Page 14
Pilot’s Operating Manual
Revision A1: Nov, 2002
Hawker 800XP Pro Line 21
Section VII - SAFETY INFORMATION
The National Weather Service classifies turbulence as follows:
Thunderstorms, squall lines and violent turbulence should be regarded as extremely dangerous and
must be avoided. Hail and tornadic wind velocities can be encountered in thunderstorms that can
destroy any airplane, just as tornadoes destroy nearly everything in their path on the ground.
Thunderstorms also pose the possibility of a lightning strike on an airplane. Any structure or equipment
which shows evidence of a lightning strike, or of being subjected to a high current flow due to a strike,
or is a suspected part of a lightning strike path through the airplane should be thoroughly inspected and
any damage repaired prior to additional flight.
A roll cloud ahead of a squall line or thunderstorm is visible evidence of extreme turbulence; however,
the absence of a roll cloud should not be interpreted as denoting that severe turbulence is not present.
Even though flight in severe turbulence must be avoided, flight in turbulent air may be encountered
unexpectedly under certain conditions.
The following recommendations should be observed for airplane operation in turbulent air:
Flying through turbulent air presents two basic problems, the answer to both of which is proper
airspeed. On one hand, if you maintain an excessive airspeed, you run the risk of structural damage
or failure; on the other hand, if your airspeed is too low, the airplane may stall.
If turbulence is encountered, reduce speed to the turbulent air penetration speed or to the
maneuvering speed, which is listed in the LIMITATIONS section of the FAA Approved Airplane
Flight Manual. These speeds give the best assurance of avoiding excessive stress loads, and at
the same time provide the proper margin against inadvertent stalls due to gusts.
Beware of over controlling in an attempt to correct for changes in attitude; applying control pressure
abruptly will build up G-forces rapidly and could cause structural damage or even failure. You
should watch particularly your angle of bank, making turns as wide and shallow as possible. Be
equally cautious in applying forward or back pressure to keep the airplane level. Maintain straight
and level attitude in either up or down drafts. Use trim sparingly to avoid being grossly out of trim
as the vertical air columns change velocity and direction.
Windshear
More windshear information is provided in Section V, Sub-section 2 - ABNORMAL HANDLING.
Class of Turbulence
Effect
Extreme
Aircraft is violently tossed about and is practically impossible to control.
May cause structural damage.
Severe
Aircraft may be momentarily out of control. Occupants are thrown
violently against the belts and back into the seat. Unsecured objects are
tossed about.
Moderate
Occupants require seat belts and occasionally are thrown against the
belt. Unsecured objects move about.
Light
Occupants may be required to use seat belts, but objects in the aircraft
remain at rest.
