GROUND SERVICING
AIRPLANE
OPERATIONS
MANUAL
1-12-20
Page
4
Code
01
REVISION 38
AOM-145/1114
Holdover times should be seen as rough approximations. They simply
reflect the average, estimated time an anti-icing fluid should prevent
the formation of frozen contaminants on the protected surfaces. Actual
holdover times can be reduced or extended due to many factors
influencing fluid effectiveness, such as high wind velocity, jet blast,
heavy precipitation rates or high moisture content. Recommended
practice is to use holdover times in conjunction with a pre-takeoff
check to ascertain that frozen deposits have not started to accumulate
on treated surfaces. This is a check normally conducted from inside
the cockpit.
The pre-takeoff contamination check is normally accomplished from
outside the airplane when the airplane cannot be effectively inspected
by a pre-takeoff check or when the holdover times has been
exceeded. The pilot-in-command must ask for the assistance of
trained and qualified ground personnel to assist in the pre-takeoff
contamination check, so that wing, empennage and fuselage, which
are not visible from the cockpit or cabin, can also be inspected. If
contamination is suspected, the airplane should be returned for
additional deicing or anti-icing. For practical results, the holdover time
must be equal to or greater than the estimated time from start of anti-
icing to start of takeoff based on existing weather conditions.
Ensure that deicing and anti-icing are performed at the latest possible
time before taxiing to the takeoff position. Always takeoff before hold-
over time expires, so as to minimize the period when the airplane
stays in line for takeoff and is exposed to contamination. Hold-over
time should not be considered an exact figure. It is just an average
time, which can be reduced by many factors affecting the fluid
effectiveness. In the case of ice build-up after deicing/anti-icing fluid
application, do not assume that ice will be blown off during takeoff roll.
Ask for deicing/anti-icing fluid reapplication. If the hold-over time
expires, carry out a pre-takeoff contamination check and another
deicing/anti-icing fluid application is required.
No holdover time guidelines exist for the conditions of snow pellets,
snow grains, ice pellets, moderate and heavy freezing rain and hail. In
such, takeoffs in snow pellets, snow grains, ice pellets or hail must be
preceded by a careful contamination check shortly before takeoff.
Takeoff in conditions of moderate and heavy freezing rain is not
approved.
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