+------+-----------------------------------------+--------+-----------+
| Subj | Revision of Multiple Burst Lightning    | Date:  | AUG 25    |
| ect: | Environment                             |        | 1993      |
+------+-----------------------------------------+--------+-----------+
| F    | Manager, Aircraft Engineering Division, | Reply  |           |
| rom: | AIR-100                                 | to     |           |
|      |                                         |        |           |
|      |                                         | Attn   |           |
|      |                                         | of:    |           |
+------+-----------------------------------------+--------+-----------+
| To:  | Manager, Transport Airplane             |        |           |
|      | Directorate, ANM-100                    |        |           |
|      |                                         |        |           |
|      | Manager, small Airplane Directorate,    |        |           |
|      | ACE-l00                                 |        |           |
|      |                                         |        |           |
|      | Manager, Rotorcraft Directorate,        |        |           |
|      | ASW-100                                 |        |           |
|      |                                         |        |           |
|      | Manager, Engine and Propeller           |        |           |
|      | Directorate, ANE-100                    |        |           |
|      |                                         |        |           |
|      | Manager, Brussels Aircraft              |        |           |
|      | Certification Staff, AEU-100            |        |           |
+------+-----------------------------------------+--------+-----------+

Appendix III in Advisory Circular (AC) 20-136, \"Protection of Aircraft
Electrical/Electronic Systems Against the Indirect Effects of
Lightning,\" defines the multiple burst lightning environment to be used
for test and analysis purposes in qualifying systems and equipment for
lightning protection. This multiple burst environment consists of 24
sets of 20 pulses each, distributed over a period of up to two seconds.
The minimum time between the individual pulses within a burst is 10
$\mu$s, the maximum is 50 $\mu$s. The 24 bursts are distributed over a
period of up to two seconds with the minimum time between subsequent
bursts being 10 ms, and the maximum being 200 ms.

As part of an ongoing review of natural lightning phenomenology and data
from in-flight measurements of electrical parameters, SAE Committee AE4L
and EUROCAE WG-31 recommended that the multiple burst definition be
modified from the current 24 burst of 20 pulses to 3 bursts of 20
pulses. The minimum time between individual pulses within a burst was
changed from 10 $\mu$s to 50 $\mu$s, and the maximum from 50 $\mu$s to
1,000 $\mu$s. In addition, the minimum time period between subsequent
bursts was changed from 10 ms to 30 ms, and the maximum time from 200 ms
to 300 ms. Attachment 1 contains the committees\' recommendation.

The Aircraft Certification Lightning Steering Committee has reviewed the
recommendation presented by AE4L arid WG-31, and has advised that these
changes be incorporated into AC 20-136. Lightning protection special
conditions that are currently being issued for new certification
projects will use the new definition for the multiple burst environment.
Certification projects currently in progress should accept this criteria
if so requested by the applicant.

If there are any questions or comments on this policy, the engineer on
my staff who is most familiar with these issues is Mr. George
Soteropoulos, AIR-120, telephone (202) 267-9796.

Signed by John K. McGrath

Attachment

Committee Correspondence

+----------------+-------------------------------------+---------------+
| Name of        | SAE AE4L (lightning)                | Date: 6 July  |
| Committee:     |                                     | 1992          |
|                | EUROCAE WG-31                       |               |
+----------------+-------------------------------------+---------------+
| Subject:       | Multiple Burst Definition           | Reply to:     |
+----------------+-------------------------------------+---------------+
| To:            | Users of SAE-AE4L and EUROCAE WG-31 |               |
|                | Lightning Criteria                  |               |
+----------------+-------------------------------------+---------------+

At our meetings of 5-6 May and 9-11 June 1992 respectively, EUROCAE
WG-31 and SAE Committee AE4L voted to recommend to users of EUROCAE
WG-31 and SAE-AE4L lightning criteria that the definition of the
Multiple Burst environment be changed from 24 bursts to 3 bursts and
otherwise be re-defined as in the attached description and figure.

This action was taken following a continuing review of natural lightning
data, including especially the data from airborne measurements of
intra-cloud lightning characteristics taken in the US and Europe. This
review has been conducted jointly by our committees, which are the focal
points in the US and Europe for technical aspects of aircraft lightning
standards. The multiple burst topic was reviewed in depth, for example,
at a meeting with lightning phenomenologists in conjunction with the
1991 International Conference on Lightning and Static Electricity in
April, 1991.

The Multiple Burst environment is published in the following
publications:

-   SAE Committee Report, SAE AE4L-87-3, Rev. B, \"Recommended Draft
    Advisory Circular Protection of Aircraft Electrical/Electronic
    Systems Against the Indirect Effects of Lightning\" Appendix III

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-   FAA Advisory Circular 20-136, \"Protection of Aircraft
    Electrical/Electronic Systems Against the Indirect Effects of
    Lightning\" Appendix III

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-   DOT/FAA/CT-89/22, \"Aircraft Lightning Protection Handbook\"

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-   US MIL-STD-1795A, \"Lightning Protection of Aerospace Vehicles and
    Hardware\"

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-   NASA STS 07636, Rev. A, \"Space Shuttle Lightning Criteria\"

Our committees recommend that, henceforth, the Multiple Burst
environment in the above documents be

replaced with the revised definition (description and figure), and that
the revised definition be the basis for future protection design and
certification/qualification tests or analyses.

It is further recommended that the revised Multiple Burst definition be
incorporated in future revisions of the above documents, and other
documents employing SAE AE4L or EUROCAE WG-31 criteria, at such times as
these documents are next revised or updated.

Our committee wishes to add that this recommended change should not
affect the lightning-related safety or certification status of systems
certified or qualified in accordance with the original Multiple Burst
definition. Questions regarding this recommendation may be addressed to
any of the undersigned.

Yours truly,

![](media/image1.png){width="6.495138888888889in"
height="3.202777777777778in"}

**Multiple Burst**

Component H represents a high rate of rise pulse whose amplitude and
time duration are much less than those of a return stroke. Such pulses
have been found to occur randomly throughout a lightning flash,
interspersed with the other current components. While not likely to
cause physical damage to the aircraft or electronic components, the
random and repetitive nature of these pulses may cause interference or
upset to certain systems. The recommended waveform comprises repetitive
Component H waveforms in 3 sets of 20 pulses each, as shown in the
multiple burst waveform in Figure AIII-5. The minimum time between
individual Component H pulses within a burst is 50 $\mu$s, the maximum
is 1000 $\mu$s. The 3 bursts are distributed according to the following
constraints:

The minimum period between subsequent bursts is 30 ms.

The maximum period between subsequent bursts is 300 ms.

(The above replaces the fourth paragraph on page 3 of Appendix III of
FAA AC 20-136. Other references to 24 bursts in this AC should also be
changed to 3 bursts.)

![](media/image2.png){width="5.885416666666667in"
height="7.302083333333333in"}