July 2, 2003: Memphis International Airport [ATL03FA115]
At 10:05AM, a Beech Baron (BE58, light twin) crashed while landing Runway 36R at Memphis International Airport [KMEM]. ATC sequenced the aircraft on final, almost two minutes behind an ERJ-145 on final to Runway 36C. ATC issued Wake Turbulence cautions, but failed to apply four-mile wake turbulence spacing for the two closely-spaced runways. The BE58 was on very short final, just seconds before touching down, when it rolled over at the runway threshold and crashed inverted in the grass to the left of the runway. Two fatalities, and two injured.
Notes & Links:
The Weather: reported at 0953, wind 290 degrees at 5 knots, visibility 10 statute miles, sky condition scattered at 3,000 feet and broken at 3,800 feet above ground level (AGL).
Runway spacing: 972′ apart; thus, ATC was required to separate the arrivals as if a single runway.
At the time of the last radar target for the ERJ-145 (on short final Runway 36C), the BE58 was 3.53 miles behind. The flight data profile shows the BE58 remained at or slightly above the ERJ-145 during most of the descent. Within the NTSB DMS, a Wake Vortex Study discusses how vortices typically travel laterally 200-300′ per minute, while dissipating on the ground, but a crosswind (as happened in this event) would push the vortex even further. The study also presents the concept of ‘vortex bounce’, where small vortices can cause the main wake vortex to bounce off the ground, climb higher, and presumably dissipate more slowly.