1. Meteorological conditions contributing to the crash of a Boeing 737 at Denver International Airport
Workshop on Aviation Turbulence
28 August 2013 NCAR, Boulder, CO
Teddie Keller
Bill Hall, Stan Trier, Bob Sharman, Larry Cornman, and Yubao Liu
Research Applications Lab
National Center for Atmospheric Research
Boulder, CO

2. Denver Int. Airport accident
20 Dec MST (21 Dec UTC )
Boeing departed left side runway 34R during take-off
Strong westerly crosswinds at time of accident
34R 2

3. Denver Int. Airport accident
20 Dec MST (21 Dec UTC )
Boeing departed left side runway 34R during take-off
Strong westerly crosswinds at time of accident
34R 3

4. Denver International Airport LLWAS wind sensor network (pink circles):
Runway 34 R (350.9o magnetic) 2 3 29

5. LLWAS winds 1:13 – 1:23 UTC (+/- 5 min of accident)x
Cornman, Weekley

7. DIA – located east of Rocky Mtns:
DIA lat , lon
**Mountain induced gravity waves common over Rockies

8. Mountain waves and windstorms
From Lilly 1978
Windstorm 11Jan1972
Solid lines – potential temperature
Large amplitude wave
+ marks where aircraft encountered turbulence
Note turbulence near Stapleton (under lee waves in stable layer)

9. Visible satellite 2030 UTC 20 Dec 2008
Persistent clear notch near Denver
Probably due to descending air in mountain wave
Meteorological conditions:
Strong westerly winds near mountain top
Stable layer above mountain top
Vertical speed shear

10. Turbulent pilot reports (PIREPs):
Mountain waves with turbulence in blue
18 UTC 20 Dec - 06 UTC 21 Dec 2008
Significant turbulence reported
Severe to extreme turbulence within 3 minutes of accident
Moderate to severe mountain waves over Rockies
Associated with altitude and airspeed changes
Waves encountered from 8,000 to 40,000 ft

11. Example pilot reports:
B /RM MOD MTN WAVE +/- 15 KT AND 200 FT UDDFS
MD /TB SVR
B /RM MOD MTN WAVE KTS
B /RM LGT-MOD MTN WAVE +/-500 FT
CL /RM MOD MTN WAVE +/-200 FT
BE /TB MOD /RM STRONG MT WAVE
A /TB MDT MTN WAVE/RM KTS
LJ /TB MDT MTN WAVE/RM KT
LJ /TB SEV-EXTREME FL
LJ /TB SEV-EXTRM

12. Numerical simulation of meteorological conditions on the day of the accident
Allows examination of three-dimensional structure of atmospheric flow
Can help determine if gustiness at DIA possibly due to large amplitude mountain waves
However - can not resolve exact strength and timing of gusts

13. Topography inner domain
Clark-Hall nonlinear, nonhydrostatic model
5 nested domains
Inner domain 250 m horizontal resolution
Outer domain initialized with RUC data (20 Dec :00 UTC)
RUC 1 hr data used to drive boundary conditions
Vertical grid stretching
Domain 5 run 00: :51 UTC with 1 min output X
Topography inner domain

14. East-west wind U - vertical slicex
X marks incident site
Note regions of high velocity air moving downward
Strong wave signature in potential temperature (black lines)
X-Z slice at latitude 39.88
Inner domain 5
cont int 5.0 m/sec
1:00 – 1:39 UTC (+/- 20 minutes)

15. East-west wind U at 14.7 m AGL
X marks incident site
Red arrows -LLWAS winds
Black arrows – model winds
Runways– black lines
Pink colors easterly flow
Part of domain 5
cont int 2.5 m/sec
1:00 – 1:39 UTC (+/- 20 minutes)

16. High resolution Clark-Hall model results show:
Lee waves in stable layer above DIA
Amplification of lee waves associated with downward penetration of high velocity air
Creates localized gustiness at airport
May or may not be a common occurrence

17. High resolution Clark-Hall model results show:
Lee waves in stable layer above DIA
Amplification of lee waves associated with downward penetration of high velocity air
Creates localized gustiness at airport
May or may not be a common occurrence
Are operational models high enough resolution to capture this event?

18. Resolution similar to HRRR X-Z slice at 1:30 UTC U wind speed (color)
WRF model control simulation – 3 km horizontal resolution; single domain
Resolution similar to HRRR
X-Z slice at 1:30 UTC
U wind speed (color)
Wave over mountains
Small wave downstream
But high velocity air not penetrating to the ground near DIA X
Near Time of Incident (0130 UTC)

19. WRF Simulations – control vs higher horizontal resolutionX
Near Time of Incident (0130 UTC)
Near Time of Incident (0132 UTC)
Control D = 3.3 km
D = 367 m

20. Conclusions
Both Clark-Hall and high resolution WRF simulations showed amplifying lee waves above DIA associated with higher velocity air penetrating close to the ground.
For this event need higher resolution than current operational model (HRRR).
Is it possible to forecast conditions favorable for this phenomena:
From low resolution model output?
From wind sensor data (LLWAS)?
This research is in response to requirements and funding by the Federal Aviation Administration (FAA). The views expressed are those of the authors and do not necessarily represent the official policy or position of the FAA.

21. backup

22. WRF higher resolution run
WRF version 3.4
Nested domains
Inner domain 367 m horizontal resolution
MYJ PBL
WSM 6-class microphysics
Noah land model
RRTM (Rapid Radiative Transfer Model) longwave
Goddard shortwave radiation schemes
Horizontal mixing - Smagorinsky type diffusion

23. DIA numerical model configuration
Clark-Hall 3-D nonlinear, nonhydrostatic terrain-following numerical model
Initialized with 22:00 UTC RUC data (20 Dec 2008)
5 nested domains:
domain DX, DY NX NY NZ domain started
km :00 UTC
km :00 UTC
km :00 UTC
km :00 UTC
km :30 UTC
Grid stretched in the vertical; domains 3-5 have 2:1 increase in z resolution compared with domains 1 and 2
Domain 5 run to 01:51 with 1 min output
RUC 1 hour data used to drive boundary conditions