NTSB: Wrong-runway lineup probable cause of midair

The collision between the Piper JetProp DLX (a PA–46-350P converted to turbine power) and a Cessna 172 doing pattern work at North Las Vegas Airport with a student and instructor aboard killed four people, two aboard each aircraft. The investigation report highlights the importance of flying accurate approaches to parallel runways, as well as the potential shortcomings of automated safety systems designed to alert pilots and air traffic controllers when aircraft get too close to other aircraft—alerts that the controller on duty at the time of the accident described as "white noise " because they occur so frequently at an airport with parallel runways separated by about 700 feet from centerline to centerline.

The final report on the July 17, 2022, accident cites the probable cause as the Piper pilot's "failure to ensure that the airplane was aligned with the correct runway" after being cleared to land on the left parallel runway as the Cessna 172 approached the right parallel runway.

While the airport was familiar to the two pilots aboard the Piper, a husband and wife who based the aircraft at the airport, the procedure may not have been. Approaching from the north on an IFR flight plan, the Piper was cleared for a visual approach and instructed to overfly the airport at midfield and make a left downwind traffic pattern entry, a new procedure that the airport had tested about two months before the accident, for about a week.

"Their lack of familiarity with the maneuver may have resulted in a miscalculation that resulted in the airplane rolling out of turn farther to the right of runway 30L than expected. A performance study indicated that, during the turn to final approach, the airplane was between 38 knots (kts) and 21 kts faster than its nominal landing approach speed of 85 kts," the final report states. "This excess speed may have contributed to the pilots' alignment with runway 30R instead of runway 30L."

Investigators calculated that the Piper would have had to bank up to 37 degrees at the speeds flown to accurately complete the continuous turn through downwind, base, and final and align with the left runway. While the Piper achieved a roll angle as high as 40 degrees during the turn, it did not maintain that bank and overshot the final approach course, aligning instead with Runway 30R.

"The high-wing configuration of the Cessna in a right turn to final, and the low-wing configuration of the Piper in a left turn to final, only exacerbated the conflict by reducing the ability of the pilots to see the other aircraft."

'Might not have provoked concern'

Investigators built a digital model of the accident to study what each pilot might have seen using ADS-B data and laser scans of similar aircraft, concluding, based on estimated head position and accounting for obstructions including aircraft structure, that the Cessna could have been visible to the Piper pilot for only 15 seconds of the final minute before the collision.

The high-wing Cessna could have had an unobstructed view of the oncoming Piper for a total of 39 seconds of that same minute, and both aircraft would have appeared to the other to be at or below the horizon, making each more difficult to identify against a complex background.

"The low-wing airplane would have passed behind the high-wing airplane pilot's left shoulder at 1202:44.5, 6.5 seconds before the collision, making it less likely that the high-wing airplane pilot would have become aware of the low-wing airplane approaching from his left aft quarter as both airplanes maneuvered onto the final approach for runway 30R," the report states, noting that both pilots were likely looking at the approaching runway, not off to the sides where they might have seen the other aircraft.

The Cessna was not equipped with a traffic information display, while the Piper did have Garmin avionics that may have generated a visual and aural alert about 22 seconds before the collision, investigators noted, though such an alert "may not have provoked concern from the flight crew, since other aircraft are to be expected while operating in the airport traffic pattern environment."

'Poor judgement'

The NTSB cited as contributing factors "the controller's failure to provide timely and adequate traffic information to either airplane and his failure to recognize the developing conflict and act in a timely manner," as well as the FAA's "insufficient staffing of the facility, which required excessive overtime that did not allow for proper controller training or adequate recovery time between shifts."

The tower controller told investigators that he did not issue traffic advisories to either aircraft, "even though the low-wing airplane crossed about 500 [feet] over the high-wing airplane as it descended over the airport toward the downwind leg of the traffic pattern. His reasoning for not providing advisories to the airplanes as they entered opposing base legs was that he expected the high-wing airplane to be over the runway numbers before the low-wing airplane would be able to visually acquire it; however, this was a flawed expectation that did not account for the differences in airplane performance characteristics," the NTSB wrote. "After clearing both airplanes for landing, he communicated with two uninvolved aircraft and did not monitor the progress of the accident airplanes to the two closely-spaced parallel runways. This showed poor judgement, particularly given that in the months before the accident, there had been a series of events at the airport in which pilots had mistakenly aligned with, landed on, or taken off from an incorrect runway."

Investigators learned from interviews with tower staff that controllers at the North Las Vegas tower were averaging 400 to 500 hours of overtime per year—at a facility that the FAA deemed to be "fully staffed."

"According to the air traffic manager (ATM), the inadequate staffing had resulted in reduced training [discussions] and the management team was unable to appropriately monitor employee performance," the NTSB wrote. "The ATM stated that everyone on the team was exhausted, and that work/life balance was non-existent. It is likely that the cumulative effects of continued deficient staffing, excessive overtime, reduced training, and inadequate recovery time between shifts took a considerable toll on the control tower workforce."

The FAA implemented various changes to local ATC procedures following the accident, including mandating traffic advisories be issued whenever aircraft are operating on opposing base legs to parallel runways; publishing information for pilots to consider when operating on parallel runways; and updating controller recurrent training. Pilots operating at North Las Vegas Airport were reminded by special notice that the threshold for Runway 30L is about 900 feet beyond the Runway 30R threshold, and more difficult to see.

The NTSB report does not mention any increase in tower staffing.