An early January midair over Denver, CO, has been laid to the failure of both pilots to see and avoid each other. The final report, released earlier this week, does note that a transponder problem contributed to the situation in which a Cessna 172 and a Piper Cheyenne collided, killing five on board both aircraft and doing extensive damage to structures on the ground in NW Denver. 

NTSB Publishes Details

On January 24, 2003, at 1720:36 mountain standard time, a Piper PA-31T, N360LL, registered to and operated by Lee Larson Aircraft Sales of Northglenn, Colorado, and a Cessna 172P, N52241, registered to EDB Air, Inc., and doing business as Key Lime Flights of Englewood, Colorado, collided in midair over Denver, Colorado. The commercial pilot-in-command and the commercial certificated pilot-passenger aboard N360LL and the private pilot and two passengers aboard N52241 were fatally injured. The Denver Police Department (DPD) reported that six persons on the ground, including a 15-year old boy and a 2-year old girl, received minor injuries from falling debris. Visual meteorological conditions prevailed, and neither pilot had filed flight plans. Both flights were being operated under Title 14 CFR Part 91. N5224's flight originated at Centennial Airport, Englewood, Colorado, at 1708, and was en route to Cheyenne, Wyoming. N360LL's flight originated at Jeffco Airport, Broomfield, Colorado, at 1716, and was en route to Centennial Airport.

At 1708, the pilot of N52241 was cleared for takeoff from Centennial Airport's runway 17L, and to proceed VFR (visual flight rules) "on course." At 1716, the pilot of N360LL was cleared for takeoff from Jeffco Airport's runway 29R, VFR, with a southbound departure. At 1717:52, the pilot of N360LL contacted Denver Terminal Radar Control (TRACON) and advised "We're just off Jeffco, down to Centennial." [At this point, radar data indicated N52241 was about 10 miles northwest of Centennial, its transponder transmitting a beacon code of 1200 (VFR)]. At 1718:04, the controller assigned the pilot a transponder beacon code of 5250. At 1718:26, he identified the airplane on radar: "Cheyenne Zero Lima Lima, radar contact, four (miles) south of Jeffco. Proceed as requested. [Note: According to NTSB's Operational Factors Division (AS-30), "proceed as requested" does not constitute an ATC clearance, which requires an aircraft to proceed under conditions specified by ATC, nor was one required because the pilot was operating in Class E airspace under visual flight rules.] I'm not getting any mode C on you. You squawking altitude?" The pilot replied, "Ah, yes, sir, we are." [At this point, radar data indicated N360LL was 10.73 miles from N52241]. At 1718:34, the controller asked the pilot for his altitude. He replied he was at 7,800 feet. [Radar data indicated the N360LL's mode C was still inoperative and it remained so throughout the flight. The radar-computed ground speed indicated "23," or 230 knots.]

At 1718:58, the pilot of N52241 contacted Denver Terminal Radar Control (TRACON): "Denver, Cessna Five Two Two Four One is over Denver at seven thousand, three hundred feet, with a request." The controller issued the pilot a transponder beacon code of 5251. The pilot acknowledged the instruction and requested clearance to climb to 8,500 feet, which would place the airplane in Class B airspace. He also advised he was en route to Cheyenne. [At this point, Centennial tower called the controller with a request for another aircraft's IFR departure release. The controller issued the release and assigned a departure heading of 050 degrees, then coordinated the departure with the south sector controller]. At 1720:04, the controller identified the airplane on radar when it was 15 miles southeast of Jeffco Airport, and asked the pilot to repeat his requested altitude. He repeated his request for 8,500 feet. [At this point, separation between N360LL and N52241 had closed to 2.91 miles. N52241's radar-computed ground indicated "11," or 110 knots. At about this time, the controller made a transmission to an aircraft that was on the downwind leg at Centennial Airport. He then vectored another airplane onto the NDB (nondirectional beacon) approach to Centennial Airport. The controller was also monitoring other aircraft that were getting close to a restricted area and the airport traffic area]. At 1720:16, the controller cleared N52241 to enter class B airspace and climb to 8,500 feet. Two seconds later, radar showed target separation as 1.64 miles. At 1720:22, target separation was 1.20 miles. At 1720:27, target separation was 0.80 miles.

At 1720:28, the controller asked the pilot of N360LL to report his altitude. The pilot replied, "(Unintelligible) six." The controller said, "Say again." At 1720:31, target separation had reduced to 0.29 miles. The pilot said, "Seven thousand, six hundred." At 1720:33, the controller issued the pilot a traffic advisory: "Traffic is at twelve o'clock and a mile at seventy seven hundred, a Cessna." The pilot did not acknowledge this transmission. At 1720:36, the two airplanes were 0.06 miles apart. Immediately thereafter, radar data indicated both targets had entered "coast" mode (i.e. computer-generated projection of targets' tracks and positions). At 1720:47, the controller advised N360LL that the previously reported traffic was no longer a factor and issued another advisory for traffic 4 miles away. Receiving no reply from the pilot, the controller attempted several times to contact both airplanes. The controller then contacted a traffic patrol pilot and asked him to fly over the area where radar contact was lost. Shortly thereafter, the traffic patrol pilot reported that it appeared there had been an accident. The TRACON controller initiated search and rescue procedures.

The collision occurred 2 minutes, 43 seconds and 1 minute, 35 seconds after the pilots of N360LL and N52241 made initial contact with Denver TRACON, respectively.

Wreckage and debris from both airplanes covered an area of approximately 24 city blocks. N52241 impacted the northeast corner of a house at 3421 W. Moncrieff Place. When examined inside the house, the airplane was in a vertical attitude. The wreckage consisted of the fuselage, both wings with control surfaces and lift struts still attached, the vertical and horizontal stabilizers with both elevators and rudder attached, and the engine and detached propeller. Smaller pieces of debris --- pieces of the engine and cowling; nose landing gear strut, wheel and tire; left main landing gear strut, wheel, and tire, and right main landing gear wheel and tire --- were scattered over the area in a generally south-to-north direction.

N360LL was located inverted in the backyard of a residence at 3221 W. 26th Avenue. The ground scar and crush lines were consistent with a left spin. Attached to the fuselage were the left wing with aileron and flap, the left engine and propeller hub with two of three attached propeller blades, and the inboard portion (to W.S. 109) of the right wing with an attached 7-foot section of flap. The third propeller blade from the left propeller assembly was found underneath the wreckage. Scattered nearby were the left tip tank, nose baggage door, and nose cone. The outboard portion of the right wing, from about W.S. 147.0 to the attached tip tank, was located in the backyard of a residence near 26th Avenue and Irving Street. The horizontal stabilizer (the right leading edge aft to the spar was missing) struck a parked automobile at 26th Avenue and Julian Street. The right engine, with attached propeller, was located in the 3100 block of W. 25th Avenue. Smaller pieces of debris --- internal wing structure, hydraulic fluid lines and fittings, engine cowling, and fuselage skin --- were scattered over the area in a generally north-to-south direction.

NTSB's Final Word

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

Both pilots' inadequate visual lookout. A contributing factor was the Cheyenne pilot operating the airplane with a known transponder deficiency.

FMI: www.ntsb.gov