The following is quoted from the NTSB report of a wake turbulence accident. It was this accident that led to the existing wake turbulence guidelines now being used by the FAA and ATC.
A Delta Air Lines, Inc., DC-9-14 crashed while attempting a go-around following a landing approach to Runway 13 at Greater Southwest International Airport, Fort Worth, Texas, at 0724 central daylight time, May 30, 1972. Three Delta Air Lines pilots and one Federal Aviation Administration air carrier operations inspector, the only occupants of the airplane, sustained fatal injuries. The aircraft was demolished by fire and impact.
The DC-9 was on a training flight scheduled for the purpose of qualifying two captain trainees for type ratings in the DC-9. A McDonnell Douglas DC-10, American Airlines, Inc., Flight 1114, also on a training flight, had completed a “touch and go” landing on Runway 13 just prior to the landing approach of the DC-9. The final approach phase of the Delta DC-9 appeared normal until the airplane passed the runway threshold. At that time, the airplane began to oscillate about the roll axis. After two or three reversals, the airplane rolled rapidly to the right and struck the runway in an extreme right-wing-low attitude. Fire occurred shortly after initial impact.
The National Transportation Safety Board determined that the probable cause of the accident was an encounter with a trailing vortex generated by a preceding “heavy” jet which resulted in an involuntary loss of control of the airplane during the final approach. Although cautioned to expect turbulence the crew did not have sufficient information to evaluate accurately the hazard or the possible location of the vortex. Existing FAA procedures for controlling VFR flight did not provide the same protection from a vortex encounter as was provided to flights being given radar vectors in either IFR or VFR conditions.
As a result of the investigation of this accident, the Safety Board made eight recommendations (for wake turbulence avoidance) to the Administrator of the Federal Aviation Administration.