05 — Turn display functions into measurable acceptance criteria

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

Learning objective: Write criteria that detect misleading, frozen or degraded display behavior.

Define what the display must do during the test

“The unit still works” is too weak an acceptance criterion. A screen can remain illuminated while showing stale information, losing a warning color or generating an unintended touch command.

The display performance specification should define measurable requirements for the functions being qualified. Useful groups include:

• Optical performance: luminance, contrast under stated illumination, color, uniformity, viewing range, dimming, defects and image retention where relevant.
• Dynamic behavior: startup, response time, refresh artifacts, flicker, image continuity, data age and latency at the display boundary.
• Controls: touch accuracy, missed or false inputs, physical-control operation and feedback.
• Integrity and recovery: validity indications, detection of frozen or corrupt images, mode retention, permitted interruptions, recovery time and any permitted operator action.
• Physical condition: cracks, delamination, leakage, loose hardware, corrosion, insulation and retention, using limits appropriate to the test.

Define the measurement setup as carefully as the number: pattern and image loading, backlight setting, temperature, stabilization, illumination direction and level, viewing angle, instrument geometry, uncertainty and observation interval. A room-temperature center-screen measurement cannot establish performance throughout the viewing envelope at an environmental extreme.

For transport-airplane flight deck displays, FAA AC 25-11B discusses readability, luminance, contrast, color, dynamic behavior and installation viewing conditions. Its scope should not be generalized into identical requirements for every aircraft or every cabin display. FAA AC 25-11B, Chapters 3 and 5.

Select operating modes separately for each hazard. Maximum brightness may drive thermal loading; another dimming setting may produce more emissions or worse susceptibility. Exercise relevant data links, touch scanning, heaters, fans and display processing. A static logo can conceal a frozen frame. A time-varying pattern, controlled input sequence and synchronized event log provide stronger evidence.

Separate during-exposure, post-exposure and survival criteria. Do not insist on powered operation during a test defined for unpowered survival, and do not accept automatic recovery where the display function requires uninterrupted operation. Any permitted degradation needs a defined duration and consequence consistent with the program’s requirements.

Worked acceptance record — illustrative customer choices

These values are invented course examples. A real program derives criteria from its function and safety assessment. A 100 ms interruption may be unacceptable for one function and irrelevant for another. Recovery after a disturbance is not adequate where uninterrupted operation is required.

Measurement uncertainty

Suppose a measured luminance is 405 cd/m² with an expanded uncertainty of 12 cd/m² and the minimum is 400. A simple measured-value rule and a rule requiring measured value minus uncertainty to meet the minimum produce different decisions. Agree the rule before testing. Do not select the favorable rule after seeing the data.

Exercise

Rewrite “display shall work after vibration.” Worked response: identify which functions must operate during vibration, required checks between axes and after exposure, the image sequence and controls exercised, permitted discontinuities, numeric optical limits, physical inspection criteria and the exact configuration. The phrase after vibration cannot silently waive a required during-test function.