JPATS Weather - NETC

JPATS AVIATION WEATHER BOOKLET
Most lightning strikes occur when aircraft are operating in one or more of the following
conditions:
1. Within 8° C of the freezing level
2. Within approximately 5000 feet of the freezing level
3. In precipitation, including snow
4. In clouds
5. In some turbulence
It should be noted that not all these conditions need to occur for a lightning strike or an
electrostatic discharge to take place.
Figure 5-4 — Lightning Hazards
Lightning strikes have varied effects on aircraft and aircrews (Figure 5-4). Usually the structural
damage is minor, but it has the potential to be severe. Normally, it will only interrupt electrical
circuits, causing damage to aircraft electrical systems, instruments, avionics, or radar.
Catastrophic fuel ignition can occur under certain conditions. In non-pressurized fuel tanks, a
mixture of vaporized fuel and air fills the space above the liquid fuel. The proper ratio of fuel
vapor to air can form a highly explosive mixture. For this reason, as well as for battle
survivability, most military aircraft fuel tanks are pressurized.
Pilots are not immune to the effects of lightning strikes, either. Temporary night vision
degradation can occur due to flash blinding, but this effect can be minimized by turning cockpit
lighting to maximum intensity. Some pilots have also experienced mild electric shock and minor
burns.
Tornadoes
A tornado is a violent, intense, rotating column of air that descends from cumulonimbus clouds
in funnel-like or tube-like shapes. If the circulation does not reach the surface, it is called a
funnel cloud. If it touches down over the water, it is called a waterspout. A tornado vortex is
normally several hundred yards wide, but some have been measured up to 2½ miles wide. Within
the tornado’s funnel-shaped circulation, winds have been measured at speeds over 300 miles per
hour, while the forward speed of tornadoes averages 30-40 knots.
5-4 Version 3.2/Dec 08