ANALYSIS: Selected NTSB Investigations Involving Wake Turbulence

December 15, 2011: Scottsdale Airport [WPR12FA067]

At 9:54AM, a Cirrus SR22 (single prop) crashed while attempting to land on Runway 03. The SR22 was inbound from Show Low [KSOW] and was instructed to make a left downwind for Runway 03. The controller was also working a Gulfstream jet, inbound for a left base to Runway 03, so the controller told the SR22 to extend downwind and look for the Gulfstream to follow. The SR22 had difficulty spotting the jet. At one point, while extending on the downwind, the SR22 pilot mentioned having the sun in his eyes, implying he was looking back toward the short final to see the jet; the controller did not clarify that the jet was in fact still on a long final. The SR22 kept extending his downwind and then made the mistake of turning his base. The turn placed the SR22 onto final, practically under the Gulfstream (the SR22 flew across final, and the Gulfstream passed this same point just 6-seconds later, and only 300′ above the SR22’s altitude). The controller delayed taking charge and climbing the SR22 away from the wake. The SR22 then turned left and continued inbound but lost control one minute later and crashed in front of a house southwest of the runway threshold. One fatality, one injured.20111215.. KSDL SR22 crash debris, view looking east

Notes & Links:

The Weather: wind was calm and skies were clear.

20111215.. KSDL SR22 crash, NMAC plotted on satellite view

Satellite view approximating the flight routes and NMAC location

20111215.. KSDL SR22 crash, Cockpit Display plots, times 09.52.24 thru 09.53.24

SR22 positions reconstructed from Cockpit Display memory

From the perspective of an experienced tower controller, this accident is almost a ‘nightmare scenario’, but may have been preventable with better ATC technique. An easy solution would have been for the controller to shorten the SR22’s approach, to land ahead of the Gulfstream onto the 8,249′ runway. For some reason, the controller locked into a sequence that extended the SR22 downwind excessively, and created conditions that helped precipitate a dangerous pilot error and NMAC. This particular SR22 flew regularly, to/from his base in Show Low. It is common in control towers for regular ‘customers’ to have a reputation with the controllers, which can bias sequencing decisions and the quality of service ATC will provide.

Here’s a series of images copied from the NTSB documents, showing radar positions of the two flights.

20111215.. KSDL SR22 crash, Flight Overview, radar plots20111215.. KSDL SR22 crash, Base Leg Turn, radar plots20111215.. KSDL SR22 crash, crop showing NMAC on final20111215.. KSDL SR22 crash, S-turns back to final and crash, cropped radar plotsHere are some key times and positions:

9:47:26 The SR22 makes his initial radio call to Scottsdale Tower, and is told to enter right traffic to Runway 03 and report five miles north. (source: ATC Factual Report, at pg.10)
9:49:11 The SR22 reports on the left downwind to Runway 03. (source: ATC Factual Report, at pg.10)
9:50:25 The Gulfstream contacts Scottsdale Tower, inbound from six miles west of the airport, VFR for a left base to Runway 03. (NOTE: the ATC transcript provided by FAA does not include radio communications with the accident pilot prior to time 9:50:46; thus, potentially critical radio communications are missing from the NTSB DMS file.)
9:50:46 ATC directs the SR22 to extend downwind to follow the Gulfstream. The SR22 acknowledges.
9:51:47 ATC clears the Gulfstream to land Runway 03.
9:51:53 ATC updates the SR22 on the position of the Gulfstream (“he just passed right to left ahead of you on base leg”) and asks the SR22 to report the Gulfstream in sight.
9:52:05 ATC again updates the SR22 on the position of the Gulfstream: “…the Gulfstream is now ahead of you and to your left, eleven o’clock and two miles, left base to final.” The SR22 replies with a comment about “…sun’s in my eyes…”. At this time of day, the sun would be positioned southeast to south of the SR22.
9:52:40 The SR22 begins a base turn. (source: Cockpit Display plots, at pg.10)
9:53:00 The SR22 crosses final and, passing under the Gulfstream flightpath, in very close proximity to 64th and Cactus. (source: Cockpit Display plots, at pg.10)
9:53:06 The Gulfstream passes over the point where the SR22 had just crossed final and begins to pull ahead of the SR22. The data indicates the Gulfstream was 300′ above the SR22. (source: Full Narrative, at ‘History of Flight’ section)
9:54:02 The last radar target for the SR22. The Gulfstream crosses this same location 30-seconds earlier, and at an altitude 150′ higher. (source: Full Narrative, at ‘History of Flight’ section)
9:54:06 An unknown pilot makes a transmission advising the tower of the accident.
  • Probable Cause (was approved 26-months later, on 2/3/14)
  • Full Narrative
  • ATC Factual Report: includes work histories, RDO’s and statements by the three controllers on duty (LC, GC, and CIC). All three had worked shifts the evening before, and returned twelve hours later to 7AM morning shifts.
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)