**ICE PELLET ALLOWANCE TIMES**

During the winter of 2006-2007, operations in ice pellets were approved
for "light ice pellets" with an allowance time of 25 minutes. That time
was based on limited research conducted late in the winter of 2005-2006
at the request of various industry groups. Additional and more
comprehensive ice pellet research was conducted jointly by the research
teams of the FAA and Transport Canada this past winter season. This
research consisted of extensive climatic chamber, wind tunnel, and live
aircraft testing with ice pellets (light and moderate) and light ice
pellets mixed with other forms of precipitation. Additionally, Type IV
anti-icing fluid with ice pellets embedded was evaluated for its aging
qualities over periods of time beyond the allowance times, when the
active precipitation time was limited to the allowance times. Results of
this research provide the basis for extended allowance times extended
allowance times for operations in light ice pellets, as well as
allowance times for operations in moderate ice pellets and light ice
pellets mixed with other forms of precipitation. Also guidance is
provided for Type IV anti-icing fluid with embedded ice pellets "aged"
beyond its allowance time when the precipitation stops at or prior to
the expiration of the allowance time.

**Operations in Light and Moderate Ice Pellets and Light Ice Pellets
mixed with other forms of precipitation.**

**(1)** Tests have shown that ice pellets generally remain in the frozen
state imbedded in Type IV anti-icing fluid, and are not absorbed by the
fluid in the same manner as other forms of precipitation. Using current
guidelines for determining anti-icing fluid failure, the presence of a
contaminant not absorbed by the fluid (remaining imbedded) would be an
indication that the fluid has failed. These imbedded ice pellets are
generally not readily detectable by the human eye during pre-takeoff
contamination check procedures. Therefore, a visual pre-takeoff
contamination check in ice pellet conditions may not be of value and is
not required.

**(2)** The research data have also shown that after proper deicing and
anti-icing, the accumulation of light ice pellets, moderate ice pellets,
and ice pellets mixed with other forms of precipitation in Type IV fluid
will not prevent the fluid from flowing off the aerodynamic surfaces
during takeoff. This flow due to shearing occurs with rotation speeds
consistent with Type IV anti-icing fluid recommended applications for up
to the applicable allowance time listed in Table-1. These allowance
times are from the start of the Type IV anti-icing fluid application.
Additionally, if the ice pellet condition stops, and the allowance time
has not been exceeded, and the OAT has remained constant or increased
from the temperature on which the allowance time was based, the operator
is permitted to consider the Type IV anti-icing fluid effective without
any further action up to 90 minutes after the start of the application
time of the Type IV anti-icing fluid.

> Examples: a) Type IV anti-icing fluid is applied with a start of
> application time of 10:00, OAT is 0^0^C, light ice pellets fall until
> 10:20 and stop and do not restart. The allowance time stops at 10:50;
> however, provided that the OAT remains constant or increases and that
> no precipitation restarts after the allowance time of 10:50 the
> aircraft may takeoff without any further action up to 11:30.
>
> b\) Type IV anti-icing fluid is applied with a start of application
> time of 10:00, OAT is 0^0^C, light ice pellets mixed with freezing
> drizzle falls until 10:10 and stops and restarts at 10:15 and stops at
> 10:20. The allowance time stops at 10:25, however provided that the
> OAT remains constant or increases and that no precipitation restarts
> after the allowance time of 10:25, the aircraft may takeoff without
> any further action up to 11:30.
>
> c\) On the other hand, if Type IV anti-icing fluid is applied with a
> start of application time of 10:00, OAT is 0^0^C, light ice pellets
> mixed with freezing drizzle falls until 10:10 and stops and restarts
> at 10:30 with the allowance time stopping at 10:25 the aircraft **may
> not takeoff,** no matter how short the time or type of precipitation
> after 10:25, without being deiced and anti-iced if precipitation is
> present.

**(3)** Operators with a deicing program approved in accordance with
Title 14 of the Code of Federal Regulations (14 CFR) part 121,
section 121.629, will be allowed, in the specified ice pellet conditions
and corresponding outside air temperatures (OAT) listed in Table-1 "Ice
Pellet Allowance Times Winter 2007-2008", up to the specific allowance
time listed in Table-1 after the start of the anti-icing fluid
application to commence the takeoff with the following restrictions:

**(a)** The aircraft critical surfaces must be free of contaminants
before applying Type IV anti-icing fluid. If not, the aircraft must be
properly deiced and checked to be free of contaminants before the
application of Type IV anti-icing fluid.

**(b)** The allowance time is valid only if the aircraft is anti-iced
with undiluted Type IV fluid.

**(c)** Due to the shearing qualities of Type IV fluids with imbedded
ice pellets, this allowance is limited to aircraft with a rotation speed
of 100 knots or greater.

**(d)** If the takeoff is not accomplished within the applicable
allowance time in Table-1, the aircraft must be completely deiced, and
if precipitation is still present, anti-iced again prior to a subsequent
takeoff. If the precipitation stops at or before the time limits of the
applicable allowance time in Table-1 and does not restart the aircraft
may takeoff up to 90 minutes after the start of the application of the
Type IV anti-icing fluid provided the temperature on which the allowance
time was based remains constant or increases.

**(e)** A pre-takeoff contamination check is not required. The allowance
time cannot be extended by an internal or external check of the aircraft
critical surfaces.

**(f)** If ice pellet precipitation becomes heavier than moderate or if
the light ice pellets mixed with other forms of allowable precipitation
exceeds the listed intensities or temperature range, the allowance time
cannot be used.

**(g)** If the temperature decreases below the temperature on which the
allowance time was based,

**1.** And the new lower temperature has an associated allowance time
for the precipitation condition and the present time is within the new
allowance time, then that new time must be used as the allowance time
limit.

**2.** And the allowance time has expired (within the 90 minute post
anti-icing window if the precipitation has stopped within the allowance
time), the aircraft may not takeoff and must be completely deiced and,
if applicable, anti-iced before a subsequent takeoff.

**Table 1. Ice Pellet Allowance Times**

  -------------------------------- ----------------- --------------------
                                   **OAT ‑5^0^ C or  **OAT Colder Than
                                   Warmer**          ‑5^0^ C**

  **Light Ice Pellets**            50 Minutes        30 Minutes

  **Moderate Ice Pellets**         25 Minutes        10 Minutes

  **Light Ice Pellets Mixed with   25 Minutes        Operations Not
  Light or Moderate Snow**                           Authorized

  **Light Ice Pellets Mixed with   25 Minutes        10 Minutes
  Light or Moderate Freezing                         (Operations Not
  Drizzle, or Light Freezing                         Authorized below
  Rain** (Operations not                             ‑10^o^ C OAT)
  authorized below ‑10^o^ C OAT)                     

  **Light Ice Pellets Mixed with   25 Minutes        (Operations Not
  Light Rain** (Operations not     (Operations Not   Authorized below
  authorized below 0^o^ C OAT)     Authorized below  0^o^ C OAT
                                   0^o^ C OAT)       
  -------------------------------- ----------------- --------------------