11 — Shock and vibration: the fixture is part of the argument
DO-160 Display Qualification | A-P02 — Draft / Not Released
Learning objective: Distinguish operational function, mechanical integrity and crash retention.
Photo: NASA Goddard Space Flight Center / Engineering and Technology Directorate · Environmental Testing: Thermal Vacuum Chamber and Vibration Table Collection · NASA imagery; generally not subject to US copyright. Original image, displayed at reduced size.
Define the load path
The display panel, bond, enclosure, mounting tabs, fasteners and aircraft structure form a load path. The test fixture should reproduce the relevant support, stiffness and attachment assumptions. Overconstraining glass or adding a support that does not exist in service can make the test less representative even if the shaker input is correct.
DO-160G Section 7 operational-shock examples use a 6 g terminal-sawtooth pulse with the selected 11 ms or 20 ms duration and the prescribed applications in each direction. The crash-safety impulse requirement is a separate 20 g condition; sustained crash loads have their own requirements. These numbers are reference points, not a complete axis, pulse-tolerance or mounting procedure.
Operational shock addresses performance and integrity under its required conditions. Crash safety addresses retention and resulting hazards; it does not generally imply a usable image throughout a crash pulse. Keep the acceptance columns separate.
Choose the vibration profile from the installation
Section 8 categories, curves and methods depend on aircraft type, equipment location and mounting. A scalar g value cannot describe a random vibration spectrum. Define the power spectral density versus frequency, overall level, duration, axes, control strategy and any resonance or endurance stages from the adopted method. For sine tests, record the prescribed amplitudes, frequency range and sweep or dwell conditions. Do not infer helicopter qualification from a fixed-wing test label.
Monitor what can go intermittent
Run changing image content, active data links and representative touch/control activity. An intermittent connector may create a single corrupted frame that disappears before the post-test inspection. Use synchronized capture with a known detection capability. Route test cables and accelerometers so they do not restrain the unit or introduce a false failure.
Exercise
The lab fixture supports the enclosure at six points but the aircraft uses four corner mounts. Worked response: compare the dynamic and structural behavior and justify representativeness or revise the fixture/test. Record mount hardware, torque, isolators, orientation and harness support. The same external acceleration command does not guarantee the same stresses in the display.
Fixed-wing and helicopter vibration selection
DO-160G §8.2 selects vibration requirements using aircraft type, test category and aircraft zone. For fixed-wing equipment, the equipment specification determines whether standard or robust vibration is required. Helicopter equipment follows a robust method. A report must identify the complete designation, curve and installation coverage; “DO-160 vibration tested” is insufficient.
| Application | Method to evaluate | What the supplier must identify |
|---|---|---|
| Fixed-wing normal operating environment | Category S standard vibration, where the applicable equipment specification permits it. | Propulsion type, zone, sine or random curve, axes, operating modes and functional acceptance. |
| Fixed-wing endurance assurance | Category R robust vibration, when long-duration resistance must be demonstrated. | Performance and endurance stages, resonance checks, specified operation and post-test integrity. |
| Fixed-wing abnormal engine imbalance | Categories H or Z where the performance requirements make the high-level, short-duration test applicable. | Applicable engine/fan assumptions and equipment function; this test supplements the standard or robust test. |
| Helicopter with known rotational frequencies | Category R helicopter sine-on-random method in §8.8.1. | Applicable zone, rotational sources and blade counts, frequency ranges, sine components, random background, performance/endurance stages and resonance dwells. |
| Helicopter with unknown rotational frequencies | Category U sine-on-random or the permitted Category U2 random alternative in §§8.8.2–8.8.3. | The selected method and its zone limits. U uses three prescribed frequency sets; U2 uses its specified random profile. Neither is an unrestricted all-helicopter approval. |
Instrument-panel, console and rack locations have their own zone treatment; do not select the generic fuselage curve simply because a display is physically inside the fuselage. If measured helicopter vibration data are available, §8.8 allows tailored testing using accepted procedures. Document the data coverage, selected profile and agreed basis rather than substituting an informal bench measurement.
Understand rotor orders before choosing a spectrum
A rotational frequency in hertz is RPM ÷ 60. Blade-passage frequency is blade count × RPM ÷ 60. Teaching example: a four-blade rotor at an assumed 300 RPM produces a 5 Hz one-per-revolution frequency and a 20 Hz first blade-passage frequency. These are illustrative inputs, not AW139 data or a complete qualification spectrum. Section 8 also accounts for the relevant tail-rotor, engine and gearbox sources and the zone-specific combinations. Its known-frequency method sweeps the specified sine components over their prescribed ±10% bands on a random background.
Typical time references are method-dependent
In DO-160G, Category S is summarized as one hour per axis. The helicopter known-frequency sine-on-random method includes performance checks of at least ten minutes at the beginning and end, and a two-hour minimum endurance stage with applicable resonance dwells; the procedure caps the required endurance-level time at three hours. Category U repeats the prescribed sequence for three frequency sets. Category U2 uses three hours of endurance per axis with performance checks before and after. Scans, checks, dwell rules and all three axes remain part of the selected procedure; these references are not standalone laboratory instructions. Use §8.8 for the complete sequence and permitted test-article allocation.
Translate the mechanical environment into display evidence
At component level, investigate optical-bond stress, glass support, backlight connections, flex-circuit motion and connector intermittency under representative support conditions. At complete-system level, test the assembled display using the specified attachment hardware and any external isolators, with representative harness restraint and dynamic display monitoring. At installation level, close the bracket, support, isolator and local-environment assumptions and verify operational readability and control use.
A compliant shaker fixture is generally rigid; it is not a substitute for assessing a flexible aircraft panel. Record control acceleration close to the equipment mounts and useful response measurements on the assembly. A resonance shift, cracked bond or intermittent frame is evidence to investigate even when a final static image looks normal.
DO-160G §8.8.1.3(e) includes a specific reading-difficulty provision when total applied-input excursion exceeds 0.5 mm. It does not establish that the crew can perform the intended cockpit task. Keep installed readability and touch/control usability requirements explicit. Nor does a robust vibration pass by itself prove a stated service life.
Sources: RTCA DO-160G, §§8.2–8.3 and 8.5–8.8; original teaching comparison and rotational-frequency example. Confirm the adopted revision and applicable changes in the program’s controlled copy.
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