5. 5 September 1996; Air France 747-400; near Ouagadougou, Burkina Faso: Severe turbulence associated with a weather front seriously injured three of the 206 passengers. One of the three passengers later died of injuries caused by an in flight entertainment screen.
g
Ri

z V 2

z
Lapse rate Wind shear
Kelvin Helmholtz Wave
Breakdown
• For Ri less than .25, flows become turbulent.
• Seldom observe Ri=.25 in atmospheric flows.
• The following are events involving in flight turbulence where at least one jet airliner passenger was killed.
1. 10 May 1980; Indian Airlines 737-200; near Rampur Hat, India: The aircraft experienced severe en route turbulence. Two of the 132 were killed.
• Clear Air Turbulence Index Forecasts • EMC/NCEP SREF home page
Other Factors in CAT
• Classical Kelvin Helmholtz waves may not account for all observed CAT.
1. Vertical wind shear 2. Horizontal wind shear 3. Convergence 4. Horizontal deformation (i.e. fronts) 5. Lapse rate discontinuities (i.e. inversions) 6. Strong horizontal thermal gradients (i.e.
Wind Shear
• Vertical wind shear can cause instability that curls the air around a horizontal axis.
Kelvin Hemholtz Turbulence
Richardson Number
• Richardson number Ri =stability over wind shear squared.
thermal wind shear)
Ellrod Index Strengths
• Easy to compute, easy to understand. • Has a good track record of defining
existence of turbulence (but not strength). • Widely available.
• Extreme Turbulence: Aircraft is violently tossed about and is practically impossible to control; may cause structural damage or injury.
Fatal Turbulence Events Since 1980
• Moderate Turbulence: Similar to light turbulence but of greater intensity. Changes in altitude and/or attitude occur but the aircraft remains in positive control at all times; usually causes variations in indicated airspeed.
6. 28 December 1997; United Airlines 747-100; over Pacific Ocean near Japan: The aircraft encountered severe turbulence during cruise about two hours after departing Japan. One of the 346 passengers was killed. None of the 23 crew members were killed but three sustained serious injuries.
• Ri typically .5 to 10 near where turbulence is observed.
• The lower the Ri, the better chance of having turbulence.
Ellrod Index
• Based on observations that Clear Air Turbulence (CAT) is frequently found near:
2. 7 October 1981; NLM CityHopper F28-4000; Moerdijk, Netherlands: Shortly after takeoff, the aircraft entered an area of severe thunderstorm activity. The aircraft apparently had a catastrophic in flight structural failure due to severe turbulence because it was seen to emerge from the clouds with one of its wings broken away. All four crew members and 13 passengers were killed.
Common Forms of Turbulence
• Boundary Layer Turbulence • Clear Air Turbulence • Mountain Wave Turbulence • Cloud Updrafts (Thunderstorms) • Wake Turbulence
• Moderate Chop: Causes rapid bumps or jolts without appreciable changes in aircraft altitude or attitude
• Severe Turbulence: Causes large, abrupt changes in altitude or attitude; usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control.
Boundary Layer
Continental Boundary layer diurnal cycle
Boundary layer profiles from DOE ARM SODARs (acoustic sounders)
wind profile
Aviation Turbulence
US-China Aviation Cooperation Program (ACP)
Embry-Riddle Training Debbie Schaum
AMS Turbulence Definition
• aircraft turbulence—Irregular motion of an aircraft in flight, especially when characterized by rapid up-anddown motion, caused by a rapid variation of atmospheric wind velocities. This can occur in cloudy areas (particularly towering cumulus and lenticular clouds) and in clear air. Turbulence is the leading cause of nonfatal passenger and flight attendant injuries.
3. 16 August 1982; China Airlines 747; near Hong Kong: The aircraft encountered severe in flight turbulence. Two of the 292 passengers were killed.
4. 3 October 1990; Eastern DC9-31; Florida, USA: The aircraft clear air turbulence at 31,000 feet. One injured passenger died three weeks later.
• Use analysis of surface lapse rate and winds
Boundary Layer Turbulence Summary
• Occurs due to surface heating and convection so most prominent during heat of the day