ESDU 08006:2009

INTRODUCTION

This Data Item should be read in conjunction with the
introductory Data Item on the treatment of risk, ESDU 08003
(Reference 1) and examples of risk analysis, ESDU 08004 and 08005
(References 2 and 3).

It is easily established that a number of factors will affect
aircraft performance and these will clearly be seen inside the
Aircraft Flight Manual (AFM) or other equivalent performance
document. When operating normally the flight crew or company
dispatchers will have access to all the information necessary for
them to load the aircraft correctly and within limits, and to
establish the performance information with regard to take-off,
thereby enabling the aircraft to make a safe flight. However,
circumstances can be envisaged where an aircraft has to be
operated, for example in a war zone, where a pick-up has to be made
in a remote and dangerous area when the operator will not have
access to airport data. Such data may be ambient temperature and
may include an uncertainty about the weight of the load to be
carried by the aircraft. In more extreme circumstances the operator
may be uncertain about the length of available runway, where runway
damage or other circumstance has restricted the length, and as a
result may not have the safety benefit of engine failure
accountability within the distance actually available.

Given the above circumstances, what are the relative risks?
Given a controlled analysis can the risks be understood and
mitigated?

The above suggested "in-theatre risk" is only one case where a
fuller understanding of the relationships between parameters
critical to the performance of the aircraft is helpful. Other
examples can be suggested, for example determining the accuracy of
measurement for each parameter of a test aircraft instrumentation
system – a "sensitivity analysis", or an airline seeking a better
understanding of where economies accruing from aircraft performance
can be made.

By making use of published performance information the
sensitivity of an aircraft to variations in those data can be
established, which in turn provides a measure of the variations in
risk.

In discussing this subject it should be made very clear that
normal operations of any aircraft must be conducted in accordance
with the AFM. The exercise demonstrated within this worked example
is to show relationships within the AFM data that enable relative
risks to be expressed and is not intended to suggest alternative
un-approved modes of operation.