Shock, vibration and installation load paths

DO-160 Display Qualification | A-P13 — Development edition

Learning objective: Distinguish operational function, mechanical integrity and crash retention.

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.

Mounting, cell gap and contrast flashes

Shock, vibration and mounting stress can bend the LCD cell and vary the local thickness of its liquid-crystal layer. This changes its optical response and can produce contrast changes, loss of contrast, nonuniformity or transient flashes. The external optical adhesive thickness and the internal LC cell gap are different dimensions. Stress can also change LC alignment or other optical layers. A flash alone does not identify the cause; also check power, backlight drive, connectors and video continuity.

Follow supplier mounting provisions. Support the module without twisting it or applying concentrated pressure to the optical area. Control fastener loading, gasket compression, harness forces and cover mass. Allow required thermal movement while providing verified retention. Do not make the polarizer laminate an unverified structural restraint.

Reducing harmful transmitted stress and vibration can improve both viewability and survivability. Every display and mounting configuration is different, so these principles cannot prescribe the mount for a specific product. Suitable compliant interfaces or isolators require selection against the actual spectrum, shock pulse, axes, mass, stiffness, damping, temperature and available travel. A passive isolator can amplify response near resonance. Cables and stops can bypass isolation or introduce new loads.

Measure the mounting input and representative display response, and synchronize them with image monitoring. Define relevant patterns, viewing conditions, allowable contrast change and transient duration before testing. Observe during the required exposure and inspect after recovery. A final static image can miss a transient usability failure. Compare design changes using the complete mounted assembly and its applicable retention requirements.

Page takeaway

Identify the actual load path, aircraft/zone, vibration method and the monitoring needed to catch intermittency.

Supporting page images

NASA Goddard composite photograph showing a thermal-vacuum chamber, support fixture and instrumented vibration shaker. — NASA Goddard environmental-test facilities, including a thermal-vacuum chamber and a vibration fixture. The equipment illustrates test arrangements; the required DO-160 category, configuration and performance evidence must be established separately.
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.

Engineering application and worked evidence

The following examples develop the display mechanisms and evidence decisions. Numerical values are teaching assumptions, not universal DO-160 limits. Use the adopted procedure for exact test conditions and the product requirements for functional acceptance.

Vibration fixture and installation

A vibration result depends on how the display attaches to the shaker. The fixture can introduce resonances or stiffness that differ from the installation. Record the mounting interfaces, fastener condition, supported mass and cable restraint. Establish the control and response measurement locations through the applicable procedure and laboratory plan. If a bracket or isolator belongs to the product, omitting it changes the system being evaluated. Conversely, an installation fixture may have to reproduce an agreed boundary rather than every part of the aircraft. Review those assumptions before the test so the qualification statement can identify exactly what the evidence covers.

Basis: RTCA DO-160G, Section 8. Retained reference in 80 Reference Library/Aerospace. Display mechanisms, design responses and worked cases are FPD.DEV engineering teaching synthesis, not additional DO-160 requirements. Numerical examples are illustrative.

Resonance and isolator trade-offs

An isolator can reduce transmitted vibration over part of the frequency range while amplifying motion near a system resonance. A softer support also allows more displacement, which affects cable strain, bezel clearance and impact against stops. Evaluate the supported mass, stiffness, damping and attachment arrangement together. Elastomer properties can change with temperature and ageing, so room-temperature behaviour may not represent the whole operating envelope. During development, compare measured input and response spectra to locate amplification. Then use the adopted qualification profile and mounting configuration for the formal test. A mount described as vibration isolating is not sufficient evidence of improved display performance.

Basis: RTCA DO-160G, Sections 4 and 8; DAEIL isolation technical notes. Retained reference in 80 Reference Library/Aerospace. Display mechanisms, design responses and worked cases are FPD.DEV engineering teaching synthesis, not additional DO-160 requirements. Numerical examples are illustrative.

Image stability during vibration

A display can survive vibration structurally and still produce distracting flashes or unreadable information. Cell-gap changes, optical-stack movement or an intermittent connector can cause different image symptoms. Use patterns and operating modes that expose the relevant behaviour, including moving indicators where required. A camera provides useful evidence, but its shutter, exposure and rolling readout can create bands or miss a short event. Verify the recording method against known changes and correlate it with interface logs and mechanical measurements. Record the duration and extent of each disturbance. Apply the product's agreed image stability criterion rather than deciding by memory after the test.

Basis: RTCA DO-160G, Section 8; retained LCD cell-gap engineering references. Retained reference in 80 Reference Library/Aerospace. Display mechanisms, design responses and worked cases are FPD.DEV engineering teaching synthesis, not additional DO-160 requirements. Numerical examples are illustrative.

Shock survival and retained function

A requirement to continue operating after an operational shock differs from a requirement that equipment remain safely retained during a crash-safety exposure. Select the applicable test and category from the installation requirements. Record the pulse characteristics, axes, mounting and operating state required by the procedure. For the display, examine the glass retention, bracket load path, fasteners and heavy internal parts as well as the electronics. A functioning image alone does not establish safe retention, and damage after a survival exposure needs evaluation against that exposure's actual acceptance criteria. Avoid carrying an operating-performance assumption into a test with a different purpose.

Basis: RTCA DO-160G, Section 7. Retained reference in 80 Reference Library/Aerospace. Display mechanisms, design responses and worked cases are FPD.DEV engineering teaching synthesis, not additional DO-160 requirements. Numerical examples are illustrative.

Practice: A vibration fixture that improves the result

The laboratory adds a stiff rear brace to stop excessive specimen motion. It is absent from the installation. The display now passes. What must the qualification record say?

Model response and review points

Retain both configurations and results. Determine whether the added brace changes the product or the installation boundary the test must represent. Unless a justified analysis supports its representativeness or the brace becomes part of the controlled design, the new result has a limited scope. Review fixture dynamics, mount loads, cable restraint and the applicable method before establishing the corrective configuration and repeat-test plan.

Frequency, severity and structural response

Selected DO-160G values below retain their category and installation scope. The calculations and animations use explicit teaching assumptions. Use the complete adopted standard for a test procedure.

Vibration and shock quantities

When we ask how much vibration power a display must withstand, we need to name the quantity. A sine input has a frequency and an acceleration amplitude, normally stated as peak g. Random vibration uses an acceleration power spectral density, or PSD, in g squared per hertz, together with an overall g RMS level. The word power here refers to a squared signal quantity. It does not specify watts delivered to the display. Shock uses a peak acceleration, pulse shape and duration. One standard g is approximately nine point eight one metres per second squared. Record whether an amplitude is peak, peak to peak or RMS, because these are different numbers.

Exposure	Frequency or time	Severity quantity
Sine vibration	Frequency in Hz	g peak or displacement
Random vibration	Frequency band in Hz	PSD g²/Hz and g RMS
Mechanical shock	Pulse duration in ms	Peak g and pulse shape

RTCA DO-160G (8 December 2010), retained local reference. Selected values and authored teaching summaries only. Use the complete adopted procedure and equipment specification. Section 8.4. Spectral Dynamics PSD and Grms technical note.

Sine motion: frequency changes travel

For sinusoidal motion, multiply frequency by two pi, square that entire quantity, then multiply by peak displacement to obtain peak acceleration. At one g peak and ten hertz, the peak displacement is about two point four eight millimetres. At one hundred hertz it is only zero point zero two four eight millimetres. Peak-to-peak travel is twice those values. The higher-frequency motion looks smaller even though the acceleration is identical. For a pure sine wave, one g peak is zero point seven zero seven g RMS. These relationships help assess clearances, shaker stroke and why a connector can experience acceleration without large visible motion.

At 1 g peak	Peak displacement	Peak-to-peak travel
10 Hz	2.484 mm	4.968 mm
100 Hz	0.02484 mm	0.04968 mm
Relationship	a peak = (2πf)² x peak	Sine RMS = peak / √2

FPD.DEV analytical teaching model. Linear, viscously damped, single-degree-of-freedom base excitation. Purdue/Embry-Riddle vibration isolation notes: https://www.purdue.edu/freeform/ervibrations/chapter-v-animations/vibration-isolation/ . Assumed parameters, not measured display performance.

Random vibration: PSD and g RMS

The PSD tells us where the mean-square acceleration lies across frequency. Integrate it over the specified band to obtain g squared, then take the square root to obtain g RMS. For this teaching example, a flat PSD of zero point zero one g squared per hertz from twenty to five hundred hertz has an area of four point eight g squared. The overall level is therefore about two point one nine g RMS. A real DO-160 profile has specified breakpoints and slopes, so we integrate every segment. Two profiles with the same overall g RMS can stress a display differently when one puts more excitation near a structural mode. Overall RMS is not an instantaneous peak limit.

Illustrative input	Calculation	Result
PSD and bandwidth	0.010 × (500 − 20)	4.80 g²
Overall acceleration	√4.80	2.19 g RMS
PSD doubled	√(2 × 4.80)	3.10 g RMS

Authored flat-PSD example, not a DO-160 profile. https://www.spectraldynamics.com/support/technical-library/power-spectral-density-psd-and-grms

DO-160G random curve B

Here are the five breakpoints for standard random curve B in Figure eight dash one of DO-160G. The PSD is zero point zero one two at ten and forty hertz, falls to zero point zero zero two at one hundred hertz, stays there through five hundred hertz, then falls to zero point zero zero zero one three at two thousand hertz. The figure lists one point four eight g RMS. This is a curve-reading example, not a universal display qualification profile. Table eight dash one connects aircraft type, category and mounting zone to the curve. Its note distinguishes B from the lower B2 option and the large-aircraft B3 option. Use the applicable selection and the full log-log profile.

Frequency (Hz)	Acceleration PSD (g²/Hz)
10	0.012
40	0.012
100	0.002
500	0.002
2,000	0.00013

RTCA DO-160G (8 December 2010), retained local reference. Selected values and authored teaching summaries only. Use the complete adopted procedure and equipment specification. Figure 8-1, printed p. 8-14 (PDF p. 86); Table 8-1 note 4, p. 8-11. Numerical excerpt transcribed and visually checked.

Resonance scans and random exposure

The resonance scan and the random exposure are different parts of this procedure. In section eight point five point two, the initial scan uses zero point five g peak from ten to two thousand hertz, with the equipment not operating. The sweep rate does not exceed one octave per minute. An octave means a doubling of frequency. Response peaks greater than twice the input identify resonant frequencies under this procedure. The equipment then operates during the applicable random performance profile for at least one hour per axis, with response PSD measurements. A final scan identifies changes. These conditions apply to this selected procedure. Other categories have different performance periods, endurance periods or dwells.

Step	Input and duration	Equipment state
Initial sine scan	0.5 g peak, 10–2,000 Hz	Not operating
Random performance	Selected PSD, ≥1 h per axis	Operating
Final sine scan	Repeat initial scan	Compare resonances
All three axes	Scan rate ≤1 octave/min	Record response

RTCA DO-160G (8 December 2010), retained local reference. Selected values and authored teaching summaries only. Use the complete adopted procedure and equipment specification. §8.5.2, printed p. 8-6 (PDF p. 78).

Natural frequencies of a display

A natural frequency describes how a structure tends to vibrate after a disturbance. A simple supported mass has a natural frequency equal to one over two pi times the square root of stiffness divided by mass. A two-kilogram assembly with an effective stiffness of about one hundred ninety-seven thousand newtons per metre has a fifty-hertz natural frequency. Doubling the mass lowers that frequency by the square root of two. Doubling stiffness raises it by the same factor. A real display has many modes: cover bending, frame motion, circuit-board flex and whole-unit motion on mounts. Their frequencies are not generally integer multiples. The model helps us reason about a change, while measurements establish the actual modes.

FPD.DEV analytical teaching model. Linear, viscously damped, single-degree-of-freedom base excitation. Purdue/Embry-Riddle vibration isolation notes: https://www.purdue.edu/freeform/ervibrations/chapter-v-animations/vibration-isolation/ . Assumed parameters, not measured display performance.

Resonance: input and response

Watch the applied motion and the response of our illustrative fifty-hertz system. Well below its natural frequency, the supported assembly follows the base. Near the natural frequency, repeated excitation produces a much larger response. With five percent damping, the steady-state absolute acceleration ratio is about ten at fifty hertz. A zero point five g peak input would therefore predict about five point zero two g peak response in this ideal linear model. Above the resonance region, the ratio decreases. The animation slows the cycles so the motion is visible and exaggerates travel. It compares steady-state cases, not the transient response during a qualification sweep. Actual response depends on the mode, mounting, damping and nonlinear limits.

FPD.DEV analytical teaching model. Linear, viscously damped, single-degree-of-freedom base excitation. Purdue/Embry-Riddle vibration isolation notes: https://www.purdue.edu/freeform/ervibrations/chapter-v-animations/vibration-isolation/ . Assumed parameters, not measured display performance.

Damping limits resonance

Damping dissipates mechanical energy and limits resonant response. In this model, increasing damping from five to twenty percent reduces the ratio at the natural frequency from about ten point zero five to two point six nine. That does not mean the most damping is always the best isolator. Well above resonance, higher damping can transmit more motion through the mount. For this simple model, the absolute-motion ratio falls below one when the excitation frequency exceeds the square root of two times the natural frequency. A fifty-hertz mount therefore starts its isolation region above about seventy point seven hertz. Clearance, shock travel, temperature and cable restraint still have to be checked.

Damping ratio	Response / input at fn	Response to 0.5 g peak
5%	10.05	5.02 g peak
10%	5.10	2.55 g peak
20%	2.69	1.35 g peak

FPD.DEV analytical teaching model. Linear, viscously damped, single-degree-of-freedom base excitation. Purdue/Embry-Riddle vibration isolation notes: https://www.purdue.edu/freeform/ervibrations/chapter-v-animations/vibration-isolation/ . Assumed parameters, not measured display performance.

Harmonics and structural modes

A harmonic is an integer multiple of a fundamental excitation frequency. A rotor turning at three hundred sixty revolutions per minute rotates six times per second. Four equally spaced blades create a blade-passage frequency of twenty-four hertz. Its second harmonic is forty-eight hertz, which could excite a display mode near forty-eight hertz. That mode is a property of the assembly. The harmonic is a property of the forcing. They can coincide, but the second structural mode need not be twice the first. In a linear system, resonance amplifies frequencies that are already present. Nonlinear contacts, looseness or other nonlinear behaviour can generate additional harmonics. The animated amplitudes are illustrative, not a measured rotor spectrum.

RTCA DO-160G (8 December 2010), retained local reference. Selected values and authored teaching summaries only. Use the complete adopted procedure and equipment specification. §8.8.1.1 and Table 8-2a. Rotor speed and four-blade example are authored assumptions.

Helicopter instrument-panel tones

Table eight dash two a gives the sinusoidal test frequencies for different helicopter zones. For Zone two, which includes the instrument panel, console and equipment rack, curve G uses main-rotor blade passage and twice that frequency. With our assumed six-hertz rotor and four blades, those tones are twenty-four and forty-eight hertz. The table leaves the third and fourth tone entries blank for this zone. Other zones can include tail-rotor, engine or gearbox frequencies. The known-frequency procedure sweeps each specified tone across plus or minus ten percent. The example therefore spans twenty-one point six to twenty-six point four hertz and forty-three point two to fifty-two point eight hertz.

Zone 2 / G tone	DO-160G relationship	360 rpm, 4 blades
f1	NM × FM	24 Hz
f2	2 × NM × FM	48 Hz
f3 and f4	No entries for Zone 2	Other zones differ

RTCA DO-160G (8 December 2010), retained local reference. Selected values and authored teaching summaries only. Use the complete adopted procedure and equipment specification. Table 8-2a p. 8-12 (PDF p. 84), §8.8.1.1 and §8.8.1.3. Selected column, with authored numerical example.

Helicopter curve G acceleration

Now apply Table eight dash two b to those two frequencies. At twenty-four hertz, curve G performance acceleration is zero point zero four times frequency, giving zero point nine six g peak. At forty-eight hertz, the performance level is one point six g peak. The endurance level is two point five g peak for each of these frequencies. These are sinusoidal components applied with the random background, not overall RMS values. The table also states that external-airflow exposure increases the sinusoidal levels by a factor of one point five. Our instrument-panel example is internal. Keep the applicable zone, frequency range, installation and procedure attached to every quoted level.

Tone	Performance (g peak)	Endurance (g peak)
24 Hz	0.04 × 24 = 0.96	2.5
48 Hz	1.6	2.5
External-airflow case	Multiply sine levels by 1.5	When note 2 applies

RTCA DO-160G (8 December 2010), retained local reference. Selected values and authored teaching summaries only. Use the complete adopted procedure and equipment specification. Table 8-2b p. 8-13 (PDF p. 85), curve G selected rows and note 2. Example frequencies are assumptions.

Sine-on-random: two severity measures

A sine-on-random test combines discrete sinusoidal tones with a broadband random background. For the curve G table, the performance background reference W zero is zero point zero one g squared per hertz, with two point seven five g RMS listed for the random curve. Endurance uses zero point zero two and three point eight nine g RMS. W zero identifies a level in a shaped spectrum. It is not a flat PSD across the entire band. The listed RMS describes the random component alone. To combine independent random and sine components for an illustrative overall RMS estimate, add their mean squares, using sine peak squared divided by two, then take the square root. Never add g peak directly to g RMS.

Random background	Performance	Endurance
W0 (g²/Hz)	0.010	0.020
Listed random g RMS	2.75	3.89
Add sine components	Use each peak² / 2	Then sum mean squares

RTCA DO-160G (8 December 2010), retained local reference. Selected values and authored teaching summaries only. Use the complete adopted procedure and equipment specification. Table 8-2b p. 8-13 and Figure 8-6 p. 8-19. Independent-component RMS calculation is teaching synthesis.

DO-160G shock pulse examples

Section seven distinguishes operational shock from crash retention. Standard operational shock uses six g peak with an eleven-millisecond nominal terminal sawtooth pulse. The low-frequency option uses six g peak and twenty milliseconds. The procedure applies three shocks in each orientation, or the specified equivalent axis arrangement. Crash impulse uses twenty g, one shock in each of six orientations, with the applicable standard or low-frequency pulse form. Crash safety also includes sustained loading when applicable. Normal operational-shock acceptance is after the shocks, and any required monitoring during a pulse belongs in the equipment specification. Retention in a crash test does not establish continued display function.

Test example	Peak and nominal duration	Count / scope
Operational, standard	6 g, 11 ms	3 per orientation
Operational, low frequency	6 g, 20 ms	3 per orientation
Crash impulse	20 g, applicable 11 / 20 ms	1 per orientation
Crash sustained	Table 7-1 loads	≥3 s per load direction

RTCA DO-160G (8 December 2010), retained local reference. Selected values and authored teaching summaries only. Use the complete adopted procedure and equipment specification. §§7.1.1, 7.2.1–7.3.3 and Figure 7-2; printed pp. 7-1 to 7-6. Authored summary.

Shock duration and ringing

A shock pulse is a transient, so it does not have a single vibration frequency. Its duration and shape determine how it excites different structural modes. Compare these ideal six-g terminal sawtooth pulses. Extending duration from eleven to twenty milliseconds increases the ideal pulse area, and therefore velocity change, from about zero point three two four to zero point five eight eight metres per second. Equal peak g does not mean equal response. A structure can ring at its damped natural frequencies after the input ends. DO-160G also notes that a twenty-millisecond pulse may be inadequate for some equipment with a lowest resonance below one hundred hertz, and says a one-hundred-millisecond pulse should be considered. That requires an appropriate test decision, not an automatic replacement.

RTCA DO-160G (8 December 2010), retained local reference. Selected values and authored teaching summaries only. Use the complete adopted procedure and equipment specification. §7.1, §7.2.1 and Figure 7-2. Plot shows ideal pulses only, not the full tolerance envelope or machine compensation. Pulse-area calculations use g0=9.80665 m/s².

Crash sustained loads: one table row

This selected row from Table seven dash one applies to fixed-wing transport aircraft with known, fixed equipment orientation. Its minimum sustained accelerations are three g up, six down, nine forward, one point five aft and four to either side. Section seven point three point three applies the appropriate loads for at least three seconds in each load direction. The directions are aircraft directions. A rotated display installation needs the corresponding equipment-axis interpretation. The table separately addresses unknown or random orientations and other aircraft types. Its caution says the listed levels may not satisfy the installation requirements in the regulations. Use this excerpt to understand the load definition, then check the actual aircraft and installation basis.

Aircraft load direction	Minimum sustained acceleration
Up	3 g
Down	6 g
Forward	9 g
Aft	1.5 g
Left and right	4 g each

RTCA DO-160G (8 December 2010), retained local reference. Selected values and authored teaching summaries only. Use the complete adopted procedure and equipment specification. Table 7-1, fixed-wing transport F row, notes 2, 4, 5 and caution; §7.3.3, printed p. 7-4 (PDF p. 64).

Monitoring the display response

Place the control accelerometer near the attachment and response sensors where the suspected modes matter. A fixture resonance or an added brace can change the result. Synchronize the acceleration record with image observation, link errors, touch events and application outputs. Look for optical flashes from cell deformation, intermittent connectors, loose fasteners and bond-edge damage. A frequency shift after exposure can indicate a stiffness or boundary-condition change, but it needs investigation. For relevant section eight procedures, the standard has a specific reading-difficulty allowance when applied input excursion exceeds half a millimetre. Preserve that provision while separately judging structural failures, electrical faults and the installation's own viewability requirements.

RTCA DO-160G (8 December 2010), retained local reference. Selected values and authored teaching summaries only. Use the complete adopted procedure and equipment specification. §§8.3, 8.5.1–8.5.2, 8.7, 8.8.1.3; display monitoring is engineering application guidance.

Worked practice: a helicopter display mode

Assume 360 rpm, four main-rotor blades, and a display mode at 48 Hz with 5% damping. Identify the first two blade-passage components. Use the selected curve G table to find their performance amplitudes. Estimate the ideal mode response to the 48 Hz tone, then identify why that estimate is insufficient for qualification.

Model response

360/60 = 6 Hz one/rev. Blade passage is 4 × 6 = 24 Hz, and its second harmonic is 48 Hz. Curve G gives 0.96 and 1.6 g peak for those two tones. At exact resonance, T = √(1+4ζ²)/(2ζ) = 10.05 for ζ = 0.05. The ideal absolute acceleration response to the 48 Hz tone is therefore approximately 16.08 g peak. This assumes one linear mode and a steady sine input. It omits the other tone, random excitation, multiple modes, nonlinearity, actual damping and installation uncertainty. It is a design warning, not a measured response or qualification result.

Worked practice: mean square and shock duration

Calculate overall RMS for a random component of 2.75 g RMS with independent sine components of 0.96 and 1.6 g peak. Compare the ideal velocity change of 6 g terminal sawtooth pulses of 11 ms and 20 ms.

Model response

Overall RMS = √(2.75² + 0.96²/2 + 1.6²/2) = 3.05 g RMS, using rounded listed background RMS and independent components. This does not specify a peak or substitute for the spectrum. Ideal sawtooth pulse area gives Δv = a peak × duration / 2: approximately 0.324 and 0.588 m/s. Equal peak g does not imply equal modal response. A shock-response-spectrum assessment includes pulse shape, duration and assumed oscillator damping.

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