Caution, wake turbulence: What do you do?

Most general aviation pilots know they need to maintain a safe distance from larger aircraft during approach and landing. The question that arises is "how much distance?" On July 2, 2003, the pilot of a Beechcraft Baron and one of his passengers were killed during an encounter with wake turbulence while on approach to Runway 36R at Memphis International Airport. Two passengers also were seriously injured in the accident.

The pilot of the Baron was in contact with Memphis Approach and was told to expect the ILS to Runway 36R. The Baron was then asked to slow down to 170 knots and was cautioned about wake turbulence from an Embraer 145 Regional Jet on approach to Runway 36C about four miles ahead. The Baron was then vectored and cleared for the ILS Runway 36R approach.

A pilot taxiing between Runways 36R and 36C saw the Baron on final approach and stated that it was about 10 to 15 feet above the runway and "had it made." The Baron then yawed and rolled to the left, appearing to try a sidestep maneuver to the other runway. The plane then pitched up about 15 degrees, abruptly rolled to the left, and hit the ground inverted.

The investigation revealed that the Baron was about 3.5 miles behind the ERJ and that the "wake vortex of the ERJ 145, in particular the right wing tip vortex (downwind counterclockwise rotating), could have migrated toward the Baron's flight path. An airplane's typical response to a counterclockwise rotating wake vortex would be to roll to the left."

The Air Traffic Controller's Handbook (FAA Order 7110-65P) states that runways that are less than 2,500 feet apart should be treated as a single runway because of the possible effects of wake turbulence, and that for a small aircraft landing behind a large aircraft, the separation should be four miles.

The NTSB determined the cause of this accident was the encounter with wake turbulence on approach, which resulted in the pilot's inability to maintain control.

According to the Aeronautical Information Manual (AIM), when landing behind a larger aircraft (including one on a parallel runway within 2,500 feet), stay at or above the larger aircraft's final approach flight path, note its touchdown point, and then land beyond it.

To learn more about wake turbulence and how to avoid it, take the AOPA Air Safety Foundation's Wake Turbulence Sporty's Safety Quiz, and read Bruce Landsberg's "Wake Turbulence: Should You Worry?" from the October 1998 issue of AOPA Pilot magazine