IEC TR 62131-2:2011

Environmental conditions - Vibration and shock of electrotechnical equipment - Part 2: Equipment transported in fixed wing jet aircraft

IEC/TR 62131-2:2011(E) reviews the available dynamic data relating to electrotechnical equipment transported in fixed wing jet transport aircraft. The intent is that from all the available data an environmental description will be generated and compared to that set out in IEC 60721.

General Information

• Status: Published
• Publication Date: 23-Feb-2011
• ICS: 19.040 - Environmental testing
• Technical Committee: TC 104 - Environmental conditions, classification and methods of test
• Drafting Committee: WG 15 - TC 104/WG 15
• Current Stage: PPUB - Publication issued
• Start Date: 24-Feb-2011
• Completion Date: 15-Jun-2011

Standards Content (Sample)

IEC/TR 62131-2 ®
Edition 1.0 2011-02
TECHNICAL
REPORT
colour
inside
Environmental conditions – Vibration and shock of electrotechnical equipment –
Part 2: Equipment transported in fixed wing jet aircraft

IEC/TR 62131-2:2011(E)
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IEC/TR 62131-2 ®
Edition 1.0 2011-02
TECHNICAL
REPORT
colour
inside
Environmental conditions – Vibration and shock of electrotechnical equipment –
Part 2: Equipment transported in fixed wing jet aircraft

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
W
ICS 19.040 ISBN 978-2-88912-383-4

– 2 – TR 62131-2 © IEC:2011(E)
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Data source and quality . 7
3.1 Lockheed Tristar KC Mk 1 . 7
3.2 BAe VC10 K . 7
3.3 Boeing 747 Combi (freight and passengers) . 8
3.4 Supplementary data . 10
3.4.1 McDonnell Douglas DC8 cargo . 10
3.4.2 Lockheed C5A (Galaxy), Lockheed C-141 (Starlifter) and Boeing NC-
135 (707) . 10
4 Intra data source comparison . 10
4.1 General remark . 10
4.2 Lockheed Tristar KC Mk 1 . 10
4.2.1 Relative severity of flight conditions . 10
4.2.2 Position within the cargo hold . 11
4.2.3 Relative severity of measurement axes . 11
4.3 BAe VC10 K . 11
4.3.1 Relative severity of flight conditions . 11
4.3.2 Position within the cargo hold . 11
4.3.3 Relative severity of measurement axes . 12
4.4 Boeing 747 Combi (freight and passengers) . 12
4.4.1 Relative severity of measurement axes . 12
4.4.2 Relative severity of flight conditions . 12
5 Inter data source comparison . 12
6 Environmental description . 13
6.1 Lockheed Tristar KC Mk 1 . 13
6.2 BAe VC10 K . 13
6.3 Boeing 747 Combi (freight and passengers) . 13
7 Supplementary data . 13
7.1 McDonnell Douglas DC8 Cargo . 13
7.2 Lockheed C5A (Galaxy), Lockheed C-141 (Starlifter) and Boeing NC-135
(707) . 14
8 Comparison with IEC 60721 . 14
9 Recommendations . 15
Bibliography . 40

Figure 1 – Schematic of Tristar aircraft . 17
Figure 2 – Tristar noise measurements . 18
Figure 3 – Tristar vibration measurements – Take-off, power and roll . 18
Figure 4 – Tristar vibration measurements – Low altitude climb . 19
Figure 5 – Tristar vibration measurements – High altitude cruise . 19
Figure 6 – Tristar vibration measurements – Landing . 20
Figure 7 – Tristar vibration measurements – Low altitude decent . 20
Figure 8 – Tristar vibration measurements – C of G Take-off/climb . 21

TR 62131-2 © IEC:2011(E) – 3 –
Figure 9 – Tristar vibration measurements – Forward take-off/climb . 21
Figure 10 – Tristar vibration measurements – Centre of gravity cruise . 22
Figure 11 – Tristar vibration measurements – Forward cruise . 22
Figure 12 – Tristar vibration measurements – Centre of gravity landing . 23
Figure 13 – Tristar vibration measurements – Forward landing . 23
Figure 14 – Tristar vibration measurements – Cruise environment . 24
Figure 15 – Tristar vibration measurements – Take-off/landing environment . 24
Figure 16 – Schematic of VC10 aircraft . 25
Figure 17 – VC10 vibration measurements – Cruise . 27
Figure 18 – VC10 vibration measurements – Maximum airframe severity . 27
Figure 19 – VC10 vibration measurement – Forward container during reverse thrust . 28
Figure 20 – VC10 vibration measurement – Rear container during reverse thrust . 28
Figure 21 – VC10 measurements – Overlaid worst case spectra . 29
Figure 22 – Vibration Measurements on a pallet in a Boeing 747 Combi aircraft
(transducer V1) . 31
Figure 23 – Vibration measurements on a pallet in a Boeing 747 Combi aircraft
(Transducer V2) . 31
Figure 24 – DC8 vibration measurements reverse thrust . 32
Figure 25 – DC8 vibration measurements acceleration and take-off . 33
Figure 26 – DC8 vibration measurements cruise . 33
Figure 27 – Foley representation of environment for NC-135, C-141 and C-5A aircraft. 34
Figure 28 – Foley landing shock environment . 34
Figure 29 – Foley test severity for take-off/landing . 35
Figure 30 – Foley test severity for cruise . 36
Figure 31 – IEC 60721-3-2 (1997) – Stationary vibration random . 37
Figure 32 – IEC 60721-3-2 (1997) – Non-stationary vibration including shock . 37
Figure 33 – Test severities – ASTM D 4728-91 . 38
Figure 34 – Test severities – Mil Std 810 issue F and G. 38
Figure 35 – Test severities – AECTP 400 (Edition 2 & 3) . 39
Figure 36 – Test severity – Def Stan 00-35, issue 3 & 4 . 39

Table 1 – Tristar flight conditions and measured r.m.s. values . 17
Table 2 – VC10 flight conditions . 25
Table 2a – VC10 measurement locations . 25
Table 3 – Overall g r.m.s. (3,25 Hz to 2 000 Hz) for VC10 airframe/container . 26
Table 4 – Overall g r.m.s. (3,25 Hz to 399 Hz) for VC 10 container measurements . 26
Table 5 – Summary of 747 air transport data . 30
Table 6 – Summary of 747 acceleration levels (g) expected to be exceeded for 1 % of
the time of the trial . 30
Table 7 – Summary of DC8 air data . 32
Table 8 – Foley test severity for take-off/landing – Sine components . 35
Table 9 – Foley test severity for cruise – Sine components . 36

– 4 – TR 62131-2 © IEC:2011(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL CONDITIONS –
VIBRATION AND SHOCK OF ELECTROTECHNICAL EQUIPMENT –

Part 2: Equipment transported in fixed wing jet aircraft

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
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The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 62131-2, which is a technical report, has been prepared by IEC technical committee
104: Environmental conditions, classification and methods of test.

TR 62131-2 © IEC:2011(E) – 5 –
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
104/507/DTR 104/536/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 62131 series, under the general title Environmental conditions
– Vibration and shock of electrotechnical equipment, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this standard may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – TR 62131-2 © IEC:2011(E)
ENVIRONMENTAL CONDITIONS –
VIBRATION AND SHOCK OF ELECTROTECHNICAL EQUIPMENT –

Part 2: Equipment transported in fixed wing jet aircraft

1 Scope
IEC/TR 62131-2, which is a technical report, reviews the available dynamic data relating to
electrotechnical equipment transported in fixed wing jet transport aircraft. The intent is that
from all the available data an environmental description will be generated and compared to
that set out in IEC 60721.
For each of the sources identified the quality of the data is reviewed and checked for self
consistency. The process used to undertake this check of data quality and that used to
intrinsically categorize the various data sources is set out in IEC/TR 62131-1.
This technical report primarily addresses data extracted from a number of different sources
for which reasonable confidence exist as to their quality and validity. The report also presents
data for which the quality and validity cannot realistically be reviewed. These data are
included to facilitate validation of information from other sources. The report clearly indicates
when it utilizes information in this latter category.
This technical report addresses data from several different transport aircraft . Although one
of these aircraft is no longer used commercially, data from it are included to facilitate
validation of information from other sources.
Relatively little of the data reviewed has been made available in electronic form. To permit
comparison, a quantity of the original (non-electronic) data have been manually digitized in
this technical report.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60721 (all parts), Classification of environmental conditions
IEC 60721-3-2:1997, Classification of environmental conditions – Part 3: Classification of
groups of environmental parameters and their severities – Section 2: Transportation
___________
Lockheed Tristar KC Mk 1, Lockheed Tristar L-1011, BAe VC10 K, Boeing 747 Combi, McDonnel Douglas DC8
Cargo, Lockheed C5A (Galaxy), Lockheed C-141 (Starlifter), Boeing NC-135 (707) are the trade names of
products supplied by Lockheed, BAe, McDonnel Douglas and Boeing, respectively. This information is given for
the convenience of users of this technical report and does not constitute anendorsement by IEC of the products
named.
TR 62131-2 © IEC:2011(E) – 7 –
3 Data source and quality
3.1 Lockheed Tristar KC Mk 1
The vibration data for the Lockheed Tristar KC Mk 1 aircraft are been taken from a Lockheed
report [1]  on a flight test carried out in support of a US DoD program. Reference [1] reports
on a single flight of a Lockheed Tristar L-1011 wide body commercial aircraft which had been
undertaken to record vibration data. Measurements were recorded at two positions within the
aircraft for a comprehensive range of flight conditions which are set out in Table 1.
The trial aircraft was fully fitted out. Although photographic evidence is poor quality, it
indicates that the aircraft had seating and [1] indicates that it had internal fixtures and fittings
and was not a bare shell. The aircraft’s gross weight for the data flight was between
190 000 Kg (at take-off) and 165 000 Kg (on landing).
Measurements were made at two positions on the Lockheed aircraft as illustrated in Figure 1.
The transducer positions were close to the centreline of the aircraft at fuselage stations 804
and 1 218. The centre of gravity (c of g) transducer positions are on the structure supporting
the cargo bay floor whereas the forward transducers are in the roof of the cabin attached via a
bracket to the aircraft structure.
The data contained in [1] seems of good quality, however, the poor quality photocopy of the
original report has resulted in poor definition of some of the spectra. The electrical noise from
the aircraft systems was recorded and shown to be at an acceptably low level. Bibliographic
reference [1] reports that a variety of no signal data were taken to provide a measure of the
noise floor of the entire instrumentation system. The noise measurement is shown in Figure 2
were made with the aircraft powered by the auxiliary power unit only.
For a number of flight conditions, (Numbers 2, 3, 7, 9 and 10 in Table 1), up to four separate
recordings were taken. The set of PSDs (Figures 3 to 7) were then further reduced by
presenting their average and maximum curves on one plot. This successfully demonstrated
that the variation in vibration response between the separate flight recordings is small. The
root mean square (r.m.s.) values computed for such cases correspond to the maximum PSD
curve.
Bibliographic reference [1] states that the analysis time for each power spectral density (PSD)
was at least 45 s and the analysis bandwidth was 1,272 5 Hz. These values produce a
normalized random error of 13 which is generally satisfactory. Also it was reported that all the
instrumentation was calibrated.
To enable the vibration responses to be overlaid on a single figure,the original data plots have
been manually digitizd using up to 80 points. Where the copy of the plots was poorly defined
those was simply enveloped to ensure that all the major peak responses were included in the
digitizd version.
For the purposes of comparison,the data for the flight conditions were grouped into take-off
and landing as well as cruise. The environment of take-off and landing includes flight
conditions 2, 3, 9 and 10 (from Table 1) which are take-off, power and roll, low altitude climb,
low altitude descent and touchdown. The cruise environment includes flight condition 7, high
altitude cruise.
3.2 BAe VC10 K
Bibliographic reference [2] presents an assessment of vibration and shock data obtained from
a flight trial carried out during April, 1985. The flight trial involved the transport of two
container assemblies within a VC10 aircraft. Data gathered during the trial included
___________
References in square brackets refer to the bibliography.

– 8 – TR 62131-2 © IEC:2011(E)
measurements made at the base of the containers. The flight trial requirements and its
analysis are presented in [1], [1], [5] and [6].
The trials not only included the usual benign conditions such as cruise at altitude, but also
several conditions relating to emergency situations, e.g. one engine inoperative, firm
landings, etc. although the scope for such emergency situations is very limited on the VC10.
The full list of the various flight conditions covered during the flight is presented in Table 2.
The load configuration for the flight is shown diagrammatically in Figure 16. The payload
consisted of two 1 800 Kg container assemblies. For the flight the loads were secured under
normal procedures and involved lashing the load containers to the appropriate aircraft tie-
down points.
Flight instrumentation consisted of 11 accelerometers, used to measure cargo hold vibration
both adjacent to the airframe and at the bases of the transported containers. The airframe
measurements were made on cargo floor tie-down fixtures. These being suitably firm
mounting locations and available at key positions in the cargo bay. The container
measurements were made at suitably rigid positions around the base of the containers, so
providing a measure of vibration input. The vibration measurement sites are indicated in
Figure 16.
The nature of the vibration environment is, in general, broad band random. The maximum
vibration amplitudes measured at the cargo hold floor tend to occur within the 200 Hz to
600 Hz bandwidth. Consequently, the flight data have been produced in acceleration power
spectral density (APSD) and acceleration-time history formats. APSD plots have been
produced over the frequency range 3,25 Hz to 2000 Hz. Amplitudes from the APSDs are the
result of averaging throughout a particular flight condition. Results are threfore valid for those
conditions when the average properties of the data are invariant with respect to time, e.g.
straight and level flight. The results of the data processing carried out are contained in [2], [1]
and [1].
A statement on the accuracy of the airframe/container measuring instrumentation states that
the overall tolerance is ±5,9 % with a typical value in the range ±4,0 %. The analysis
resolution bandwidth was 3,25 Hz and the variance error in the range 3 % to 12 %.
To enable the vibration responses to be overlaid on a single figure the original data plots have
been hand digitized using up to 80 points. Where the copy of the plots was poorly defined the
poorly defined portion was simply enveloped to ensure that all the major peak responses were
included in the digitized version.
No discernible shocks were observed during either normal or ‘touch-and-go' landings ([1]
contains a figure demonstrating this but it is not reproducible).
Although the VC10 was originally designed and operated as a commercial passenger and
freight aircraft, it is no longer operated commercially. The only known current operator is the
UK military. Vibration information for this aircraft is included in this assessment because it has
the potential to support the validity of data from other sources.
3.3 Boeing 747 Combi (freight and passengers)
A field study was conducted on board a Boeing 747 Combi (freight and passenger) aircraft on
the route Stockholm (Arianda) via Oslo (Gardermoen) to New York (John F. Kennedy Airport)
and return to Stockholm (Arianda). Shock and vibration acting on the cargo during air
transportation were measured and analysed.
The study encompassed all phases of the flight, including taxiing, climbing, cruising during
both calm and turbulent conditions, descent and approach, landing (including touchdown and
taxiing to apron). The phases considered to be the most interesting as regards cargo-
influencing vibrations and which were analysed from the field trials are as follows:

TR 62131-2 © IEC:2011(E) – 9 –
i) taxiing;
ii) take-off;
iii) initial climb;
iv) cruise, normal conditions;
v) cruise, gusts or air pockets;
vi) descent and approach;
vii) landing (touchdown, braking and roll-out);
viii) taxiing to apron.
The field data, reported in [7], were analysed by conventional frequency analysis and
modelling techniques. In order to generalize the results, flight recorder data from the field trial
and from other flights are included.
The fixture with the tri-axial accelerometer test set-up was mounted on the pallet with double
sided tape and was placed approximately midway of the length of the pallet, about 0,5 m from
the pallet edge. A fourth, separate, vertical accelerometer was mounted near the end of the
pallet, approximately 0,5 m from the corner. Mounting the transducers on the pallet rather
than on the aircraft deck meant that the accelerations to which the pallet was exposed, i.e.
input to the cargo, were recorded. Mounting the transducers on the cargo would have meant
that the accelerations recorded were dependent on the type of cargo. Of course, the products
and their weight do influence the registered signals, therefore the pallet loads chosen were
'typical'. In field trial number 1 the weight of the test pallet was 1 470 kg and in field trial
number 2 the weight was 2 550 kg.
The aircraft used in the field trials, a Boeing 747, is one of the most common for freight and
passenger transportation. The plane in question, Dan Viking, happened to be plane number
500 in the 747 series, and was a Combi version delivered in 1981. In both trials, the pallet
was placed on the main deck to the right of and close to the centre of gravity.
The field data recorded during the trip have been computer analysed in the time and
frequency domains. The frequency domain analysis was carried out using both conventional
spectral analysis and autoregressive modelling techniques. The sampling frequency chosen
was 100 Hz and the signal was low-pass filtered at 31,5 Hz. However, since the signal/noise
ratio of the recorded signal was good, the post analysis data was compensated to allow
estimates up to 50 Hz to be made. This was essentially achieved by compensating for the
filtering. The number of records, each spanning 256 samples, varied depending on the length
of the flight phase studied. Values for the cruise phase en route have been limited to 350
records, i.e. a sampling time of about 15 min. The window mostly used for the frequency
analysis was the Blackman window. For the analysis using autoregressive modelling for the
spectral estimation, the Hamming window was used.
A summary of recorded extreme values and g r.m.s. values is given in Table 5. Transducer V2
is the separate, vertical accelerometer placed on the pallet corner, V1 is the vertical
accelerometer placed near the pallet centre, T is the transversal accelerometer and L is the
longitudinal accelerometer; V1, T and L were located on the tri-axial test set-up. Since there
are no distinct dividing lines between different flight phases, the signal characteristics
together with the test protocol have been used as a means of separation. In Table 5
touchdown is represented by the first four records of the landing phase.
In Table 6 the acceleration levels that can be expected to be exceeded for more than 1 % of
the test time, when normal distribution is assumed, have been calculated based on standard
deviations. In this case the standard deviation should be multiplied by a factor of 2,576
according to a normal distribution table. This means that 0,5 % of the values have greater
positive values and 0,5 % have greater negative values. Thus, Table 6 describes the
distribution of instantaneous values.

– 10 – TR 62131-2 © IEC:2011(E)
3.4 Supplementary data
3.4.1 General remark
The data collection exercise identified some additional relevant sets of information, which
come from reputable sources, but for which the data quality could not be adequately verified.
They are included here to facilitate validation of data from other sources. Care should be
taken when utilizing information in this category.
3.4.2 McDonnell Douglas DC8 cargo
Information is contained within the French military specification GAM EG 13 ([1]) from the
cargo hold of a DC8 cargo aircraft. Information is presented for three transducers and eight
flight conditions. A summary of the severities for the eight flight conditions is presented in
Table 7. Spectra for the most severe flight conditions are presented in Figures 24, 25 and 26.
For the most part the data presented in [1] are of low level to the extent that the
measurements appear close to the measurement system noise floor (see Figure 26).
3.4.3 Lockheed C5A (Galaxy), Lockheed C-141 (Starlifter) and Boeing NC-135 (707)
As part of an exercise in the early 1970’s to authenticate test severities for the US military
specification Mil Std 810, J.T. Foley ([1]) at Sandia National Laboratories in the US undertook
an extensive exercise to establish transportation severities on a number of platforms. One of
those was for transportation in jet aircraft. Although the measurements encompassed three
transport aircraft, C5A, C-141 and NC-135, the process adopted does not allow information
from individual aircraft to be identified. Moreover, the analysis process Foley used throughout
his work is relatively unique and not immediately compatible with other information presented
in this assessment. Nevertheless, Foley did generated test spectra which can be usefully
compared with those from other methods and sources (see Figures 27 to 30 and Tables 8
and 9).
4 Intra data source comparison
4.1 General remark
The purpose of the following paragraphs is to review each data source for self consistency.
The process for evaluating the vibration data takes into account the variation of vibration due
to operational usage and aircraft characteristics. The levels of confidence resulting from this
review directly influences the levels of factoring and enveloping that are used when deriving
environmental levels.
4.2 Lockheed Tristar KC Mk 1
From the data provided in [1], an assessment of the relative severity of different flight
conditions, different positions in the cargo hold and different measurement axes has been
undertaken to establish both the variability and characteristics of the vibration environment
within the Tristar aircraft. This comparison is partly limited as the test only included a single
flight of one aircraft and therefore no firm conclusions can be made regarding any aircraft to
aircraft or flight to flight variations including different aircraft weights. Moreover, only two
measurement positions were used giving only an indication of the variation of the vibration
levels with respect to position within the aircraft.
4.2.1 Relative severity of flight conditions
The conditions of take-off, maximum power and roll provide the highest vibration levels and
correspond to those that require the most power from the engines. Similarly the flight
conditions for climb and acceleration produce APSDs with levels greater than cruise. Landing
at touchdown specifically in the fore and aft direction also exhibits high levels but these are
almost certainly as a result of the application of reverse thrust following aircraft touchdown.

TR 62131-2 © IEC:2011(E) – 11 –
4.2.2 Position within the cargo hold
In general the vibration levels for the forward transducers are higher than those recorded at
the centre of gravity (c of g) for the same flight condition. This is particularly apparent for the
lateral responses whose r.m.s. levels are up to four times higher. Only for touchdown are the
c of g r.m.s. levels higher which is due to the application of reverse thrust and hence the
higher engine induced responses in the 200 Hz to 600 Hz bandwidth. The spectral
characteristics of the measurements recorded at the forward position are different to those
recorded at the c of g position. Figure 8 and Figure 9 as well as Figure 12 and Figure 13 show
typical vibration responses at the forward and c of g measurement positions for take-off (flight
conditions 2 and 3) and landing (flight conditions 9 and 10). The responses at the forward
position show consistent peak responses at 35 Hz, 100 Hz, 130 Hz and 180 Hz to 250 Hz and
very low responses above 250 Hz whereas the responses at the c of g are predominantly flat
with peaks in the frequency range 400 Hz to 600 Hz. Figure 10 and Figure 11 show typical
vibration responses at the forward and c of g measurement positions for cruise.
4.2.3 Relative severity of measurement axes
For the responses measured at the c of g, the fore and aft direction consistently exhibits the
highest vibration levels due almost certainly to the transducers proximity and alignment to the
engines. The vertical and lateral responses at the c of g are broadly similar. For the
responses measured by the forward group the longitudinal and transverse directions provide
an equal number of the highest responses. The responses in the vertical direction tend to be
lower than the other directions.
4.3 BAe VC10 K
4.3.1 General remark
For the purpose of establishing trends only data originating from the airframe sites have been
considered. This is because airframe vibration, being a measure of vibration input to the
cargo hold floor, constitutes the most complete description of the input environment. For the
purpose of trend identification discussed below, the data have been examined in terms of
overall acceleration (g) r.m.s. vibration in the frequency band 3,25 Hz to 2000 Hz and are
shown in Table 3. A summary of container acceleration (g) r.m.s. vibration levels in the
bandwidth 3,25 Hz to 399 Hz which excludes the power supply noise components, is
presented in Table 4.
4.3.2 Relative severity of flight conditions
The vibration levels recorded during cruise were very low; the maximum being 0,156 g r.m.s.
at the starboard aft (vertical) location, during cruise at 11 000 m (37 000 ft) and Mach 0,83.
This is depicted in the APSD plot shown in Figure 17 where it may be seen that APSD levels
do not exceed 0,000 1 g /Hz. The maximum vibration tended to occur during take-off, descent
and reverse thrust upon landing. Vibration during these short duration events was up to four
times greater than that during cruise. The maximum vibration recorded during the trials was
during reverse thrust after landing. In this condition 0,674 g r.m.s. was measured at the
starboard aft location in the vertical axis. The corresponding maximum APSD level was
0,001 4 g /Hz. as may be seen in Figure 18. No discernible differences were apparent in
vibration when one of the aircraft’s engines was throttled right back.
4.3.3 Position within the cargo hold
The character of vibration within the cargo hold was of increasing vibration towards the rear of
the aircraft where the engines are situated. This is particularly apparent during those flight
conditions which demanded high power from the engines, such as take-off. In such conditions
acceleration (g) r.m.s. levels recorded at the rear of the hold were around three times greater
than those towards the nose.
– 12 – TR 62131-2 © IEC:2011(E)
4.3.4 Relative severity of measurement axes
For maximum consistency, the relative severity of vibration in the three measurement axes
was undertaken using data from triaxial accelerometers. Results indicate that vibration in the
vertical, transverse and fore/aft axes are generally in the ratio of 1,0: 0,8: 0,3 respectively.
Data originating from the forward container, however, do not conform to this pattern. This
behaviour is attributed to the effects of power supply noise on the low vibration levels
recorded. This view is supported by a comparison of APSDs from the forward and rear
mounted containers, as shown in Figures 19 and 20. Furthermore, a comparison of
acceleration (g) r.m.s. in the frequency band of 3,25 Hz to 399 Hz, presented in Table 4,
which excludes noise components, does conform to expectations regarding the relative
severity of axes.
4.4 Boeing 747 Combi (freight and passengers)
4.4.1 General remark
The data gathering exercise, on the 747 reported in [7], was accompanied by another
exercise measuring the vibration and shock conditions during ground handling at airports.
With this experience [1] precedes its review of the aircraft severities with the following
observation:
“As far as stress levels are concerned, the ground handling and ground transport phases
of an air transport are the severest, next come take-off and landing. Less severe from the
point of view of accelerations are phases when the aircraft is airborne.”
4.4.2 Relative severity of measurement axes
The vertical accelerations generally are the greatest. The difference between vertical
acceleration at a pallet corner and vertical acceleration at the middle of the pallet is relatively
small, but noticeable. This means that the vertical accelerations at the pallet corner are
'rattling'. The transverse and fore/aft accelerations are generally smaller than the vertical
accelerations. The relation between them is dependent on the phase of the flight. In phases
where the aircraft is markedly inclined, such as climb and descent, the fore/aft accelerations
are greatest. This is also the case during the acceleration at take-off and braking after
touchdown. During the cruise phase the transverse accelerations are normally somewhat
larger than the fore/aft accelerations.
4.4.3 Relative severity of flight conditions
The largest maximum acceleration levels have been recorded during landing where
touchdown gave 0,42 g pk in the frequency range studied.
5 Inter data source comparison
For the most part the data from the various sources not only indicates a reasonable degree of
self consistency but also a fairly good degree of consistency across the various sources.
None of the verified data sources is obviously significantly different from the remainder to the
extent that its validity (or that of the remainder) is called into question.
The broad trends are consistent for all the aircraft addressed. Of particular note is that all the
data indicates take-off to be marginally less severe than landing, but both are markedly more
severe than cruise conditions. In several cases the most severe condition during landing is
identified as occurring during the application of reverse thrust. The extent (and frequency
range) of this condition varies, but this is not surprising given the different engine
configurations of the aircraft concerned.
Two of the three good data sources indicate that responses in the vertical axis are marginally
greater than transverse which in turn are slightly greater than fore/aft. Insufficient data is
available to identify a definitive trend of the vibration along the length of the aircraft. Mostly

TR 62131-2 © IEC:2011(E) – 13 –
the data coincides with the expectation that vibrations at the rear of the aircraft are more
severe than at the forward locations. This being due to the boundary layers being thicker at
the rear of the aircraft, the proximity of the engines and the engine jet flow.
All the data sources, with one exception, have utilized acceleration power spectral density as
the means of analysing the vibration data. This approach is unquestionably valid for the
analysis of cruise vibrations which not only have a broad band random characteristic (mainly
originating from aerodynamic flow over the fuselage), but also are relatively stat
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