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• August 13, 2017 Create Date
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Consolidation and Analysis of Loading Data in Firefighting Operations - Analysis of Existing Data and Definition of Preliminary Air Tanker and Lead Aircraft Spectra

This report proposes normal acceleration spectra for airplanes used in firefighting and lead roles.
Spectra for heavy, medium, and light airplanes are provided and compared. These spectra were
based exclusively on data, which were obtained a number of years ago. There are, however, a
number of issues regarding the use of the spectra contained in this report, which need to be
addressed, explained, and considered.

The report suggests that a severity factor for firefighting operations can be derived. Although
this is true, such a factor assumes that the internal stress levels in the structure do not change as a
result of the addition of tank(s) filled with fire-retardant chemicals. Although this report does
not attempt to address the load redistribution to the aircraft structure due to the addition of the
tank(s), regulatory authorities are well aware that this issue is recognized to be an important
consideration for the continued safe operation of these airplanes. For example, during the
analysis of the conversion of the DeHavilland DASH-8 for firefighting operations, a load case
became critical (was not originally) such that the aircraft would not be able to meet the
certification requirements. When similar circumstances exist for other aircraft modified for
firefighting operations, the operator must ensure that the stress cycles associated with the new
configuration are computed and not ignored. Without adequate knowledge of the new load
distribution, the increase in stress would go unnoticed and the use of a simple severity factor
would be inappropriate. This report does, however, adequately describe the extent to which the
number of load occurrences in the firefighting role can be directly measured and subsequently
compared to a normal acceleration spectrum of these aircraft during prior service.

In the past, the severity factor was generally applied to a Supplemental Inspection Document
without any investigation of additional locations that may have now become more severe. One
of the suggestions made in this report is for continuous loads monitoring to be done for the life of
the aircraft equipped with strain gauges sufficient to estimate stress for all major aircraft
components. Should an applicant be required to monitor his aircraft continuously, the cost may
be prohibitive; should a large number of strain gauges be required, their long—term reliability will
come into question. Thus, the argument of economic burden would play a large role in the use of
such a process. Alternatives to this approach need to be investigated and researched and cost—
effective measures implemented.