ANALYSIS: Selected NTSB Investigations Involving Wake Turbulence

June 12, 2006: Kansas City International Airport [CHI06FA154]

At 7:11PM, a Piper Saratoga (PA32, single prop) crashed while on approach to the Kansas City International Airport [KMCI], killing two dentists from Colorado. ATC had cleared the PA32 for a Visual Approach to Runway 01L, at the same time that a Boeing B737 was being vectored on an approach to Runway 01R. ATC vectored the PA32 to cross under the B737’s flightpath in two locations, but issued no Wake Turbulence Advisory. At the second location, the PA32 was at 3,300′ and nearly two-minutes behind where the B737 had passed at 3,900′. The left wing and portions of the right wing and empennage separated in flight. Two fatalities.

Notes & Links:

The Weather: wind 050 degrees at 8 knots, visibility 10 statute miles, scattered clouds at 3,000′ above ground level (AGL), broken clouds at 20,000′ AGL.

20060612.. KMCI PA32 WakeTurb upset, sketch

The red arrow marks the approximate route of the PA32, on a 280 heading; the blue arrow shows the B737 route, on base and final. Crossings #1 and #2 are marked in yellow.

The B737 was southbound turning right downwind to right base when traffic was issued to the PA32. The scattered cloud layer apparently prevented the PA32 pilot from seeing the B737. No traffic sighting was made and ATC later told the PA32 pilot that traffic was no factor.

ATC put the PA32 on a heading of 280, but then tightened spacing with a heading of 300. This 300 heading caused the PA32 to cross under the B737 flight route in two locations. The second crossing caused the fatal upset.

The first (non-upset) crossing occurred at 1910:48PM, with the PA32 at 3,900′ and 2-minutes nine-seconds after the B737 passed at 5,500′.

The second (upset) crossing occurred at 1911:25PM, with the PA32 at 3,300′ and 1-minutes 55-seconds after the B737 passed at 3,900′. The upset caused the left wing and portions of the right wing and empennage to separate in flight.

At the time of the upset, the B737 was heading NNW, and the PA32 was heading ‘NW’ (heading 300); thus, in that location, they were essentially flying the same route, with the B737 turning base to final for Runway 10R and the PA32 on a long diagonal to final while on a Visual Approach to Runway 10L.

The Full Narrative cites AC 90-23, mentioning wake descent rates of a few hundred feet per minute. Thus, two-minutes in trail and 600′ below while tracking essentially the same heading puts the PA32 squarely in the descending wake of the B737.

The Full Narrative also claims that the PA32 pilot exceeded safe maneuvering speeds (up to 183 KCAS), but NTSB offers no evidence to support this claim. Plausibly, these speeds are not true data but are crude calculations by the radar system based on imprecise target locations.

The ATC regulations at FAA Order 7110.65 para 5-5-4(e) and (f) require that a small aircraft must be at least 4-miles in trail at the time a leading large aircraft crosses the runway threshold. In general terms, this 4-mile spacing is equivalent to 2-minutes in-trail. Oddly, this regulation applies to landing, but not to flights at altitude. Thus, it appears that FAA’s regulations do not restrict a controller from passing a small aircraft directly under the flightpath of a large aircraft with any time or distance separation.

20060612.. KMCI PA32 WakeTurb upset, debris pic

Main debris, in a soybean field south of KMCI

In this incident, the post-accident data analysis shows that the wake behind a B737 remains lethally powerful for minutes, thus FAA needs to add a rule against vectoring into wake turbulence.

  • Probable Cause (was approved 14-months later, on 8/30/07)
  • Full Narrative
  • NTSB DMS files — (there is no DMS folder for this case; why not?)
  • StuckMic: A lengthy online-discussion (including many controllers) about wake turbulence separation on radar arrivals
pg.1 Overview
pg.2 7/2/03: BE58 landing at Memphis, TN
pg.3 6/12/06: PA32 on approach to Kansas City, MO
pg.4 12/15/11: SR22 landing at Scottsdale, AZ
pg.5 7/27/13: PA28 overflight at Lake Michigan (near Milwaukee, WI)