N190GCDehavilland DHC-6-300 · 1970

On July 25, 2014, about 1646 Pacific daylight time, a landing Eurocopter/Airbus EC-130 helicopter, N154GC, and a taxiing DeHavilland DHC-6 airplane, N190GC, collided at Boulder City airport (BVU) Boulder City, Nevada. Neither the two pilots on board the airplane, nor the pilot and six passengers aboard the helicopter, were injured. The helicopter, operated by Papillon Airways Inc. (dba Papillon Grand Canyon Helicopters dba Grand Canyon Helicopters) as an aerial sightseeing flight, sustained substantial damage. That flight was being conducted under the provisions of Title 14 Code of Federal Regulations Part 135. The airplane, operated by Grand Canyon Airlines, was beginning a repositioning flight, and was being operated under the provisions of Title 14 Code of Federal Regulations Part 91. Both Papillon and Grand Canyon Airlines (GCA) are part of the same parent company, Papillon Airways. Day visual meteorological conditions prevailed.

According to the helicopter pilot, he was inbound from the south, and planned to land on the airport location designated as "Spot 2," which was a dedicated helicopter arrival and departure location. He followed the company-designated arrival procedure, in which the helicopter flew a descending pattern first north along the centerline of taxiway A (also referred to as "alpha"), and then west along the centerline of taxiway D (also referred to referred to as delta) to Spot 2. Spot 2 was a 50 foot painted square situated on the airport ramp. Taxiway Delta was 40 feet wide, was oriented approximately east-west, and comprised the southern perimeter of the previously-cited ramp. The center of Spot 2 was located about 50 feet north of the centerline of taxiway Delta. Since BVU was not equipped with an operating air traffic control tower, the pilot communicated his positions and intentions via radio transmissions on the BVU common traffic advisory frequency (CTAF).

The helicopter pilot first saw the airplane when the helicopter was making the left turn from north to west near the junction of taxiways Alpha and Delta. At that time, the airplane was moving south, towards taxiway Delta, along a taxi line just east of Spot 1, on ramp about 600 feet east of Spot 2. The airplane crew announced their intentions on CTAF to taxi to runway 15 via taxiway Delta. The helicopter pilot reported that the last time that he saw the airplane prior to the accident was as the helicopter overflew the intersection of taxiway Delta and the taxi line just east of Spot 1. At that time, the airplane was turning westbound onto taxiway Delta. The helicopter pilot realized the potential for conflict, since the two aircraft were now both traveling westbound along taxiway Delta. The helicopter pilot stated that he "immediately" queried on CTAF whether the airplane crew had him in sight. The helicopter pilot heard a "double click" on the CTAF frequency, which he interpreted as acknowledgement by the airplane crew that they had him in sight. Based on this information, the helicopter pilot was convinced that the airplane was behind him, and that its flight crew had him in sight.

The helicopter pilot therefore continued his descent along the centerline of taxiway Delta towards Spot 2. About 8 to 10 seconds later, as the helicopter came almost abeam of Spot 2, the pilot began a right pedal turn to traverse to and set down on Spot 2. At the commencement of that pedal turn, the pilot simultaneously spotted the wings and nose of the airplane through his chin windows, and felt an" impact." He stopped the turn and descent, transitioned to the ramp, descended, and landed on Spot 2.

The flight crew of the airplane was unaware that there had been a collision, and they continued with their taxi-out and departure from BVU. Shortly after departure, the airplane was recalled to BVU by company personnel, after the company personnel learned of the collision. The airplane was equipped with a cockpit voice recorder (CVR). The device was obtained by the NTSB, and sent to the NTSB recorders laboratory in Washington DC for readout.

Helicopter Pilot

Papillon records indicated that the pilot held a commercial pilot certificate with a helicopter instrument and instructor ratings. He had approximately 1,102 total hours of flight experience, all of which was in helicopters, and which included approximately 9 hours in the accident helicopter make and model. His most recent flight review was completed on July 22, 2014, and his most recent FAA second-class medical certificate was issued on December 2, 2013.

The helicopter pilot had recently been hired by Papillon, and the accident occurred on his first day flying in revenue service for the operator. The helicopter pilot did not recall whether he observed the airplane stop on the ramp prior to its turn onto taxiway Delta.

Airplane Captain

The captain of the airplane was an 11 year employee of the operator, and was also an instructor pilot. The captain had been on duty for 8 of the 9 days before the accident. He began his duty day at 0507 that morning, and the collision occurred during his sixth flight of the day. He was off duty the day prior to the accident. The day prior to that, he was on duty from about 0645 to 1845, and flew 7 trips, with a total of 3.5 hours of flight time.

In his written account of the event, the Captain stated that the crew completed the before takeoff checklist prior to taxiing, which was "a procedure designed to ensure maximum situational awareness, so each pilot can listen for pertinent radio calls and look outside the aircraft for conflicting aircraft" during taxi. Nowhere in his written statement did the Captain report that he stopped the airplane on the ramp prior to turning onto taxiway Delta. Except for his description of the closest proximity of the helicopter and airplane, the Captain's report did not include any information regarding his awareness of the helicopter.

Airplane First Officer

According to Grand Canyon Airlines, the First Officer was on his second day as a pilot for the airline.

Except for his description of the closest proximity of the helicopter and airplane, the First Officer's written report did not include any information regarding his awareness of the helicopter. His report did not state whether the airplane did or did not stop on the ramp prior to turning onto taxiway Delta.

Helicopter

The single-main-rotor helicopter was manufactured in 2010, and was powered by a single turboshaft engine. It was used for aerial tours, and was configured to seat seven passengers. It was flown by a single pilot, who operated from the left front seat.

Airplane

The high-wing, twin-turboprop airplane was manufactured in 1970. It was used for aerial tours, and was configured to seat 17 passengers. It was operated by a two-person crew.

The 1646 BVU automated weather observation included winds from 160 degrees at 15 knots, gusts to 23 knots, visibility 10 miles, clear skies, temperature 40 degrees C, dew point 11 degrees C, and an altimeter setting of 29.84 inches of mercury.

BVU was equipped with a dedicated CTAF for radio communications use by arriving and departing aircraft, and the CTAF communications were recorded. Radio transmissions from both the helicopter (radio call sign "Papillon 31") and the airplane (radio call sign "Canyon View 90") were captured by the CTAF system, and reviewed by investigators.

The helicopter pilot first reported on the CTAF at 1644:10, and announced that he was "south of the [electrical power] substation," a geographic reference landmark, at an altitude of 2,800 feet above mean sea level, and flying towards "the ponds," another geographic reference landmark that was situated just south of the airport. At 1644:55, the airplane crew first reported on the CTAF, announcing that it was taxiing from the "east apron" (a BVU ramp area) to runway 27 via taxiway Delta. That runway selection and taxi route required the airplane to first taxi south on the ramp, and then east on taxiway Delta.

At 1645:08, the helicopter pilot announced that he was "over the Ponds, coming over [taxiway] Alpha for a westbound [taxiway] Delta approach." At 1645:39, the airplane crew announced that it was "taxiing [taxiway] Delta [taxiway] Bravo for runway one five." That new runway selection required that the airplane taxi westbound on taxiway Delta, instead of eastbound as originally planned. According to the airplane captain's written statement, that radio call was made as the airplane was turning right (westbound) onto taxiway Delta. The captain also noted that at that time, he "looked out the left window," but did not "see any in or out bound helicopters."

At 1645:45 the helicopter pilot radioed "Canyon View Papillon 31 right above you for Spot Two." The helicopter pilot's vocal cadence in that communication was different than that of his previous transmissions, and the transmission was accompanied by noticeable breathing, which was not evident in his prior transmissions.

The next communication from either aircraft was at 1647:51, when the airplane crew announced that it was "taking runway one five" for departure.

According to information provided by the operator, the first officer was handling the radio communications, and the captain was taxiing the airplane. The first officer was aware of the inbound helicopter, but the captain was not specifically aware of that helicopter.

BVU elevation was 2,200 feet. BVU was equipped with two runways, 9/27 and 15/33. The runways intersected at about the midpoint of 9/27 and the two-thirds point of runway 15. The ramp area was oriented east-west, and situated about 750 feet north of runway 9/27. Taxiway Delta was the paint-demarcated southern boundary of the ramp area. Taxiway Alpha was oriented north-south, and connected the threshold end of runway 27 with taxiway Delta and the ramp area. Taxiway Bravo was parallel to, and on the east-northeast side of runway 15/33.

The airport maintained a dedicated website to provide relevant airport information, including a two-page document of helicopter arrival and departure procedures. That document contained both text and pictorial descriptions of those procedures, and also depicted the airplane runway traffic patterns. The descriptions included the geographic landmarks referenced by the helicopter pilot.

The FAA airport/facilities directory entry for BVU contained a note that stated "LARGE NUMBER OF GRAND CANYON TOUR ACFT OPERATIONS IN VICINITY. HELICOPTERS CROSS ACTIVE RYS AND TWYS." (emphasis original)

The CVR from the airplane was successfully read out at the NTSB recorders laboratory in Washington DC. The recorded intra- and extra-cockpit communications were essentially congruent with the pilots' accounts of events that were provided to the NTSB at the beginning of the investigation.

Examination of the two aircraft revealed that the most significant damage occurred where the inboard trailing edge of the helicopter's right horizontal stabilizer contacted the leading edge of the airplane's vertical stabilizer at about the vertical stabilizer's two-thirds span point. Additional damage was observed on the underside end of at least one of the helicopter main rotor blades, and the top of the airplane's vertical stabilizer.

Aircraft Right of Way Information

Paragraph 91.113 of the Federal Aviation Regulations (FAR) provides some guidance on aircraft right of way rules. Subparagraph 'b' stated that "vigilance shall be maintained by each person operating an aircraft so as to see and avoid other aircraft," and that the "pilot shall give way to that aircraft and may not pass over, under, or ahead of it unless well clear." Subparagraph 'g' stated that "Aircraft, while on final approach to land or while landing, have the right-of-way over other aircraft in flight or operating on the surface."

The FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25) reiterated the essence of the applicable FAR, and augmented it with the statement "Even if entitled to the right-of-way, a pilot should yield if another aircraft seems too close."

Three days after the accident, GCA's Flight Operations department published and distributed "Read and Initial File" (RIF) 2014-02 to its pilots. The RIF "designated taxiway Delta between Alpha and Bravo as a Hot Spot," and stated that "Regardless of direction traveling on taxiway Delta, extra vigilance is required." In addition, the RIF explicitly required that pilots of airplanes departing the ramp are to come to a "complete stop," report their position, and scan for traffic prior to taxiing onto taxiway Delta.

Cockpit Visibility

According to a representative of GCA, the external visibility from the cockpit of the DHC-6 was somewhat limited, and could have impeded the captain's ability to visually detect the inbound helicopter. Subsequent to the accident, the two operators began a program to familiarize the helicopter and airplane pilots' with each other's aircraft and procedures, with a focus on cockpit visibility as one area of emphasis.

Operator Communications Regarding Accident

In January 2016, the Papillon Airways "Chief Operating Officer/Director of Operations" provided a 4 page document which presented an accident summary, numerous operator-implemented safety improvement steps, and a "root-cause analysis" regarding the accident. The document bore "Papillon Airways, Inc" on its first page, but was otherwise unidentified and unattributed. It was not dated. In response to an NTSB query, to the Papillon COO/DO, the document was reported to be the result of an investigation by Papillon "President and CEO...with the Papillon and GCA senior management team."

The "root cause analysis" segment of the document posted the following as relevant facts:

a) The airplane First Officer saw an "inbound helicopter" after Papillon 31 made its CTAF call

b) The airplane Captain did not hear the radio call or see a helicopter inbound

c) The airplane had taxied onto taxiway Delta prior to making its CTAF announcement that it was doing so

Item b) was not substantiated or otherwise known to the NTSB except as stated in this Papillon report, and efforts to independently verify that statement were unsuccessful.