NTSB Factual Report

HISTORY OF FLIGHT

On May 11, 1996, at 1134 mountain daylight time, a Jerrell RV-4, N44AZ, registered to the pilot, collided in midair with a Sukhoi Su-29, N55SU, registered to its pilot, while landing at Englewood, Colorado. Visual meteorological conditions prevailed at the time, and no flight plans were filed. N44AZ was destroyed, and N55SU sustained minor damage. The private pilot in N44AZ was fatally injured, and the airline transport pilot in the N55SU was not injured. Both personal flights were being conducted under Title 14 CFR Part 91. The flight of N44AZ originated at Peyton, Colorado, approximately 1100. The flight of the N55SU originated at Watkins, Colorado, approximately 1115.

The pilot of N44AZ obtained a weather briefing via telephone from the Denver Automated Flight Service Station (AFSS), and was advised that VFR flight was not recommended due to localized fog in the Colorado Springs area. At the time, Centennial Airport was hosting an open house. It featured static displays of aircraft and a fly-by, called the "Parade of Flight."

According to Centennial Control Tower tape recordings and transcripts, the pilot of N44AZ contacted the west controller at 1127:50 and advised he was "en route your airport...directly south of the airport, south of the power lines." He was instructed to report entering a right downwind leg for runway 17R. The pilot acknowledged. Shortly thereafter, at 1128:20, the pilot of 55SU contacted the east controller and advised he was "Aurora Reservoir, landing." The controller told him to "plan a left base entry abeam Cherry Creek, (runway) one seven left." The pilot acknowledged.

At 1130:41, the pilot of N55SU advised he was "over the Aurora Reservoir, just west of the reservoir now." He was told he would be "following a flight of four, the lead is a DC-3. The wingman are T-6s. That's who you're following, there. High to your left, turning left base." The pilot reported he had the traffic in sight. At 1131:03, the pilot of N44AZ reported he was "entering downwind runway one seven right."

The pilot of N55SU was cleared to land on runway 17L at 1132:10 and again at 1133:55. Both times he acknowledged the clearances and repeated the landing runway to which he had been assigned. At 1132:16, the pilot of N44AZ was told he was "number three, follow a twin Cessna on right base north of Arapahoe Road. Runway one seven right, cleared to land. Report traffic in sight." The pilot replied, "I understand. I do not have the traffic in sight. I'll proceed north to Arapahoe (Road)."

The pilot of the twin Cessna turned onto final approach and inadvertently aligned himself with runway 17L. The controller called the pilot at 1132:56 and asked him to "verify lined up for runway one seven right. You appear to be lined up for the left." The pilot replied, "I requested left. I thought you gave it to me..." The controller then reiterated the clearance to land on runway 17R. At 1133:30, the controller advised the pilot of N44AZ, "...your traffic's over the numbers. The pilot replied, "I got him, I see him now." Seconds later, the SU-29 landed on top of the RV-4. The collision occurred approximately 800 feet past the threshold of runway 17L.

The Su-29 is a 2-place, tandem seat airplane and the pilot flies solo from the rear seat. The pilot told investigators that because he was in the rear seat and forward visibility is restricted, he was forced to do "periodic slight S-turns to check for traffic...the runway (17L) was clear, I continued the approach until contact was made with an aircraft on the approach end on runway 17L. I landed and rolled to a stop in the center of 17L." The pilot said that his approach speed was 180 km (112 mph).

PERSONNEL INFORMATION

According to N44AZ pilot's logbook, he had flown into Centennial Airport on at least nine different occasions. The pilot of N55SU, a Boeing 737 captain for a major U.S. airline, said he routinely flew into Centennial Airport and was familiar with the airport layout and air traffic control procedures.

AERODROME INFORMATION

Centennial Airport's (APA) runway 17L is 10,001 feet long and 100 feet wide. It is asphalt paved, grooved, and the main precision instrument runway. Runway 17R is 7,003 feet long and 77 feet wide. It is also asphalt paved with a porous friction coarse overlay. There are no instrument approaches to this runway, and it is used for VFR operations only. According to control tower supervisor, the threshold of runway 17R is 1800 ft beyond the threshold of runway 17L. The two runways are 700 ft apart.

WRECKAGE AND IMPACT INFORMATION

The collision between N44AZ and N55SU occurred approximately 800 feet from the threshold of runway 17L. The pilot of N55SU said he felt a mild bump and he eased back the control stick. The airplane rose slightly, then settled back to the runway. As the airplane rolled out, the pilot noticed there were "stubs where the propeller blades use to be." He stopped the airplane alongside the runway, secured the engine, and got out to assess the airplane damage. When he looked back and saw the wreckage of N44AZ in the middle of the runway, he realized he had been involved in a midair collision.

After being struck, N44AZ rolled approximately 200 feet before coming to a halt. Several witnesses said N44AZ was on the runway when the collision occurred. Others said it was still airborne over the runway.

When the NTSB investigator arrived on the scene, N44AZ was still on runway 17L. Cockpit controls (fuel selector, mixture, magnetos) had been secured by CFR (crash/fire/rescue) personnel. Examination disclosed the right elevator trailing edge and the top of the vertical stabilizer had slash marks similar to propeller strikes. The dorsal fin forward of the vertical stabilizer had been torn off. The canopy was shattered. Slightly aft of the canopy was another slash mark. There were black rubber smears on the tops of both wings, and the wings were compressed downward. The left wing fuel tank had been compromised. The main landing gear was pushed down and out. The intact 2-blade wooden propeller remained attached to the crankshaft. The back surfaces of the propeller were painted black, and there were scratch marks on these surfaces.

Prior to the arrival of NTSB, FAA officials had given airport personnel permission to tow N55SU to a nearby hangar. Examination disclosed all three composite propeller blades were shattered. A potion of the propeller spinner was missing. There were black paint transfer marks on the dented lower left engine cowling.

MEDICAL AND PATHOLOGICAL INFORMATION

Dr. Michael J. Dobersen of the Arapahoe County Coroner's Office performed an autopsy (#96-76) on the pilot of N44AZ. A toxicological screen was performed by FAA's Civil Aeromedical Institute. No cyanide, ethanol, or drugs were detected. A carbon monoxide test was not possible.

TESTS AND RESEARCH

An Air Traffic Control specialist from NTSB's Operational Factors Division was dispatched to assist in the investigation. According to his report, 6 controllers --- were on duty in the control tower at the time of the accident: two local controllers, two spotters, a ground controller, and an area supervisor. All of the controllers were interviewed.

Local Controller 2, who was handling west operations, stated he first observed N44AZ when it was on downwind, almost abeam the tower, at an altitude between 6,500 and 6,600 feet msl. He advised the pilot his landing sequence, assigned runway, and traffic he was following. He next saw the airplane on base leg for runway 17R, and he reiterated the traffic advisory. His attention was diverted to new traffic depicted on the BRITE radar, an airplane that was turning off the runway, and another airplane that was blocking an intersection. When he looked up, he saw the collision. The controller said he felt the briefing he received on the airport open house and "Parade of Flight" was "open and accommodating." Prior to coming on duty, he was well rested and felt fine. He described air traffic to be of "moderate density" and "difficult complexity," then decreasing and becoming orderly.

His spotter said she first observed N44AZ when it was 2 miles southwest of the airport on downwind. She then saw the airplane when it was on base leg. She then turned to retrieve a water bottle from the refrigerator and did not see the accident. She said "Parade of Flight" and traffic briefing she received that morning seemed to be "rushed" and more time should have been spent to explain operational procedures. She was not given any rest break. She described her workload as "busy." Heavy traffic complexity and density caused the control tower to be "noisy." Just prior to the accident, activity seemed to decrease.

Local Controller 1, who was handling east operations, stated he did not observe any other traffic ahead of N55SU, and he scanned the runway to make sure it was clear. His attention was then diverted to traffic departures on runway 10. When he looked back at runway 17L, the accident had already occurred. The controller felt the open house briefing reflected "ridiculous planning and timing." Pilots in the "Parade of Flight" seemed confused and communications were beginning to break down. When he brought this to his supervisor's attention, he was told to do the best he could. He said there was "no real game plan." When he entered the control room, the controllers "appeared to be tired" and "looked fatigued" because they had been in position for quite awhile with no breaks due to reduced staffing. He described his workload as "very busy" due to a moderate volume of traffic. The control room was noisy and coordination between controllers was "chaotic."

His spotter said that the last time she saw N55SU, it was north of the tower on left base for runway 17L, and had been cleared to land. The runway was clear, so she turned around to spot other aircraft in the southeast quadrant of the airport. When she turned around again, she saw the two airplanes collide. She said she had been "surprised" and "dismayed" by the heavy and extremely complex volume of traffic. She said at least weekly there would be an incident involving a pilot lining up with the wrong runway due to the thresholds of the two runways being offset. A pilot turning right base for runway 17R would first observe the threshold of runway 17L.

Neither the ground controller nor the area supervisor saw the accident. The ground controller said traffic was "very heavy, very complex...not a standard operation." She asked for and was denied assistance.

ADDITIONAL INFORMATION

N55SU was released to the owner on May 11, 1996. The wreckage of N44AZ was released to a representative of the pilot's estate on May 20, 1996. The National Air Traffic Controllers Association was the only party to the investigation.

NTSB Probable Cause

failure of the pilot of the RV-4, N44AZ, to comply with an ATC clearance by landing on the wrong runway, and the failure of the pilot of the SU-29, N55SU, to maintain an adequate visual lookout. Factors in the accident were: the failure of the air traffic controller to restate the landing runway to the pilot of the RV-4 during a critical period of flight, his failure to advise the pilot of the RV-4 that operations were being conducted on the adjacent runway, a high traffic workload which resulted from an airport open house, and a lack of coordination to accommodate the high traffic workload.