Meteorological conditions contributing to the crash of a Boeing 737 at Denver International Airport

Teddie Keller

Bill Hall, Stan Trier, Bob Sharman, Larry Cornman, and Yubao Liu

Research Applications Lab

National Center for Atmospheric Research

Boulder, CO

Workshop on Aviation Turbulence 28 August 2013 NCAR, Boulder, CO

Denver Int. Airport accident

20 Dec 2008 - 1818 MST (21 Dec 2008 - 0118 UTC )Boeing 737-500 departed left side runway 34R during take-offStrong westerly crosswinds at time of accident

34R

Denver Int. Airport accident

20 Dec 2008 - 1818 MST (21 Dec 2008 - 0118 UTC )Boeing 737-500 departed left side runway 34R during take-offStrong westerly crosswinds at time of accident

34R

Denver International AirportLLWAS wind sensor network (pink circles):

Runway 34 R (350.9o magnetic)

2

3

29

LLWAS winds 1:13 – 1:23 UTC (+/- 5 min of accident)

x

Cornman, Weekley

LLWAS wind speed (kts) - 0:30 - 2:00 UTC

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Time UTC 21 Dec 2008

Win

d s

pee

d (

kts)

Station 29 sp Station 2 sp Station 3 sp

DIA lat 39.8617, lon -104.6732

DIA – located east of Rocky Mtns:

**Mountain induced gravity waves common over Rockies

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)

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

Turbulent pilot reports (PIREPs): Mountain waves with turbulence in blue

• 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

18 UTC 20 Dec - 06 UTC 21 Dec 2008

20081220 1510 B737 37.75 -103.69 37000 /RM MOD MTN WAVE +/- 15 KT AND 200 FT UDDFS

20081220 1820 MD80 35.11 -105.04 26000 /TB SVR

20081220 2120 B737 35.11 -105.04 37000 /RM MOD MTN WAVE +- 15 KTS

20081220 2142 B737 39.41 -108.33 39000 /RM LGT-MOD MTN WAVE +/-500 FT

20081220 2240 CL60 39.40 -105.82 40000 /RM MOD MTN WAVE +/-200 FT

20081220 2255 BE35 39.57 -104.85 8000 /TB MOD /RM STRONG MT WAVE

20081220 2256 A319 36.77 -104.64 37000 /TB MDT MTN WAVE/RM + - 15 KTS

20081220 2256 LJ45 36.80 -104.71 47000 /TB MDT MTN WAVE/RM -+ 15 KT

20081221 0115 LJ25 40.36 -105.44 17000-19000 /TB SEV-EXTREME FL190-170

20081221 0118 LJ25 40.62 -105.12 19000 /TB SEV-EXTRM

Example pilot reports:

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

X

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 2008 22:00 UTC)

• RUC 1 hr data used to drive boundary conditions

• Vertical grid stretching

• Domain 5 run 00:30 - 01:51 UTC with 1 min output

East-west wind U - vertical slice

cont int 5.0 m/sec

x

• 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

1:00 – 1:39 UTC (+/- 20 minutes)

East-west wind U at 14.7 m AGL

cont int 2.5 m/sec

• X marks incident site• Red arrows -LLWAS

winds• Black arrows – model

winds• Runways– black lines• Pink colors easterly

flow• Part of domain 5

1:00 – 1:39 UTC (+/- 20 minutes)

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

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?

X

Near Time of Incident (0130 UTC)

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

WRF Simulations – control vs higher horizontal resolution

D = 367 m

X X

Near Time of Incident (0130 UTC) Near Time of Incident (0132 UTC)

Control D = 3.3 km

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.

backup

WRF higher resolution run

WRF version 3.4 Nested domainsInner domain 367 m horizontal resolutionMYJ PBL WSM 6-class microphysicsNoah land model RRTM (Rapid Radiative Transfer Model) longwaveGoddard shortwave radiation schemesHorizontal mixing - Smagorinsky type diffusion

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---------- ---------- ---- ----- ------ --------------------- 1 18 km 130 194 81 22:00 UTC 12-20-08 2 6 km 194 290 140 22:00 UTC 3 3 km 194 290 134 23:00 UTC 4 1 km 290 434 128 00:00 UTC 12-21-08 5 .25 km 587 866 122 00:30 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