MIL-PRF-32516
APPENDIX A
A.2.3.1.a. General. The accumulated effects of vibration-induced stress may affect
LRU/WRA performance under other environmental conditions such as temperature, altitude,
humidity, leakage, or electromagnetic interference (EMI/EMC). When evaluating the cumulative
environmental effects of vibration and other environments, expose the LRU/WRA to all
environmental conditions, with vibration testing generally performed first. If another
environment (e.g., temperature cycling) is projected to produce damage that would make the
LRU/WRA more susceptible to vibration, perform tests for that environment before vibration
tests. For example, thermal cycles might initiate a fatigue crack that would grow under vibration
or vice versa.
A.2.3.1.b. Unique to this method. Generally, expose the LRU/WRA to the sequence of
individual vibration tests that follow the sequence of the life cycle. For most tests, this can be
varied if necessary to accommodate test facility schedules, or for other practical reasons.
Complete any maintenance associated preconditioning prior to tests representing mission
environments. Perform tests representing critical end-of-mission environments last.
A.2.4 Worst case operational vibration. Functional testing is conducted to verify that
the LRU/WRA functions as required while exposed to worst case operational vibration.
Functional level vibration testing in accordance with MIL-STD-810, Test Method 514 is
recommended. Fully verify the function at the beginning, middle and end of each test segment.
Monitor basic separate functional and endurance tests are required, split the functional test
duration, with one half accomplished before the endurance test, and one half after the endurance
test (in each axis). The duration of each half should be sufficient to fully verify materiel function.
This arrangement has proven to be a good way of adequately verifying that materiel survives
endurance testing in all respects. In some cases, materiel that must survive severe worst case
environments may not be required to function or function at specification levels during worst
case conditions. Typically "operating" and "non-operating" envelopes are established. Tailor
functional tests to accommodate non-operating portions by modifying required functional
monitoring requirements as appropriate.
A.2.4.1 Category 7 (see MIL-STD-810, Test Method 514), jet aircraft. Vibration
environments on jet aircraft are broadband random in nature. The maximum vibrations are
usually engine exhaust noise generated and occur during takeoff. Levels drop off rapidly after
takeoff to lower level cruise levels that are boundary layer noise generated.
A.2.4.2 Category 8 (see MIL-STD-810, Test Method 514), propeller aircraft. Vibration
environments on propeller aircraft are dominated by relatively high amplitude, approximately
sinusoidal spikes at propeller passage frequency and harmonics. Because of engine speed
variations, the frequencies of the spikes vary over a bandwidth. There is wide band vibration at
lower levels across the spectra. This wide band vibration is primarily due to boundary layer flow
over the aircraft.
A.2.4.3 Category 9 (see MIL-STD-810, Test Method 514), helicopter. Vibration
environments on helicopters are characterized by a continuous wideband, low-level background
with strong narrowband peaks superimposed. This environment is a combination of many
sinusoidal or near sinusoidal components due to main and tail rotors, rotating machinery and
low-level random components due to aerodynamic flow.
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