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Traditional reliability growth models provide assessments for two types of testing and corrective action strategies: test-fix-test and test-find-test. In test-fix-test, failure modes are found during testing and corrective actions for these modes are incorporated during the test. Data from this type of test can be modeled appropriately with the Crow-AMSAA model. In test-find-test, modes are found during testing but all of the corrective actions are delayed and incorporated after the completion of the test. Data from this type of test can be modeled appropriately with the Crow-AMSAA Projection model. However, a common strategy involves a combination of these two approaches, namely some corrective actions are incorporated during the test and some corrective actions are delayed and incorporated at the end of the test. This strategy is referred to as test-fix-find-test. Data from this test can be modeled appropriately with the Crow Extended reliability growth model, which is described next.
Recall that B failure modes are all failure modes that will receive a corrective action. In order to provide the assessment and management metric structure for corrective actions during and after a test, two types of B modes are defined. BC failure modes are corrected during the test and BD failure modes are delayed until the end of the test. Type A failure modes are defined as before; i.e. those failure modes that will not receive a corrective action, either during or at the end of the test.
Let λBD
denote the constant failure intensity for the BD failure modes and let
h(t|BD)
denote the first occurrence function for the BD failure modes. In addition,
as before, let K
be the number of BD failure modes, let di
be the effectiveness factor for the ith
BD failure mode and let 
be the average effectiveness factor.
The Crow Extended model projected failure intensity is given by: 
(9)where
λCA = λβTβ-1
is the achieved failure intensity at time Τ.
The Crow Extended model projected MTBF is: 
This is the MTBF after the delayed
fixes have been implemented. Under the extended reliability growth model,
the demonstrated failure intensity before the delayed fixes is the first
term, λCA.
The demonstrated MTBF at time Τ
before the delayed fixes is given by: 
If
you assume that there are no delayed corrective actions (BD modes) then
the model reduces to the special case of the Crow-AMSAA
model (the first term only in Eqn. (9)) and the achieved MTBF equals
the projection. That is, there is no jump. If you assume that there are
no corrective actions during the test (BC modes) then the model reduces
to the test-find-test scenario.
In the general estimation of the Crow Extended model, it is required that all failure times during the test are known. Furthermore, the ID of each A, BC and BD failure mode needs to be entered.
The estimate of the projected failure intensity for the Crow Extended
model is given by: 
(10)
where Ni
is the total number of failures for the ith
BD mode and di
is the corresponding assigned EF. In order to obtain the first term, 
,
fit all of the data (regardless of mode classification) to the Crow-AMSAA
model to estimate 
and 
, thus:
The remaining terms are analyzed with the Crow Extended model, which is applied to only the BD data.
is the
unbiased estimated of β
for the Crow-AMSAA model based on the first occurrence of M distinct BD modes.
The structure for the Crow Extended model includes the following special data analysis cases:
The growth potential and some maturity metrics for the Crow Extended model are calculated as follows.
and:
where
and 
are the estimators
of the Crow-AMSAA model for all data regardless of the failure mode
classification (i.e. A, BC or BD).
where 
and 
are the
estimators of the Crow-AMSAA model for the first occurrence of distinct
BC modes.
where NBC
is the total number of observed BC modes, MBC
is the number of unique BC modes and 
is the
MLE for the first occurrence of distinct BC modes. If 
then 
equals
zero.
(11)
