Investigation Summary
The DC-9 was operating under Instrument Flight Rules (IFR) and was under positive radar control, descending from 6,000 feet to an assigned 2,500 feet. The Piper PA-28 was being flown by a student pilot on a solo cross-country flight under Visual Flight Rules (VFR) at 3,500 feet. Although visibility was 15 miles, intervening clouds and the relative positions of the aircraft prevented the crews from seeing each other until seconds before impact. The Indianapolis approach controller did not observe the Piper's primary radar target, which lacked a transponder, and thus did not issue a traffic advisory to the DC-9 crew.
Final Conclusions
The NTSB determined the probable cause was the deficiency in the collision avoidance capability of the ATC system in a terminal area with mixed IFR and VFR traffic. Contributing factors included the inadequacy of the see-and-avoid concept, technical limitations of radar in detecting small aircraft without transponders, and the lack of regulations providing adequate separation for mixed traffic in terminal areas.
Video Analysis
An Almost Forgotten Crash That Made Flying Safer | Allegheny Airlines Flight 853 — The story of Allegheny Airlines Flight 853 and the mid-air collision over Indiana that led to significant changes in air traffic control and terminal area regulations.
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Airframe & Maintenance
Allegheny Airlines AL853 — McDonnell Douglas DC-9-31 · N988VJ
Crew Experience
Captain
Captain James M. Elrod
First Officer
First Officer William T. Heckendorn
Student Pilot
Robert N. Carey
Systems & Failure Modes
See-and-Avoid
The primary method of collision avoidance for VFR flight, which proved inadequate due to closure speeds and cloud interference.
Primary Radar
The ATC radar relied on physical reflections for the Piper, which were insufficient for the controller to identify the conflict.
Horizontal Stabilizer
The DC-9's T-tail stabilizer was destroyed in the collision, rendering the aircraft unflyable.
Interesting Facts
- 01The DC-9's tail assembly was sheared off by the Piper's left wing, leading to an immediate loss of control.
- 02The DC-9 impacted the ground in an inverted, nose-down attitude.
- 03The Piper PA-28 was not equipped with a transponder, making it difficult to detect on the radar systems of the era.
- 04The collision occurred just two seconds after the DC-9 first officer likely made a required 3,500-foot altitude call.
- 05The student pilot of the Piper was wearing glasses and had his anti-collision beacon on at departure.
Safety Actions & Advisories
Radar Reflectivity Standards
The NTSB recommended establishing minimum standards for the radar reflectivity of small aircraft to improve detection.
Scanning Training
Mandatory aircrew training programs were recommended to improve effective visual scanning patterns and procedures.
Terminal Area Separation
The accident accelerated the development of Terminal Control Areas (now Class B airspace) to strictly segregate VFR and IFR traffic.