Final Report: Severe turbulence exceeded airframe limits

 - October 10, 2007, 11:31 AM

ROCKWELL AERO COMMANDER 690B, HOMERVILLE, GA., MARCH 27, 2003–An in-flight encounter with unforecast severe turbulence resulted in the design limits of Aero Commander 690B N53LG being exceeded an overload failure of the airframe, concluded the NTSB. The airplane was at 27,000 feet when the turbulence was encountered and the pilot called “Mayday” to Jacksonville Center. Within several seconds, the airplane accelerated from 175 knots through 300 knots groundspeed and descended to 16,500 feet. The airplane disappeared from radar coverage and crashed in a swampy area 15 miles north of Homerville. The crash debris line extended for 8,081 feet. Examination of the airframe components revealed all failures were due to overload and the airframe design limits were exceeded. Although the aircraft was on an IFR flight plan from Mount Pleasant, Tenn., to Titusville, Fla., and in IMC, the pilot did not obtain a weather briefing.

The accident site was located south of a stationary front and downstream of a low-pressure system.

A subtropical jet stream was depicted over central Florida to the south of the accident site with indicated winds of 125 knots at 30,000 feet, which resulted in an approximately 60 knots per 150 miles horizontal wind shear from the accident site to the maximum wind across central Florida. Between 24,100 feet and 31,000 feet, there was a 100-percent probability of severe turbulence.

The satellite data imagery surrounding the time of the accident depicted a large area of high “cirrostratus” type cloud cover that was indicated by enhanced colors over eastern Georgia, and northern Florida, which extended over the accident site. The cloud band had a defined edge located approximately 30 miles west and northwest of the accident site which corresponded to cloud tops near 33,000 feet.

Review of in-flight weather advisories revealed there were no areas of organized turbulence forecast.

Paroxetine, an antidepressant, was detected in the body of the pilot, but was not considered a factor.