Apache Junction, AZ, USA
N416NV
MCDONNELL DOUGLAS DC-9-83(MD-83)
A Boeing/McDonnell Douglas MD-83 and a Cessna 182 passed within 600 feet vertically and 0.36 nautical miles laterally about 6,300 feet mean sea level. The pilots of both airplanes were in contact with air traffic control. The air traffic controller followed merging target procedures as required by Federal Aviation Administration directives and provided traffic advisories in sufficient time to be useful to both pilots. However, the pilots did not maneuver their airplanes to result in diverging flight paths and the conflict and a traffic alert and collision avoidance system resolution advisory occurred. The dark night conditions may have limited the pilots’ ability to visually identify and avoid approaching the other airplane.
On June 27, 2011, at 2058 Mountain standard time, a reported near midair collision (NMAC) associated with a Traffic Alert and Collision Avoidance System (TCAS) resolution advisory occurred when Allegiant Airlines flight 169 (AAY169), a Boeing/McDonnell Douglas MD-83, and N1421K, a Cessna 172 Skyhawk, passed within 600 feet vertically and 0.36 nautical miles laterally at approximately 6,300 feet over Apache Junction, Arizona. AAY169, a Boeing/McDonnell Douglas MD-83, was a scheduled 14 Code of Federal Regulations (CFR) part 121 passenger flight operating from Quad City International Airport, Moline, Illinois, to Phoenix-Mesa Gateway Airport (IWA), Mesa, Arizona. N1421K was a Cessna 182T operating as an unscheduled 14 CFR part 91 personal flight, landing at Falcon Field (FFZ), Mesa, Arizona. There was no reported damage to either aircraft, and no reported injuries to passengers or crew. At 2053:10, the pilot of AAY169 contacted the Phoenix Terminal Radar Approach Control (TRACON) Santan sector controller, reporting descent to 10,000 feet and requesting a visual approach to IWA. At 2053:21, the Santan sector controller cleared AAY169 for a visual approach to IWA and the pilot acknowledged. At 2057:34, the Santan sector controller transmitted “Allegiant 169 traffic at eleven to twelve o’clock, six miles northbound, a Skyhawk descending VFR out of 7,700.” The pilot acknowledged and responded they were looking for the traffic. The controller immediately transmitted the position of AAY169 to the pilot of the Cessna, who responded “Traffic in sight 21 Kilo, we are descending.” At 2058:14, the Santan sector controller transmitted “Allegiant 169, the Cessna now about eleven thirty, 3 miles, 7000 feet.” The pilot responded “Allegiant 169 I believe we have him.” Twelve seconds later AAY169 reported they were responding to a TCAS resolution advisory and were descending. The Santan sector controller again pointed out the position of AAY169 to the pilot of the Cessna, who again reported the MD83 in sight. The Santan sector controller instructed the pilot of the Cessna to “maintain separation” and the pilot acknowledged. The Cessna pilot continued descending, and the aircraft passed within 600 feet and 0.36 of a nautical mile of AAY169. At 2059:38, AAY169 advised the Santan sector controller that they had received a resolution advisory (RA) to descend followed by an RA to climb. At 2100:58, AAY169 advised they were canceling their IFR clearance and asked the controller what altitude the Cessna had been cleared to. The controller responded that the Cessna was descending under visual flight rules (VFR) into Falcon Field, outside the Class Bravo airspace. AAY169 landed at IWA without further incident. Air Traffic Procedural Requirements Traffic advisories were provided to both pilots in accordance with Federal Aviation Administration Order 7110.65, paragraphs 2-1-21 "Traffic Advisories", and 5-1-8 "Merging Target Procedures", which state in part: 2-1-21 Unless an aircraft is operating within Class A airspace or omission is requested by the pilot, issue traffic advisories to all aircraft (IFR or VFR) on your frequency when, in your judgment, their proximity may diminish to less than the applicable separation minima. Where no separation minima applies, such as for VFR aircraft outside of Class B/Class C airspace, or a TRSA, issue traffic advisories to those aircraft on your frequency when in your judgment their proximity warrants it. Provide this service as follows: a. To radar identified aircraft: 1. Azimuth from aircraft in terms of the 12-hour clock, or 2. When rapidly maneuvering aircraft prevent accurate issuance of traffic as in 1 above, specify the direction from an aircraft's position in terms of the eight cardinal compass points (N, NE, E, SE, S, SW, W, and NW). This method shall be terminated at the pilot's request. 3. Distance from aircraft in miles. 4. Direction in which traffic is proceeding and/or relative movement of traffic. 5. If known, type of aircraft and altitude. 6. When requested by the pilot, issue radar vectors to assist in avoiding the traffic, provided the aircraft to be vectored is within your area of jurisdiction or coordination has been effected with the sector/facility in whose area the aircraft is operating. ... c. For aircraft displaying Mode C, not radar identified, issue indicated altitude. 5-1-8 a. Except while they are established in a holding pattern, apply merging target procedures to all radar identified: ... 2. Turbojet aircraft regardless of altitude. ... b. Issue traffic information to those aircraft listed in subpara a whose targets appear likely to merge unless the aircraft are separated by more than the appropriate vertical separation minima. The air traffic controller issued traffic calls to both pilots. The first traffic call occurred at 2057:34, when the aircraft were 6 miles apart. The second traffic call was made at 2057:14 when the aircraft were 3 miles apart. Both pilots reported the opposing traffic in sight. When the initial traffic call was made, the C182 was descending through 7,700 feet and AAY169 was leaving 7,200 feet. When the second traffic call was made, the C182 was leaving 7,100 feet and AAY169 was leaving 6,700 feet. Twelve seconds later the pilot of AAY169 received a descend RA because the C182 traffic was above his aircraft. According to radar data, the C182 pilot increased his descent rate and quickly descended below the altitude of AAY169, causing the RA to reverse to a climb command. The area where the reported NMAC occurred is a heavily traveled north-south VFR flyway. The route crosses the flight path of IFR traffic landing at IWA. According to information provided by Phoenix TRACON and review of TCAS reports received by the NTSB, conflicts between VFR and IFR traffic in the area have been the source of multiple reported TCAS RA events. Phoenix TRACON and the Phoenix Airspace Users Workgroup (PAUWG) have recognized these conflicts and have developed several mitigation efforts. These efforts were undertaken as required by Federal Aviation Administration Order 7400.2G, “Procedures for Handling Airspace Matters,” as a precursor to a proposed rulemaking to establish Class C airspace. The order requires that non-rulemaking efforts be tried before any proposal for an airspace reclassification be considered or recommended. The first mitigation effort was the voluntary decision of area flight schools to route transiting VFR aircraft operating between Falcon Field and the south practice areas farther east of IWA and at a lower altitude. These routes were developed by plotting locations of reported TCAS resolution advisories on sectional maps and de-conflicting the routes and altitudes needed by flight schools. The routes have been moved to the east, increasing vertical separation between the IWA arrivals and the VFR traffic crossing the IWA arrival route. This effort was looked at favorably by all of the flight schools. The second mitigation effort was development of a Standard Terminal Arrival Route (STAR) into IWA by Phoenix TRACON. The PAUWG determined that publishing an arrival procedure into IWA would permit VFR users to better anticipate IFR traffic and plan maneuvers to remain clear. The STAR has been developed and will be scheduled for publication during 2012. The Phoenix Terminal Area Chart will also be modified to depict suggested VFR routes through the area to assist pilots in minimizing conflicts with IWA arrival traffic.
The failure of the pilots of both airplanes to see and avoid each other and to maneuver as advised by the air traffic controller in time to prevent the conflict that resulted in the reported near midair collision.
Source: NTSB Aviation Accident Database
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