TM 1-1520-238-T-4
Change 9
5–53
5–21.
FLIGHT CHECK AND ADJUSTMENT USING AVA EQUIPMENT (cont)
5–21
NOTE
The AUTO weighting feature for the 6.1 software will not cause vibration
levels to increase. The WEIGHTING MODE in the Edit Defaults screen is set
to DEFAULT for the AH–64 script file. If the RESOLVE TO LIMIT feature is
utilized the WEIGHTING MODE will be automatically changed to AUTO
during the diagnostic calculations. The AVA technical manual’s definition
for the AUTO weighting mode on page 2–45 and 2–46 is incorrect. This
definition is for the old 3.1 software. The 6.1 software does not disregard
the software presets. This feature 6.1 software was changed to utilize the
script to script file presets with minor modifications. The CAUTION on page
46 and the restrictions for use of the AUTO weighting feature do not apply
for the 6.1 software.
Utilizing the MAXIMUM # OF ADJUSTMENTS from the Edit Defaults screen
a. Another method that can be utilized is to use the MAXIMUM # OF ADJUSTMENTS from the Edit Defaults
in the diagnostic menu. The AVA usually recommends multiple moves. Some of the moves are small and it may
be worthwhile to obtain a solution with fewer adjustments. Remember, every adjustment made to the rotor system
is an opportunity for an error to be introduced. In the Edit Defaults screen the MAXIMUM # OF ADJUSTMENTS is
defaulted to 0. This means that the AVA is not restricted in the number of adjustments. When using MAXIMUM
NUMBER OF ADJUSTMENTS it is recommended that RESOLVE TO LIMIT is toggled OFF and WAITING MODE
is toggled to DEFAULT. For example, let’s say the AVA is recommending 4 adjustments, and 2 of these
adjustments are small. Enter the Edit Defaults and change the MAX # of ADJUSTMENTS TO 2 and press DO,
then the EDIT ADJUSTABLES screen will appear so you can restrict the solution more if desired, but it is not
recommended. Press DO and the AVA will choose the 2 best adjustments from all of the adjustables. once the
solution is obtained compare the predictions from the default adjustments to see if the vibration environment is
going to be reduced to a satisfactory level with only 2 moves. This is a very powerful feature of the AVA, and it’s
possible that the AVA would recommend 4 moves of which 3 of them are small, and with one move you can
reduce the majority of vibration, save time, and lesson the chance of a wrong/backwards move. Many variations
of this method are utilized in the field. Whatever solution is utilized, always view the Predictions to ensure that the
vibration levels are decreasing to a satisfactory level.
b. TAB ONLY SOLUTION: One method that users have had success with is to only adjust tabs in flight. This
procedure is more to line with the manufacturers procedure which did not measure or take into account vertical
vibration levels. If this method is utilized, you must enter the EDIT ADJUSTABLES and toggle off the adjustments
for weight and pitch links, and press DO to obtain a tab only solution.
COMPARING MOVES BETWEEN FLIGHTS
It is always recommended to compare the vibration from one measurement to the next (mainly to ensure that the
aircraft is responding in a normal manner). For the FLIGHT flight plan the VERTICAL readings should be trended.
To trend more than one data set, perform the following:
With the latest flight ID picked enter the Display mode by pressing “F2”.
Select “Trend Flights” and press “DO”.
Select the desired channel to trend (usually interested in vertical readings in flight, 60K, 80K,
100K, 120K) and press “DO”.
Enter the number of test states to trend (the easiest to understand is just trend the last two flights
by entering 2, which will trend the most current flight with the previous flight), then arrow down to
“Draw Axis” and change to “NO” by pressing the “right arrow” (this will make the polar chart
easier to read), and then press DO.
