, which addresses flammable atmospheres.

For the display assembly, assess trapped volumes, vent paths, bonded optical cavities, glass retention, seals and electrical clearances. A steady-altitude test cannot demonstrate the mechanical effects of a rapid pressure change. Conversely, a short decompression exposure does not replace the separate altitude endurance test.

Check your interpretation

“−55 °C to +85 °C qualified” leaves both the operating state and the category unclear. “10 degrees per minute” leaves endpoints, stabilization, power sequencing and performance checks unclear. “65,000 ft decompression” leaves initial pressure, final absolute pressure, transition time and required operation unclear. Each sentence needs a test profile, not just a more impressive number.

For a linear transition, time = temperature difference / ramp rate. From −40 °C to +70 °C the difference is 110 °C: 22 minutes at 5 °C/min and 11 minutes at 10 °C/min. These are idealized transition times only. The plots do not reproduce Figure 5-1 or the complete Section 5 procedure.

Exercise

A report includes a three-hour unpowered +85 °C survival exposure. Can it support a contract requiring continuous +85 °C display operation? Worked response: the survival evidence is relevant to survival; it does not demonstrate the operating requirement. The operating state, stabilization, duration, monitored functions and numeric limits must be evaluated separately.